Optimal Dose for Second-Trimester Termination

OB/GYN News, May 1, 2000 by Kate Johnson

MIAMI BEACH -- Intravaginal misoprostol 400 mcg every six hours is the most effective dosage for terminating a second-trimester pregnancy, while keeping maternal side effects to a minimum, Dr. Jan Dickinson recommended at the annual meeting of the Society for Maternal Fetal Medicine.

In a study aimed at nailing down an optimal dosage schedule for the abortifacient agent, Dr. Dickinson and her colleagues at the University of Western Australia in Perth randomly assigned 150 pregnant women who sought abortions between 14 and 30 Weeks' gestation to one of three regimens.

Those regimens were: 200 mcg misoprostol intravaginally every 6 hours, to a maximum of 48 hours; 400 mcg of misoprostol intravaginally every 6 hours to a maximum of 48 hours; or a 600-mcg loading dose of misoprostol followed every 6 hours by another 200 mcg.

Overall, about 90% of the women delivered within 48 hours.

Delivery within 24 hours occurred in 59% of the 200-mcg group, 76% of the 400-mcg group, and 80% of the 600-mcg group.

Women in the lowest dosage group experienced a median 18-hour interval from the time of induction to delivery a period that was significantly longer than the 15-hour interval among patients' in the 400-mcg group and the 13-hour interval among patients in the 600-mcg group, Dr. Dickinson found.

In cases in which induction was started after intrauterine fetal death, the median time to delivery was about 13 hours in all three groups.

By contrast, when the fetus was alive at the commencement of induction, the median time to delivery was significantly longer and dosing group assignment made a difference.

Patients in the lowest-dosage group waited a median of 23 hours before delivery, compared with 18 and 17 hours, respectively, in the medium- and highest-dosage groups.

"Smaller institutions with limited medical staff should be aware of the potential prolongation of the induction-to-delivery interval" in cases in which the fetus is alive at the start of induction, said Dr. Dickinson, a maternal-fetal medicine specialist, who is also at the Women and Infants' Research Foundation and King Edward Memorial Hospital in Perth.

Optimizing the dosage allows for faster delivery times with the least side effects, particularly in the more complicated cases, she continued.

Significantly more women in the 600-mcg group experienced vomiting and diarrhea within the first 3 hours, and there was also a significantly higher incidence of fever in this group, compared with the other groups.

The higher dosages of misoprostol were equally effective in achieving delivery within 24 hours--an advantage that Dr. Dickinson acknowledged was "significant both in terms of patient desire and health economics.

But Dr. Dickinson maintained that the 400-mcg dosing schedule should be the treatment of choice because it produces fewer side effects.