Analgesic action of amfenac Na, a non-steroidal anti-inflammatory agent

Amfenac Na is a new non-steroidal analgesic anti-inflammatory drug which is clinically used for ailments such as rheumatoid arthritis and pain and/or inflamation after surgery. In this paper, amfenac Na is studied on the bradykinin induced-flexor reflex and the simultaneous recording of the cortical somatosensory-evoked response (SER) and the electromyogram of digastric muscle (d-EMG) evoked by a tooth pulp stimulation. Amfenac Na at doses of 0.1-1 mg/kg p.o. suppressed hindlimb flexor reflexes induced by bradykinin infusion in the rat. This effect was the most potent among the drugs used; the order of potency was as follows: amfenac Na greater than floctafenine greater than loxoprofen much greater than piroxicam = emorfazone greater than mefanamic acid. Similarly, the intravenous injection of amfenac Na completely suppressed the flexor reflex with a dose as low as 0.1 mg/kg; the potency was almost equal to that of morphine. On the SER and d-EMG evoked by tooth pulp stimulation, a high dose (100 mg/kg i.v.) of amfenac Na showed very weak inhibition, whereas morphine (10 mg/kg i.v.) suppressed those responses. These data suggest that amfenac Na showed a very potent analgesic effect comparable to morphine, and that the site of action is mainly the periphery.