Author: kodiac

  • Sildenafil

    Selective phosphodiesterase type 5 (PDE5) inhibitor of the pyrazolopyrimidinone structural class

    A pyrazolopyrimidinone-based cyclic GMP-specific phosphodiesterase type 5 inhibitor originally developed at Pfizer as an antianginal agent, repositioned as the first oral pharmacotherapy for erectile dysfunction and subsequently approved for pulmonary arterial hypertension, with an expanding preclinical evidence base in cardioprotection, neuroprotection, and vascular inflammation.

    Abstract

    Sildenafil (UK-92480) is a potent, competitive, and selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), the enzyme principally responsible for hydrolytic degradation of cGMP in vascular smooth muscle, the corpus cavernosum, and the pulmonary vasculature. The compound was synthesized at the Pfizer Global Research and Development laboratories in Sandwich, Kent, United Kingdom in 1989 as part of a medicinal chemistry program targeting selective PDE5 inhibition for the treatment of angina pectoris and hypertension. Phase I clinical trials revealed limited antianginal efficacy but a pronounced and reproducible effect on penile erection, prompting repositioning toward erectile dysfunction. Sildenafil received United States Food and Drug Administration (FDA) approval on 27 March 1998 as the first oral pharmacotherapy for erectile dysfunction (marketed as Viagra) and subsequently received FDA approval in June 2005 for the treatment of World Health Organization Group I pulmonary arterial hypertension (marketed as Revatio).

    The pharmacological mechanism is inhibition of PDE5 at the catalytic site with an IC50 of approximately 3.5 nanomolar and selectivity over PDE1 through PDE4 of 80- to 19,000-fold, with approximately 10-fold selectivity over the structurally related retinal PDE6, the latter accounting for the dose-dependent visual disturbances observed clinically [1, 2]. PDE5 inhibition potentiates the nitric oxide (NO)/soluble guanylyl cyclase (sGC)/cGMP signaling cascade: in tissues where NO release occurs (penile corpus cavernosum during sexual stimulation, pulmonary vascular endothelium), sildenafil amplifies the downstream smooth muscle relaxation by preventing cGMP breakdown. The compound does not directly initiate smooth muscle relaxation in the absence of NO signaling, a pharmacological distinction that differentiates PDE5 inhibitors from direct NO donors and from soluble guanylyl cyclase stimulators.

    Pharmacokinetics are characterized by rapid oral absorption (time to peak plasma concentration approximately 60 minutes under fasting conditions), moderate absolute oral bioavailability of approximately 41 percent (limited by hepatic first-pass metabolism), a plasma elimination half-life of approximately 3 to 5 hours, and high plasma protein binding of approximately 96 percent [3, 4]. Metabolism is predominantly hepatic via cytochrome P450 3A4 (CYP3A4, major pathway) and CYP2C9 (minor pathway), producing the active N-desmethyl metabolite (UK-103,320) that retains approximately 50 percent of the parent compound potency at PDE5 and has a similar terminal half-life [3]. The CYP3A4 dependence creates clinically significant drug-drug interactions with strong CYP3A4 inhibitors (ritonavir, ketoconazole, itraconazole, erythromycin), which can elevate sildenafil plasma concentrations by 3- to 11-fold.

    The clinical evidence base spans two FDA-approved indications (erectile dysfunction and pulmonary arterial hypertension) and multiple investigational applications including Raynaud phenomenon, heart failure, altitude sickness, and neuroprotection. The SUPER-1 trial in 278 patients with pulmonary arterial hypertension demonstrated significant improvement in six-minute walk distance across all sildenafil dose groups (20, 40, and 80 mg three times daily) compared to placebo [5]. A 2024 dose-ranging trial by Hoeper et al. further demonstrated dose-dependent benefit, with the 80 mg three times daily group achieving a median gain of 52 meters in six-minute walk distance [6]. Preclinical pharmacology has established cardioprotective effects against ischemia-reperfusion injury through mitochondrial ATP-sensitive potassium channel opening, neuroprotective effects in rodent stroke and neurodegeneration models through cGMP-mediated anti-apoptotic signaling, and anti-inflammatory effects through suppression of NF-kappaB-driven cytokine release.

    The compound is well tolerated at approved doses. Principal adverse events are headache (16 percent), flushing (10 percent), dyspepsia (7 percent), nasal congestion (4 percent), and dose-dependent visual disturbances (chromatopsia, increased light sensitivity) reflecting PDE6 cross-inhibition in retinal photoreceptors [7]. The critical safety concern is the absolute contraindication with organic nitrates and nitric oxide donors, where co-administration produces synergistic and potentially fatal hypotension through additive cGMP-mediated vasodilation [8]. This monograph reviews the chemistry, synthesis, and structural pharmacology of sildenafil; the molecular mechanism across PDE isoforms; comprehensive human pharmacokinetics; the clinical evidence base across approved and investigational indications; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse-event signal; and a comparative assessment of five PDE5 inhibitor and vasodilator alternatives against sildenafil on five competency standards.

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  • Pinealon

    Synthetic bioregulatory tripeptide (Glu-Asp-Arg) with proposed epigenetic neuromodulatory activity

    A synthetic tripeptide bioregulator derived from the pineal gland peptide fraction, investigated as a neuroepigenetic modulator of gene expression with reported neuroprotective, antioxidant, and geroprotective activity in preclinical oxidative stress, ischemia, and neurodegeneration models.

    Abstract

    Pinealon (EDR peptide; L-glutamyl-L-aspartyl-L-arginine) is a synthetic tripeptide bioregulator developed at the Saint Petersburg Institute of Bioregulation and Gerontology under the direction of Vladimir Khavinson as part of a multigenerational program to identify tissue-specific short-chain peptides capable of modulating gene expression through direct interaction with chromatin. The compound was identified as one of the shortest biologically active sequences within Cortexin, a complex peptide fraction extracted from bovine cerebral cortex tissue that has been used clinically in several post-Soviet jurisdictions for the treatment of traumatic brain injury, ischemic stroke, and cognitive impairment. Pinealon was subsequently synthesized as a standalone tripeptide and advanced through a series of in vitro and in vivo investigations spanning antioxidant activity, neuroprotection, serotonin biosynthesis regulation, dendritic spine preservation in Alzheimer’s disease models, and preliminary open-label clinical observations in elderly patients with cognitive decline and in patients recovering from craniocerebral trauma.

    The proposed mechanism of action is unconventional relative to classical receptor-mediated peptide pharmacology. Due to its low molecular weight (418.41 g/mol) and cationic character, Pinealon is reported to penetrate lipid bilayers and nuclear membranes without requiring surface receptor engagement, gaining direct access to chromatin. Molecular modeling and in vitro binding studies from the Khavinson laboratory have identified complementary binding sites in the promoter regions of several genes relevant to neuroprotection and neurodegeneration, including TPH1 (tryptophan hydroxylase 1, the rate-limiting enzyme in serotonin biosynthesis), SOD2 (mitochondrial superoxide dismutase), GPX1 (glutathione peroxidase 1), PPARA and PPARG (peroxisome proliferator-activated receptor alpha and gamma), CASP3 (caspase-3), and APOE (apolipoprotein E). The proposed binding occurs at specific DNA sequences, principally d(CCTGCC)2 and d(CCAGC)2, through sequence-specific steric and electrostatic complementarity with the major groove of double-stranded DNA. The functional consequence is reported to be destabilization of local DNA secondary structure, alteration of histone modification patterns, and increased accessibility of regulatory regions to transcription factors, resulting in upregulation of neuroprotective gene products and downregulation of pro-apoptotic pathways.

    Preclinical pharmacology studies, conducted predominantly by the Khavinson group and affiliated Russian laboratories, have reported that Pinealon produces dose-dependent suppression of reactive oxygen species accumulation in cerebellar granule cells, neutrophils, and pheochromocytoma (PC12) cells; increases cell viability under oxidative stress conditions; delays ERK1/2 activation in neurons exposed to homocysteine; reduces caspase-3 expression and p53 protein synthesis in brain tissue; increases serotonin synthesis in neuronal cultures of rat cerebral cortex; normalizes superoxide dismutase and glutathione peroxidase activity in the brains of hypoxia-sensitive rats; prevents the loss of mushroom-shaped dendritic spines in hippocampal neurons from 5xFAD transgenic mice (a model of familial Alzheimer’s disease); and protects rat offspring from prenatal hyperhomocysteinemia-induced cognitive deficits. In an open-label clinical observation in 72 patients with traumatic brain injury, addition of Pinealon to standard rehabilitation therapy improved memory function in approximately 59 percent of patients.

    No completed, peer-reviewed randomized controlled trial of Pinealon has been published in English-language indexed journals as of the date of this monograph. No Phase 1 formal safety study, no Phase 2 efficacy trial, and no Phase 3 registration study exist in any population. The compound has no approved indication in any jurisdiction recognized by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use. Virtually all published Pinealon research originates from the Khavinson laboratory and closely affiliated institutions; independent replication by Western academic laboratories is absent. The chromatin-interaction model, while supported by computational molecular modeling and fluorescence microscopy studies from the originating group, has not been independently validated by structural biology methods (X-ray crystallography, cryo-electron microscopy) at the resolution required to confirm the proposed binding geometry. This monograph documents the chemistry, proposed mechanism, preclinical pharmacology, clinical observations, sourcing and handling, and comparative assessment of the compound, and identifies the principal evidence gaps that currently limit its positioning in the research-clinical translation pipeline.

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  • Thymalin

    Plain-language summaryIntrigue 58 / 100

    Thymalin is a Russian-developed bovine thymus peptide preparation used as an immunomodulator for elderly patients and immune disorders. Combined with epitalon in Khavinson’s longevity research. Not stocked by Kodiac. This monograph is provided for research and educational reference.

    Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

    Thymic polypeptide bioregulator complex with immunomodulatory and geroprotective activity

    A heterogeneous polypeptide complex isolated from calf thymus, developed at the Military Medical Academy in Leningrad as a thymic bioregulator for immune restoration, distinguished from other thymic peptide preparations by its multicomponent composition containing the immunomodulatory dipeptides L-glutamyl-L-tryptophan and L-lysyl-L-glutamic acid and the tripeptide L-glutamyl-L-aspartyl-L-proline.

    Abstract

    Thymalin is a standardized polypeptide complex isolated from the thymus gland of calves by acid hydrolysis and ultrafiltration, containing peptide fractions in the 1,000 to 10,000 dalton molecular weight range. Developed at the Military Medical Academy in Leningrad (now Saint Petersburg) by Vladimir Khavinson and Vyacheslav Morozov in the 1970s, the preparation was registered as an immunomodulatory pharmaceutical in the Soviet Union in 1982 and has remained in clinical use in the Russian Federation for more than four decades. Unlike the structurally defined thymic peptides thymosin alpha-1 (a 28-amino-acid single-sequence peptide), thymulin (a zinc-dependent nonapeptide), and thymopentin (a synthetic pentapeptide fragment of thymopoietin), Thymalin is a multicomponent extract whose principal bioactive constituents have been identified by reversed-phase high-performance liquid chromatography as the dipeptide L-glutamyl-L-tryptophan (Glu-Trp, subsequently developed independently as Thymogen), the dipeptide L-lysyl-L-glutamic acid (Lys-Glu, developed as Vilon), and the tripeptide L-glutamyl-L-aspartyl-L-proline (Glu-Asp-Pro, developed as Crystagen). The molecular mechanism of the immunoprotective activity is attributed to the capacity of these short peptides to bind selectively to double-stranded DNA sequences and to histone proteins, thereby modulating chromatin conformation, gene expression, and the synthesis of immune system proteins including interleukins, interferons, heat-shock proteins, and components of the fibrinolytic system. In experimental systems, Thymalin stimulates the differentiation and functional activity of T-lymphocyte subpopulations (CD4+ and CD8+), normalizes the ratio of T-helper to T-suppressor cells, enhances natural killer cell activity and phagocytosis, and modulates the balance between pro-inflammatory and anti-inflammatory cytokines. The geroprotective properties of Thymalin are supported by a prospective clinical observation of 266 elderly subjects over 6 to 8 years conducted at the St. Petersburg Institute of Bioregulation and Gerontology and the Institute of Gerontology of the Ukrainian Academy of Medical Sciences, in which Thymalin-treated subjects exhibited 2.0- to 2.1-fold lower mortality compared to controls receiving standard geriatric care, with further reductions (4.1-fold lower mortality) observed in a subgroup receiving annual combined Thymalin and Epithalamin treatment for 6 years. More recently, a prospective randomized single-blind controlled trial of Thymalin (10 mg intramuscular daily for 10 days) in 80 elderly patients with severe COVID-19 reported a 92 percent increase in blood lymphocytes, 6.5-fold reduction in interleukin-6, halved in-hospital mortality (19.4 percent versus 40.9 percent in controls), and more rapid clinical improvement (80.5 percent versus 59 percent). In vitro studies have demonstrated that Thymalin reduces expression of the stem cell markers CD44 and CD117 by 2- to 3-fold while increasing expression of CD28 (a marker of mature T lymphocytes) by 6.8-fold, consistent with stimulation of hematopoietic stem cell differentiation into functional T cells. The compound is administered by intramuscular or subcutaneous injection in short cyclical courses of 5 to 10 days at doses of 5 to 10 mg daily, with clinical effect reported to persist for weeks to months following each treatment course. The safety record across more than 40 years of clinical use indicates minimal adverse events, principally limited to injection-site reactions. This monograph reviews the composition, extraction, and characterization of Thymalin; the molecular pharmacology of its constituent peptides at the level of DNA binding, histone interaction, and gene expression regulation; the pharmacokinetic properties; the preclinical evidence base across immune restoration, geroprotection, and oncology models; the clinical evidence in elderly immune decline, respiratory infections, perioperative immune suppression, and COVID-19; sourcing and quality verification considerations; reconstitution and handling protocols; stack interactions with other immunomodulatory agents; the adverse-event and safety profile; and a comparative assessment of five alternative thymic and immunomodulatory peptide preparations against Thymalin on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).

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  • Superdrol

    Synthetic 17-alpha-alkylated anabolic-androgenic steroid derived from 5-alpha-dihydrotestosterone

    A potent orally active 2-alpha,17-alpha-dimethylated dihydrotestosterone derivative with a high anabolic-to-androgenic dissociation ratio, originally synthesized by Syntex in 1956, never marketed pharmaceutically, and classified as a Schedule III controlled substance following its illicit distribution as an over-the-counter designer steroid supplement beginning in 2005.

    Abstract

    Superdrol (methasterone; 2-alpha,17-alpha-dimethyl-5-alpha-androstan-17-beta-ol-3-one) is a synthetic, orally active anabolic-androgenic steroid (AAS) of the 5-alpha-dihydrotestosterone (DHT) structural class. The compound was first synthesized by researchers at Syntex Corporation in 1956 and characterized in a 1959 publication as a potent orally active anabolic agent exhibiting only weak androgenic activity. Despite this favorable preclinical dissociation profile, methasterone was never advanced to clinical development or marketed as a prescription pharmaceutical. The compound resurfaced in 2005 when it was introduced to the United States consumer market under the trade name Superdrol, sold as an over-the-counter dietary supplement and marketed deceptively as a prohormone to circumvent the Anabolic Steroid Control Act of 1990. In preclinical rat bioassays using methyltestosterone as the reference standard, methasterone demonstrated approximately 400 percent anabolic potency and 20 percent androgenic potency, yielding a Q-ratio (anabolic-to-androgenic dissociation index) of 20, among the highest reported for any oral AAS. The compound’s oral bioavailability (approximately 50 percent) is conferred by the 17-alpha-methyl group, which protects the steroid nucleus from hepatic first-pass metabolism but simultaneously renders the compound hepatotoxic through a mechanism common to all C17-alpha-alkylated androgens. Methasterone is non-aromatizable owing to its 5-alpha-reduced A-ring saturation, and therefore does not produce estrogenic effects such as gynecomastia or water retention. Hepatotoxicity is the principal and most serious adverse effect: a distinctive pattern of bland cholestatic liver injury, characterized by severe hyperbilirubinemia with only modest aminotransferase elevation, has been documented in multiple case series and case reports. A comprehensive literature review of 52 reported cases identified a median presentation bilirubin of 314 micromol/L, peak bilirubin of 705 micromol/L occurring approximately 28 days after cessation, and resolution over a median of 90 days with supportive care alone; no deaths or liver transplantations were reported in the published literature. Acute kidney injury occurred in 43 percent of cases, with peak creatinine correlating with peak bilirubin. The World Anti-Doping Agency placed methasterone on its prohibited list in 2006. The United States Drug Enforcement Administration classified methasterone as a Schedule III controlled substance in January 2012 under the Controlled Substances Act, and the Designer Anabolic Steroid Control Act of 2014 further expanded regulatory authority over designer steroids of this class. Methasterone has no approved medical indication in any jurisdiction. This monograph documents the complete chemistry, synthesis, pharmacology, pharmacokinetics, hepatotoxicity profile, clinical case evidence, sourcing considerations, handling, combination interactions, adverse event signal, and a comparative assessment against five alternative oral anabolic-androgenic steroids (oxandrolone, oxymetholone, stanozolol, methyltestosterone, and epistane) on five competency standards.

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  • Aticaprant

    Selective kappa-opioid receptor (KOR) antagonist with short-acting, non-inactivating pharmacodynamic profile

    A potent, orally bioavailable aminobenzyloxyarylamide kappa-opioid receptor antagonist developed at Eli Lilly and advanced through Phase 3 clinical evaluation for adjunctive treatment of major depressive disorder with anhedonia, distinguished from earlier KOR antagonists by favorable drug-like properties, short-acting receptor blockade, and a well-characterized safety profile.

    Abstract

    Aticaprant (LY-2456302, CERC-501, JNJ-67953964) is a potent, selective, orally bioavailable antagonist of the kappa-opioid receptor (KOR) with a binding affinity (Ki) of 0.81 nM, approximately 30-fold selectivity over the mu-opioid receptor (Ki = 24.0 nM), and approximately 190-fold selectivity over the delta-opioid receptor (Ki = 155 nM). The compound belongs to the aminobenzyloxyarylamide chemical class and was designed at Eli Lilly Research Laboratories as a clinically viable therapeutic targeting the endogenous dynorphin/KOR neuromodulatory system, a pathway implicated in the pathophysiology of stress-induced anhedonia, dysphoria, and addictive behaviors. In contrast to earlier KOR antagonists such as JDTic and nor-binaltorphimine, which exhibit ultra-long-duration receptor inactivation persisting for weeks after a single dose, aticaprant produces short-acting, reversible KOR blockade with an elimination half-life of 30 to 40 hours, enabling conventional once-daily oral dosing and predictable pharmacokinetic management.

    The preclinical pharmacology of aticaprant was characterized in the seminal Rorick-Kehn et al. (2014) report, which demonstrated that oral administration selectively and potently occupied central KOR in vivo (ED50 = 0.33 mg/kg) without evidence of mu- or delta-opioid receptor occupancy at doses up to 30 mg/kg. In rodent behavioral models, aticaprant produced antidepressant-like effects in the mouse forced swim test, enhanced the efficacy of imipramine and citalopram, reduced ethanol self-administration in alcohol-preferring (P) rats, and reversed unpredictable chronic mild stress-induced anhedonia in C57BL/6J mice, as measured by sucrose preference, nest building, and forced swim endpoints. Positron emission tomography (PET) imaging in humans confirmed near-complete saturation of brain KOR at a 10 mg oral dose (94% receptor occupancy at 2.5 hours post-dose), with sustained occupancy (82% at 24 hours for a 25 mg dose), supporting the translational pharmacology from preclinical models to human central nervous system target engagement.

    Clinical development of aticaprant has proceeded through multiple sponsors. Eli Lilly conducted the initial Phase 1 single- and multiple-ascending dose studies (Lowe et al. 2014), establishing safety, tolerability, and the absence of clinically significant interactions with ethanol. Cerecor Inc. acquired the compound in 2015 and initiated early clinical studies in mood and substance use disorders. Janssen Pharmaceuticals (Johnson and Johnson) acquired the compound in 2017 and advanced it through Phase 2 and Phase 3 programs for adjunctive treatment of major depressive disorder (MDD) in patients with inadequate response to selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). The Phase 2 randomized, double-blind, placebo-controlled study (Jacobsen et al. 2024) in 181 participants with MDD and moderate-to-severe anhedonia demonstrated a statistically significant reduction of 2.1 points on the Montgomery-Asberg Depression Rating Scale (MADRS) for aticaprant 10 mg versus placebo (p = 0.04), with favorable tolerability and no new safety signals. However, the compound did not separate from placebo on secondary measures of anhedonia (Snaith-Hamilton Pleasure Scale), global illness severity (CGI-S), anxiety (HAM-A), or patient-reported depression outcomes.

    Janssen subsequently initiated the VENTURA Phase 3 program comprising five pivotal trials in MDD with anhedonia. On 6 March 2025, Johnson and Johnson announced discontinuation of the VENTURA program due to insufficient efficacy in the target population, while noting that the compound remained safe and well tolerated with no new safety signals detected. The most common treatment-emergent adverse events in clinical trials were headache (11.8% versus 7.1% placebo), diarrhea (8.2% versus 2.4%), nasopharyngitis (5.9% versus 2.4%), and pruritus (5.9% versus 0%). Johnson and Johnson has indicated that it will explore future development opportunities for aticaprant in other areas of high unmet need. The compound is not approved by any regulatory authority for any indication. This monograph reviews the chemistry, synthesis, receptor pharmacology, pharmacokinetics, preclinical and clinical evidence base, sourcing and quality considerations, reconstitution and handling, stack interactions, adverse-event profile, and a comparative assessment of five KOR antagonist candidates against aticaprant on five competency standards.

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  • Dianabol

    Synthetic 17-alpha-alkylated anabolic-androgenic steroid; testosterone derivative with C1-C2 dehydrogenation

    A 17-alpha-methylated, delta-1-dehydrogenated testosterone derivative developed at CIBA as an orally bioavailable anabolic agent, historically prescribed for catabolic wasting, osteoporosis, and nitrogen-balance restoration, and now principally encountered as a controlled substance of research interest in androgen receptor pharmacology, steroid metabolism, and anabolic-androgenic steroid toxicology.

    Abstract

    Metandienone (International Nonproprietary Name), known commercially as Dianabol and chemically as 17-alpha-methyl-delta-1-testosterone, is a synthetic anabolic-androgenic steroid (AAS) of the androstane class first synthesized at CIBA Pharmaceuticals in Switzerland in the mid-1950s and introduced to the United States prescription market in 1958. The compound is a structural modification of testosterone bearing two critical alterations: a methyl group at the C17-alpha position that confers oral bioavailability by resisting hepatic first-pass metabolism, and a delta-1 (C1-C2) double bond that modifies the anabolic-to-androgenic activity ratio relative to the parent hormone. Metandienone binds the androgen receptor (AR) in skeletal muscle, prostate, and other androgen-responsive tissues, initiating genomic signaling cascades that increase protein synthesis, nitrogen retention, and glycogenolysis. The compound undergoes aromatization by the CYP19A1 (aromatase) enzyme to 17-alpha-methylestradiol, producing dose-dependent estrogenic effects including fluid retention and gynecomastia. Hepatic metabolism proceeds principally through CYP3A4-catalyzed 6-beta-hydroxylation, with additional pathways including 5-beta-reduction, 3-alpha and 3-beta oxidation, and 17-epimerization; the 17-alpha-alkylation that confers oral bioavailability simultaneously produces the hepatotoxicity characteristic of this structural class.

    The compound was originally developed and marketed for the treatment of catabolic states, post-surgical recovery, osteoporosis, and hypogonadism. Clinical trials conducted in the late 1950s and 1960s demonstrated significant positive nitrogen balance at oral doses of 5 to 10 mg per day, with measurable increases in lean body mass and appetite stimulation. However, escalating recognition of the hepatotoxic, cardiovascular, endocrine-suppressive, and estrogenic adverse-effect profile led to progressive restriction of approved indications, and the United States Food and Drug Administration withdrew approval in 1983. The compound is currently classified as a Schedule III controlled substance in the United States under the Controlled Substances Act and is prohibited by the World Anti-Doping Agency. It is not approved for any medical indication in any major regulatory jurisdiction.

    Despite the absence of current clinical approval, metandienone remains a compound of substantial research interest. Its well-characterized androgen receptor pharmacology, its defined hepatotoxic mechanism as a model 17-alpha-alkylated steroid, its known metabolic pathways and urinary metabolite profile (exploited extensively in anti-doping analytical chemistry), and its historical clinical dataset in nitrogen-balance and muscle-wasting research provide a comprehensive pharmacological record. Preclinical studies in rat models have demonstrated that metandienone stimulates levator ani muscle hypertrophy through androgen receptor activation, suppresses the hypothalamic-pituitary-testicular axis, and modulates myostatin signaling pathways. This monograph reviews the chemistry, synthesis, and stereochemistry of metandienone; the androgen receptor pharmacology and mechanism of action; the comprehensive pharmacokinetic record including hepatic metabolism and urinary metabolite detection; the historical clinical evidence base; sourcing and quality verification considerations for research-grade material; reconstitution and handling; stack-interaction considerations; the adverse-event and safety signal across hepatic, cardiovascular, endocrine, and estrogenic domains; and a comparative assessment of five alternative anabolic-androgenic steroids (testosterone, oxandrolone, oxymetholone, stanozolol, nandrolone decanoate) against metandienone on five competency standards (oral bioavailability, anabolic efficacy, hepatotoxicity profile, estrogenic burden, and overall risk-benefit in research contexts).

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  • Arimistane

    Steroidal mechanism-based (suicide) aromatase inhibitor derived from the 7-oxo-dehydroepiandrosterone metabolic pathway

    A naturally occurring androstadienedione metabolite of 7-keto-DHEA that functions as an irreversible steroidal aromatase inactivator, distinguished from pharmaceutical aromatase inhibitors by its endogenous biosynthetic origin and concurrent reported activity on cortisol regulation through competitive inhibition of 11-beta-hydroxysteroid dehydrogenase type 1.

    Abstract

    Androsta-3,5-diene-7,17-dione, marketed and commonly known as Arimistane, is a steroidal mechanism-based irreversible inhibitor of aromatase (cytochrome P450 19A1, CYP19A1) that occupies a distinctive position in the landscape of estrogen-modulating compounds. Structurally, it is an androstadienedione bearing conjugated 3,5-diene unsaturation in the A/B ring system and a 7-oxo group on the B ring, with the characteristic 17-ketone of the androstane series. The compound is a downstream metabolite of 7-keto-dehydroepiandrosterone (7-keto-DHEA, 3-beta-hydroxyandrost-5-ene-7,17-dione), itself produced from dehydroepiandrosterone (DHEA) by hepatic cytochrome P450 7B1 (CYP7B1) or CYP3A-mediated 7-alpha-hydroxylation followed by 11-beta-hydroxysteroid dehydrogenase (11-beta-HSD) oxidation at the 7-position and subsequent dehydration. This endogenous biosynthetic origin distinguishes Arimistane from fully synthetic aromatase inhibitors such as exemestane, letrozole, and anastrozole.

    The aromatase-inhibitory mechanism of Arimistane belongs to the type I (steroidal, mechanism-based) class characterized by Covey and colleagues in the early 1980s for the structurally related androst-5-ene-7,17-dione series [1, 2]. Mechanism-based inhibition proceeds through initial competitive binding of the steroidal inhibitor to the substrate-binding pocket of aromatase, followed by enzyme-catalyzed oxidative processing that generates a reactive intermediate capable of forming a covalent bond with amino acid residues at or near the active site. The covalent modification permanently inactivates the enzyme molecule; restoration of aromatase activity requires de novo protein synthesis rather than simple inhibitor dissociation. This irreversible (“suicide”) mechanism produces sustained estrogen suppression that persists beyond the plasma residence time of the parent compound, a pharmacodynamic feature shared with the clinically approved steroidal aromatase inactivator exemestane.

    Beyond aromatase inhibition, Arimistane has been reported to modulate cortisol metabolism through competitive inhibition of 11-beta-hydroxysteroid dehydrogenase type 1 (11-beta-HSD1), the microsomal enzyme that catalyzes the reduction of cortisone to the biologically active glucocorticoid cortisol in liver, adipose tissue, and central nervous system. This activity, attributed to the 7-oxo-androstane structural motif shared with 7-keto-DHEA and its metabolites, is proposed to reduce local cortisol regeneration without affecting adrenal cortisol synthesis directly. The dual aromatase-inhibitory and cortisol-modulatory profile has driven interest in Arimistane within the bodybuilding and sports-performance supplement industry, where the compound has been marketed as a post-cycle therapy agent and estrogen-control supplement.

    The regulatory status of Arimistane is restrictive. The United States Food and Drug Administration (FDA) has determined that androsta-3,5-diene-7,17-dione does not meet the statutory definition of a dietary ingredient under section 201(ff)(1) of the Federal Food, Drug, and Cosmetic Act, and has issued multiple warning letters to supplement manufacturers marketing products containing the compound [3]. The World Anti-Doping Agency (WADA) added Arimistane to the Prohibited List in 2017 under the category of hormone and metabolic modulators (class S4), specifically as an aromatase inhibitor [4]. The compound is not approved as a pharmaceutical in any jurisdiction.

    The clinical evidence base for Arimistane is sparse relative to pharmaceutical aromatase inhibitors. No registration-quality clinical trials have been conducted. Published human data are limited to manufacturer-sponsored tolerability assessments and analytical chemistry studies characterizing the compound as a urinary metabolite of 7-keto-DHEA in anti-doping contexts [5]. The pharmacological characterization rests principally on in vitro aromatase inhibition assays, structure-activity relationship inference from the broader androstene-7,17-dione series studied by Covey, Brodie, and colleagues in the 1980s and 1990s [1, 2, 6], and extrapolation from the more extensive clinical pharmacology of the structurally related steroidal aromatase inactivator exemestane. This monograph reviews the chemistry, biosynthetic origin, mechanism of aromatase inactivation, reported pharmacokinetics, preclinical and clinical evidence, sourcing and quality considerations, stack interactions, adverse-event signal, and a comparative assessment of Arimistane against five alternative aromatase-modulating compounds on five competency standards.

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  • Anadrol

    17-alpha-alkylated anabolic-androgenic steroid; synthetic dihydrotestosterone derivative with potent erythropoietic and anabolic activity

    A 17-alpha-alkylated oral anabolic-androgenic steroid derived from dihydrotestosterone, developed at Syntex in the late 1950s for the treatment of anemias characterized by deficient red blood cell production, distinguished by potent erythropoietic stimulation, marked nitrogen retention, and significant hepatotoxic liability.

    Abstract

    Oxymetholone, marketed as Anadrol-50 (Syntex, later Unimed Pharmaceuticals, now Alaven Pharmaceutical) and Anapolon (Imperial Chemical Industries and generics), is a synthetic 17-alpha-alkylated derivative of dihydrotestosterone first described by Ringold et al. at Syntex in 1959 and introduced into clinical medicine in the early 1960s for the treatment of anemias, osteoporosis, and catabolic wasting states. The compound is the 2-hydroxymethylene analog of 17-alpha-methyl-dihydrotestosterone (mestanolone), bearing an unusual hydroxymethylene substituent at the C2 position that confers oral bioavailability through resistance to first-pass hepatic inactivation and that can be metabolically cleaved to yield mestanolone as an active metabolite. Oxymetholone is one of the most potent oral anabolic-androgenic steroids in clinical use, exhibiting a high ratio of anabolic to androgenic activity in classical levator ani and ventral prostate bioassays while paradoxically demonstrating low direct binding affinity for the androgen receptor in competitive displacement studies. The principal pharmacodynamic effects are stimulation of erythropoiesis through increased renal erythropoietin production (with urinary erythropoietin levels elevated up to fivefold at therapeutic doses), promotion of positive nitrogen balance and skeletal muscle protein synthesis, and a poorly characterized but clinically significant estrogenic activity that occurs despite the compound’s structural inability to undergo aromatization, possibly through direct activation of estrogen receptor alpha. The compound received approval from the United States Food and Drug Administration for the treatment of anemias caused by deficient red blood cell production, including acquired aplastic anemia, congenital aplastic anemia, myelofibrosis, and hypoplastic anemias due to the administration of myelotoxic drugs. In the mid-1970s, the FDA restricted the approved indication exclusively to anemias characterized by deficient erythropoiesis, withdrawing prior approvals for osteoporosis and general catabolic states. Clinical investigation has subsequently extended to HIV/AIDS-associated wasting (Hengge et al. 2003 Phase III trial demonstrating 3.0 to 3.5 kg weight gain over 16 weeks at 100 to 150 mg daily), antithrombin III deficiency, and pediatric growth failure, with varying degrees of success. The hepatotoxic liability of the 17-alpha-alkylated structure is the principal safety concern: cholestatic jaundice occurs in approximately 1 percent of treated patients, typically within 1 to 4 months of initiation; peliosis hepatis (blood-filled sinusoidal cysts) develops with prolonged administration and has resulted in fatal hepatic rupture and hemorrhage in case reports; and hepatocellular carcinoma and hepatic adenoma have been reported after 2 to 15 years of continuous use, predominantly in patients with Fanconi anemia and aplastic anemia receiving chronic androgen therapy. The compound is classified as a Schedule III controlled substance in the United States under the Controlled Substances Act and is subject to equivalent regulatory controls in most jurisdictions. This monograph reviews the chemistry, synthesis, and structure-activity relationships of oxymetholone; the androgen receptor, erythropoietic, and estrogenic pharmacology; the limited but clinically relevant pharmacokinetic record; the preclinical pharmacology in animal models of anemia and wasting; the clinical evidence base across anemia, HIV wasting, and ancillary indications; sourcing and quality verification for research applications; reconstitution and handling; stack interactions and combinations with other anabolic and therapeutic agents; the adverse-event and safety signal including detailed hepatotoxicity characterization; and a comparative assessment of five alternative anabolic-androgenic agents (oxandrolone, nandrolone decanoate, stanozolol, testosterone enanthate, danazol) against oxymetholone on five competency standards.

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  • Tadalafil

    Selective phosphodiesterase type 5 (PDE5) inhibitor with secondary PDE11 activity

    A long-acting beta-carboline-derived cyclic GMP phosphodiesterase inhibitor developed by ICOS and Eli Lilly for erectile dysfunction, subsequently approved for benign prostatic hyperplasia and pulmonary arterial hypertension, distinguished from other PDE5 inhibitors by a 17.5-hour plasma half-life, food-independent absorption, and emerging preclinical interest in neuroprotection and cognitive enhancement.

    Abstract

    Tadalafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), approved by the United States Food and Drug Administration for the treatment of erectile dysfunction (ED), the signs and symptoms of benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension (PAH). Structurally a beta-carboline (pyrazinopyridoindole) derivative bearing a methylenedioxyphenyl substituent, tadalafil is chemically and pharmacologically distinct from the pyrimidinone-based PDE5 inhibitors sildenafil and vardenafil. The compound was originally synthesized at ICOS Corporation as IC351, advanced through clinical development in a joint venture with Eli Lilly and Company (Lilly ICOS LLC), and received its first regulatory approval in the European Union in November 2002 and in the United States in November 2003 under the trade name Cialis for the on-demand treatment of ED at 10 mg and 20 mg oral doses [1, 2].

    The defining pharmacokinetic feature of tadalafil is its prolonged plasma elimination half-life of approximately 17.5 hours, roughly three to five times longer than the half-lives of sildenafil (3 to 5 hours) and vardenafil (4 to 5 hours), enabling a clinically meaningful therapeutic window of 24 to 36 hours from a single oral dose and supporting a once-daily 2.5 mg or 5 mg dosing regimen approved for both ED and BPH [3, 4]. Absorption is not affected by food, a further distinction from sildenafil and vardenafil, whose absorption is delayed by high-fat meals. Tadalafil is metabolized predominantly by hepatic cytochrome P450 3A4 (CYP3A4) to the pharmacologically inactive methylcatechol glucuronide conjugate; approximately 61 percent of an administered dose is excreted in feces and 36 percent in urine [5].

    The molecular mechanism is inhibition of PDE5, the enzyme responsible for hydrolysis of cGMP in vascular smooth muscle. In the corpus cavernosum, nitric oxide released during sexual stimulation activates soluble guanylate cyclase, which synthesizes cGMP from guanosine triphosphate; cGMP in turn activates protein kinase G, producing smooth muscle relaxation, vasodilation, and penile erection. By preventing cGMP degradation, tadalafil amplifies and sustains the nitric oxide signaling cascade. The same mechanism operates in the pulmonary vasculature (where PDE5 inhibition reduces pulmonary arterial pressure) and in the smooth muscle of the prostate, bladder neck, and urethra (where PDE5 inhibition alleviates lower urinary tract symptoms associated with BPH) [6, 7]. Tadalafil is more than 10,000-fold selective for PDE5 over PDE3 (cardiovascular), approximately 700-fold selective over PDE6 (retinal), but only approximately 40-fold selective over PDE11A, a dual-specificity phosphodiesterase expressed in skeletal muscle, prostate, testes, and other tissues. The relatively low PDE5/PDE11 selectivity ratio is the presumed molecular basis for the back pain and myalgia adverse events that occur at higher frequency with tadalafil than with the other PDE5 inhibitors [8, 9].

    Clinical efficacy in ED has been established across multiple randomized, double-blind, placebo-controlled trials enrolling populations with mild through severe dysfunction, with overall response rates of 60 to 70 percent on validated questionnaires. The 40 mg once-daily dose for PAH produced a statistically significant 33-meter improvement in six-minute walk distance over placebo in the PHIRST registration trial [10]. The 5 mg once-daily dose for BPH produced a statistically significant improvement in International Prostate Symptom Score (IPSS) of approximately 2 points over placebo across four pivotal 12-week trials [11]. Common adverse events include headache (approximately 15 percent at 20 mg), dyspepsia (approximately 10 percent), back pain (approximately 6 percent), myalgia (approximately 4 percent), nasal congestion, and flushing. The compound is absolutely contraindicated with organic nitrates (the combination produces severe, potentially fatal hypotension) and with soluble guanylate cyclase stimulators [12, 13]. Rare but serious postmarketing signals include nonarteritic anterior ischemic optic neuropathy (NAION), sudden sensorineural hearing loss, and priapism. The compound is not recommended in patients with recent myocardial infarction, unstable angina, uncontrolled hypertension, or in patients in whom sexual activity is medically inadvisable.

    This monograph documents the chemistry, synthesis, and stereochemistry of tadalafil; the PDE5 inhibitory mechanism in molecular and physiological detail; the comprehensive human pharmacokinetic record; the preclinical pharmacology across vascular, urological, pulmonary, and neuroprotective domains; the clinical evidence base for all approved and investigational indications; sourcing and quality verification considerations; reconstitution and handling; stack-interaction implications for concurrent pharmacotherapy; adverse-event and safety signal characterization; and a structured comparative assessment of five PDE5 inhibitor alternatives (sildenafil, vardenafil, avanafil, mirodenafil, udenafil) against tadalafil on five competency standards: novelty, effect size, promising potential, side-effect profile, and overall validation.

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  • Telmisartan

    Non-peptide angiotensin II type 1 receptor antagonist with selective partial peroxisome proliferator-activated receptor gamma agonism

    A biphenyl-benzimidazole angiotensin II receptor blocker developed at Boehringer Ingelheim, distinguished from other sartans by intrinsic partial agonist activity at the nuclear peroxisome proliferator-activated receptor gamma and downstream metabolic, anti-inflammatory, and neuroprotective activity.

    Abstract

    Telmisartan is a non-peptide, orally active antagonist of the angiotensin II type 1 receptor (AT1R) and a selective partial agonist of the nuclear peroxisome proliferator-activated receptor gamma (PPARgamma), approved by the United States Food and Drug Administration in 1998 for the treatment of hypertension and subsequently for cardiovascular risk reduction in patients intolerant to angiotensin-converting enzyme inhibitors. The compound is marketed as Micardis (Boehringer Ingelheim) and is available in extensive generic competition worldwide. Among the eight clinically marketed angiotensin II receptor blockers (ARBs), telmisartan is distinguished by three pharmacological and pharmacokinetic features: the longest terminal elimination half-life (approximately 24 hours), the largest volume of distribution (approximately 500 liters), and a structurally defined partial agonist interaction with PPARgamma that is not shared at clinically meaningful potency by any other marketed sartan. The PPARgamma partial agonism, first formally characterized by Benson et al. (2004) in a systematic screen of ARBs against nuclear receptor panels, produces downstream modulation of carbohydrate and lipid metabolism gene expression, reduction of insulin resistance markers, suppression of NF-kappaB-driven proinflammatory cytokine release, and enhancement of adiponectin secretion, all at concentrations achieved by the registered 80 mg oral dose [1]. These pleiotropic activities extend the pharmacological profile of telmisartan substantially beyond the hemodynamic consequences of AT1R blockade and have driven a preclinical and clinical research literature encompassing metabolic syndrome, type 2 diabetes prevention, neuroprotection, renoprotection, and anti-inflammatory applications.

    The clinical evidence base for telmisartan is anchored by two landmark randomized controlled trials. The ONTARGET trial (Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial; N = 25,620) demonstrated that telmisartan 80 mg daily was non-inferior to ramipril 10 mg daily on a composite cardiovascular endpoint of cardiovascular death, myocardial infarction, stroke, or hospitalization for heart failure in high-risk patients, with superior tolerability and fewer treatment discontinuations [2]. The TRANSCEND trial (Telmisartan Randomised Assessment Study in ACE Intolerant Subjects with Cardiovascular Disease; N = 5,926) demonstrated that telmisartan modestly reduced the composite of cardiovascular death, myocardial infarction, or stroke compared with placebo in ACE-inhibitor-intolerant patients, leading to the 2009 FDA supplemental indication for cardiovascular risk reduction [3]. Additional large-scale trials include PRoFESS (Prevention Regimen for Effectively Avoiding Second Strokes; N = 20,332), which evaluated telmisartan for secondary stroke prevention, and DETAIL (Diabetics Exposed to Telmisartan and Enalapril; N = 250), which demonstrated renoprotective non-inferiority to enalapril in type 2 diabetic patients with early nephropathy.

    Pharmacokinetics are characterized by dose-dependent oral bioavailability (42 percent at 40 mg, 58 percent at 160 mg), negligible cytochrome P450-mediated metabolism (less than 3 percent of the dose is glucuronidated; the remainder is excreted unchanged in bile and feces), a terminal elimination half-life of approximately 24 hours supporting once-daily dosing, and greater than 99.5 percent plasma protein binding. The compound is poorly soluble in water but freely soluble in dimethyl sulfoxide and dimethylformamide. Telmisartan does not require dose adjustment for renal impairment but should be used with caution in severe hepatic impairment owing to the predominantly biliary elimination pathway.

    This monograph reviews the chemistry, synthesis, and structural pharmacology of telmisartan; the dual AT1R antagonist and PPARgamma partial agonist mechanism in molecular detail; the comprehensive human pharmacokinetic record; the preclinical pharmacology across cardiovascular, metabolic, neuroprotective, and renoprotective models; the clinical evidence base across all studied indications; sourcing and quality verification considerations; reconstitution and handling for laboratory use; stack-interaction implications; adverse-event signal; and a structured comparative assessment of five alternative ARBs (losartan, valsartan, irbesartan, olmesartan, candesartan) against telmisartan on five competency standards.

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