Pharmacokinetic Properties of Single-Dose Lamivudine/Adefovir Dipivoxil Fixed-Dose Combination in Healthy Chinese Male Volunteers

Understanding adefovir pharmacokinetics as a component of a transporter phenotyping cocktail

PURPOSE

Adefovir (as dipivoxil) was selected as a probe drug in a previous transporter cocktail phenotyping study to assess renal organic anion transporter 1 (OAT1), with renal clearance (CLR) as the primary parameter describing renal elimination. An approximately 20% higher systemic exposure of adefovir was observed when combined with other cocktail components (metformin, sitagliptin, pitavastatin, and digoxin) compared to sole administration. The present evaluation applied a population pharmacokinetic (popPK) modeling approach to describe adefovir pharmacokinetics as a cocktail component in more detail.

METHODS

Data from 24 healthy subjects were reanalyzed. After establishing a base model, covariate effects, including the impact of co-administered drugs, were assessed using forward inclusion then backward elimination.

RESULTS

A one-compartment model with first-order absorption (including lag time) and a combination of nonlinear renal and linear nonrenal elimination best described the data. A significantly higher apparent bioavailability (73.6% vs. 59.0%) and a lower apparent absorption rate constant (2.29 h-1 vs. 5.18 h-1) were identified in the combined period compared to the sole administration period, while no difference was seen in renal elimination. The population estimate for the Michaelis-Menten constant (Km) of the nonlinear renal elimination was 170 nmol/L, exceeding the observed range of adefovir plasma maximum concentration, while the maximum rate (Vmax) of nonlinear renal elimination was 2.40 µmol/h at the median absolute estimated glomerular filtration rate of 105 mL/min.

CONCLUSION

The popPK modeling approach indicated that the co-administration primarily affected the apparent absorption and/or prodrug conversion of adefovir dipivoxil, resulting in the minor drug-drug interaction observed for adefovir as a victim. However, renal elimination remained unaffected. The high Km value suggests that assessing renal OAT1 activity by CLR has no relevant misspecification error with the cocktail doses used.

Overview of the Chromatographic and Mass Spectrometry Analytical Methods for Determination of Lamivudine in Biological Fluids

Background:

Lamivudine was approved by Food and Drug Administration of the United States for the treatment of both HIV and HBV infection, which has been widely used as monotherapy or a component of combination therapy in clinics in many countries and nationalities.

Methods:

In this paper, the recent chromatographic and mass spectrometry analytical methods for the determination of lamivudine individually or combination with other drugs simultaneously were presented. These methods were widely applied in pharmacokinetics studies, bioequivalence studies, therapeutic drug monitoring studies, cell and animal experiments.

Conclusion:

The review paper might provide references for determining lamivudine in biological fluids, the intracorporal process of lamivudine, and the clinical practice by monitoring plasma concentration of lamivudine in the future.

Single-dose pharmacokinetic properties, bioavailability, and tolerability of two lamivudine 100-mg tablet formulations: a randomized crossover study in healthy Chinese male subjects

BACKGROUND

Lamivudine is used in the treatment of HIV and chronic hepatitis B (HBV) infections. Since 1999, at least 2 million Chinese HBV patients have been treated with lamivudine, but there are limited studies on the pharmacokinetics and safety of the drug in Chinese populations.

OBJECTIVE

This study was designed to assess the bioequivalence of a newly developed lamivudine tablet (test drug) and a branded lamivudine tablet (reference drug) in healthy Chinese male volunteers.

METHODS

A single-center, single-dose, randomized, open-label, 2-period crossover study was conducted in 28 healthy Chinese male volunteers. Blood samples were collected up to 24 hours after the administration of oral lamivudine 100 mg in each period. Plasma lamivudine concentrations were analyzed by a validated LC-MS/MS method. Pharmacokinetic and bioavailability parameters were calculated. Adverse events (AEs) were recorded.

RESULTS

There were no significant differences in mean (SD) pharmacokinetic parameters between the test and reference drugs, including Cmax (1239 [328.9] ng/mL vs 1176 [341.5] ng/mL), AUC0-t (4096 [599.1] ng · h/mL vs 4064 [678.2] ng · h/mL), and AUC0-∞ (4200 [607.7] ng · h/mL vs 4162 [672.2] ng · h/mL). The geometric mean test/reference ratios (90% CI) calculated for the log-transformed parameters were Cmax, 1.06 (96.21-116.90); AUC0-t, 1.01 (96.53-105.39); and AUC0-∞, 1.01 (96.81-105.16), all of which were within the acceptance limits for bioequivalence. No serious AEs were reported, and all mild AEs were recovered quickly without treatment.

CONCLUSION

These findings suggest that the test formulation of lamivudine 100 mg meets the FDA regulatory standards for bioequivalence with the reference formulation. Both formulations were well tolerated.