PT-141 (Bremelanotide) Research & Studies

Efficacy outcomes are only informative to the extent that they are validated. We examined the measurement properties of efficacy measures from the phase III ("RECONNECT") bremelanotide trials for hypoactive sexual desire disorder (HSDD) in women. Continuous efficacy outcomes, including a) the Female Sexual Function Index (FSFI) and its Desire domain (FSFI-D) and b) the Female Sexual Distress Scale-Desire/Arousal/Orgasm (FSDS-DAO) and its item assessing distress due to low desire (FSDS-DAO #13) have questionable, at best, validity evidence for women with HSDD. We found no validity evidence for previously published categorical treatment response outcomes from the RECONNECT trials. All efficacy results should be reported, but results on 8 of the 11 clinicaltrials.gov-specified efficacy outcomes were heretofore unpublished (including FSDS-DAO total score, FSFI total score, FSFI arousal domain, and items from the Female Sexual Encounter Profile-Revised). We analyzed these outcomes, upon which effect sizes ranged from nil to small. Several other continuous and categorical outcomes generated modest apparent benefits, though nearly all of these outcomes were likely derived post-hoc. Across RECONNECT trial data from two prior publications and the current study, bremelanotide's benefits are statistically modest and limited to outcomes for which scant evidence of validity among women with HSDD exists.

The melanocortin 4 receptor (MC4R) plays a central role in appetite regulation, and agonistic activity at this receptor promotes satiety. Results from two randomized controlled clinical trials examine the effects of bremelanotide's agonism at MC4R on caloric intake and body weight.

Hypoactive sexual desire disorder (HSDD) is a common female sexual dysfunction and is estimated to affect approximately 10% of women in the United States. It has been suggested that HSDD is associated with an imbalance of hormone and neurotransmitter levels in the brain, resulting in decreased excitation, increased inhibition, or a combination of both. Evidence suggests neurotransmitters, including dopamine (DA), norepinephrine, and serotonin, as well as hormones such as estradiol and testosterone, contribute to female sexual desire and response. Current treatments for HSDD include psychotherapy, and two US Food and Drug Administration-approved medications for premenopausal women: flibanserin, a serotonin mixed agonist and antagonist, and bremelanotide, a melanocortin receptor (MCR) agonist. Melanocortins are endogenous neuropeptides associated with the excitatory pathway of the female sexual response system. MCRs are found throughout the body, including the brain. Bremelanotide is an MCR agonist that nonselectively activates several of the receptor subtypes, of which subtype 4 (MC4R) is the most relevant at therapeutic doses. MC4R is predominantly expressed in the medial preoptic area (mPOA) of the hypothalamus in the brain, and is important for female sexual function. Animal studies suggest that bremelanotide may affect female sexual desire by activating presynaptic MC4Rs on neurons in the mPOA of the hypothalamus, leading to increased release of DA, an excitatory neurotransmitter that increases sexual desire. This review presents what is known about the mechanism of action of bremelanotide in the context of treating HSDD.

Hypoactive sexual desire disorder (HSDD) is a persistent deficiency or absence of sexual fantasies and desire resulting in significant distress or interpersonal difficulty. Women with this disorder may display a lack of motivation for sexual activity, reduced responsiveness to erotic cues, a loss of interest during sexual activity, and avoidance of situations that could lead to sexual activity. The pathophysiology of HSDD is thought to be centered around inhibitory and excitatory hormones, neurotransmitters, and specific brain anatomy. Due to the multifactorial nature of HSDD, treatment can be complex and must attempt to target the biological and psychosocial aspects of the disorder. Bremelanotide is a melanocortin receptor agonist and has been recently approved by the FDA to treat HSDD. Bremelanotide is administered intranasally or as a subcutaneous injection. The recommended dosage of bremelanotide is 1.75 mg injected subcutaneously in the abdomen or thigh at least 45 min before sexual activity. Studies showed improvements in desire, arousal, and orgasm scores when 1.75 mg of bremelanotide was administered before sexual activity compared to a placebo. Bremelanotide is a promising way to treat HSDD.

Kingsberg et al. described results from two 24-week Phase III trials of bremelanotide for treating hypoactive sexual desire disorder (HSDD) in women. 72.72% of protocol-listed outcomes were not reported by Kingsberg et al., who provided results of 15 secondary measures which were not listed in the study protocols. None of their efficacy outcomes were reported in line with CONSORT data reporting standards and no secondary outcome had a stated rationale or cited evidence of validity. My meta-analysis of the trials' data, based on the FDA New Drug Application, found similar results to Kingsberg et al. However, Kingsberg et al. did not report that a) adverse event-induced study discontinuation was substantially higher on bremelanotide: OR = 11.98, 95% CI = 3.74-38.37, NNH: 6 or b) participants preferred placebo, measured by the combination of both 1) completing a clinical trial and 2) electing to participate in the follow-up open-label study (OR = 0.30, 95% CI = .24-.38, NNH: 4). Bremelanotide's modest benefits on incompletely reported post-hoc measures of questionable validity in combination with participants substantially preferring to take placebo suggest that the drug is generally not useful. Kingsberg et al.'s data reporting and measurement practices were incomplete and lacked transparency.

To evaluate the long-term safety and efficacy of bremelanotide as treatment for hypoactive sexual desire disorder in premenopausal women.

Bremelanotide (Vyleesi™) is a melanocortin receptor agonist recently approved in the USA for the treatment of premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD), as characterized by low sexual desire that causes marked distress or interpersonal difficulty. It is a self-administered, on-demand subcutaneous therapy. Initially developed by Palatin Technologies who sponsored the Phase 3 clinical trials, bremelanotide was subsequently out-licensed to AMAG Pharmaceuticals Inc. for exclusive North American rights to develop and commercialize the drug, including submitting the New Drug Application to the US FDA. Bremelanotide is a synthetic peptide analogue of the neuropeptide hormone alpha melanocyte-stimulating hormone (α-MSH) with high affinity for the melanocortin type 4 receptor (thought to be important for sexual function), giving it the potential to modulate brain pathways involved in sexual response. This article summarizes the milestones in the development of bremelanotide leading to this first regulatory approval.

Responder analyses are used to determine whether changes that occur during a clinical trial are clinically meaningful; for subjective endpoints such as those based on patient-reported outcomes (PROs), responder analyses are particularly useful.

To evaluate the safety and efficacy of bremelanotide for the treatment of premenopausal women with hypoactive sexual desire disorder.

We evaluated the safety and efficacy of intranasal bremelanotide in men with erectile dysfunction who did not respond to sildenafil.

Bremelanotide is an analogue of the naturally occurring peptide alpha-melanocyte-stimulating hormone (alpha-MSH). It stimulates erection in men and male rats, and is currently in clinical trials for the treatment of erectile dysfunction.

Palatin, under license from Competitive Technology, is developing the peptide PT-141, a synthetically modified analog of PT-14, as a nasal spray for the potential treatment of erectile dysfunction (ED) and female sexual dysfunction. In September 2003, Palatin had completed a phase IIb trial in patients with ED and in February 2004, Palatin planned to start phase III trials in early 2005.