Gene variant may be key to fentanyl response: patients with the genetic variant didn't require as much fentanyl as did the patients without the variant.(Obstetrics)

PALM DESERT, CALIF. -- Women with a common genetic variant on the [mu]-opioid receptor had a markedly reduced need for intrathecal fentanyl during labor, raising the strong possibility that genes influence analgesic response to the drug.

An international research team that was led by Ruth Landau, M.D., of the University Hospital of Geneva, announced their findings at the annual meeting of the Society for Obstetric Anesthesia and Perinatology.

Genetic polymorphism of the [mu]-opioid receptor is very common, found in roughly 10%-28% of the world's population.

When Dr. Landau and her associates genotyped the DNA of 113 nulliparous Swiss women at less than 35 weeks' gestation, the A118G variant was discovered in 32%.

Patients who went into spontaneous early labor and requested analgesia all received a starting dose of 18 mcg of fentanyl with a testing interval between patients of 2 mcg.

After that point, their fentanyl dose was allocated in a blinded fashion according to an up-down allocation protocol until anesthesia success was reached, defined as a visual analog score of 1 or less for at least 60 minutes.

Failure was defined as a patient not reaching that degree of pain relief within 20 minutes, or analgesia wearing off before 60 minutes.