PT-141 10mg Bienestar

The PT-141 mechanism is central and articulates primarily around melanocortin receptors. Five subtypes MC1R-MC5R exist in humans: MC1R (skin/hair pigmentation), MC2R (adrenal cortex, cortisol), MC3R and MC4R (central nervous system, food intake, sexual function), MC5R (exocrine glands). PT-141 is a preferential MC3R/MC4R agonist with reduced affinity for MC1R (key difference with Melanotan II, which minimises pigmentation).

MC4R activation in the paraventricular nucleus of the hypothalamus triggers a neuroendocrine cascade: oxytocin release from magnocellular neurons, dopamine increase in the ventral tegmental area and nucleus accumbens (reward circuits), spinal parasympathetic activation (sacral parasympathetic nucleus). These three effects converge towards facilitation of sexual arousal: oxytocin modulates motivation and attachment, dopamine creates anticipatory desire, and parasympathetic activation potentiates the peripheral vascular response (tumescence).

Unlike PDE5 inhibitors, PT-141 does not act directly on guanylate cyclase or vascular nitric oxide. It cannot therefore cause prolonged erection of the priapism type by blocking the detumescence inhibitor system. The erection or lubrication obtained under PT-141 remains controlled by normal physiological mechanisms, simply potentiated by activated central desire.

Pharmacokinetics: after subcutaneous injection of 1.75 mg, plasma peak in 1 hour, half-life 2-2.7 hours, urinary elimination. Biological effect (desire and arousal) peaks at 1-2 hours, perceptible duration 4-10 hours depending on subjects. Metabolisation is minimal, the peptide is excreted intact or slightly hydrolysed.

Central collateral effect: MC4R hypothalamic stimulation also affects appetite (transient reduction 20-40 %), anxiety (variability between subjects: mild anxiolysis for some, activation for others) and thermoregulation. Residual MC1R activation can cause discreet tanning at repeated doses.

The most frequent side effect is nausea (~40 % of subjects in RECONNECT trials), mediated by MC4R activation central and peripheral at the chemoreceptor vomiting zone. This nausea is moderate, dose-dependent and attenuated by injection after light meal, preventive antiemetic, or dose fractionation.

PT-141 and bremelanotide literature covers more than 100 publications over 20 years.

Discovery and initial development: Wessells 1998 Urology described the first human trial on 10 men with erectile dysfunction, showing a dose-dependent erectile response by intranasal and subcutaneous routes. Rosen 2004 J Sex Med confirmed on 271 ED men the effect on 30 % of better satisfactory erections versus placebo, including in sildenafil non-responders. Diamond 2006 J Sex Med published the first female data on 18 subjects with female sexual arousal disorder.

Female HSDD clinical development: Clayton 2016 Obstet Gynecol and Kingsberg 2019 Obstet Gynecol (pivotal RECONNECT-I and II trials) included 1247 premenopausal women with HSDD over 24 weeks, with bremelanotide 1.75 mg SC PRN (as needed, before sexual activity). Results: significant increase in FSFI-desire score (+0.5 to +0.7 vs placebo), reduction in FSDS sexual distress score, 35-45 % clinically significant responders. This trial supported 2019 FDA approval.

Male erectile dysfunction non-responder to PDE5: Safarinejad 2008 Int J Impot Res showed in 120 sildenafil/tadalafil non-responder men a response rate of 33 % under PT-141 SC 20 mg versus 8 % placebo. Molinoff 2003 Int J Impot Res studied the intranasal route (former formulation) in 271 ED men. Male indication was not pushed to approval by Palatin after intranasal development was stopped.

Neurobiology and animal models: Pfaus 2011 Obstet Gynecol Clin North Am summarised PT-141 neurobiology in rat and primate models: activation of hypothalamic oxytocin, lordosis in female rats in receptive behaviour, restoration of sexual behaviour after castration. Andersson 2011 Eur Urol characterised nerve pathways by c-Fos brain imaging.

Cardiovascular: the RECONNECT trial measured a transient elevation of systolic blood pressure of 1.9 mmHg and diastolic of 1.7 mmHg after injection (peak 2-4h), without clinical impact in healthy subjects. In poorly controlled hypertensive subjects, monitoring is recommended. No pressor rebound after 10 hours.

Pharmacovigilance: on Vyleesi sales since 2019, the profile is consistent with trials: nausea 40 %, hot flashes 20 %, headache 15 %, site pain 13 %. No priapism reported (different mechanism from PDE5). A few rare cases of focal cutaneous pigmentation reported in chronic use (residual MC1R activation).

Off-label and community male use: PT-141 is used off-label in men for ED non-responder to PDE5 and in longevity/performance research communities. Observational data are abundant but non-randomised.

Critical limitation: the RECONNECT trial was criticised for the modesty of the clinical effect (increase of 0.5-0.7 point FSFI on a 1-5 scale), the high dropout proportion (23 %), and the large placebo effect (20-25 % placebo responders). PT-141 remains a useful tool but not a magic solution. In men, the absence of a dedicated phase 3 trial limits generalisations.