Pain is sensed, transmitted, and modified by a variety of mediators and receptors.
Histamine is a well-known mediator of
pain. In addition to their anti-histaminic effects, the classical, or 1st generation, anti-histamines (1st AHs) possess, to various degrees, anti-
muscarinic, anti-serotonergic, anti-
adrenergic, and other pharmacologic effects. Although there have been attempts to use 1st AHs as
analgesics and/or
analgesic adjuvants, the advent of non-steroidal anti-inflammatory drugs (
NSAIDs) discouraged such trials. We previously reported that in patients with
temporomandibular disorders,
osteoporosis, and/or
osteoarthritis, the
analgesic effects of certain 1st AHs (
chlorpheniramine and
diphenhydramine) are superior to those of the
NSAIDs flurbiprofen and
indomethacin. Here, we compared
analgesic effects among 1st AHs and
NSAIDs against responses shown by mice to intraperitoneally injected 0.7%
acetic acid. Since 1st AHs are water soluble, we selected water-soluble
NSAIDs. For direct comparison, drugs were intravenously injected 30 min before the above tests. Histamine-H1-receptor-deficient (H1R-KO) mice were used for evaluating H1-receptor-independent effects. The tested 1st AHs (especially
cyproheptadine) displayed or tended to display
analgesic effects comparable to those of
NSAIDs in normal and H1R-KO mice. Our data suggest that the anti-serotonergic and/or anti-
adrenergic effects of 1st AHs make important contributions to their
analgesic effects. Moreover, combination of a 1st AH with an
NSAID (cyclooxygenase-1 inhibitor) produced remarkably potent
analgesic effects. We propose that a 1st AH, by itself or in combination with a
cyclooxygenase-1 inhibitor, should undergo testing to evaluate its usefulness in
analgesia.