Demerol

Meperidine hydrochloride (Demerol), either alone or in combination with promethazine hydrochloride (Phenergan), has the advantage of a history of extensive use in labor. Common dosing is 50 to 100 mg of meperidine and 25 to 50 mg of promethazine IM every 3 to 4 hours.  Both medications can be given IV, but at reduced dosages of 25 to 50 mg of meperidine (diluted to 10 mg/mL) and 25 mg of promethazine. Since metabolic by-products of meperidine may have half-lives of 8 to 21 hours and will accumulate in patients with renal impairment and in their premature fetuses and neonates, the risk-benefit ratio requires re-evaluation before repeated dosing. The manufacturers recommend giving no more than 100 mg of promethazine during 24 hours of labor.