A woman 38 weeks gestation experiencing severe preeclampsia has been receiving magnesium sulfate by intravenous infusion for 8 hours. The nurse assesses the client and documents the following findings: temperature of 37.1°C, pulse rate of 96 beats per minute, respiratory rate of 24 breaths per minute, BP of 170/112 mm Hg. 3+ DTRs, and no ankle clonus. The nurse calls the provider with an update. The nurse should anticipate an order for which medication first?