Pharmacokinetic Equivalence of Calcium Gluconate and Calcium Chloride in Parturients

Calcium is a life saving medicine in the care of parturients. It has many important uses including treatment of hypocalcemia, treatment of magnesium toxicity, prevention of hypocalcemia during blood transfusion (of citrate containing blood products), treatment of hyperkalemia, and others. Recent clinical trials also suggest that calcium given after cord clamping may decrease blood loss in patients undergoing cesarean delivery. 2 FDA approved forms of calcium can be given intravenously: calcium chloride and calcium gluconate. Over the last decade there have been times with drug shortages of either calcium chloride or calcium gluconate. So there have been and likely will continue to be times when one formulation or the other may not be adequately available. Despite the importance of calcium and the frequency in which it is used in parturients, there are no published studies in parturients to determine dose equivalence between calcium gluconate and calcium chloride. In this study the investigators will determine the population pharmacokinetics of calcium gluconate and calcium chloride in parturients and calculate the dose equivalent ratio the two drugs. This will help clinicians select appropriate doses of calcium and provide resilience to the drug supply chain in our era of frequent drug shortages.

2 grams of calcium gluconate, infused intravenously over 10 minute infusion beginning upon umbilical cord clamping

0.5mg calcium chloride, infused intravenously over 10 minute infusion beginning upon umbilical cord clamping

Ionized calcium will be measured in each participant from a maximum of 6 venous blood draws of 0.5mL (1/10th of a teaspoon). These draws will occur at the following target times: prior to calcium administration, at 6 minutes, 10 minutes, 15 minutes, minutes, minutes after beginning calcium administration. The ionized blood calcium levels will be immediately analyzed using an Abbott iStat machine.

Baseline prior to calcium infusion, 6 minutes, 10 minutes, 15 minutes, 30 minutes, 60 minutes after initiation of infusion

Serum pH will be measured in each participant from a maximum of 6 venous blood draws of 0.5mL (1/10th of a teaspoon). These blood draws will be the same blood draws used to measure serum ionized calcium concentration, no additional blood draws will be necessary. These draws will occur at the following target times: prior to calcium administration, at 6 minutes, 10 minutes, 15 minutes, minutes, minutes after beginning calcium administration. The serum pH levels will be immediately analyzed using an Abbott iStat machine.

Baseline prior to calcium infusion, 6 minutes, 10 minutes, 15 minutes, 30 minutes, 60 minutes after initiation of infusion

Inclusion Criteria: Pregnant female subjects delivering at the study institution via scheduled cesarean delivery at term (>=37 weeks gestation) Exclusion Criteria: severe range blood pressure (BP >160/>110) within the 48 hours prior to delivery patient age <18 years or >45 years renal dysfunction with serum Cr > 1.0 mg/dL known history of congenital or acquired cardiac disease or history of arrhythmia patient taking digoxin patient currently taking a calcium channel blocker Weight <55kg or >100kg, or receiving magnesium infusion within 24 hours prior to or during cesarean delivery administration of intraoperative doses of calcium by the anesthesiology team for clinical indications