Lithium Pharmacokinetics in the Perinatal Patient With Bipolar Disorder

The pharmacokinetics of lithium, the gold standard for the treatment of bipolar disorder, are well described in nonpregnant patients. Because lithium is commonly prescribed to women of childbearing age, more data are essential to characterize lithium pharmacokinetics during the perinatal period. Lithium is primarily eliminated by the kidney. As a result, shifts in lithium elimination clearance parallel pregnancy-related changes in glomerular filtration rate. Lithium's narrow therapeutic window increases the risk for therapeutic failure and toxicity when lithium elimination clearance is altered. To characterize the pharmacokinetics of lithium in pregnancy and postpartum, 3 women treated with lithium for bipolar disorder completed serial blood sampling protocols during each trimester of pregnancy and at least once postpartum. The trajectory of lithium elimination clearance, creatinine clearance, and serum lithium concentrations were determined. Manic, depressive, and anxiety symptoms were also assessed at each study visit. Compared to the nonpregnant state, lithium elimination clearance increased an average of 63.5% by the third trimester. Lithium elimination clearance was inversely related to changes in serum lithium concentration. Mood symptoms worsened with declines in serum lithium concentration. Lithium elimination clearance returned to baseline at 4 to 9 weeks postpartum. To maintain lithium effectiveness during pregnancy and prevent toxicity postpartum, lithium therapeutic drug monitoring and dose adjustments are warranted.