A review of systemic opioids commonly used for labor pain relief.

Parenteral opioids for pain relief during labor have been the subject of research for many decades. Commonly used systemic opioids provide limited pain relief during labor yet are used extensively for managing labor pain. These opioids share similar pharmacologic profiles but differ in potency, pharmacokinetics, and side effects. This article reviews the pharmacokinetics, pharmacodynamics, and clinical research related to the commonly used systemic labor pain analgesics morphine, meperidine, fentanyl, remifentanil, butorphanol, and nalbuphine.