Interpersonal Transfer of Topical Applied Medicines

The number of topically applied therapeutic agents, either for local treatment or systemic delivery, has substantially increased over last decades. Millions of baby boomers use transdermal estradiol or testosterone for hormone replacement. However, the safety of these therapies over full lifetimes needs to be evaluated and addressed from a public health perspective. In general, only 1% to 20% of medicines topically applied to the skin surface are absorbed into living cutaneous tissue or the systemic circulation during a 24-hour period. The efficiency of transdermal delivery on balance is better, but still more drug is usually left in patches than is actually therapeutically used. The rest of the medicine stays on the skin surface, within the superficial layers of skin, in the applied patches, or is transferred to clothing, etc., when semisolids and patches are applied. Therefore, the fate and safety of nonabsorbed medicine on the skin surface has to be evaluated not only for patients but also for the others who might have close or direct skin contact with them. Several studies have showed the measurable transfer of topically applied testosterone and estradiol gels (85,86). As a consequence of the public safety concern, the potential for testosterone transfer has been included in the new labeling of products that contain this ingredient. It is important for physicians, nurses, pharmacists, and patients to understand that pharmacological significant or clinically undesirable transfer of topically applied therapeutic agents can occur and should be avoided. The same is true for patches as these have been transferred from patient to a loved one following intimate contact, with very serious ill effects. The used patches should be collected and kept away from children. The application sites of patches, gels, creams, or ointments should be thoroughly washed before having contact with partners, children, and others. Furthermore, the environmental impact of nonabsorptable medicines and hormones following the massive and long-term use of topical products has not been fully investigated and understood.

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