Methodological considerations in the evaluation of analgesic combinations: acetaminophen (paracetamol) and hydrocodone in postpartum pain.

1 In a double-blind study, 108 postpartum patients received single oral doses of either placebo, acetaminophen (paracetamol) 1000 mg, hydrocodone 10 mg, the combination of acetaminophen plus hydrocodone, or codeine 60 mg. 2 In the 2X2 factorial analysis, both the acetaminophen and hydrocodone effects were statistically significant, whereas the interaction contrast was not. This indicates that the analgesic effect of the combination represents the additive effect of its constituents and is consistent with the assumption that these constituents are producing analgesia by different mechanisms. 3 Although significantly superior to placebo, codeine seemed to be inferior to the other treatments. 4 Compared with placebo, both codeine and hydrocodone (centrally acting narcotics) seemed relatively more effective in uterine cramp than episiotomy pain; the reverse seemed true with acetaminophen (a peripherally acting analgesic). 5 Some methodological implications for the evaluation of analgesic combinations are discussed.