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Mechanism Of Action
TRIZIVIR is an antiretroviral agent [see Microbiology].
Pharmacokinetics in Adults
In a single-dose, 3-way crossover bioavailability trial of 1 TRIZIVIR tablet versus 1 ZIAGEN tablet (300 mg), 1 EPIVIR tablet (150 mg), plus 1 RETROVIR tablet (300 mg) administered simultaneously in healthy subjects (n = 24), there was no difference in the extent of absorption, as measured by the area under the plasma concentration-time curve (AUC) and maximal peak concentration (Cmax), of all 3 components. One TRIZIVIR tablet was bioequivalent to 1 ZIAGEN tablet (300 mg), 1 EPIVIR tablet (150 mg), plus 1 RETROVIR tablet (300 mg) following single-dose administration to fasting healthy subjects (n = 24).
Abacavir: Following oral administration, abacavir is rapidly absorbed and extensively distributed. After oral administration of 300 mg of abacavir twice daily in 20 subjects, Cmax was 3.0 ± 0.89 mcg per mL (mean ± SD) and AUC(0-12 h) was 6.02 ± 1.73 mcg•hour per mL. Binding of abacavir to human plasma proteins is approximately 50% and was independent of concentration. Total blood and plasma drug-related radioactivity concentrations are identical, demonstrating that abacavir readily distributes into erythrocytes. The primary routes of elimination of abacavir are metabolism by alcohol dehydrogenase to form the 5'-carboxylic acid and glucuronyl transferase to form the 5'-glucuronide.
Lamivudine: Following oral administration, lamivudine is rapidly absorbed and extensively distributed. 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).
Zidovudine: Following oral administration, zidovudine is rapidly absorbed and extensively distributed. Binding to plasma protein is low. Zidovudine is eliminated primarily by hepatic metabolism. The major metabolite of zidovudine is GZDV. GZDV AUC is about 3-fold greater than the zidovudine AUC. Urinary recovery of zidovudine and GZDV accounts for 14% and 74% of the dose following oral administration, respectively. A second metabolite, 3'-amino-3'deoxythymidine (AMT), has been identified in plasma. The AMT AUC was one-fifth of the zidovudine AUC.
In humans, abacavir, lamivudine, and zidovudine are not significantly metabolized by cytochrome P450 enzymes.
The pharmacokinetic properties of abacavir, lamivudine, and zidovudine in fasting subjects are summarized in Table 3.
Table 3: Pharmacokinetic Parametersa for
Abacavir, Lamivudine, and Zidovudine in Adults
|Oral bioavailability (%)||86 ± 25||n = 6||86 ± 16||n = 12||64 ± 10||n = 5|
|Apparent volume of distribution (L/kg)||0.86 ± 0.15||n = 6||1.3 ± 0.4||n = 20||1.6 ± 0.6||n = 8|
|Systemic clearance (L/h/kg)||0.80 ± 0.24||n = 6||0.33 ± 0.06||n = 20||1.6 ± 0.6||n = 6|
|Renal clearance (L/h/kg)||0.007 ± 0.008||n = 6||0.22 ± 0.06||n = 20||0.34 ± 0.05||n = 9|
|Elimination half-life (h)||1.45 ± 0.32||n = 20||5 to 7b||0.5 to 3b|
|aData presented as mean ± standard deviation
except where noted.
Effect of Food on Absorption of TRIZIVIR
Administration with food in a single-dose bioavailability trial resulted in lower Cmax, similar to results observed previously for the reference formulations. The average [90% CI] decrease in abacavir, lamivudine, and zidovudine Cmax was 32% [24% to 38%], 18% [10% to 25%], and 28% [13% to 40%], respectively, when administered with a high-fat meal, compared with administration under fasted conditions. Administration of TRIZIVIR with food did not alter the extent of abacavir, lamivudine, and zidovudine absorption (AUC), as compared with administration under fasted conditions (n = 24) [see DOSAGE AND ADMINISTRATION].
Renal Impairment: TRIZIVIR: The effect of renal impairment on the combination of abacavir, lamivudine, and zidovudine has not been evaluated (see the U.S. prescribing information for the individual abacavir, lamivudine, and zidovudine components).
Hepatic Impairment: TRIZIVIR: The effect of hepatic impairment on the combination of abacavir, lamivudine, and zidovudine has not been evaluated (see the U.S. prescribing information for the individual abacavir, lamivudine, and zidovudine components).
Pregnancy: Abacavir: No data are available on the pharmacokinetics of abacavir during pregnancy.
Lamivudine: Lamivudine pharmacokinetics were studied in 36 pregnant women during 2 clinical trials conducted in South Africa. Lamivudine pharmacokinetics in pregnant women were similar to those seen in non-pregnant adults and in postpartum women. Lamivudine concentrations were generally similar in maternal, neonatal, and umbilical cord serum samples.
Zidovudine: Zidovudine pharmacokinetics have been studied in a Phase 1 trial of 8 women during the last trimester of pregnancy. Zidovudine pharmacokinetics were similar to those of nonpregnant adults. Consistent with passive transmission of the drug across the placenta, zidovudine concentrations in neonatal plasma at birth were essentially equal to those in maternal plasma at delivery.
Although data are limited, methadone maintenance therapy in 5 pregnant women did not appear to alter zidovudine pharmacokinetics.
Geriatric Patients: The pharmacokinetics of abacavir, lamivudine, and zidovudine have not been studied in subjects over 65 years of age.
Gender: There are no significant or clinically relevant gender differences in the pharmacokinetics of the individual components (abacavir, lamivudine, or zidovudine) based on the available information that was analyzed for each of the individual components.
Race: Abacavir and Lamivudine: There are no significant or clinically relevant racial differences in pharmacokinetics of abacavir or lamivudine based on the available information that was analyzed for each of the individual components.
Zidovudine: The pharmacokinetics of zidovudine with respect to race have not been determined.
The drug interaction trials described were conducted with abacavir, lamivudine or zidovudine as single entities; no drug interaction trials have been conducted using TRIZIVIR. No clinically significant drug interactions are expected between abacavir, lamivudine, and zidovudine.
Cytochrome P450 Enzymes: Abacavir, lamivudine, and zidovudine are not significantly metabolized by cytochrome P450 enzymes; therefore, it is unlikely that clinically significant drug interactions will occur with drugs metabolized through these pathways.
Glucuronyl Transferase: Due to the common metabolic pathways of abacavir and zidovudine via glucuronyl transferase, 15 HIV-1-infected subjects were enrolled in a crossover trial evaluating single doses of abacavir (600 mg), lamivudine (150 mg), and zidovudine (300 mg) alone or in combination. Analysis showed no clinically relevant changes in the pharmacokinetics of abacavir with the addition of lamivudine or zidovudine or the combination of lamivudine and zidovudine. Lamivudine exposure (AUC decreased 15%) and zidovudine exposure (AUC increased 10%) did not show clinically relevant changes with concurrent abacavir.
Ethanol: Abacavir has no effect on the pharmacokinetic properties of ethanol. Ethanol decreases the elimination of abacavir causing an increase in overall exposure.
Interferon Alfa: There was no significant pharmacokinetic interaction between lamivudine and interferon alfa in a trial of 19 healthy male subjects.
Methadone: In a trial of 11 HIV-1-infected subjects receiving methadone-maintenance therapy (40 mg and 90 mg daily), with 600 mg of abacavir twice daily (twice the currently recommended dose), oral methadone clearance increased 22% (90% CI: 6% to 42%) [see DRUG INTERACTIONS]. The addition of methadone has no clinically significant effect on the pharmacokinetic properties of abacavir.
Ribavirin: In vitro data indicate ribavirin reduces phosphorylation of lamivudine, stavudine, and zidovudine. However, no pharmacokinetic (e.g., plasma concentrations or intracellular triphosphorylated active metabolite concentrations) or pharmacodynamic (e.g., loss of HIV-1/HCV virologic suppression) interaction was observed when ribavirin and lamivudine (n = 18), stavudine (n = 10), or zidovudine (n = 6) were coadministered as part of a multi-drug regimen to HIV-1/HCV co-infected subjects [see WARNINGS AND PRECAUTIONS].
The effects of other coadministered drugs on abacavir, lamivudine, or zidovudine are provided in Table 4.
Table 4: Effect of Coadministered Drugs on Abacavir,
Lamivudine, and Zidovudine AUCa
|Coadministered Drug and Dose||Drug and Dose||n||Concentrations of Abacavir, Lamivudine, or Zidovudine||Concentration of Coadministered Drug|
|Ethanol 0.7 g/kg||Abacavir single 600 mg||24||↑41%||90% CI: 35% to 48%||↔b|
|Nelfinavir 750 mg every 8 h x 7 to 10 days||Lamivudine Single 150 mg||11||↑10%||95% CI: 1% to 20%||↔|
|Trimethoprim 160 mg/ Sulfamethoxazole 800 mg daily x 5 days||Lamivudine Single 300 mg||14||↑43%||90% CI: 32% to 55%||↔|
|Atovaquone 750 mg every 12 h with food||Zidovudine 200 mg every 8 h||14||↑31%||Range: 23% to 78%c||↔|
|Clarithromycin 500 mg twice daily||Zidovudine 100 mg every 4 h x 7 days||4||↓12%||Range: ↓34% to ↑14%||Not Reported|
|Fluconazole 400 mg daily||Zidovudine 200 mg every 8 h||12||↑74%||95% CI: 54% to 98%||Not Reported|
|Methadone 30 to 90 mg daily||Zidovudine 200 mg every 4 h||9||↑43%||Range: 16% to 64%c||↔|
|Nelfinavir 750 mg every 8 h x 7 to 10 days||Zidovudine single 200 mg||11||↓35%||Range: 28% to 41%||↔|
|Probenecid 500 mg every 6 h x 2 days||Zidovudine 2 mg/kg every 8 h x 3 days||3||↑106%||Range: 100% to 170%c||Not Assessed|
|Rifampin 600 mg daily x 14 days||Zidovudine 200 mg every 8 h x 14 days||8||↓47%||90% CI: 41% to 53%||Not Assessed|
|Ritonavir 300 mg every 6 h x 4 days||Zidovudine 200 mg every 8 h x 4 days||9||↓25%||95% CI: 15% to 34%||↔|
|Valproic acid 250 mg or 500 mg every 8 h x 4 days||Zidovudine 100 mg every 8 h x 4 days||6||↑80%||Range: 64% to 130%c||Not Assessed|
|↑ = Increase; ↓ = Decrease; ↔ = no
significant change; AUC = area under the concentration versus time curve; CI =
aSee DRUG INTERACTIONS for additional information on drug interactions.
bThe drug-drug interaction was only evaluated in males.
cEstimated range of percent difference.
Mechanism of Action
Abacavir: Abacavir is a carbocyclic synthetic nucleoside analogue. Abacavir is converted by cellular enzymes to the active metabolite, carbovir triphosphate (CBV-TP), an analogue of deoxyguanosine-5'-triphosphate (dGTP). CBV-TP inhibits the activity of HIV-1 reverse transcriptase (RT) both by competing with the natural substrate dGTP and by its incorporation into viral DNA.
Lamivudine: Lamivudine is a synthetic nucleoside analogue. Intracellularly, lamivudine is phosphorylated to its active 5'-triphosphate metabolite, lamivudine triphosphate (3TC-TP). The principal mode of action of 3TC-TP is inhibition of RT via DNA chain termination after incorporation of the nucleotide analogue.
Zidovudine: Zidovudine is a synthetic nucleoside analogue. Intracellularly, zidovudine is phosphorylated to its active 5'-triphosphate metabolite, zidovudine triphosphate (ZDV-TP). The principal mode of action of ZDV-TP is inhibition of RT via DNA chain termination after incorporation of the nucleotide analogue.
Abacavir: The antiviral activity of abacavir against HIV-1 was assessed in a number of cell lines including primary monocytes/macrophages and peripheral blood mononuclear cells (PBMCs). EC50 values ranged from 3.7 to 5.8 microM (1 microM = 0.28 mcg per mL) and 0.07 to 1.0 microM against HIV-1IIIB and HIV-1BaL, respectively, and the mean EC50 value was 0.26 ± 0.18 microM against 8 clinical isolates. The median EC50 values of abacavir were 344 nM (range: 14.8 to 676 nM), 16.9 nM (range: 5.9 to 27.9 nM), 8.1 nM (range: 1.5 to 16.7 nM), 356 nM (range: 35.7 to 396 nM), 105 nM (range: 28.1 to 168 nM), 47.6 nM (range: 5.2 to 200 nM), 51.4 nM (range: 7.1 to 177 nM), and 282 nM (range: 22.4 to 598 nM) against HIV-1 clades A-G and group O viruses (n = 3 except n = 2 for clade B), respectively. The EC50 values against HIV-2 isolates (n = 4), ranged from 0.024 to 0.49 microM.
Lamivudine: The antiviral activity of lamivudine against HIV-1 was assessed in a number of cell lines including monocytes and PBMCs using standard susceptibility assays. EC50 values were in the range of 0.003 to 15 microM (1 microM = 0.23 mcg per mL). The median EC50 values of lamivudine were 60 nM (range: 20 to 70 nM), 35 nM (range: 30 to 40 nM), 30 nM (range: 20 to 90 nM), 20 nM (range: 3 to 40 nM), 30 nM (range: 1 to 60 nM), 30 nM (range: 20 to 70 nM), 30 nM (range: 3 to 70 nM), and 30 nM (range: 20 to 90 nM) against HIV-1 clades AG and group O viruses (n = 3 except n = 2 for clade B), respectively. The EC50 values against HIV-2 isolates (n = 4) ranged from 0.003 to 0.120 microM in PBMCs. Ribavirin (50 microM) used in the treatment of chronic HCV infection decreased the anti-HIV-1 activity of lamivudine by 3.5-fold in MT-4 cells.
Zidovudine: The antiviral activity of zidovudine against HIV-1 was assessed in a number of cell lines including monocytes and fresh human peripheral blood lymphocytes. The EC50 and EC90 values for zidovudine were 0.01 to 0.49 microM (1 microM = 0.27 mcg per mL) and 0.1 to 9 microM, respectively. HIV-1 from therapy-naive subjects with no amino acid substitutions associated with resistance gave median EC50 values of 0.011 microM (range: 0.005 to 0.110 microM) from Virco (n = 92 baseline samples) and 0.0017 microM (range: 0.006 to 0.0340 microM) from Monogram Biosciences (n = 135 baseline samples). The EC50 values of zidovudine against different HIV-1 clades (A-G) ranged from 0.00018 to 0.02 microM, and against HIV-2 isolates from 0.00049 to 0.004 microM. Ribavirin has been found to inhibit the phosphorylation of zidovudine in cell culture.
Neither abacavir, lamivudine, nor zidovudine were antagonistic to tested anti-HIV agents, with the exception of stavudine where an antagonistic relationship with zidovudine has been demonstrated in cell culture. See full prescribing information for ZIAGEN (abacavir), EPIVIR (lamivudine), RETROVIR (zidovudine).
HIV-1 isolates with reduced susceptibility to abacavir, lamivudine, or zidovudine have been selected in cell culture and were also recovered from subjects treated with abacavir, lamivudine, and zidovudine, or the combinations of the individual components.
Abacavir and Lamivudine: HIV-1 isolates with reduced susceptibility to the combination of abacavir and lamivudine have been selected in cell culture with amino acid substitutions, K65R, L74V, Y115F, and M184V/I emerging in HIV-1 RT. M184V or I substitutions resulted in high-level resistance to lamivudine and an approximately 2-fold decrease in susceptibility to abacavir. Substitutions K65R, L74M, or Y115F with M184V or I conferred a 7- to 8-fold reduction in abacavir susceptibility, and combinations of three substitutions were required to confer more than an 8-fold reduction in susceptibility.
Zidovudine: Genotypic analyses of the isolates selected in cell culture and recovered from zidovudine-treated subjects showed thymidine analog mutation (TAM) substitutions in HIV-1 RT (M41L, D67N, K70R, L210W, T215Y or F, and K219E/R/H/Q/N) that confer zidovudine resistance. In general, higher levels of resistance were associated with a greater number of substitutions. In some subjects harboring zidovudine-resistant virus at baseline, phenotypic sensitivity to zidovudine was restored by 12 weeks of treatment with lamivudine and zidovudine.
Cross-resistance has been observed among NRTIs. The combination of abacavir/lamivudine has demonstrated decreased susceptibility to viruses with a K65R substitution with or without an M184V/I substitution, viruses with L74V plus the M184V/I substitution, and viruses with TAM substitutions (M41L, D67N, K70R, L210W, T215Y/F, K219 E/R/H/Q/N) plus M184V. An increasing number of TAMs is associated with a progressive reduction in abacavir susceptibility.
TAMs are selected by zidovudine and confer cross-resistance to abacavir, didanosine, stavudine, and tenofovir. Cross-resistance between lamivudine and zidovudine has not been reported.
Animal Toxicology And/Or Pharmacology
Myocardial degeneration was found in mice and rats following administration of abacavir for 2 years. The systemic exposures were equivalent to 7 to 24 times the expected systemic exposure in humans at a dose of 600 mg. The clinical relevance of this finding has not been determined.
The following trial was conducted with the individual components of TRIZIVIR [see CLINICAL PHARMACOLOGY].
CNA3005 was a multicenter, double-blind, controlled trial in which 562 HIV-1-infected, therapy-naive adults were randomized to receive either ZIAGEN (300 mg twice daily) plus COMBIVIR® (lamivudine 150 mg/zidovudine 300 mg twice daily), or indinavir (800 mg 3 times a day) plus COMBIVIR twice daily. The trial was stratified at randomization by pre-entry plasma HIV-1 RNA 10,000 to 100,000 copies per mL and plasma HIV-1 RNA greater than 100,000 copies per mL. Trial participants were male (87%), Caucasian (73%), black (15%), and Hispanic (9%). At baseline the median age was 36 years,; the median pretreatment CD4+ cell count was 360 cells per mm³, and median plasma HIV-1 RNA was 4.8 log10 copies per mL. Proportions of subjects with plasma HIV-1 RNA less than 400 copies per mL (using Roche AMPLICOR HIV-1 MONITOR® Test) through 48 weeks of treatment are summarized in Table 5.
Table 5: Outcomes of Randomized Treatment through Week
|Outcome||ZIAGEN plus Lamivudine/ Zidovudine
(n = 262)
|Indinavir plus Lamivudine/ Zidovudine
(n = 265)
|Discontinued due to adverse reactions||10%||12%|
|Discontinued due to other reasonsc||11%||10%|
|aSubjects achieved and maintained confirmed
HIV-1 RNA less than 400 copies per mL.
bIncludes viral rebound and failure to achieve confirmed less than 400 copies per mL by Week 48.
cIncludes consent withdrawn, lost to follow-up, protocol violations, those with missing data, clinical progression, and other.
Treatment response by plasma HIV-1 RNA strata is shown in Table 6.
Table 6: Proportions of Responders through Week 48 by
Screening Plasma HIV-1 RNA Levels (CNA3005)
|Screening HIV-1 RNA (copies/mL)||ZIAGEN plus Lamivudine/ Zidovudine
(n = 262)
|Indinavir plus Lamivudine/ Zidovudine
(n = 265)
|< 400 copies/mL||n||< 400 copies/mL||n|
|≥ 10,000 - ≤ 100,000||50%||166||48%||165|
In subjects with baseline viral load greater than 100,000 copies per mL, percentages of subjects with HIV-1 RNA levels less than 50 copies per mL were 31% in the group receiving abacavir vs. 45% in the group receiving indinavir.
Through Week 48, an overall mean increase in CD4+ cell count of about 150 cells per mm³ was observed in both treatment arms. Through Week 48, 9 subjects (3.4%) in the group receiving abacavir (6 CDC classification C events and 3 deaths) and 3 subjects (1.5%) in the group receiving indinavir (2 CDC classification C events and 1 death) experienced clinical disease progression.
Last reviewed on RxList: 10/23/2015
This monograph has been modified to include the generic and brand name in many instances.
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