Double blind comparison of mefenamic acid and acetaminophen (paracetamol) in migraine

We have assessed the role of mefenamic acid, a non-steroidal anti-inflammatory drug known to inhibit both the synthesis and actions of prostaglandins, as an analgesic in migraine by comparing it with the established analgesic paracetamol (acetaminophen) in a double-blind cross-over trial. Forty ambulant migraine patients were supplied with oral medication for six consecutive attacks; metoclopramide 10 mg was administered in all attacks, and paracetamol 500 mg and mefenamic acid 500 mg for three attacks each. The patients recorded the intensity of the headache at the time the medication was taken, and again after 3 hours, on a linear analogue scale. Twenty-two patients completed the trial satisfactorily. Seven had insufficient attacks and the remainder were lost to follow-up. The mean reduction in headache intensity was 36 +/- 11% on mefenamic acid and 27 +/- 10% (both mean +/- SEM) on paracetamol. While this difference is not quite statistically significant (0.1 greater than P greater than 0.05) there still remains a 28% probability that mefenamic acid is twice as potent as an analgesic. The responses in each individual patient to the two drugs were very closely correlated (P much less than 0.001). Our failure to demonstrate a convincing difference between the two analgesics leads us to speculate that peripheral prostaglandin mediated pain pathways, in which paracetamol is inactive, may be less important than central pathways, which are inhibited by both drugs.