Comparison of the relative effects of aspirin, mefenamic acid, dihydrocodeine, dextropropoxyphene and paracetamol on visceral pain, respiratory rate and prostaglandin biosynthesis.

A comparison was made between the relative effects of aspirin, mefenamic acid, dihydrocodeine , dextropropoxyphene and paracetamol on visceral pain (chemically-inducing writhing), respiratory rate and prostaglandin (PG) biosynthesis (cyclo-oxygenase activity). A close correlation was found to exist between inhibition of PG biosynthesis and inhibition of visceral pain for mefenamic acid, aspirin and paracetamol. Analysis of the complete activity profiles derived from evaluation of the test parameters yielded the following rank order of overall ratios of their beneficial anti-writhing/anti-cyclo-oxygenase to respiratory depressive activities: (1) mefenamic acid, (2) aspirin, (3) dihydrocodeine , (4) dextropropoxyphene and paracetamol.