PT-141 Dosage Calculator

PT-141 (bremelanotide) is a cyclic heptapeptide melanocortin receptor agonist derived from Melanotan II by removal of the C-terminal amide and cleavage of the lactam bridge, shifting its receptor selectivity profile toward MC4R. It is the only melanocortin-based compound to receive FDA approval for a sexual function indication — marketed as Vyleesi (1.75 mg subcutaneous auto-injector) for hypoactive sexual desire disorder (HSDD) in premenopausal women, approved in 2019 by AMAG Pharmaceuticals (now Palatin Technologies licensee).

Unlike PDE5 inhibitors (sildenafil, tadalafil) that act peripherally on vascular smooth muscle, PT-141 acts centrally through melanocortin receptors in the central nervous system — particularly the melanocortin 4 receptor (MC4R) in hypothalamic nuclei governing sexual arousal and motivation. This central mechanism means PT-141 is effective in both men and women and addresses the neurological component of sexual dysfunction rather than purely vascular mechanics, making it a subject of research interest for conditions including female sexual arousal disorder, male erectile dysfunction (particularly in cases where peripheral vascular mechanisms are insufficient), and loss of libido.

PT-141 exerts its primary biological effects through agonism of the melanocortin 4 receptor (MC4R), a G-protein-coupled receptor expressed throughout the central nervous system with dense expression in the paraventricular nucleus and dorsomedial nucleus of the hypothalamus — brain regions critical for regulating sexual motivation, arousal, and behavior. MC4R activation in these regions increases dopaminergic tone in limbic reward circuits and activates descending pro-erectile neural pathways that produce erection in males via oxytocin-driven spinal cord mechanisms.

Unlike Melanotan II, PT-141 has reduced affinity for MC1R (the melanocyte receptor responsible for skin darkening), meaning PT-141 produces significantly less pigmentation effect at therapeutic doses. MC3R agonism contributes to secondary effects on cardiovascular regulation and feeding behavior. The pharmacological selectivity of PT-141 for the sexual arousal pathway was identified as the key differentiating feature from Melanotan II during the development process, enabling clinical development as a specific sexual dysfunction agent.

PT-141 lyophilized powder is reconstituted with bacteriostatic water for injection. For a 10 mg vial, inject 5 mL of bacteriostatic water slowly down the side wall of the vial. Allow to rest for 60 seconds, then swirl gently until fully dissolved. The solution should be clear and colorless. A 10 mg vial with 5 mL gives 2,000 mcg/mL.

A 1 mg (1,000 mcg) dose requires 0.50 mL (50 IU on a U100 syringe). The FDA-approved Vyleesi dose of 1.75 mg requires 0.875 mL (87.5 IU from this concentration), or you can reconstitute with 2 mL to get 5,000 mcg/mL and draw 0.35 mL for the 1.75 mg dose. Administer subcutaneously into the abdomen or thigh approximately 30–60 minutes before the intended activity. Use 27–30 gauge insulin syringes.

The FDA-approved dosing for Vyleesi (bremelanotide) in HSDD is 1.75 mg subcutaneously, administered 30–60 minutes before anticipated sexual activity, no more than once every 24 hours and no more than eight times per month. This dosing framework is directly derived from the Phase 3 RECONNECT clinical trial program (two trials: Rekynda and Reconnect).

Pre-clinical and Phase 1/2 research used a broader range of doses from 0.5 mg to 3 mg. Early clinical work at Palatin Technologies used doses up to 10 mg (higher than ultimately approved), with efficacy signals at doses ≥ 0.75 mg and dose-dependent adverse effects. In male erectile dysfunction research (Phase 2 trials), doses of 4–20 mcg/kg demonstrated erection-facilitating effects, with a dose-response relationship observed for the proportion of subjects achieving erections compared to placebo.

Using the calculator: a 10 mg vial with 5 mL of bacteriostatic water gives 2,000 mcg/mL. For the Vyleesi dose of 1,750 mcg, this requires 0.875 mL (87.5 IU). For a 1 mg (1,000 mcg) research dose, draw 0.50 mL (50 IU).

Lyophilized PT-141 powder is stable when stored at 2–8°C and protected from light. Do not freeze the powder. Once reconstituted in bacteriostatic water, store at 2–8°C and use within 28–30 days. The Vyleesi auto-injector is labeled for storage between 2°C and 30°C for up to 60 days or until the expiry date. For reconstituted research vials, adhere to the conservative 28-day refrigerated storage guideline. Inspect the solution before each use; discard if cloudy, discolored, or particulate matter is visible.

In the Phase 3 RECONNECT trials, the most common adverse effects were nausea (40% of subjects), flushing (20%), headache (11%), and injection-site bruising/discomfort. Hyperpigmentation was reported in a small percentage of subjects (predominantly women with more pigment-prone skin types), consistent with residual MC1R agonism. Transient blood pressure elevations were observed in Phase 1/2 studies; PT-141 is contraindicated in subjects with cardiovascular disease, uncontrolled hypertension, or in those taking antihypertensive medications. The nausea is dose-dependent and substantially dose-limiting at doses above 1.75–2 mg. All research use must comply with appropriate protocols; this compound is approved for a specific indication only and should be treated as a research chemical for laboratory investigation beyond that context.