230. Quantifying adherence to antihypertensive medication for chronic hypertension during pregnancy

Introduction The incidence of chronic hypertension in pregnancy is around 3%. Non-adherence to antihypertensive medication is a barrier to effective treatment of chronic hypertension and may impact maternal and perinatal outcome; there are no robust estimates of adherence in pregnancy. The aim of this study was to evaluate adherence amongst pregnant women with chronic hypertension randomised to antihypertensive treatment. Method Spot urine samples were collected from pregnant women (12 +0 to 35 +6 weeks’ gestation) who participated in the PANDA trial (labetalol versus nifedipine for control of chronic hypertension in pregnancy) from three maternity units. Liquid chromatography-tandem mass spectrometry instrumentation was used to identify metabolites of labetalol and nifedipine in spot urine samples. Data were analysed using the statistical software Stata/SE version 14. Results Samples from 75 women randomised to first-line antihypertensive treatment were included in the analysis (n = 39 labetalol, n = 36 nifedipine). Mean highest blood pressure between randomisation and delivery was comparable in each treatment arm (165/97 mmHg labetalol versus 165/99 mmHg nifedipine). In 120 of 136 (88%) samples, documented prescribing and urine metabolite detection were concordant. No antihypertensive medication metabolite was detected in the urine of 9 of 136 (6.6%) samples; three (8%) of the women assigned to labetalol had no metabolite detected (dose range 200–1200 mg/day) and six (17%) women assigned to nifedipine had no metabolite detected (dose range 10–80 mg/day). There were no significant differences in BP (non-adherent mean 134/87 mmHg versus adherent 133/84 mmHg) or birthweight Conclusion Assessment of urinary antihypertensive metabolites in women with chronic hypertension in pregnancy provides a novel insight into treatment adherence. Identifying non-adherence could facilitate initiation of interventions to improve blood pressure control.