# PT-141 Half-Life and Pharmacokinetics: The Measured Constants

> PT-141 half life is ~2.7 h (range 1.9-4.0 h) subcutaneous per the label. Tmax, volume of distribution, clearance, and excretion — the full PK profile, cited.

Terminal t1/2 ~2.7 h. Tmax, volume of distribution, clearance, protein binding, excretion. Each figure cited.

## The short version

PT-141 half life is short. After an injection under the skin, the terminal half-life — the time for blood levels to fall by half once they are declining — is about 2.7 hours, with a measured range of 1.9 to 4.0 hours [7]. It peaks fast (within about half an hour to an hour) and clears within a day [7].

That short half-life is why it is dosed as-needed rather than daily, and it is why the blood-pressure effect is transient rather than sustained [7]. Below are the full pharmacokinetic constants from the prescribing information, stated as measured values.

## PT-141 half-life and absorption

Terminal half-life is approximately 2.7 hours (range 1.9–4.0 h) after subcutaneous administration, per the US prescribing information [7]. Early intranasal studies reported a shorter 1.85–2.09 h [7]. Median Tmax (time to peak concentration) is roughly 0.5–1.0 hours after subcutaneous injection [7]. The fast absorption and short half-life together define the as-needed dosing rhythm — the compound is present for the window around use and gone soon after.

## Distribution, clearance, and excretion

Volume of distribution is about 25.0 L and clearance approximately 6.5 L/hr [7]. Serum protein binding is roughly 21% [7]. Metabolism proceeds by hydrolysis of the cyclic-peptide amide bonds and peptidase digestion — a peptide breakdown route, which is why drug-drug interactions are minimal [7][10]. Excretion of a radiolabelled dose was 64.8% renal and 22.8% fecal [7].

## How long does PT-141 last

Pharmacokinetically, PT-141 lasts on the order of a day: a ~2.7 h terminal half-life means roughly five half-lives (~13–14 h) to near-complete clearance [7]. The desire effect outlasts the drug in plasma — the fMRI study reported increased desire for up to 24 hours after a single dose, consistent with a downstream central effect rather than continuous receptor occupancy [5]. So "how long it lasts" has two answers: hours in the blood, up to a day for the measured behavioural effect.

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A drafting-table dossier of the bremelanotide literature — annotations on the studies, not a prescription pad.