PT 141 10mg

PT-141 (Bremelanotide) is a synthetic cyclic heptapeptide (MW: 1025.2 Da) derived from α-MSH (melanocyte-stimulating hormone), developed as a selective agonist of melanocortin receptors MC3R and MC4R. Unlike its predecessors (Melanotan I/II), PT-141 exhibits optimized selectivity for applications related to sexual function and arousal, with an improved side effect profile.

Molecular Structure:

• Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH
• Cyclization: Asp-Lys lactam bridge (conformational stability)
• Modifications
  • Nle (Norleucine) position 4: prevents oxidation vs Met
  • D-Phenylalanine position 7: resistance to proteolytic degradation
  • N-terminal acetylation: exopeptidase protection
• Selectivity: MC3R/MC4R > MC1R (less pigmentation effect vs. Melanotan II)

Melanocortin System and Receptors

The melanocortin system comprises 5 receptor subtypes (MC1R-MC5R), each with specific tissue distribution and functions:

Molecular Mechanisms of Sexual Action:

1. Central MC3R/MC4R Activation:

Neural Circuits Excitation:

• Paraventricular Nucleus (PVN) Hypothalamus:
  • High MC4R density, integration of excitatory signals
  • Descending projections of the sacral spinal cord
  • Amygdala-prefrontal cortex connections (emotional component)
• Medial Preoptic Area (MPOA)
  • “Sexual integration center” brain
  • MC3R/MC4R expression in key neurons
  • Nitric oxide (NO) release via nitrergic neurons

Neurotransmission

• Nitric Oxide (NO):
  • Upregulation of nNOS (neuronal nitric oxide synthase) 200-300%
  • Genital vasodilation: cavernous/clitoral smooth muscle relaxation
  • Central effects: facilitation of sexual arousal/response
• Dopamine
  • Increased VTA release, nucleus accumbens
  • Sexual motivation, reward, proceptive behavior
  • D1/D2 receptor interaction: potentiation of response
• Endogenous melanocortins:
  • α-MSH, β-MSH: tonic modulators of arousal
  • AgRP (Agouti-related peptide): endogenous MC3R/MC4R antagonist
  • Agonist/antagonist balance: regulation of basal sexual function

2. Peripheral Effects:

Male Genitalia

• Smooth muscle cavernosum: NO/cGMP-mediated relaxation
• Penile blood flow: increase of 250–400%
• Intracavernous pressure: 40-60 mmHg
• Mechanism: independent testosterone, complementary PDE5 inhibitors

Female Genitalia:

• Clitoral/labial vasocongestion: volume increase 35-50%
• Vaginal lubrication: increased plasma transudation of epithelium
• Tactile sensitivity: enhancing sensory responses
• Vaginal smooth muscle: relaxation facilitating penetration

Pharmacokinetics

• Bioavailability SC: 100% (the only approved/studied method)
• Tmáx: 60-90 minutes (effects start 30-45 min)
• Duration of effects: 6-12 hours (sexual receptivity window)
• Median life 2-3 hours (elimination)
• Metabolism: proteolytic degradation, with no known active metabolites
• Excretion primary renal (80%), fecal (20%)

Blood-brain barrier efficient cross (central action mechanism)

1. FEMALE SEXUAL DYSFUNCTION (HSDD – Hypoactive Sexual Desire Disorder)

Hypoactive Sexual Desire Disorder

Definition and Prevalence:

• HSDD: Absence/decrease in sexual thoughts/fantasies + lack of sexual response desire
• Prevalence: 8–121 TP3T in premenopausal women, 12–261 TP3T in postmenopausal women
• Impact: Significant personal distress, relationship conflicts

PT-141 Pivotal Clinical Studies:

RECONNECT Study (Kingsberg et al., 2019):

• Design: Phase 3 RCT, n=1,247 premenopausal women with HSDD
• Dosage: 1.75 mg SC on-demand (45 min before anticipated sexual activity)
• Duration: 24 weeks
• Primary outcomes:
  • Satisfying Sexual Events (SSE) +1.2 vs +0.4 placebo (p<0.001)
  • Desire (FSFI-D): Improves 0.3 points vs placebo (p<0.001)
  • Response rate (≥1.2 SSE increase): 35% vs. 23% placebo

RECONNECT 2 (Portman et al., 2020):

• n=1,281 women, similar design
• SSE increase: +1.2 events/month vs +0.6 placebo
• Sexual distress: reduction from 25% to 15% with placebo (FSD-R scale)
• Spontaneous desire: reported improvement 42% vs. 31%

HSDD Mechanisms

• MC4R PVN activation: increased sexual motivation (“wanting”)
• Mesolimbic dopamine: Restoration of reward/anticipation circuits
• Inhibition reduction: serotonin modulation (indirect 5-HT₂C antagonism)
• Peripheral sensitization: improved perception of genital tactile stimulation

2. MALE ERECTILE DYSFUNCTION (Preclinical/Early Clinical Research)

Erection Mechanisms

Central Route (Predominant PT-141):

• MC4R PVN activation → spinal cord proerectile projections
• Sacral autonomic nuclei (S2-S4): parasympathetic output
• Nitrenergic neurons: release of NO in cavernous tissue
• Independent direct tactile stimulation: “central” erections”

Preliminary Human Studies

• Phase 2a (Wessells et al., 2000): n=20 men with psychogenic/mixed ED
  • Dosage: 0.5-20 mg IN (intranasal, early formulation)
  • Answer: Spontaneous erections in 60% participants
  • Duration: 2-6 hours response window
  • Adverse effects: nausea 40%, flushing 30%
• Comparative study vs. Sildenafil (Diamond et al., 2004):
  • PT-141: Effective for psychogenic/neurogenic
  • Sildenafil: superior vasculogenic ED
  • Complementarity: different mechanisms of action

Specific Populations Benefit:

• Neurogenic bladder Spinal cord injury, diabetic neuropathy
• Psychogenic Performance anxiety, psychological inhibition
• No responders PDE5i Patients who did not respond to sildenafil/tadalafil (10-30%)
• Post-prostatectomy Nerve preservation uncertain

3. LIBIDO AND SEXUAL MOTIVATION (Both Sexes)

Sexual Desire Components:

Dual Model (Excitation/Inhibition):

• Excitement (SES): Facilitation of sexual response (dopamine, melanocortin)
• Inhibition (SIS): Braking response (serotonin, endogenous opioids)
• PT-141: shift balance toward arousal (↑ SES, ↓ SIS)

Libido Effects: Base

• Sexual thoughts: increased frequency 30-40%
• Sexual fantasies: improving vividness/emotional content
• Receptivity: greater openness initiation/response activity
• Subjective arousal: amplification of perceived arousal

Sex Differences

• Women: greater improvement in spontaneous desire (30–401 TP3T responders)
• Men: Libido effects + erectile function (dual benefit)
• Individual variability: 30–50% robust response, 20–30% minimum

4. ANORGASMIA AND ORGASMIC RESPONSE

Orgasmic Dysfunction

Potential Mechanisms:

• Spinal reflex awareness: facilitation of the orgasmic reflex arc
• Sensory amplification: increased processing of genital signals
• Orgasm umbra: reduced stimulation needed
• Subjective intensity: enhances pleasurable experience

Preliminary Evidence:

• Open-label studies: improved orgasmic capacity in 25-35% women with secondary anorgasmia
• Orgasm latency: reduction in time required for stimulation
• Multiple orgasms: facilitation in a subgroup of women
• Orgasm quality: increased intensity/satisfaction (qualitative reports)

5. ANTIDEPRESSANT SIDE EFFECTS (SSRI-Induced Sexual Dysfunction)

SSRI-induced Sexual Dysfunction

Prevalence and Mechanisms:

• 40-65%: SSRI patients: sexual dysfunction (desire, arousal, orgasm)
• Mechanism: 5-HT₂C agonism (dopamine/NO inhibition)
• Adherence: 20-30% discontinued due to sexual side effects
• Quality of life: significant impact, factor in maintaining depression

PT-141 as a Potential Antidote:

• Counterregulation: Dopamine/Melanocortin vs. Serotonergic Inhibition
• Case study: improving sexual function while maintaining antidepressant efficacy
• Dosage: on-demand vs chronic (research needed)
• Current alternatives: bupropion (less dysfunction), SSRI dose reduction

6. NON-SEXUAL RESEARCH APPLICATIONS

Motivation and Reward System:

Anhedonia (Depression/Addiction):

• MC4R nucleus accumbens: reward circuit modulation
• Awareness pleasure: response to natural stimuli (food, social)
• Motivational Approach: Goal-Directed Behaviors

Social Cognition:

• Oxytocin: Melanocortin-Oxytocin System Interaction
• Facial emotion recognition: processing improvement
• Prosocial behavior: increase affiliative behaviors

Appetite/Weight Regulation (Hypothalamic MC4R):

Satiety

• MC4R paraventricular nucleus: potent anorexigenic signal
• Food intake: reduction of 15–251 TP3T (adverse effects at high doses)
• Balance: Pro-sexual doses (<2 mg) minimal appetite effect
• Melanotan II difference: this last one is a potent anorectic (limited use)

Dosage Preclinical Research

Rodents (Rats/Mice):

Non-Human Primates

Experimental Models of Sexual Behavior

Rodent Paradigms

Standard Copulatory Test (Rats)

1. Female receptive (estrus) + experimental male
2. PT-141: 30-60 min pre-administration female
3. Observation 30-60 min: video recording
4. Parameters:
   • Mount latency: Time first attempt copulation
   • Riding frequency: number of attempts
   • Ejaculatory latency copulatory efficiency
   • Post-ejaculatory interval refractory period

Conditioned Place Preference (CPP) Sexual:

• Context + sexual experience association
• PT-141: Sexual Reward Potentiation
• Measurement: Associated Camera Time vs. Neutral
• Interpretation: Sexual approach motivation

Sexual Motivation Test:

• Appetitive behaviors: active mate searching
• Overcome barriers: effort (climbing, bar pressure)
• PT-141: increased motivation for approach
• Separation: Appetitive vs. Consummatory Effects

Physiological Studies

Intracavernous Pressure (ICP) - Erection Models:

• Anesthesia: physiological maintenance
• Corpus cavernosum catheterization: pressure measurement
• Cavernous nerve stimulation: erectile response
• Systemic PT-141: response potentiation 40-60%
• Analysis: AUC pressure, peak pressure, duration

Genital Blood Flow (Laser Doppler):

• Clitoral/penile perfusion: continuous measurement
• PT-141: Flow increase 200-350% vs. baseline
• Correlation: subjective vs. objective vasocongestion
• Timing: 60-90 minutes post-administration

Functional Neuroimaging (fMRI) – Humans:

• Brain activation: response to erotic stimuli
• PT-141 vs. placebo: activation differences
• Regions of interest: PVN, amygdala, insula, prefrontal cortex
• Connectivity: functional networks sexual circuits

PT-141 Preparation

PT-141 is typically supplied as a sterile lyophilized powder, requiring reconstitution before laboratory handling.

Standard Reconstitution Protocol:

1. Initial Preparation:
   • Balance vial PT-141 at room temperature for 10-15 minutes
   • Disinfect the rubber cap with isopropyl alcohol 70%
   • Prepare sterile area (laminar flow hood or clean surface)
2. Diluent Selection
   • First choice: Sterile bacteriostatic water (0.9% benzyl alcohol)
   • Alternative Sterile 0.9% NaCl saline solution
   • Target pH: 6.0-7.0 (PT-141 stable wide range)
   • Diluent temperature: ambient (20-25°C)
3. Recommended Concentrations:
   • Vial 10mg: Add 2.0mL → 5mg/mL (5000 μg/mL)
     • Lab volumetric reference: 1.75mg = 0.35mL at this concentration
   • Vial 10mg: Add 5.0 mL → 2 mg/mL (more diluted, higher injection volume)
   • For animal research: Lower concentrations (0.5-1.0 mg/mL)
4. Reconstitution Technique
   • Insert 22-25G needle at a 45° angle against the inner vial wall
   • Inject diluent SLOWLY (45-60 seconds) per wall
   • Do not direct a direct stream onto freeze-dried powder denaturation
   • Remove needle, rotate vial GENTLY in a circular motion
   • Do not shake vigorously ni vortex (loss of activity)
   • Dissolution time: 2-5 minutes typically
   • Rest 2-3 minutes: microbubble removal
5. Quality Check:
   • Solution must be transparent and colorless
   • Without visible particles, aggregates, or precipitation
   • Without turbidity or color change
   • Discard if any visual anomaly

Post-Reconstitution Storage:

Critical Considerations

• Moderate photosensitivity Protect from direct light (amber vials)
• Freeze-thaw cycles: Maximum of 2 cycles (loss of ~20–301 TP3T activity per cycle)
• Defrost Thaw in refrigerator at 4°C overnight (never microwave/hot water bath)
• Infertility Strict aseptic technique (microbial contamination)

PT-141 vs. PDE5 Inhibitors (Sildenafil, Tadalafil)? R: Mechanisms and different applications:

PT-141:

• Mechanism: Central (cerebral MC3R/MC4R activation)
• Effects: desire + arousal + genital function
• Timing: 30-45 min start, duration 6-12h
• Optimal indications: Female HSDD, psychogenic/neurogenic ED, reduced libido
• Adverse effects: nausea (40%), flushing (15%), headache (10%)

PDE5 Inhibitors:

• Mechanism: Peripheral (NO/cGMP potentiation in genitalia)
• Effects: Primarily erectile function (not direct libido)
• Timing: 30-60 min (sildenafil), up to 36h (tadalafil)
• Optimal indications: Vasculogenic erectile dysfunction, primary
• Adverse effects: headache (16%), flushing (10%), dyspepsia (7%)

Complementarity Different mechanisms allow potential combination (limited research).

Why is nausea such a common side effect? R: MC4R activation of the area postrema:

• Area postrema: lacks a complete blood-brain barrier, high MC4R expression
• “Vomiting center” brain: chemoreceptor trigger zone
• Dose-dependent: nausea at doses of 40–50% (1.75–2.0 mg), 15–20% at doses <1.0 mg
• Adaptation: partial tolerance to repeated use (50% cases)
• In the literature, the incidence of nausea was inversely associated with the administered dose (documented dose-dependent effect).

Q: What is the documented pharmacokinetic window in the studies? R: 30-90 minute window:

• Pharmacological Tmax: 60-90 min (peak concentration)
• Onset of subjective effects: 30-45 min (range 20-60 min)
• Peak effects: 90-180 min post-administration
• Receptivity window duration: 4-8 hours typical, up to 12 hours in some individuals
• In the trial protocols, administration was documented 45-60 min prior to the assessed event.

Tachyphylaxis or tolerance with chronic use? R: Limited tolerance:

• 24-week studies: sustained efficacy without significant loss
• Receptor downregulation: minimal (typical on-demand use)
• Some users: reduction of nausea with repeated use (positive adaptation)
• In studies, the on-demand regimen showed less receptor desensitization than continuous exposure.

Significant drug interactions? R: Favorable interactions profile:

• No interactions: PDE5 inhibitors, hormonal contraceptives, antidepressants (most)
• Theoretical caution: Dopaminergic agonists/antagonists (additive/antagonistic effects)
• Avoid unstudied combinations: α-MSH analogs, other melanocortin agonists
• Cardiovascular medication No absolute contraindications, monitor blood pressure

P: Differences Melanotan II vs PT-141? R: PT-141 is an enhanced derivative:

Melanotan II:

• Non-selective agonist: MC1R (pigmentation), MC3R/MC4R (sexual)
• Side effects: noticeable tanning, darkening of nevi, severe nausea
• Potent anorectic: significant appetite loss
• Action duration: 24-48h (long half-life)

PT-141:

• Enhanced selectivity: MC3R/MC4R > MC1R (lower pigmentation)
• Tanning: minimal/absent therapeutic doses
• Appetite: Minimal effects pro-sexual doses
• Duration: 6-12h (more controllable profile)
• Clinical Development: FDA Approval (Melanotan II not approved)

What do studies in postmenopausal models/populations document? R: Reported findings:

• Studies: include postmenopausal women with positive results
• Efficacy: comparable in premenopausal women (central mechanism, non-hormonal)
• Atrophic vaginitis: PT-141 does not correct (consider additional topical estrogen)
• Hormone therapy: compatible, no interactions
• Advantage: Non-hormonal alternative when TRH is contraindicated

Required monitoring for prolonged studies? R: Periodic reviews

• Blood pressure Baseline, weeks 2, 4, 8, every 8 weeks
  • Transitory increase of 10-15 mmHg systolic post-dose (monitor)
• Skin pigmentation Visual inspection, standardized photographs
• Sexual function Validated scales (FSFI, IIEF) monthly
• Adverse effects: Prospective registration events, severity

Laboratory Metabolic profile, baseline liver/kidney function, and semester (optional)

1. Kingsberg SA, et al. (2019) “Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials” – Obstetrics and Gynecology 134(5):899-908. [PubMed: 31599832]
2. Portman DJ, et al. (2020) “Continued efficacy and safety of bremelanotide for hypoactive sexual desire disorder” – J Womens Health 29(6):861-869. [PubMed: 31895612]
3. Wessells H, et al. (2000) “Melanocortin receptor agonists, penile erection, and sexual motivation” – Ann NY Acad Sci 897:349-357. [PubMed: 10676462]
4. Diamond LE, et al. (2004) “An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141)” – J Sex Med 3(4):628-638. [PubMed: 16839318]
5. Pfaus JG, et al. (2004) “Facilitation of sexual behavior in the male rat by a melanocortin agonist” – Hormones and Behavior46(4):431-436. [PubMed: 15465528]
6. Clayton AH, et al. (2016) “Bremelanotide for female sexual dysfunctions in premenopausal women” – J Sex Med13(9):1506-1513. [PubMed: 27671968]
7. Molinoff PB, et al. (2003) “PT-141: A melanocortin agonist for the treatment of sexual dysfunction” – Ann NY Acad Sci 994:96-102. [PubMed: 12851304]

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