Drugs in Human Milk Part 1: Practical and Analytical Considerations in Measuring Drugs and Metabolites in Human Milk.

Human milk is a remarkable biofluid that provides essential nutrients and immune protection to newborns. Breastfeeding women consuming medications could pass the drug through their milk to neonates. Drugs can be transferred to human milk by passive diffusion or active transport. The physicochemical properties of the drug largely impact the extent of drug transfer into human milk. A comprehensive understanding of the physiology of human milk formation, composition of milk, mechanisms of drug transfer, and factors influencing drug transfer into human milk is critical for appropriate selection and use of medications in lactating women. Quantification of drugs in the milk is essential for assessing the safety of pharmacotherapy during lactation. This can be achieved by developing specific, sensitive, and reproducible analytical methods using techniques such as liquid chromatography coupled with mass spectrometry. The present review briefly discusses the physiology of human milk formation, composition of human milk, mechanisms of drug transfer into human milk, and factors influencing transfer of drugs from blood to milk. We further expand upon and critically evaluate the existing analytical approaches/assays used for the quantification of drugs in human milk.

The Dosing Regimen for 17-hydroxyprogesterone caproate was Suboptimal Lessons for Future Pharmacotherapy for Pregnant Women.

BACKGROUND: Makena (17-hydroxyprogesterone caproate) was FDA approved for prevention of recurrent spontaneous preterm birth in 2011 under the accelerated approval pathway but fundamental pharmacokinetic or pharmacodynamic (phase1 and phase 2) studies were not performed. At the time, there were no dose-response or concentration-response data. The therapeutic concentration was not known. The lack of such data questions whether the dosing regimen for 17-hydroxyprogesterone caproate was optimized. OBJECTIVE: The purpose of this study was to evaluate the dosing regimen for 17-hydroxyprogesterone by analyzing three data sets that evaluated 17-hydroxyprogesterone caproate pharmacology: the Maternal-Fetal Medicine Omega 3 study, the Obstetric-Fetal Pharmacology Research Units study and the Obstetrical-Fetal Pharmacology Research Centers study. If an inappropriate dosing regimen could be identified, such information could inform future studies of pharmacotherapy in pregnancy. STUDY DESIGN: Data from the Omega 3 study were utilized to determine if plasma concentration was related to spontaneous preterm birth risk and if a threshold concentration could be identified. Data from the Obstetric-Fetal Pharmacology Research Units study were used to determine the half-life of 17-hydroxyprogesterone caproate and to develop a model to simulate drug concentrations with various dosing regimens. Data from the Obstetrical-Fetal Pharmacology Research Centers study were used to determine the relationship between dose and safety outcomes. RESULTS: Analysis of the Omega 3 dataset indicated that the risk of spontaneous preterm birth decreased as the log of 17-hydroxyprogesterone caproate increased [odds ratio (95%CI) 0.04 (0.00 - 0.90)]. A steady state concentration> 9 ng/ml (equivalent to > 8 ng/ml at 25-28 weeks) was associated with the lowest risk of spontaneous preterm birth [hazard ratio (95%CI) 0.52 (0.27-0.98, p=0.04)]; this concentration was not achieved in 25% of subjects receiving the 250 mg weekly dose. In the Obstetrical-Fetal Pharmacology Research Units study, the adjusted half-life (median and IQR) of 17-hydroxyprogesterone caproate was 14.0 (11.5-17.2) days. Simulations indicated that with the 250 mg weekly dose, > 5 weekly injections were required to reach the 9 ng/ml target; however, those with the shortest half-life (corresponding to higher clearance), never reached the targeted 9 ng/ml concentration. In 75% of subjects, a loading dose of 500 mg weekly for 2 weeks followed by 250 mg weekly achieved and maintained the 9 ng/ml concentration within two weeks but in those 25% with the shortest half-life, concentrations exceeded the 9 ng/ml target for only 3 weeks. In the Obstetrical-Fetal Pharmacology Research Centers study, all 65 subjects receiving a weekly dose of 500 mg exceeded the 9 ng/ml steady state. CONCLUSIONS: The dosing regimen for 17-hydoxyprogesterone caproate was inadequate. There is a significant inverse relationship between drug concentration and spontaneous preterm birth. Risk is lowest when concentration exceeds 9 ng/ml but 25% of women receiving the 250 mg weekly dose will never reach and maintain this concentration. The drug's long half-life necessitates a loading dose to achieve therapeutic concentrations rapidly. The omission of basic pharmacologic studies to determine the proper dosing may have compromised the effectiveness of 17-hydroxyprogesterone caproate. Future pharmacotherapy trials in pregnancy must first complete fundamental pharmacology studies.

Applications of Volumetric Absorptive Microsampling Technique: A Systematic Critical Review.

METHODS: A novel microsampling device called Volumetric Absorptive microsampling (VAMS), developed in 2014, appears to have resolved the sample inhomogeneity inherent to dried blood spots, with improved precision in the volume of sample collected for measuring drug concentration. A literature search was conducted to identify several analytical and pharmacokinetic studies that have used VAMS in recent years. RESULTS: The key factors for proper experimental design and optimization of the extraction of drugs and metabolites of interest from the device were summarized. This review focuses on VAMS and elaborates on bioanalytical factors, method validation steps, and scope of this technique in clinical practice. CONCLUSIONS: The promising microsampling method VAMS is especially suited for conducting pharmacokinetic studies with very small volumes of blood, especially in special patient populations. Clinical validation of every VAMS assay must be conducted prior to the routine practical implementation of this method.

Maternal-Fetal Pharmacology of Drugs: A Review of Current Status of the Application of Physiologically Based Pharmacokinetic Models.

Pregnancy and the postpartum period are associated with several physiological changes that can alter the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs. For certain drugs, dosing changes may be required during pregnancy and postpartum to achieve drug exposures comparable to what is observed in non-pregnant subjects. There is very limited data on fetal exposure of drugs during pregnancy, and neonatal exposure through transfer of drugs via human milk during breastfeeding. Very few systematic clinical pharmacology studies have been conducted in pregnant and postpartum women due to ethical issues, concern for the fetus safety as well as potential legal ramifications. Over the past several years, there has been an increase in the application of modeling and simulation approaches such as population PK (PopPK) and physiologically based PK (PBPK) modeling to provide guidance on drug dosing in those special patient populations. Population PK models rely on measured PK data, whereas physiologically based PK models incorporate physiological, preclinical, and clinical data into the model to predict drug exposure during pregnancy. These modeling strategies offer a promising approach to identify the drugs with PK changes during pregnancy to guide dose optimization in pregnancy, when there is lack of clinical data. PBPK modeling is also utilized to predict the fetal exposure of drugs and drug transfer via human milk following maternal exposure. This review focuses on the current status of the application of PBPK modeling to predict maternal and fetal exposure of drugs and thereby guide drug therapy during pregnancy.