The chemical name of lamivudine is (2R,cis)-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one. Lamivudine is the (-)enantiomer of a dideoxy analogue of cytidine. Lamivudine has also been referred to as (-)2′,3′-dideoxy, 3′-thiacytidine. It has a molecular formula of C8H11N3O3S and a molecular weight of 229.3 daltons. It has the following structural formula:
Lamivudine Structural Formula (D89c5e30 3a62 4f41 B1ff Edffcac143f7 02)
Lamivudine is a white to off-white crystalline solid with a solubility of approximately 70 mg/mL in water at 20°C.
The antiviral activity of lamivudine against HIV-1 was assessed in a number of cell lines (including monocytes and fresh human peripheral blood lymphocytes) using standard susceptibility assays. EC50 values were in the range of 0.003 to 15 μM (1 μM = 0.23 mcg/mL). HIV-1 from therapy-naive subjects with no amino acid substitutions associated with resistance gave median EC50 values of 0.429 µM (range: 0.200 to 2.007 µM) from Virco (n = 92 baseline samples from COLA40263) and 2.35 µM (1.37 to 3.68 µM) from Monogram Biosciences (n = 135 baseline samples from ESS30009). The EC50 values of lamivudine against different HIV-1 clades (A-G) ranged from 0.001 to 0.120 µM, and against HIV-2 isolates from 0.003 to 0.120 μM in peripheral blood mononuclear cells. Ribavirin (50 μM) decreased the anti–HIV-1 activity of lamivudine by 3.5 fold in MT-4 cells.
The combination of abacavir and lamivudine has demonstrated antiviral activity in cell culture against non-subtype B isolates and HIV-2 isolates with equivalent antiviral activity as for subtype B isolates. Abacavir/lamivudine had additive to synergistic activity in cell culture in combination with the nucleoside reverse transcriptase inhibitors (NRTIs) emtricitabine, stavudine, tenofovir, zalcitabine, zidovudine; the non-nucleoside reverse transcriptase inhibitors (NNRTIs) delavirdine, efavirenz, nevirapine; the protease inhibitors (PIs) amprenavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir; or the fusion inhibitor, enfuvirtide. Ribavirin, used in combination with interferon for the treatment of HCV infection, decreased the anti-HIV-1 potency of abacavir/lamivudine reproducibly by 2- to 6-fold in cell culture.
Following oral administration, lamivudine is rapidly absorbed and extensively distributed. After multiple-dose oral administration of lamivudine 300 mg once daily for 7 days to 60 healthy volunteers, steady-state Cmax (Cmax,ss) was 2.04 ± 0.54 mcg/mL (mean ± SD) and the 24-hour steady-state AUC (AUC24,ss) was 8.87 ± 1.83 mcg•hr/mL. Binding to plasma protein is low. Approximately 70% of an intravenous dose of lamivudine is recovered as unchanged drug in the urine. Metabolism of lamivudine is a minor route of elimination. In humans, the only known metabolite is the trans-sulfoxide metabolite (approximately 5% of an oral dose after 12 hours).
The steady-state pharmacokinetic properties of the EPIVIR 300-mg Tablet once daily for 7 days compared with the EPIVIR 150-mg Tablet twice daily for 7 days were assessed in a crossover study in 60 healthy volunteers. EPIVIR 300 mg once daily resulted in lamivudine exposures that were similar to EPIVIR 150 mg twice daily with respect to plasma AUC24,ss; however, Cmax,ss was 66% higher and the trough value was 53% lower compared with the 150-mg twice-daily regimen. Intracellular lamivudine triphosphate exposures in peripheral blood mononuclear cells were also similar with respect to AUC24,ss and Cmax24,ss; however, trough values were lower compared with the 150-mg twice-daily regimen. Inter-subject variability was greater for intracellular lamivudine triphosphate concentrations versus lamivudine plasma trough concentrations. The clinical significance of observed differences for both plasma lamivudine concentrations and intracellular lamivudine triphosphate concentrations is not known.
In humans, abacavir and lamivudine are not significantly metabolized by cytochrome P450 enzymes.
The pharmacokinetic properties of abacavir and lamivudine in fasting patients are summarized in Table 1.
Table 1. Pharmacokinetic Parameters* for Abacavir and Lamivudine in Adults| * Data presented as mean ± standard deviation except where noted. |
| † Approximate range. |
| Parameter | Abacavir | Lamivudine |
| Oral bioavailability (%) | 86 ± 25 | n = 6 | 86 ± 16 | n = 12 |
| Apparent volume of distribution (L/kg) | 0.86 ± 0.15 | n = 6 | 1.3 ± 0.4 | n = 20 |
| Systemic clearance (L/hr/kg) | 0.80 ± 0.24 | n = 6 | 0.33 ± 0.06 | n = 20 |
| Renal clearance (L/hr/kg) | .007 ± .008 | n = 6 | 0.22 ± 0.06 | n = 20 |
| Elimination half-life (hr) | 1.45 ± 0.32 | n = 20 | 5 to 7† |
No clinically significant alterations in lamivudine or zidovudine pharmacokinetics were observed in 12 asymptomatic HIV-1-infected adult patients given a single dose of zidovudine (200 mg) in combination with multiple doses of lamivudine (300 mg q 12 hr). Lamivudine pharmacokinetics are not significantly affected by abacavir.
Table 2. Effect of Coadministered Drugs on Abacavir and Lamivudine AUC*| ↑ = Increase; ↔ = no significant change; AUC = area under the concentration versus time curve; CI = confidence interval. |
| * See PRECAUTIONS: Drug Interactions for additional information on drug interactions. |
| Note: ROUTINE DOSE MODIFICATION OF ABACAVIR AND LAMIVUDINE IS NOT WARRANTED WITH COADMINISTRATION OF THE FOLLOWING DRUGS. |
| Drugs That May Alter Abacavir Blood Concentrations |
Coadministered Drug and Dose | Abacavir Dose | n | Abacavir Concentrations | Concentration of Coadministered Drug |
| AUC | Variability |
Ethanol
0.7 g/kg | Single 600 mg | 24 | ↑41% | 90% CI:
35% to 48% | ↔ |
| Drugs That May Alter Lamivudine Blood Concentrations |
Coadministered Drug and Dose | Lamivudine Dose | n | Lamivudine Concentrations | Concentration of Coadministered Drug |
| AUC | Variability |
Nelfinavir
750 mg q 8 hr x 7 to 10 days | Single 150 mg | 11 | ↑10% | 95% CI:
1% to 20% | ↔ |
Trimethoprim 160 mg/ Sulfamethoxazole
800 mg daily x 5 days | Single 300 mg | 14 | ↑43% | 90% CI:
32% to 55% | ↔ |
Safety and efficacy of lamivudine have not been established for treatment of chronic hepatitis B in patients dually infected with HIV-1 and HBV. In non-HIV-1-infected patients treated with lamivudine for chronic hepatitis B, emergence of lamivudine-resistant HBV has been detected and has been associated with diminished treatment response (see EPIVIR-HBV package insert for additional information). Emergence of hepatitis B virus variants associated with resistance to lamivudine has also been reported in HIV-1-infected patients who have received lamivudine-containing antiretroviral regimens in the presence of concurrent infection with hepatitis B virus.
Patients co-infected with HIV-1 and HBV should be informed that deterioration of liver disease has occurred in some cases when treatment with lamivudine was discontinued. Patients should be advised to discuss any changes in regimen with their physician.
Trimethoprim (TMP) 160 mg/sulfamethoxazole (SMX) 800 mg once daily has been shown to increase lamivudine exposure (AUC). No change in dose of either drug is recommended. The effect of higher doses of TMP/SMX on lamivudine pharmacokinetics has not been investigated (see CLINICAL PHARMACOLOGY).
Lamivudine and zalcitabine may inhibit the intracellular phosphorylation of one another. Therefore, use of EPZICOM in combination with zalcitabine is not recommended.
See CLINICAL PHARMACOLOGY for additional drug interactions.
Studies in pregnant rats showed that lamivudine is transferred to the fetus through the placenta. Reproduction studies with orally administered lamivudine have been performed in rats and rabbits at doses producing plasma levels up to approximately 35 times that for the recommended adult HIV dose. No evidence of teratogenicity due to lamivudine was observed. Evidence of early embryolethality was seen in the rabbit at exposure levels similar to those observed in humans, but there was no indication of this effect in the rat at exposure levels up to 35 times those in humans.
Lamivudine is excreted in human breast milk and into the milk of lactating rats.
Because of both the potential for HIV-1 transmission and the potential for serious adverse reactions in nursing infants, mothers should be instructed not to breastfeed if they are receiving EPZICOM.
One case of an adult ingesting 6 grams of lamivudine was reported; there were no clinical signs or symptoms noted and hematologic tests remained normal. It is not known whether lamivudine can be removed by peritoneal dialysis or hemodialysis.