In vitro investigations into the roles of drug transporters and metabolizing enzymes in the disposition and drug interactions of dolutegravir, a HIV integrase inhibitor

A review of pharmacological interactions between HIV or hepatitis C virus medications and opioid agonist therapy: implications and management for clinical practice

Global access to opioid agonist therapy and HIV/hepatitis C virus (HCV) treatment is expanding but when used concurrently, problematic pharmacokinetic and pharmacodynamic interactions may occur. Articles published from 1966 to 2012 in Medline were reviewed using the following keywords: HIV, AIDS, HIV therapy, HCV, HCV therapy, antiretroviral therapy, highly active antiretroviral therapy, drug interactions, methadone and buprenorphine. In addition, a review of abstracts from national and international meetings and conference proceedings was conducted; selected reports were reviewed as well. The metabolism of both opioid and antiretroviral therapies, description of their known interactions and clinical implications and management of these interactions were reviewed. Important pharmacokinetic and pharmacodynamic drug interactions affecting either methadone or HIV medications have been demonstrated within each class of antiretroviral agents. Drug interactions between methadone, buprenorphine and HIV medications are known and may have important clinical consequences. Clinicians must be alert to these interactions and have a basic knowledge regarding their management.

Pharmacokinetics of dolutegravir in HIV-seronegative subjects with severe renal impairment

PURPOSE

Dolutegravir (DTG), an unboosted HIV integrase inhibitor (INI), is metabolized by UGT1A1 and to a minor extent by CYP3A. Renal elimination of unchanged DTG is very low (< 1 %). As renal impairment may affect pharmacokinetics (PK), even for drugs primarily metabolized or secreted in bile, this study investigated the effect of renal impairment on the PK of DTG.

METHODS

This was an open-label, single-dose study of oral DTG 50 mg administered to subjects with severe renal impairment (creatinine clearance [CLcr] <30 mL/min; not on dialysis) and to healthy controls (CLcr >90 mL/min) matched for gender, age and body mass index (8 subjects per group). Serial PK samples were collected up to 72 h post-dose for determination of DTG and DTG-glucuronide (DTG-Gluc) concentrations in plasma. DTG unbound fraction in plasma was determined at 3 and 24 h. PK parameters were determined by non-compartmental methods and compared between groups by analysis of covariance.

RESULTS

DTG was well tolerated with a low incidence of Grade 1 adverse events. DTG PK parameters showed significant overlap between groups. DTG mean exposure was lower in subjects with severe renal impairment compared to healthy, matched subjects: AUC(0-∞) and Cmax were 40 % and 23 % lower, while mean DTG-Gluc was increased. Renal impairment did not affect DTG fraction unbound in plasma.

CONCLUSIONS

The modest reductions in mean PK exposures for DTG and increases for DTG-Gluc in the severe renal impairment group are not considered clinically significant. DTG does not require dose adjustment in patients with renal impairment.

Rilpivirine inhibits drug transporters ABCB1, SLC22A1, and SLC22A2 in vitro

Rilpivirine is a nonnucleoside reverse transcriptase inhibitor approved for treatment of HIV-1 infection in antiretroviral-naive adult patients. Potential interactions with drug transporters have not been fully investigated. Transport by and inhibition of drug transporters by rilpivirine were analyzed to further understand the mechanisms governing rilpivirine exposure and determine the potential for transporter-mediated drug-drug interactions. The ability of rilpivirine to inhibit or be transported by ABCB1 was determined using ABCB1-overexpressing CEMVBL100 cells and Caco-2 cell monolayers. The Xenopus laevis oocyte heterologous protein expression system was used to clarify if rilpivirine was either transported by or inhibited the function of influx transporters SLCO1A2, SLCO1B1, SLCO1B3, SLC22A2, SLC22A6, and SLC22A8. The ability of rilpivirine to inhibit or be transported by SLC22A1 was determined using SLC22A1-expressing KCL22 cells. Rilpivirine showed higher accumulation in SLC22A1-overexpressing KCL22 cells than control cells (27% increase, P = 0.03) and inhibited the functionality of SLC22A1 and SLC22A2 transport with 50% inhibitory concentrations (IC50s) of 28.5 μM and 5.13 μM, respectively. Inhibition of ABCB1-mediated digoxin transport was determined for rilpivirine, which inhibited digoxin transport in the B-to-A direction with an IC50 of 4.48 μM. The maximum rilpivirine concentration in plasma in patients following a standard 25-mg dosing regimen is around 0.43 μM, lower than that necessary to substantially inhibit ABCB1, SLC22A1, or SLC22A2 in vitro. However, these data indicate that SLC22A1 may contribute to variability in rilpivirine exposure and that interactions of rilpivirine with substrates of SLC22A1, SLC22A2, or ABCB1 may be possible.

Lack of pharmacokinetic interaction between rilpivirine and integrase inhibitors dolutegravir and GSK1265744

Dolutegravir (DTG) and GSK1265744 are HIV integrase inhibitors (INIs) in clinical development. The oral formulation of rilpivirine (RPV), a nonnucleoside reverse transcriptase inhibitor (NNRTI), has been approved for treatment-naive HIV infection. Long-acting depot injections of GSK1265744 and RPV are also being developed. This study evaluated the potential for drug interactions between RPV and these INIs. This phase 1, open-label, two-cohort, three-period, single-sequence crossover study evaluated oral coadministration of RPV with DTG or GSK1265744. Healthy subjects received DTG (50 mg every 24 h for 5 days) or GSK1265744 (30 mg every 24 h for 12 days) in period 1 followed by a washout, RPV (25 mg every 24 h for 11 or 12 days) in period 2, immediately followed by RPV (25 mg every 24 h) plus DTG (50 mg every 24 h) for 5 days or GSK1265744 (30 mg every 24 h) for 12 days in period 3. Steady-state pharmacokinetic (PK) parameters were estimated using noncompartmental analysis of data collected on the last day of each period. The combinations of RPV and DTG (n = 16) and of RPV and GSK1265744 (n = 11) were well tolerated; no grade 3 or 4 adverse events (AEs) or AE-related discontinuations were observed. The 90% confidence intervals for the area under the curve from time zero until the end of the dosage interval [AUC0-τ] and maximum concentration of drug in serum (Cmax) geometric mean ratios were within 0.8 to 1.25. Following administration of DTG + RPV, DTG and RPV Cτ increased by 22% and 21%, respectively. Following administration of GSK1265744 + RPV, RPV Cτ decreased 8%. DTG and GSK1265744 can be administered with RPV without dosage adjustment for either agent. These results support coadministration of RPV with DTG or GSK1265744 as either oral or long-acting depot injection regimens. (This study has been registered at ClinicalTrials.gov under registration no. NCT01467531.).

Effect of prednisone on the pharmacokinetics of the integrase inhibitor dolutegravir

Prednisone, a corticosteroid frequently used to treat common AIDS-related illnesses and comorbidities, has been shown to induce drug metabolism. This study was performed to determine whether prednisone coadministration affected the pharmacokinetics of dolutegravir (DTG). In this open-label, repeat-dose study, 12 healthy subjects were administered DTG at 50 mg daily alone for 5 days and then with concomitant prednisone for 10 days (prednisone at 60 mg daily for 5 days, followed by a 5-day taper). Serial blood sampling and safety assessments were performed during the trial. Pharmacokinetic parameters were determined using noncompartmental methods and geometric least-square mean ratios, and 90% confidence intervals were generated. Coadministration of DTG and 5-day high-dose prednisone with a 5-day taper had a modest effect on DTG exposure. The area under the DTG plasma concentration-time curve, maximum observed DTG concentration, and 24-hour postdose DTG concentration were increased by 11%, 6%, and 17%, respectively, on day 10 of the combination. Similar results were observed after 5 days of DTG and prednisone. Dolutegravir and prednisone coadministration was well tolerated. The changes in plasma exposures of DTG in healthy individuals as a result of prednisone dosing were not clinically significant. No dose adjustment is required for DTG coadministered with prednisone. (This study has been registered at ClinicalTrials.gov under registration no. NCT01425099.).

Metabolism, excretion, and mass balance of the HIV-1 integrase inhibitor dolutegravir in humans

The pharmacokinetics, metabolism, and excretion of dolutegravir, an unboosted, once-daily human immunodeficiency virus type 1 integrase inhibitor, were studied in healthy male subjects following single oral administration of [(14)C]dolutegravir at a dose of 20 mg (80 μCi). Dolutegravir was well tolerated, and absorption of dolutegravir from the suspension formulation was rapid (median time to peak concentration, 0.5 h), declining in a biphasic fashion. Dolutegravir and the radioactivity had similar terminal plasma half-lives (t1/2) (15.6 versus 15.7 h), indicating metabolism was formation rate limited with no long-lived metabolites. Only minimal association with blood cellular components was noted with systemic radioactivity. Recovery was essentially complete (mean, 95.6%), with 64.0% and 31.6% of the dose recovered in feces and urine, respectively. Unchanged dolutegravir was the predominant circulating radioactive component in plasma and was consistent with minimal presystemic clearance. Dolutegravir was extensively metabolized. An inactive ether glucuronide, formed primarily via UGT1A1, was the principal biotransformation product at 18.9% of the dose excreted in urine and the principal metabolite in plasma. Two minor biotransformation pathways were oxidation by CYP3A4 (7.9% of the dose) and an oxidative defluorination and glutathione substitution (1.8% of the dose). No disproportionate human metabolites were observed.

Meeting report: Urinary Pathology; sixth Research Triangle Park Rodent Pathology Course

Urinary system toxicity is a significant concern to pathologists in the hazard identification, drug and chemical safety evaluation, and diagnostic service industries worldwide. There are myriad known human and animal urinary system toxicants, and investigatory renal toxicology and pathology is continually evolving. The system-specific Research Triangle Park (RTP) Rodent Pathology Course biennially serves to update scientists on the latest research, laboratory techniques, and debates. The Sixth RTP Rodent Pathology Course, Urinary Pathology, featured experts from the government, pharmaceutical, academic, and diagnostic arenas sharing the state of the science in urinary pathology. Speakers presented on a wide range of topics including background lesions, treatment-related non-neoplastic and neoplastic lesions, transgenic rodent models of human disease, diagnostic imaging, biomarkers, and molecular analyses. These seminars were accompanied by case presentation sessions focused on usual and unusual lesions, grading schemes, and tumors.