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Pregnant women with preeclampsia who received sildenafil citrate (Viagra) had a small but significant increase in pregnancy duration compared with women given placebo in a 100-patient randomized trial.

The increase averaged 4 days (14.4 days from the start of therapy, 95% CI 12.5-16.6, versus 10.4 days, 95% CI 8.4-12.3, P=0.008), reported , of Federal University of Santa Catarina in Brazil, and colleagues in .

The authors said that one factor in the development of preeclampsia may be a failure of nitric oxide, a "potent vasodilator," which helps to maintain low vascular resistance in utero. Phosphodiesterase-5 inhibitors such as sildenafil boost NO availability.

"We speculate that this prolongation [of pregnancy] may be the result of better control of blood pressure, improvement of maternal and fetal blood flow, or a combination thereof," they argued, adding that the drug had previously shown "promising outcomes" and in .

Sildenafil in the trial also performed well in secondary outcomes. A significantly higher proportion of patients in the drug group experienced reductions in the pulsatility indices -- or Doppler measurements of systolic and diastolic velocities -- in both the uterine and the umbilical arteries compared to the placebo group (22.5% versus 2.1% and 18.5% versus 2.5%, respectively, P<0.001 for both).

Patients receiving sildenafil also experienced significantly lower mean arterial blood pressure 24 hours after the administration of the drug compared to baseline (103 ±5.6 mm Hg versus 116.4 ±5.1 mm Hg, P<0.05). But no significant difference was observed in maternal blood pressure in the placebo group.

"Reduction in [mean arterial pressure] without compromising uterine artery blood flow, provides reassurance that sildenafil may be useful as an antihypertensive drug in the context of placental vascular insufficiency," the authors wrote.

Women with singleton pregnancies from 24 to 33 weeks gestation, with preeclampsia were randomized to either 50 mg oral sildenafil citrate or placebo every 8 hours. Demographic characteristics were similar in both groups. Most of these patients also received α-methyl-dopa, an antihypertensive drug, and a beta-blocker to prevent cardiac arrhythmia.

However, a significantly higher portion of the placebo group needed an additional antihypertensive agent or an increased dose of α-methyl-dopa than in the sildenafil group (58% versus 32%, P<0.001).

Three patients stopped taking medication due to headache (one in the sildenafil group and two in the control group). There were no significant differences in adverse events or neonatal outcomes between the two groups. The majority of patients in both groups delivered via cesarean section (84% in the sildenafil group versus 88% in control group) and most received antenatal steroids prior to delivery (84% versus 80%, respectively).

Trapani and colleagues said that based on the mechanism of action in the endothelium, sildenafil can be compared to other preeclampsia treatments, such as -- where this anti-angiogenic factor is removed from a patient's blood -- as well as and the hormone .

"The benefit of sildenafil therapy would likely be in cost, access and bypassing the counterproductive risks of nitric oxide donors, which ... led to instead of vasodilation," they wrote.

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