Prompt analgesic effect of antihistaminic diphenhydramine ointment on bone-joint-muscle pain as assessed by skin impedance

Pain is sensed, transmitted, and modified via a variety of mediators and their receptors. Histamine is a well-known mediator of pain. In addition to their antagonistic effects against histamine, classical antihistaminics possess, to various degrees, antimuscarinergic, antiserotonergic, antiadrenergic, local anesthetic, membrane-stabilizing and other pharmacologic actions. Although there have been many attempts to use classical antihistaminics as analgesics and/or analgesic adjuvants, the appearance of non-steroidal anti-inflammatory drugs discouraged such efforts. Here, we compared the analgesic effect of an ointment containing 1% diphenhydramine (a typical first-generation antihistaminic drug) with that of indomethacin (a typical non-steroidal anti-inflammatory drug) in elderly patients with osteoarthritis and/or osteoporosis who complained of bone-joint-muscle pain. Analgesic effects were evaluated by measuring skin impedance and by subjective pain assessments (using a visual recording system) before and after ointment application. Diphenhydramine ointment exerted a prompt and marked analgesic effect that lasted for several hours, as assessed by either skin impedance or subjective pain evaluation. In contrast, the analgesic effect of indomethacin ointment was marginal, and significant only an hour or more later than that of diphenhydramine. These results suggest that diphenhydramine ointment may be useful for the relief of the bone-joint-muscle pains that are common in elderly subjects.