Drug interaction profile of the HIV integrase inhibitor cabotegravir: assessment from in vitro studies and a clinical investigation with midazolam.

1. Cabotegravir (CAB; GSK1265744) is a potent HIV integrase inhibitor in clinical development as an oral lead-in tablet and long-acting injectable for the treatment and prevention of HIV infection. 2. This work investigated if CAB was a substrate for efflux transporters, the potential for CAB to interact with drug-metabolizing enzymes and transporters to cause clinical drug interactions, and the effect of CAB on the pharmacokinetics of midazolam, a CYP3A4 probe substrate, in humans. 3. CAB is a substrate for Pgp and BCRP; however, its high intrinsic membrane permeability limits the impact of these transporters on its intestinal absorption. 4. At clinically relevant concentrations, CAB did not inhibit or induce any of the CYP or UGT enzymes evaluated in vitro and had no effect on the clinical pharmacokinetics of midazolam. 5. CAB is an inhibitor of OAT1 (IC50 0.81 µM) and OAT3 (IC50 0.41 µM) but did not or only weakly inhibited Pgp, BCRP, MRP2, MRP4, MATE1, MATE2-K, OATP1B1, OATP1B3, OCT1, OCT2 or BSEP. 6. Based on regulatory guidelines and quantitative extrapolations, CAB has a low propensity to cause clinically significant drug interactions, except for coadministration with OAT1 or OAT3 substrates.

Metformin's Intrinsic Blood-to-Plasma Partition Ratio (B/P): Reconciling the Perceived High In Vivo B/P > 10 with the In Vitro Equilibrium Value of Unity.

Blood cells are considered an important distributional compartment for metformin based on the high blood-to-plasma partition ratio (B/P) in humans (>10 at Cmin). However, literature reports of metformin's intrinsic in vitro B/P values are lacking. At present, the extent and rate of metformin cellular partitioning was determined in incubations of fresh human and rat blood with [(14)C]metformin for up to 1 week at concentrations spanning steady-state plasma Cmin, Cmax, and a concentration associated with lactic acidosis. The results showed that metformin's intrinsic equilibrium B/P was ∼0.8-1.4 in blood, which is <10% of the reported clinical value. Kinetics of metformin partitioning into human blood cells and repartitioning back into plasma were slow (repartitioning half-life ∼32-39 hours). These data, along with in vivo rapid and efficient renal clearance of plasma metformin (plasma renal extraction ratio ∼90%-100%), explain why the clinical terminal half-life of metformin in plasma (6 hours) is 3- to 4-fold shorter than the half-life in whole blood (18 hours) and erythrocytes (23 hours). The rate constant for metformin repartitioning from blood cells to plasma (∼0.02 h(-1)) is far slower than the clinical renal elimination rate constant (0.3 h(-1)). Blood distributional rate constants were incorporated into a metformin physiologically-based pharmacokinetic model, which predicted the differential elimination half-life in plasma and blood. The present study demonstrates that the extent of cellular drug partitioning in blood observed in a dynamic in vivo system may be very different from the static in vitro values when repartitioning from blood cells is far slower than clearance of drug in plasma.

The comparative disposition and metabolism of dolutegravir, a potent HIV-1 integrase inhibitor, in mice, rats, and monkeys.

1. Plasma clearance of dolutegravir, an unboosted HIV-1 integrase inhibitor, was low in rat and monkey (0.23 and 2.12 mL/min/kg, respectively) as was the volume of distribution (0.1 and 0.28 L/kg, respectively) with terminal elimination half-life approximately 6 h. Dolutegravir was rapidly absorbed from oral solution with a high bioavailability in rat and monkey (75.6 and 87.0% respectively), but solubility or dissolution rate limited when administered as suspension. 2. Dolutegravir was highly bound (>99%) to serum proteins in rat and monkey, similar to binding to plasma and serum proteins in human. Radioactivity was associated with the plasma versus cellular components of blood across all species. 3. Following oral administration to rats, [(14)C]dolutegravir-related radioactivity was distributed to most tissues, due in part to high permeability; however, because of high plasma protein binding, tissue to blood ratios were low. In mouse, rat and monkey, the absorbed dose was extensively metabolized and secreted into bile, with the majority of the administered radioactivity eliminated in feces within 24 h. 4. The primary route of metabolism of dolutegravir was through the formation of an ether glucuronide. Additional biotransformation pathways: benzylic oxidation followed by hydrolysis to an N-dealkylated product, glucose conjugation, oxidative defluorination, and glutathione conjugation.

Disposition and metabolism of GSK2251052 in humans: a novel boron-containing antibiotic.

(S)-3-(Aminomethyl)-7-(3-hydroxypropoxy)-1-hydroxy-1,3-dihydro-2,1-benzoxaborole (GSK2251052) is a novel boron-containing antibiotic that inhibits bacterial leucyl tRNA synthetase, and that has been in development for the treatment of serious Gram-negative infections. In this study, six healthy adult male subjects received a single i.v. dose of [¹4C]GSK2251052, 1500 mg infused over 1 hour. Blood, urine, and feces were collected over an extended period of 14 days, and accelerator mass spectrometry was used to quantify low levels of radioactivity in plasma at later time points to supplement the less-sensitive liquid scintillation counting technique. An excellent mass balance recovery was achieved representing a mean total of 98.2% of the dose, including 90.5% recovered in the urine. Pharmacokinetic analysis demonstrated that radioactivity was moderately associated with the blood cellular components, and together with GSK2251052, both were highly distributed into tissues. The parent compound had a much shorter half-life than total radioactivity in plasma, approximately 11.6 hours compared with 96 hours. GSK2251052 and its major metabolite M3, which resulted from oxidation of the propanol side chain to the corresponding carboxylic acid, comprised the majority of the plasma radioactivity, 37 and 53% of the area under the plasma versus time concentration curve from time zero to infinity, respectively. Additionally, M3 was eliminated renally, and was demonstrated to be responsible for the long plasma radioactivity elimination half-life. A combination of in vitro metabolism experiments and a pharmacokinetic study in monkeys with the inhibitor 4-methylpyrazole provided strong evidence that alcohol dehydrogenase, potentially in association with aldehyde dehydrogenase, is the primary enzyme involved in the formation of the M3 metabolite.

Human metabolism of lapatinib, a dual kinase inhibitor: implications for hepatotoxicity.

Lapatinib (Tykerb, Tyverb) is an important orally active dual tyrosine kinase inhibitor efficacious in combination therapy for patients with progressive human epidermal receptor 2-overexpressing metastatic breast cancer. However, clinically significant liver injury, which may be associated with lapatinib metabolic activation, has been reported. We describe the metabolism and excretion of [(14)C]lapatinib in six healthy human volunteers after a single oral dose of 250 mg and the potential relationships between metabolism and clinical hepatotoxicity. Overall, elimination showed high intersubject variability, with fecal elimination being the predominant pathway, representing a median of 92% of the dose with lapatinib as the largest component (approximate median 27% of the dose). In plasma, approximately 50% of the observed radioactivity was attributed to metabolites. Analysis of a 4-h pooled plasma extract identified seven metabolites related by an N- and α-carbon oxidation cascade. Fecal metabolites derived from three prominent pathways: N- and α-carbon oxidation, fluorobenzyl oxidative cleavage, and hydroxypyridine formation. Several of the lapatinib metabolites can undoubtedly be linked to reactive species such as aldehydes or quinone imines. In addition to the contribution of these potentially reactive metabolites as suspects in clinical liver injury, the role of other disposition factors, including interaction with drug transporters, pharmacogenetics, or magnitude of the therapeutic dose, should not be discounted.

Assessment of the drug interaction risk for remogliflozin etabonate, a sodium-dependent glucose cotransporter-2 inhibitor: evidence from in vitro, human mass balance, and ketoconazole interaction studies.

Remogliflozin etabonate is the ester prodrug of remogliflozin, a selective sodium-dependent glucose cotransporter-2 inhibitor. This work investigated the absorption, metabolism, and excretion of [(14)C]remogliflozin etabonate in humans, as well as the influence of P-glycoprotein (Pgp) and cytochrome P450 (P450) enzymes on the disposition of remogliflozin etabonate and its metabolites to understand the risks for drug interactions. After a single oral 402 ± 1.0 mg (106 ± 0.3 µCi) dose, [(14)C]remogliflozin etabonate is rapidly absorbed and extensively metabolized. The area under the concentration-time curve from 0 to infinity [AUC((0-∞))] of plasma radioactivity was approximately 14-fold higher than the sum of the AUC((0-∞)) of remogliflozin etabonate, remogliflozin, and 5-methyl-4-({4-[(1-methylethyl)oxy]phenyl}methyl)-1H-pyrazol-3-yl-ß-d-glucopyranoside (GSK279782), a pharmacologically active N-dealkylated metabolite. Elimination half-lives of total radioactivity, remogliflozin etabonate, and remogliflozin were 6.57, 0.39, and 1.57 h, respectively. Products of remogliflozin etabonate metabolism are eliminated primarily via renal excretion, with 92.8% of the dose recovered in the urine. Three glucuronide metabolites made up the majority of the radioactivity in plasma and represent 67.1% of the dose in urine, with 5-methyl-1-(1-methylethyl)-4-({4-[(1-methylethyl)oxy]phenyl}methyl)-1H-pyrazol-3-yl-ß-d-glucopyranosiduronic acid (GSK1997711) representing 47.8% of the dose. In vitro studies demonstrated that remogliflozin etabonate and remogliflozin are Pgp substrates, and that CYP3A4 can form GSK279782 directly from remogliflozin. A ketoconazole clinical drug interaction study, along with the human mass balance findings, confirmed that CYP3A4 contributes less than 50% to remogliflozin metabolism, demonstrating that other enzyme pathways (e.g., P450s, UDP-glucuronosyltransferases, and glucosidases) make significant contributions to the drug's clearance. Overall, these studies support a low clinical drug interaction risk for remogliflozin etabonate due to the availability of multiple biotransformation pathways.

The Effect of Dolutegravir on the Pharmacokinetics of Metformin in Healthy Subjects.

BACKGROUND: Dolutegravir is an integrase strand transfer inhibitor (INSTI) licensed for use in HIV-1 infection and is an inhibitor of organic cation transporter 2 (OCT2). This study assessed the effect of dolutegravir on the pharmacokinetics of metformin, an OCT2 substrate. DESIGN: This was an open-label, parallel-group, 3-period crossover study in healthy adult subjects. Subjects were enrolled into 1 of 2 treatment cohorts (15 subjects/cohort) receiving metformin 500 mg q12h for 5 days in period 1; metformin 500 mg q12h plus dolutegravir 50 mg q24h (cohort 1) or 50 mg q12h (cohort 2) for 7 days in period 2; and metformin 500 mg q12h for 10 days in period 3. There were no washout periods between treatments. Effects of dolutegravir on metformin transport and paracellular permeability were evaluated in vitro. RESULTS: Co-administration of dolutegravir 50 mg q24h increased metformin area under the curve(0-τ) by 79% and Cmax by 66%, whereas dolutegravir 50 mg q12h increased metformin area under the curve(0-τ) and Cmax by 145% and 111%, respectively. Metformin t(1/2) remained unchanged. Increased metformin exposure during dolutegravir co-administration returned to period 1 levels after dolutegravir discontinuation in period 3. Co-administration of dolutegravir and metformin was well tolerated. In vitro, dolutegravir was not a clinically relevant inhibitor of OCT1, OCT3, multidrug and toxin extrusion protein 1, multidrug and toxin extrusion protein 2-K, or plasma membrane monoamine transporter, and it did not affect metformin paracellular permeability or uptake into an intestinal cell line. CONCLUSIONS: Dolutegravir significantly increased metformin plasma exposure, which can be partially explained by OCT2 inhibition. It is recommended that dose adjustments of metformin be considered to maintain optimal glycemic control when patients are starting/stopping dolutegravir while taking metformin.

Neuromuscular blocking activity and therapeutic potential of mixed-tetrahydroisoquinolinium halofumarates and halosuccinates in rhesus monkeys.

Structure-activity relationships in rhesus monkeys for a novel mixed-onium class of ultra-short-acting nondepolarizing tetrahydroisoquinolinium neuromuscular blockers (NMBs) are described. Bis-onium chlorofumarate 20a with (1R,2S)-benzyltetrahydroisoquinolinium groups was a potent lead compound (ED(95) = 0.079 mg/kg) with an ultra-short duration of NMB effect (7.1 min) and a selectivity index (SI: defined as a ratio of the cardiovascular threshold dose to the ED(95)) similar to that of mivacurium (3). The mean threshold dose for cardiovascular effects with 20a was ca. 20 times its ED(95) value (SI = 20). A novel mixed-onium analogue of 20a was prepared by replacing the benzyltetrahydroisoquinolinium group distal to the fumarate chlorine atom with a (1S,2R)-phenyltetrahydroisoquinolinium moiety. The resulting mixed-onium chlorofumarate 24a displayed good NMB potency (ED(95) = 0.063 mg/kg), ultra-short duration of action (5.6 min) and an improved selectivity index (SI = 57). Several other mixed-onium derivatives containing octanedioate (25a; ED(95) = 0.103 mg/kg), difluorosuccinate (27c; ED(95) = 0.056 mg/kg), and fluorofumarate (28a; ED(95) = 0.137 mg/kg) linkers were also potent, ultra-short-acting NMBs with good to excellent selectivity index values (SI = 37-96). Octanedioate 25a was longer acting at higher doses compared to difluorosuccinate 27c and chlorofumarate 24a. Durations of NMB effect following a 0.4 mg/kg bolus dose (100% block) of 25a, 27c, and 24a were 16.9, 13.0, and 10.0 min, respectively. Recovery time for mixed-onium chlorofumarate 24a following a 1 h continuous infusion at 10-20 microg/kg/min (95-100% block) was ca. 5 min which is similar to that observed following a 0.2 mg/kg bolus dose of this compound and indicates a lack of cummulative effects. Preliminary studies with chlorofumarate 24a in whole human blood revealed that mixed-onium thiazolidine 29 was the major metabolite and that plasma cholinesterases do not play the primary role in duration of NMB effect. The NMB properties of 24a in rhesus monkeys led to its clinical evaluation as a possible alternative to succinylcholine.

Metabolite structure analysis by high-resolution MS: supporting drug-development studies.

Effective characterization of drug metabolites in complex biological matrices is facilitated by mass spectrometers with high resolving power, mass accuracy and sensitivity. This review begins with an overview of high-resolution MS terminology and the different types of instrumentation that are currently available. Metabolite structure analysis offers unique challenges and, therefore, the different types of approaches used to solve problems are highlighted through specific examples. Overall, this review describes the value that high-resolution MS brings to drug-metabolism studies.

Safety, Pharmacokinetics, and Pharmacodynamic Effects of a Selective TGR5 Agonist, SB-756050, in Type 2 Diabetes.

TGR5 is a bile acid receptor and a potential target for the treatment of type 2 diabetes (T2D). We report here the safety, pharmacokinetics, and pharmacodynamic effects of a selective TGR5 agonist, SB-756050, in patients with T2D. Fifty-one subjects were randomized to receive either placebo or one of four doses of SB-756050 for 6 days. A single 100 mg dose of sitagliptin was co-administered on Day 6 to all subjects. SB-756050 was well-tolerated; it was readily absorbed, exhibited nonlinear pharmacokinetics with a less than dose-proportional increase in plasma exposure above 100 mg, and demonstrated no significant changes in exposure when co-administered with sitagliptin. SB-756050 demonstrated highly variable pharmacodynamic effects both within dose groups and between doses, with increases in glucose seen at the two lowest doses and no reduction in glucose seen at the two highest doses. The glucose effects of SB-756050 + sitagliptin were comparable to those of sitagliptin alone, even though gut hormone plasma profiles were different. This study was registered at ClinicalTrials.gov (NCT00733577).