The active ingredient of Valtrex is Valacyclovir which transforms in the antiviral drug Acyclovir after first pass metabolism in the liver. The use of Valacyclovir allows to achieve a greater rate of Acyclovir bioavailability - 85% when compared to Acyclovir administered over the oral route - 15%. The preparation is commonly prescribed in treatment of genital herpes, herpes zoster and cytomegalovirus infestation. The drug has proven its effectiveness over the years of use and is currently being studied in treatment of pregnant women.

Women with a history of genital herpes or a primary herpes episode experienced a reduction in both subclinical and active disease recurrence when treated prophylactically with Valtrex from 36 weeks' gestation until delivery.

As a result, these women underwent fewer cesarean sections for active disease, and showed less laboratory evidence of subclinical infection on culture and polymerase chain reaction (PCR) tests.

These findings emerged from a randomized controlled trial presented at the annual meeting of the American College of Obstetricians and Gynecologists. The study, which included 350 women with herpes simplex virus (HSV) in pregnancy, was awarded first prize during the meeting.

The results suggest that prophylactic Valtrex is a safe and effective method of reducing neonatal transmission of HSV, reported Jeanne S. Sheffield, M.D., of the University of Texas Southwestern Medical Center in Dallas, the study's lead investigator.

Although ACOG currently recommends C-section delivery in women with active genital HSV lesions or prodromal symptoms, it does not recommend prophylactic treatment, although it suggests this approach could be considered in women with a history of HSV, Dr. Sheffield said in an interview.

But up to 70% of all cases of neonatal herpes transmission are in women who shed HSV asymptomatically near the time of delivery. "This has become a major public health problem for ob.gyns. ... and it has prompted a number of investigators to search for other modalities to try to prevent neonatal transmission near delivery," she said.

Of the 350 women in the study, 81% had recurrent genital herpes; 12% had first episode, nonprimary genital herpes, and 7% had first episode primary genital herpes.