P-glycoprotein-based loperamide-cyclosporine drug interaction at the rat blood-brain barrier: prediction from in vitro studies and extrapolation to humans

We have shown that the rat can quantitatively predict the verapamil-cyclopsorine A (CsA) drug-drug interaction (DDI) at the human blood-brain barrier (BBB). In addition, the potency (EC(50)) of CsA to inhibit rat BBB P-gp can be predicted from in vitro studies in MDRI-transfected cells. To assess if these excellent agreements extend to other substrates, we determined the magnitude of P-gp-based DDI at the rat BBB between loperamide (Lop) or its metabolite, N-desmethyl Lop (dLop), and escalating CsA blood concentrations. The percent increase in the brain:blood Lop concentration ratio was described by the Hill equation, E(max) = 2000%, EC(50) = 7.1 μM and γ = 3.7. The potency (EC(50)) of CsA to inhibit P-gp at the rat BBB was independent of the substrate used (verapamil, Lop, or dLop). Like the verapamil-CsA DDI, the potency (EC(50)) of CsA to inhibit rat BBB P-gp could be predicted from studies in MDRI-transfected cells. When (11)C-Lop was coadministered with a 10 mg/kg iv infusion of CsA (1) yielding ~5.6 uM CsA blood concentration to healthy volunteers, the brain distribution of (11)C-radioactivity was increased by 110%. (1) When corrected for diffusible Lop metabolite(s), this translates into an increase in (11)C-Lop brain distribution of 457%. Based on our rat data, we estimated a similar value at 5.6 μM blood CsA concentration, 588% increase in Lop brain distribution. These data support our conclusion that the rat is a promising model to predict P-gp based DDI at the human BBB.     

Quantification of human hepatocyte cytochrome P450 enzymes and transporters induced by HIV protease inhibitors using newly validated LC-MS/MS cocktail assays and RT-PCR

Human immunodeficiency virus (HIV) protease inhibitors (PIs) produce profound and unpredictable drug-drug interactions (DDIs) that cannot be explained fully by their inhibition/inactivation of CYP3A enzymes. Delineating and quantifying the CYPs and transporters inducible by PIs are crucial in developing an integrative mechanistic understanding and prediction of PI-based DDIs. To do so, two LC-MS/MS cocktail assays were modified and validated simultaneously to quantify the CYP activity of CYP3A, 2B6, 2C8, 2C9, 2C19, 1A, 2E1, 2A6 and 2D6 enzymes. These new assays were applied to evaluate the induction potential of eight PIs in microsomes isolated from PI-treated human hepatocytes. The mRNA expression of these CYPs and transporters (OATP1B1, OATP1B3, OATP1A2, MDR1, MRP2 and MRP4) was also evaluated using relative RT-PCR. The majority of PIs were net inducers of CYP3As and 2B6 at both the mRNA and activity level (> 2-fold), while ritonavir, saquinavir, nelfinavir or lopinavir did not induce CYP3A activity (< 2-fold), presumably due to CYP3A inactivation. OATP1B1 and MDR1 were the only two hepatic transporters induced (> 2-fold) by the PIs. Amprenavir was the most potent net inducer. In conclusion, our validated cocktail assays can be implemented to comprehensively quantify CYP activities in human liver microsomes and hepatocyte studies. The results also provide the much needed data on the net induction potential of the PIs for hepatic CYPs and transporters. A qualitative agreement was observed between our results and published PI-based DDIs, suggesting that human hepatocytes are a useful platform for more extensive and quantitative in vitro-in vivo prediction of PI-based DDIs.     

In vitro LC-MS cocktail assays to simultaneously determine human cytochrome P450 activities

Using liquid chromatography-mass spectrometry (LC-MS), two sensitive cocktail assays were developed, one to simultaneously determine activities of the cytochrome P450 enzymes, CYP1A2 (phenacitin), 2B6 (bupropion), 2C8 (amodiaquine) and 2C19 (omperazole), and the other to determine simultaneously activities of CYP3A4/5 (testosterone), 2C9 (tolbutamide) and 2D6 (dextromethorphan). These cocktail assays are sensitive, require only a small amount of microsomal protein, employ selective and high turnover CYP substrates and do not require post-incubation extraction. In each of these cocktails, no interactions were observed between the substrates. Combining the two cocktails into a single cocktail resulted in significant inhibition of CYP2D6 by amiodiaquine. These assays were used successfully to determine induction of CYP enzymes in microsomes isolated from human hepatocytes treated (72 h) with or without the prototypic inducer, rifampin.     

New insights into the pharmacology and cytotoxicity of gemcitabine and 2',2'-difluorodeoxyuridine

In a clinical study with oral gemcitabine (2',2'-difluorodeoxycytidine, dFdC), 2',2'-difluorodeoxyuridine (dFdU) was extensively formed and accumulated after multiple oral dosing. Here, we have investigated the in vitro cytotoxicity, cellular uptake, efflux, biotransformation, and nucleic acid incorporation of dFdC and dFdU. Short-term and long-term cytotoxicity assays were used to assess the cytotoxicity of dFdC and dFdU in human hepatocellular carcinoma HepG2, human lung carcinoma A549, and Madin-Darby canine kidney cell lines transfected with the human concentrative or equilibrative nucleoside transporter 1 (hCNT1 or hENT1), or empty vector. Radiolabeled dFdC and dFdU were used to determine cellular uptake, efflux, biotransformation, and incorporation into DNA and RNA. The compounds dFdC, dFdU, and their phosphorylated metabolites were quantified by high-performance liquid chromatography with UV and radioisotope detection. dFdU monophosphate, diphosphate, and triphosphate (dFdU-TP) were formed from dFdC and dFdU. dFdU-TP was incorporated into DNA and RNA. The area under the intracellular concentration-time curve of dFdC-TP and dFdU-TP and their extent of incorporation into DNA and RNA inversely correlated with the IC(50) of dFdC and dFdU, respectively. The cellular uptake and cytotoxicity of dFdU were significantly enhanced by hCNT1. dFdU inhibited cell cycle progression and its cytotoxicity significantly increased with longer duration of exposure. dFdU is taken up into cells with high affinity by hCNT1 and phosphorylated to its dFdU-TP metabolite. dFdU-TP is incorporated into DNA and RNA, which correlated with dFdU cytotoxicity. These data provide strong evidence that dFdU can significantly contribute to the cytotoxicity of dFdC.     

Pharmacokinetics and safety of stavudine in HIV-infected pregnant women and their infants: Pediatric AIDS Clinical Trials Group protocol 332

This study evaluates the safety, tolerance, and pharmacokinetics of stavudine (d4T) in human immunodeficiency virus (HIV)-infected zidovudine (ZDV)-intolerant/refusing pregnant women and of single-dose d4T in their infants. Women received d4T and lamivudine (3TC) from enrollment until labor. During labor, women received oral 3TC and either intravenous or oral d4T. Infants received ZDV and 3TC for 6 weeks and a single dose of oral d4T at weeks 1 and 6. Mean maternal antenatal d4T pharmacokinetics (terminal plasma half-life [T1/2], 83.5+/-16.8 min; area under the plasma-concentration time curve [AUC0-infinity), 81.6+/-22.0 microg.min/mL; n=6) were not significantly different from those during labor (T(1/2), 87.3+/-24.7 min; AUC0-infinity, 88.1+/-16.6 microg.min/mL; n=6). Umbilical-cord and maternal plasma concentrations were not significantly different from one another. The oral clearance of d4T in infants was significantly greater at week 6 versus week 1 (6.8+/-1.0 vs. 5.6+/-1.2 mL/min/kg). There were no toxicities, in women or infants, that required discontinuation or modification of the study drug. No infants had positive HIV viral diagnostic tests. d4T with or without 3TC is a potential alternative to ZDV for HIV-infected pregnant women.     

Rapid solid-phase extraction method to quantify [C]-verapamil, and its [C]-metabolites, in human and macaque plasma

IntroductionP-glycoprotein (P-gp), an efflux transporter, is a significant barrier to drug entry into the brain and the fetus. The positron emission tomography (PET) ligand, [¹¹C]-verapamil, has been used to measure in vivo P-gp activity at various tissue–blood barriers of humans and animals. Since verapamil is extensively metabolized in vivo, it is important to quantify the extent of verapamil metabolism in order to interpret such P-gp activity. Therefore, we developed a rapid solid-phase extraction (SPE) method to separate, and then quantify, verapamil and its radiolabeled metabolites in plasma.MethodsUsing high-performance liquid chromatography (HPLC), we established that the major identifiable circulating radioactive metabolite of [¹¹C]-verapamil in plasma of humans and the nonhuman primate, Macaca nemestrina, was [¹¹C]-D-617/717. Using sequential and differential pH elution on C₈ SPE cartridges, we developed a rapid method to separate [¹¹C]-verapamil and [¹¹C]-D-617/717. Recovery was measured by spiking the samples with the corresponding nonradioactive compounds and assaying these compounds by HPLC.ResultsVerapamil and D-617/717 recovery with the SPE method was >85%. When the method was applied to PET studies in humans and nonhuman primates, significant plasma concentration of D-617/717 and unknown polar metabolite(s) were observed. The SPE and the HPLC methods were not significantly different in the quantification of verapamil and D-617/717.ConclusionsThe SPE method simultaneously processes multiple samples in less than 5 min. Given the short half-life of [¹¹C], this method provides a valuable tool to rapidly determine the concentration of [¹¹C]-verapamil and its [¹¹C]-metabolites in human and nonhuman primate plasma.     

Skilled Nursing Facility Placement Process After Total Hip and Total Knee Arthroplasty: Revised Rating System and Opportunities for Intervention

BackgroundWith the advent of bundled payment models, identifying high-performing skilled nursing facilities (SNFs) has become increasingly important. The goal of this study is to develop a rating system to rank SNFs within our health system and to use this system to improve the SNF discharge process at our institution.MethodsAll SNF-discharged primary total joint arthroplasty cases in 2017 at a multi-hospital academic health system were queried. Discharge patterns were assessed using heat map analysis. Regression analyses in conjunction with structured discussions with subject matter experts were used to identify measures of SNF efficiency and care quality. A revised rating system was developed and used to identify high-performing facilities within our health system. Opportunities to re-direct patients to higher performing facilities were identified.ResultsA revised rating system for SNFs was constructed based on risk-adjusted SNF length of stay, 30-day re-admission rate, and 30-day emergency department visit rate. As 82% of patients were discharged to SNFs in close proximity to their home, high-performing SNFs (according to the revised rating system) were identified by geographic region. Mapping of the discharge process revealed multiple opportunities where patients could be re-directed to a higher performing SNF in their area. Using conservative estimates (25% of discharges re-directed), this is expected to achieve a cost saving of $2,600,000 over a 5-year period, mainly through reductions in SNF length of stay.ConclusionThis study describes the development of a revised rating system for SNFs which, when implemented, is expected to achieve substantial cost savings over a 5-year period.     

Interaction of Zidovudine (Azidothymidine) with Isoprinosine and Probenecid in Macaca fascicularis

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