Pharmacokinetics of Amlodipine Besylate at Delivery and During Lactation

We plan to evaluate the pharmacokinetics of amlodipine besylate at the time of delivery, to determine if transplacental passage of the drug occurs. We will also examine the drug kinetics in postpartum lactation to establish whether amlodipine is excreted into breast milk. The outcomes of interest are plasma concentration of amlodipine at delivery and the drug concentrations in blood and breast milk over a twenty-hour steady-state period following milk-supply establishment. Fifteen patients already taking 5 mg of amlodipine during pregnancy for the treatment of chronic hypertension will be recruited from the antepartum Obstetric Complications Clinic at Parkland Hospital. Only women who are breastfeeding will be eligible for the study. Patients who elect to participate in the study will continue their amlodipine 5 mg dosing through delivery and into the postpartum period. Maternal blood will be drawn within one hour of delivery and fetal cord blood collected at the time of delivery. Patients will then have blood drawn over a 24 hour period beginning on postpartum day 2 after delivery following administration of their once-daily amlodipine dose. At each blood draw, the patient will also use a breast pump to express breast milk for paired analysis. Both blood and breast milk amlodipine levels will be calculated for all samples. The levels will be used to determine the pharmacokinetics of amlodipine in the peri- and postpartum patient, including concentrations in plasma and breast milk.

In addition to collecting maternal data, a range of clinical information will be collected on each study patient's infant including weight, Apgar scores, hemodynamic parameters, physical examination and hospital course. This information will be used to screen for any potential complications associated with infant exposure to amlodipine. An infant blood sample will also be obtained in conjunction with the routine neonatal blood collection that occurs at 1-2 days of postnatal life and this will be analyzed to determine serum amlodipine concentration in breastfeeding infants.

Inclusion criteria

• 18 years or older;
• Pregnant female
• Already taking amlodipine 5 mg for treatment of chronic hypertension in pregnancy;
• Hospitalized following routine term vaginal delivery or uncomplicated cesarean delivery
• Breastfeeding or breast and bottle-feeding their infant

Exclusion criteria

• Known kidney disease
• Delivery complicated by chorioamnionitis, endometritis or postpartum hemorrhage
• Administration of greater than 5 mg of amlodipine in 24 hour period