Percutaneous absorption of minoxidil in man

Area of Science:

• Dermatology
• Pharmacokinetics
• Radiochemistry

Background:

• Minoxidil is a widely used topical treatment for androgenetic alopecia.
• Understanding its percutaneous absorption and systemic exposure is crucial for safety and efficacy.

Purpose of the Study:

• To quantify the percutaneous absorption and excretion of topical minoxidil.
• To assess the systemic exposure following repeated topical application of minoxidil solutions.

Main Methods:

• 12 adult males received topical applications of 1% or 5% carbon-14 labeled minoxidil solutions.
• Radioactivity was measured in urine, feces, skin washes, and pillowcases over the study period.
• Subjects received nine topical applications on a bald scalp area, with radiolabeled solutions applied on days 1 and 9.

Main Results:

• Urinary excretion of radioactivity was low, ranging from 1.6% to 3.9% of the applied dose.
• No radioactivity was detected in fecal samples.
• Recovery of radioactivity from skin surface and washes was between 41% and 45% of the applied dose, indicating poor systemic absorption.

Conclusions:

• Topical minoxidil exhibits poor percutaneous absorption through the scalp.
• Despite low absorption, potential systemic exposure can occur with widespread scalp application.
• No adverse reactions were observed, suggesting a favorable safety profile for topical minoxidil.