OBJECTIVE: To determine nifedipine plasma concentrations after a loading dose of nifedipine 10mg capsules, 40 mg over 1h followed by slow-release tablets (60 mg/d) versus gastrointestinal therapeutic system (GITS) tablets (90 mg/d) for tocolysis. STUDY DESIGN: Prospective study in 14 pregnant women treated for threatened preterm labor. RESULTS: Following capsule administration there was a rapid rise in plasma concentration of drug achieving a peak of 97.5 microg/l (median) at 1h, then declined to 59.5 microg/l (median) at 5h. The concentration measured at 7200 min (120 h) was non-significantly higher in the slow-release group (median 25.5, range 6.9-67.2 microg/l) than in the GITS group (median 14.6, range 6.0-20.0 microg/l). Area under the curve (AUC) increased with the applied dose in both groups in a linear regression. Headache was more frequent in the slow-release group than in the GITS group (P=0.001). CONCLUSIONS: GITS tablets 90 mg/d are an alternative dosage regimen to previous used slow-release tablets 60 mg/d for tocolysis with similar pharmacokinetic profile and a good tolerance. However, tocolysis with GITS tablets is simpler than that with slow-release tablets and may be associated with a higher compliance. GITS tablets are therefore also qualified for home monitoring.