A CASE-CONTROL EVALUATION OF TREATMENT EFFICACY - THE EXAMPLE OF MAGNESIUM-SULFATE PROPHYLAXIS AGAINST ECLAMPSIA IN PATIENTS WITH PREECLAMPSIA

Randomized trials are the optimal approach for evaluations of treatmen t efficacy but may not always be feasible. We study the adequacy of th e cast-control design in evaluating efficacy in a situation where the investigated therapy, namely the administration of magnesium sulfate f or the prevention of eclampsia in patients with preeclampsia, has a su spected strong protective effect. A total of 66 cases of eclampsia wer e ascertained from among deliveries occurring between 1977 and 1992 at two hospitals in Houston, Texas. Randomly selected preeclamptic contr ols were matched to cases based on hospital and month of delivery. Mag nesium sulfate administration prior to seizure occurrence had a strong protective effect against eclampsia in patients with preeclampsia (OR , 0.02; 95% CI, 0.01-0.05). This protective effect remained when contr ols were stratified by the degree of severity of preeclampsia (mild-to -moderate OR, 0.03, 95% CI, 0.01-0.09 and severe OR, 0.005; 95% CI, 0. 0005-0.04) and when cases were stratified by the timing of the first s eizure (antepartum and intrapartum seizures OR, 0.01; 95% CI, 0.003-0. 05 and postpartum seizures OR, 0.03; 95% CI, 0.005-0.15). The effect a lso remained after adjustment for other important predictors in a mult ivariate logistic regression model (OR, 0.11; 95% CI, 0.03-0.38). The results of this study are in support of a recent randomized trial on t he efficacy of magnesium sulfate as a prophylactic agent against eclam psia. Although there are serious potential sources of bias in this stu dy, the magnitude of the protective effect of magnesium sulfate minimi zes the likelihood that this effect can be explained by bias. Observat ional studies could be appropriate complements or alternatives to rand omized trials in situations where a strong treatment effect is expecte d. (C) 1997 Elsevier Science Inc.