Importance of Drug Transporters in Pharmacokinetics and Drug Safety

Simultaneous determination of nirmatrelvir and ritonavir in human plasma by LC-MS/MS and its pharmacokinetic application in healthy Chinese subjects

Paxlovid, a co-packaged medication of nirmatrelvir tablets (150 mg) and ritonavir tablets (100 mg) developed by Pfizer, is one of the first orally accessible COVID-19 antiviral medicines to be approved for the emergency usage. In this research, an efficient LC-MS/MS method for simultaneous determining nirmatrelvir and ritonavir in human plasma was established and validated with remdesivir as an internal standard. Chromatographic separations were carried out on a Thermo BDS Hypersil C18 (4.6mm×100, 2.4μm) column using deionized water and methanol as mobile phase, both added with 0.1% (v/v) formic acid. Based on the positive electrospray ionization mode, nirmatrelvir and ritonavir were analyzed by selective reaction monitoring. Excellent precision, accuracy, recovery, and linearity were demonstrated covering the range of 50-5000 ng/mL for nirmatrelvir and 10-1000 ng/mL for ritonavir. Then, the established method was utilized to the pharmacokinetic profile of Paxlovid in healthy Chinese subjects. The Pharmacokinetic parameters, including C_max , T_max , t_1/2 and AUC_0-∞ of western subjects correspond well with the results of this pharmacokinetic investigation.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.