Background: This study sought to assess the cutaneous (peripheral) analgesic effects of antihistamine chlorpheniramine, compared with the long-lasting local anesthetic bupivacaine.
Methods: After chlorpheniramine and bupivacaine were subcutaneously injected under the dorsal skin of the rats, the cutaneous analgesia effect was quantitatively evaluated by scoring the number to which the animal failed to react (cutaneous trunci muscle reflex). The quality and duration of chlorpheniramine and bupivacaine on infiltrative cutaneous analgesia were compared.
Results: We revealed that subcutaneous chlorpheniramine, as well as the local anesthetic bupivacaine elicited cutaneous analgesia in a dosage-dependent manner. Based on their ED50s (50% effective doses), the relative potency was found to be chlorpheniramine [1.13 (1.05-1.22) μmol] < bupivacaine [0.52 (0.46-0.58) μmol] (p < 0.01). When comparing the ED25s, ED50s and ED75s, full recovery time induced by chlorpheniramine was longer (p < 0.01) than that induced by bupivacaine.
Conclusions: Our preclinical data demonstrated that both chlorpheniramine and bupivacaine dose-dependently provoked the cutaneous analgesic effects. Chlorpheniramine with a more prolonged duration was less potent than bupivacaine in inducing cutaneous analgesia.
Keywords: Bupivacaine; Chlorpheniramine; Infiltrative cutaneous analgesia; Needle pinprick.