Physiologically Based Pharmacokinetic Modeling for Multiple Oral Administration Labetalol in Pregnant Women.

Background: Labetalol has an irreplaceable role in treating Hypertensive disorders of pregnancy (HDP), a common disease during pregnancy with a prevalence of 5.2-8.2%. However, there were big differences in dosage regimens between various guidelines.

Purpose: A physiologically-based pharmacokinetics (PBPK) model was established and validated to evaluate the existing oral dosage regimens, and to compare the difference in plasma concentration between pregnant and non-pregnant women.

Methods: First, non-pregnant woman models with specific plasma clearance or enzymatic metabolism (UGT1A1, UGT2B7, CYP2C19) were established and validated. For CYP2C19, slow, intermediate, and rapid metabolic phenotypes were considered. Then, a pregnant model with proper structure and parameters adjustment was established and validated against the multiple oral administration data.

Results: The predicted labetalol exposure captured the experimental data well. The following simulations with criteria lowering 15 mmHg blood pressure (corresponding to around 108 ng/ml plasma labetalol) found that the maximum daily dosage in the Chinese guideline may be insufficient for some severe HDP patients. Moreover, similar predicted steady-state trough plasma concentration was found between the maximum daily dosage in the American College of Obstetricians and Gynecologists (ACOG) guideline, 800 mg Q8h and a regimen of 200 mg Q6h. Simulations comparing non-pregnant and pregnant women found that the difference in labetalol exposure highly depended on the CYP2C19 metabolic phenotype.

Conclusions: In summary, this work initially established a PBPK model for multiple oral administration of labetalol for pregnant women. This PBPK model may lead to personalized labetalol medication in the future.