Timing Of Women's Labor May Determine Effectiveness Of Pain Medication

"Our research shows that the time of day that the medication isdelivered is important in determining its effectiveness," said Peter H.Pan, M.D., an obstetrical anesthesiologist. "In the future, doctors mayconsider time of day, as well as patient's weight and other factors,when determining the best dose or method of drug delivery."

The study's goal was to determine if the body's naturalinternal rhythms can affect the effectiveness of pain medication forlaboring women. The study, reported in the current issue ofAnesthesiology, involved 77 women who were in labor with their firstbabies and requested spinal-epidural pain medication.

The research is part of the field of chronobiology thatstudies biologic rhythms. These rhythms include the circadian rhythm,the 24-hour body clock, and the ultradian rhythm,shorter-than-24-hour-cycles, which determine sleeping and eatingpatterns and can also affect blood pressure, heart rate and bodytemperature. Some rhythms are controlled by sunlight and others arecontrolled internally.

The researchers found that women who labored between noon and6 p.m. got an average of 27 percent longer pain relief from a singledose of the spinal-epidural medication fentanyl than women whose laborwas between 8 p.m. and 2 a.m. Fentanyl is one of the commonly useddrugs for labor pain relief in the United States. However, this is oneof the first studies to examine whether there are chronobiologicalvariations in its effectiveness for labor pain relief.

"The right treatment given at the wrong time can be ineffectiveor create a crisis of escalating toxicity," wrote Dominique Chassard,M.D., and colleagues with Hotel-Dieu Hospital in France in an editorialaccompanying the study. "Conversely, even a weak treatment, if given atthe right moment, could prove surprisingly effective."

Pan said that knowing more about how time of administrationinfluences the drug's effects could have significant practicalimplications for how it is prescribed and delivered. For example, thedose could be tailored to the time of day or a smart, programmable,time-released version of the drug could be developed to optimizedesired drug effects and minimize undesired side effects both for womenin labor and patients with other pain syndromes.

Pan's co-investigators were Sherman Lee, M.D., and Lynn Harris, B.S.N, both with Wake Forest Baptist.