Skin pigmentation potentially influences the pharmacokinetics of several widely prescribed drugs, according to scientists from the University of California, Riverside.

“Melanin, the pigment responsible for skin colour, shows a surprising affinity for certain drug compounds,” says Simon Groen, an assistant professor of evolutionary systems biology at the university’s Institute for Integrative Genome Biology. “Melanin’s implications for drug safety and dosing have been largely overlooked, raising alarming questions about the efficacy of standard dosing since people vary a lot in skin tones.”

Eumelanin (one of the pigment’s main forms) binds drugs as diverse as iron, paracetamol, several antibiotics and some beta-blockers. In rats, nicotine accumulated 20 times more in pigmented than albino hair. This raises questions about nicotine patches for smoking cessation. “Are we inadvertently short changing smokers with darker skin tones if they turn to these patches in their attempts to quit?” Groen asks.

The researchers hope to encourage pharma companies and academia to systematically evaluate the effect of skin pigmentation on drug kinetics in preclinical research. 

Various non-dermatological parts of the body, including the hair, eyes and brain, contain melanin. Potentially toxic melanin-interacting substances are also used in, among others, the cosmetics, cleaning and agricultural industries.