Metkephamid and meperidine analgesia after episiotomy

Metkephamid is an analog of methionine enkephalin. The efficacy, safety, and time course of analgesia with 70 or 140 mg metkephamid were compared with those of 100 mg meperidine and placebo in 59 hospitalized women with severe postpartum episiotomy pain. There were two separate trials with single intramuscular doses and identical designs, including parallel groups, randomized blocks, and double-blind conditions. Using subjective reports as indexes of response, patients rated pain intensity, pain relief, and side effects at periodic interviews for 6 hr. Almost all measures of summed and peak analgesia exhibited important differences among the three treatments in both trials. Metkephamid at the 140-mg dose was the most effective and meperidine, 100 mg, was next, whereas metkephamid, 70 mg, and placebo were least effective. Only metkephamid, 140 mg, and meperidine were measurably superior to placebo. Both treatments took effect within 30 min and peaked at 1 to 2 hr; with 140 mg metkephamid, maximum analgesia was sustained 6 hr, i.e., 2 hr longer than with meperidine. Metkephamid, 70 mg, could not be distinguished from placebo throughout its entire time course. Although dizziness was experienced with meperidine, the two metkephamid doses induced other side effects, including sensation of heavy limbs, dry mouth, eye redness, and nasal stuffiness. None were distressing. Our results suggest that 140 mg metkephamid compares favorably with 100 mg meperidine for analgesia after episiotomy, but it induces minor side effects more frequently.