Safety and pharmacokinetics of sulfasalazine and its metabolite sulfapyridine for treatment of preterm preeclampsia in Australia (SIP): an early phase, unblinded, single-arm, proof of concept clinical trial

Background: Preeclampsia is a hypertensive pregnancy disorder marked by systemic inflammation and endothelial dysfunction. Sulfasalazine, an anti-inflammatory agent, may have therapeutic potential in preeclampsia. This study investigated its pharmacokinetics, placental transfer, and safety profile of sulfasalazine and its metabolite, sulfapyridine in women with preterm preeclampsia. Methods: A prospective, open-label pharmacokinetic trial was conducted at two hospitals in Melbourne, Australia, (February 2018-December 2020). Participants between 24+0- and 36+0- weeks' gestation with a singleton, non-anomalous pregnancies and a diagnosis of preeclampsia were included received 3 g/day of oral sulfasalazine. Serial maternal blood samples were collected post-dose. Maternal and umbilical cord blood and placental tissue were collected at birth. Primary outcomes were maternal-fetal safety and pharmacokinetics. Maternal plasma levels of soluble fml-like tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) were measured. All participants receiving at least one dose were included in analyses. The trial was prospectively registered with ANZCTR (12617000226303). Findings: Twelve participants were enrolled, seven had pharmacokinetic sampling. No serious adverse events occurred relating to sulfasalazine use. Sulfasalazine and its metabolite sulfapyridine were detected in maternal plasma, placenta and in the fetal circulation. Maternal-to-fetal transfer of both compounds was confirmed, with some participants showing higher concentrations in cord blood than maternal blood, suggesting potential active or saturable transport mechanisms. Antiangiogenic biomarkers, including sFlt-1, increased post-treatment in most participants. Interpretation: Sulfasalazine was well tolerated in women with preterm preeclampsia and showed maternal and fetal exposure. Placental transfer was evident. These findings support the feasibility of sulfasalazine use in this population and warrant further investigation in a larger clinical trial to evaluate efficacy. Funding: Norman Beischer Medical Research Foundation, University of Melbourne, and NHMRC. Funders had no role in study conduct or manuscript preparation.