Analgesic Activity as Determined by the Nilsen Method

The Nilsen method for determining analgesic activity (pain stimulus and electrical pulsations to the mouse tail) was compared with the hot-plate procedure for several compounds including “pure” analgesics (agonists) (morphine, codeine, and meperidine), a known “pure” antagonist (naloxone), several so-called mixed agonist-antagonists (nalorphine, pentazocine, and cyclazocine), one antagonist that appears to be naloxonelike, and two compounds of relatively unknown pharmacology. The results obtained confirm the validity of the Nilsen test for the agonists and indicate its superior predictive value (to the hot-plate, Smith D′Amour, and perhaps writhing methods) for man with those substances possessing antagonist properties. The Nilsen technique may also be complementary to other procedures now used to predict “pure” antagonism. Refinements in methodology and instrumentation are described.