Drug dosing during pregnancy-opportunities for physiologically based pharmacokinetic models

Drugs can have harmful effects on the embryo or the fetus at any point during pregnancy. Not all the damaging effects of intrauterine exposure to drugs are obvious at birth, some may only manifest later in life. Thus, drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus. Dosing of drugs during pregnancy is often empirically determined and based upon evidence from studies of non-pregnant subjects, which may lead to suboptimal dosing, particularly during the third trimester. This review collates examples of drugs with known recommendations for dose adjustment during pregnancy, in addition to providing an example of the potential use of PBPK models in dose adjustment recommendation during pregnancy within the context of drug-drug interactions. For many drugs, such as antidepressants and antiretroviral drugs, dose adjustment has been recommended based on pharmacokinetic studies demonstrating a reduction in drug concentrations. However, there is relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Examples of using pregnancy PBPK models to predict feto-maternal drug exposures and their applications to facilitate and guide dose assessment throughout gestation are discussed.

Impact of high plasma concentrations of linezolid in Taiwanese adult patients- therapeutic drug monitoring in improving adverse drug reactions

BACKGROUND

Previous studies have shown that the development of thrombocytopenia was associated with the elevated plasma concentration of linezolid, but little is known about the relationship between other uncommon adverse drug reactions (ADRs) and plasma concentration. The appropriate dosing adjustment has remained controversial. This prospective observational study was conducted to investigate the association between the plasma concentration of linezolid, ADRs, and clinical outcomes.

METHODS

Adult patients on linezolid treatment undergoing at least one therapeutic drug monitoring (TDM) were enrolled. The association between linezolid concentrations and ADRs was examined by multivariate Cox regression model. Predictors of linezolid concentrations was determined by linear regression model. The cut-off point of linezolid concentration and the effect of dosing adjustments based on TDM was also explored.

RESULTS

Of 50 patients enrolled in the study, plasma concentrations were 1.5-3 times higher than what was described in the prescribing information. The median minimum concentration (C_min) was significantly higher in patients with thrombocytopenia compared to patients without thrombocytopenia (13.0 vs. 7.2 μg/mL, P = 0.0273), and a higher median maximum concentration was also observed in patients with lactic acidosis (33.0 vs. 27.5 μg/mL, P = 0.0420). The C_min was elevated in patients with advanced age and severely impaired renal function. Dosing adjustment tailored by early TDM with the upper limit of C_min 9 μg/mL may improve platelet counts.

CONCLUSION

Elevated linezolid concentrations were associated with thrombocytopenia and lactic acidosis. TDM-guided dosing adjustment could be considered as a pragmatic way to mitigate thrombocytopenia.