Correlation between ketoprofen plasma levels and analgesic effect in acute lumbar pain and radicular pain.

Fourteen patients with acute lumbar pain and cervico-brachial radicular pain were treated with a single oral dose of 100 mg ketoprofen. The analgesic effect of the substance was investigated, using an analog pain scale, in correlation with drug plasma levels. Blood samples were taken at zero, one-half, one, two, three, four, five, six, eight, and ten hours after oral administration of ketoprofen. On an average, pain was at its lowest two hours after the plasma level of ketoprofen was at its highest. Within the ten hour observation period, the maximum reduction in pain increased as the maximum plasma level rose. Five patients with a maximum plasma level greater than 9 microliter/ml experienced pain reduction of at least 50%.