Lamivudine (3TC) phosphorylation and drug interactions in vitro

Self Cite

There is interest in evaluating the efficacy of lower doses of certain antiretrovirals for clinical care. We determined here the bioequivalence of plasma lamivudine (3TC) and intracellular 3TC-triphosphate (3TC-TP) concentrations after the administration of two different doses. ENCORE 2 was a randomized crossover study. Subjects received 3TC at 300 and 150 mg once daily for 10 days (arm 1; n ‫؍‬ 13) or vice versa (arm 2; n ‫؍‬ 11), separated by a 10-day washout. Pharmacokinetic (PK) profiles (0 to 24 h) were assessed on days 10 and 30. Plasma 3TC and 3TC-TP levels in peripheral blood mononuclear cells were quantified by highperformance liquid chromatography-tandem mass spectrometry. Within-subject changes in PK parameters ( L amivudine (3TC), a commonly used nucleoside reverse transcriptase inhibitor (NRTI), is an inactive prodrug that requires transport into the cell and stepwise phosphorylation by intracellular kinases to produce its active triphosphate form-lamivudine triphosphate (3TC-TP) (5). The active triphosphate competes with the corresponding endogenous nucleoside triphosphate, dCTP, for binding to the viral reverse transcriptase. Once incorporated into viral DNA, chain termination results due to absence of a 3=-hydroxy group to which 3=-5=-phosphodiester linkages are normally made (12).Studies conducted in HIV-infected patients have failed to establish clear pharmacokinetic-pharmacodynamic relationships between the plasma 3TC concentrations and antiviral efficacy and safety, whereas the concentrations of its intracellular triphosphate, 3TC-TP, have been shown to be the critical parameter to predict efficacy and toxicity in vivo (1, 8).The active nucleoside triphosphates are trapped intracellularly due to the presence of ionic phosphate groups and this confers the long intracellular half-lives compared to the respective parent compounds in plasma. Since 3TC-TP is characterized by a long intracellular half-life (ca. 15 to 16 h), active triphosphate concentrations persist in cells after plasma 3TC (half-life, ϳ5 h) concentrations have decreased, thus enabling less frequent dosing (18).3TC is currently approved at a dose of 150 mg twice daily (BID) or 300 mg once daily (QD). During the clinical development of 3TC, no clear correlation between its dose and reductions in HIV-RNA or other surrogate markers in HIV-infected individuals were demonstrated; including in the NUCB2001 trial, at doses of 35 to 1,400 mg/day (27). The NUCA3001 (treatment naive) and NUCA3002 (treatment experienced) trials reported no differences in reduction in HIV-RNA between patients taking 3TC at 300 mg BID versus 150 mg BID (4, 7) and, in a pharmacokinetic substudy of NUCA3001, only small elevations in 3TC triphosphate concentrations were found in patients receiving the 300-mg BID regimen (18). Similarly, a pharmacokinetic study found intracellular 3TC-TP exposures to be bioequivalent at 150-mg BID and 300-mg QD doses (28), and in a phase III (treatment naive) trial, no differences in efficacy were reported between these regimens (...

Section: Discussionmentioning

confidence: 99%

Pharmacokinetics of Lamivudine and Lamivudine-Triphosphate after Administration of 300 Milligrams and 150 Milligrams Once Daily to Healthy Volunteers: Results of the ENCORE 2 Study

Else

Jackson

Puls

et al. 2012

Self Cite

“…This is also suggested by our chain termination experiments with 3TC both in tissue culture and in cell-free systems (see above). Of course, we recognize that these relationships are complex, both in cells and in vivo, e.g., the ability of 3TC to be phosphorylated might be affected by the presence of other drugs, such as dideoxycytidine (20).…”

Section: Discussionmentioning

confidence: 99%

Lamivudine Can Exert a Modest Antiviral Effect against Human Immunodeficiency Virus Type 1 Containing the M184V Mutation

Quan

Brenner

Oliveira

et al. 2003

The M184V mutation in human immunodeficiency virus (HIV) reverse transcriptase is associated with high-level resistance to both (؊)2,3-dideoxy-3-thiacytidine (3TC) and (؊)2,3-dideoxy-5-fluoro-3-thiacytidine as well as low-level resistance to 2,3-dideoxyinosine, 2,3-dideoxycytidine, and abacavir. This mutation is also associated with diminished HIV replicative fitness as well as several functional changes in enzyme activity, including diminutions in polymerase processivity, pyrophosphorylysis, and nucleotide primer unblocking. Despite the fact that M184V encodes up to 1,000-fold resistance to 3TC, we asked whether this drug might still display some antiviral effect in regard to viruses containing this mutation. Cell-free assays revealed that high concentrations of 3TC triphosphate (i.e., >100 M) could affect chain termination and/or inhibit purified reverse transcriptase containing the M184V substitution. This effect became more pronounced with elongation of reverse transcriptase products. In newly infected cells (i.e., peripheral blood mononuclear cells), we found that the amount of full-length reverse transcriptase product was diminished in the presence of 2 to 10 M 3TC, although no decrease in the first product of the reverse transcriptase reaction, i.e., minus strong-stop DNA, was observed. In the presence of two other HIV inhibitors, e.g., nevirapine and indinavir, 3TC exerted additive effects in tissue culture at concentrations only marginally higher than the 50% inhibitory concentration (IC 50 ). Reverse transcriptases cloned from clinical isolates harboring M184V in the context of multidrug resistance had similar IC 50 values for 3TC triphosphate compared to reverse transcriptase containing only the M184V mutation. These results suggest that viruses containing M184V can retain a higher degree of sensitivity to 3TC than previously assumed.

“…Blood samples were collected from fasted subjects on day 7 of each regimen period. During the twice-daily regimen, sampling was done before the morning dose (0 h) and at 1,2,4,8,12,13,14,16,18,20, and 24 h postdose for determination of plasma lamivudine and intracellular lamivudine-TP. During the once-daily regimen, blood sampling was done at all of the times pertinent to the twice-daily period, except at 13, 14, 18, and 20 h postdose.…”

Section: Methodsmentioning

confidence: 99%

Equivalent Steady-State Pharmacokinetics of Lamivudine in Plasma and Lamivudine Triphosphate within Cells following Administration of Lamivudine at 300 Milligrams Once Daily and 150 Milligrams Twice Daily

Yuen¹,

Lou²,

Bumgarner³

et al. 2004

Once-daily administration of 300 mg of lamivudine in combination with other antiretroviral agents has been proposed as a possible way to optimize anti-human immunodeficiency virus (HIV) treatment and to facilitate adherence. A single-center, randomized, two-way, crossover study was conducted in 60 healthy subjects to compare the steady-state pharmacokinetics of lamivudine in plasma and its putative active anabolite, lamivudine 5-triphosphate (lamivudine-TP), in peripheral blood mononuclear cells (PBMCs) following 7 days of treatment with lamivudine at 300 mg once daily and 7 days of the standard regimen of 150 mg twice daily. Serial blood samples were collected over 24 h for determination of plasma lamivudine concentrations by liquid chromatography-mass spectrometry and intracellular lamivudine-TP concentrations in peripheral blood mononuclear cells by high-performance liquid chromatography/radioimmunoassay methods. Pharmacokinetic parameters were calculated based on lamivudine and lamivudine-TP concentration-time data. Regimens were considered bioequivalent if 90% confidence intervals (CI) for the ratio (once daily/twice daily) of geometric least-squares (GLS) means for lamivudine and lamivudine-TP pharmacokinetic values fell within the acceptance range of 0.8 to 1.25. Steady-state plasma lamivudine pharmacokinetics following the once-and twicedaily regimens were bioequivalent with respect to the area under the drug concentration-time curve from 0 to 24 h at steady state (AUC 24,ss ) (GLS mean ratio, 0.94; 90% CI, 0.92, 0.97) and average plasma lamivudine concentration over the dosing interval (C ave,ss ) (GLS mean ratio, 0.94; 90% CI, 0.92, 0.97). Steady-state intracellular lamivudine-TP pharmacokinetics after the once-and twice-daily regimens were bioequivalent with respect to AUC 24,ss (GLS mean ratio, 0.99; 90% CI, 0.88, 1.11), C ave,ss (GLS mean ratio, 0.99; 90% CI, 0.88, 1.11), and maximum lamivudine concentration (C max,ss ) (GLS mean ratio, 0.93; 90% CI, 0.81, 1.07). Lamivudine-TP trough concentrations were modestly lower (by 18 to 24%) during the once-daily regimen; the clinical importance of this is unclear, given the large intersubject variability in values that was observed (coefficient of variation, 48 to 124%). Once-daily lamivudine was as well tolerated as the twice-daily regimen. Overall, the results of this study suggest that for key AUC-related parameters, lamivudine at 300 mg once daily is pharmacokinetically equivalent to lamivudine at 150 mg twice daily.Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) that is frequently used as a core component of highly active antiretroviral therapy (HAART) regimens in the treatment of human immunodeficiency virus (HIV) infection (13). In clinical trials conducted over 48 weeks, twice-daily regimens combining lamivudine at 150 mg with the NRTIs zidovudine (300 mg) and abacavir (300 mg) have proved equivalent to lamivudine-zidovudine-protease inhibitor combinations in reducing HIV-1 RNA levels and elevating CD4 cell counts (19;