Abacavir, Lamivudine and ZidovudineTablets

Abacavir, lamivudine and zidovudine tablets contain 300 mg of abacavir as abacavir sulfate, 150 mg of lamivudine, and 300 mg of zidovudine. The tablets are blue-green colored, oval shaped, biconvex, film-coated, debossed with "LU" on one side and "N51" on the other side.

Hypersensitivity Reactions

Serious and sometimes fatal hypersensitivity reactions have occurred with abacavir, a component of abacavir, lamivudine and zidovudine tablets. These hypersensitivity reactions have included multi-organ failure and anaphylaxis and typically occurred within the first 6 weeks of treatment with abacavir (median time to onset was 9 days); although abacavir hypersensitivity reactions have occurred any time during treatment [see ADVERSE REACTIONS (6.1)]. Patients who carry the HLA-B*5701 allele are at a higher risk of abacavir hypersensitivity reactions; although, patients who do not carry the HLA-B*5701 allele have developed hypersensitivity reactions. Hypersensitivity to abacavir was reported in approximately 206 (8%) of 2,670 patients in 9 clinical trials with abacavir-containing products where HLA-B*5701 screening was not performed. The incidence of suspected abacavir hypersensitivity reactions in clinical trials was 1% when subjects carrying the HLA-B*5701 allele were excluded. In any patient treated with abacavir, the clinical diagnosis of hypersensitivity reaction must remain the basis of clinical decision making.

Due to the potential for severe, serious, and possibly fatal hypersensitivity reactions with abacavir:

• All patients should be screened for the HLA-B*5701 allele prior to initiating therapy with abacavir, lamivudine and zidovudine tablets or reinitiation of therapy with abacavir, lamivudine and zidovudine tablets, unless patients have a previously documented HLA-B*5701 allele assessment.
• Abacavir, lamivudine, and zidovudine tablets are contraindicated in patients with a prior hypersensitivity reaction to abacavir and in HLA-B*5701-positive patients.
• Before starting abacavir, lamivudine and zidovudine tablets, review medical history for prior exposure to any abacavir-containing product. NEVER restart abacavir, lamivudine and zidovudine tablets or any other abacavir-containing product following a hypersensitivity reaction to abacavir, regardless of HLA-B*5701 status.
• To reduce the risk of a life-threatening hypersensitivity reaction, regardless of HLA-B*5701 status, discontinue abacavir, lamivudine and zidovudine tablets immediately if a hypersensitivity reaction is suspected, even when other diagnoses are possible (e.g., acute onset respiratory diseases such as pneumonia, bronchitis, pharyngitis, or influenza; gastroenteritis; or reactions to other medications).
• If a hypersensitivity reaction cannot be ruled out, do not restart abacavir, lamivudine and zidovudine tablets or any other abacavir-containing products because more severe symptoms, which may include life-threatening hypotension and death, can occur within hours.
• If a hypersensitivity reaction is ruled out, patients may restart abacavir, lamivudine and zidovudine tablets. Rarely, patients who have stopped abacavir for reasons other than symptoms of hypersensitivity have also experienced life-threatening reactions within hours of reinitiating abacavir therapy. Therefore, reintroduction of abacavir, lamivudine and zidovudine tablets or any other abacavir-containing product is recommended only if medical care can be readily accessed.
• A Medication Guide and Warning Card that provide information about recognition of abacavir hypersensitivity reactions should be dispensed with each new prescription and refill.

Hematologic Toxicity/Bone Marrow Suppression

Zidovudine, a component of abacavir, lamivudine and zidovudine tablet, has been associated with hematologic toxicity including neutropenia and anemia, particularly in patients with advanced HIV-1 disease. Abacavir, lamivudine and zidovudine tablets should be used with caution in patients who have bone marrow compromise evidenced by granulocyte count less than 1,000 cells per mm3 or hemoglobin less than 9.5 grams per dL [see ADVERSE REACTIONS (6.1)].

Frequent blood counts are strongly recommended in patients with advanced HIV-1 disease who are treated with abacavir, lamivudine and zidovudine tablets. Periodic blood counts are recommended for other HIV-1-infected patients. If anemia or neutropenia develops, dosage interruption may be needed.

Myopathy

Myopathy and myositis, with pathological changes similar to that produced by HIV-1 disease, have been associated with prolonged use of zidovudine, and therefore may occur with therapy with abacavir, lamivudine and zidovudine tablets.

Lactic Acidosis and Severe Hepatomegaly with Steatosis

Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogues and other antiretrovirals. See full prescribing information for ZIAGEN® (abacavir), EPIVIR® (lamivudine), and RETROVIR® (zidovudine). Treatment with abacavir, lamivudine and zidovudine tablets should be suspended in any patient who develops clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity (which may include hepatomegaly and steatosis even in the absence of marked transaminase elevations).

Patients with Hepatitis B Virus Co-infection

Posttreatment Exacerbations of Hepatitis

Clinical and laboratory evidence of exacerbations of hepatitis have occurred after discontinuation of lamivudine. See full prescribing information for EPIVIR® (lamivudine). Patients should be closely monitored with both clinical and laboratory follow-up for at least several months after stopping treatment.

Emergence of Lamivudine-Resistant HBV

Safety and efficacy of lamivudine have not been established for treatment of chronic hepatitis B in subjects dually infected with HIV-1 and HBV. Emergence of hepatitis B virus variants associated with resistance to lamivudine has been reported in HIV–1-infected subjects who have received lamivudine-containing antiretroviral regimens in the presence of concurrent infection with hepatitis B virus. See full prescribing information for EPIVIR® (lamivudine).

Use with Interferon- and Ribavirin-Based Regimens

 Patients receiving interferon alfa with or without ribavirin and abacavir, lamivudine and zidovudine tablets should be closely monitored for treatment-associated toxicities, especially hepatic decompensation, neutropenia, and anemia. See full prescribing information for EPIVIR® (lamivudine) and RETROVIR® (zidovudine). Discontinuation of abacavir, lamivudine and zidovudine tablets should be considered as medically appropriate. Dose reduction or discontinuation of interferon alfa, ribavirin, or both should also be considered if worsening clinical toxicities are observed, including hepatic decompensation (e.g., Child-Pugh greater than 6) (see full prescribing information for interferon and ribavirin).

Exacerbation of anemia has been reported in HIV-1/HCV co-infected patients receiving ribavirin and zidovudine. Coadministration of ribavirin and abacavir, lamivudine and zidovudine tablet is not advised.

Immune Reconstitution Syndrome

Immune reconstitution syndrome has been reported in patients treated with combination antiretroviral therapy, including abacavir, lamivudine and zidovudine tablets. During the initial phase of combination antiretroviral treatment, patients whose immune systems respond may develop an inflammatory response to indolent or residual opportunistic infections (such as Mycobacterium avium infection, cytomegalovirus, Pneumocystis jirovecii pneumonia [PCP], or tuberculosis), which may necessitate further evaluation and treatment.

Autoimmune disorders (such as Graves' disease, polymyositis, and Guillain-BarrÉ syndrome) have also been reported to occur in the setting of immune reconstitution; however, the time to onset is more variable, and can occur many months after initiation of treatment.

Fat Redistribution

Redistribution/accumulation of body fat including central obesity, dorsocervical fat enlargement (buffalo hump), peripheral wasting, facial wasting, breast enlargement, and "cushingoid appearance" have been observed in patients receiving antiretroviral therapy. The mechanism and long-term consequences of these events are currently unknown. A causal relationship has not been established.

Myocardial Infarction

In a published prospective, observational, epidemiological trial designed to investigate the rate of myocardial infarction (MI) in patients on combination antiretroviral therapy, the use of abacavir within the previous 6 months was correlated with an increased risk of MI. In a sponsor-conducted pooled analysis of clinical trials, no excess risk of MI was observed in abacavir-treated subjects as compared with control subjects. In totality, the available data from the observational cohort and from clinical trials are inconclusive.

As a precaution, the underlying risk of coronary heart disease should be considered when prescribing antiretroviral therapies, including abacavir, and action taken to minimize all modifiable risk factors (e.g., hypertension, hyperlipidemia, diabetes mellitus, smoking).

Therapy-Experienced Patients

In clinical trials, subjects with prolonged prior nucleoside reverse transcriptase inhibitor (NRTI) exposure or who had HIV-1 isolates that contained multiple mutations conferring resistance to NRTIs had limited response to abacavir. The potential for cross-resistance between abacavir and other NRTIs should be considered when choosing new therapeutic regimens in therapy- experienced patients [see Microbiology (12.4)].

The following adverse reactions are discussed in other sections of the labeling:

• Serious and sometimes fatal hypersensitivity reactions [see BOXED WARNING, WARNINGS AND PRECAUTIONS (5.1)] .
• Hematologic toxicity, including neutropenia and anemia [see BOXED WARNING, WARNINGS AND PRECAUTIONS (5.2)] .
• Symptomatic myopathy [see BOXED WARNING, WARNINGS AND PRECAUTIONS (5.3)] .
• Lactic acidosis and severe hepatomegaly with steatosis [see BOXED WARNING, WARNINGS AND PRECAUTIONS (5.4)] .
• Exacerbations of hepatitis B [seeBOXED WARNING, WARNINGS AND PRECAUTIONS (5.5)] .
• Hepatic decompensation in patients co-infected with HIV-1 and hepatitis C [see WARNINGS AND PRECAUTIONS (5.6)] .
• Exacerbation of anemia in HIV-1/HCV co-infected patients receiving ribavirin and zidovudine [see WARNINGS AND PRECAUTIONS (5.6)] .
• Immune reconstitution syndrome [see WARNINGS AND PRECAUTIONS (5.7)] .
• Fat redistribution [see WARNINGS AND PRECAUTIONS (5.8)] .
• Myocardial infarction [see WARNINGS AND PRECAUTIONS (5.9)] .

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Serious and Fatal Abacavir-Associated Hypersensitivity Reactions

In clinical trials, serious and sometimes fatal hypersensitivity reactions have occurred with abacavir, a component of abacavir, lamivudine and zidovudine tablets [see BOXED WARNING, WARNINGS AND PRECAUTIONS (5.1)]. These reactions have been characterized by 2 or more of the following signs or symptoms: (1) fever; (2) rash; (3) gastrointestinal symptoms (including nausea, vomiting, diarrhea, or abdominal pain); (4) constitutional symptoms (including generalized malaise, fatigue, or achiness); (5) respiratory symptoms (including dyspnea, cough, or pharyngitis). Almost all abacavir hypersensitivity reactions include fever and/or rash as part of the syndrome.

Other signs and symptoms have included lethargy, headache, myalgia, edema, arthralgia, and paresthesia. Anaphylaxis, liver failure, renal failure, hypotension, adult respiratory distress syndrome, respiratory failure, myolysis, and death have occurred in association with these hypersensitivity reactions. Physical findings have included lymphadenopathy, mucous membrane lesions (conjunctivitis and mouth ulcerations), and maculopapular or urticarial rash (although some patients had other types of rashes and others did not have a rash). There were reports of erythema multiforme. Laboratory abnormalities included elevated liver chemistries, elevated creatine phosphokinase, elevated creatinine, and lymphopenia, and abnormal chest x-ray findings (predominantly infiltrates, which were localized).

Additional Adverse Reactions with Use of Abacavir, Lamivudine and Zidovudine Tablets

Treatment-emergent clinical adverse reactions (rated by the investigator as moderate or severe) with a frequency greater than or equal to 5% during therapy with abacavir 300 mg twice daily, lamivudine 150 mg twice daily, and zidovudine 300 mg twice daily compared with indinavir 800 mg 3 times daily, lamivudine 150 mg twice daily, and zidovudine 300 mg twice daily from CNA3005 are listed in Table 1.

Five subjects receiving abacavir in CNA3005 experienced worsening of pre-existing depression compared to none in the indinavir arm. The background rates of pre-existing depression were similar in the 2 treatment arms.

Laboratory Abnormalities

Laboratory abnormalities in CNA3005 are listed in Table 2.

Other Adverse Events

In addition to adverse reactions in Tables 1 and 2, other adverse events observed in the expanded access program for abacavir were pancreatitis and increased GGT.

Postmarketing Experience

The following adverse reactions have been identified during postmarketing use. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Abacavir

Cardiovascular:

Myocardial infarction.

Skin:

Suspected Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been reported in patients receiving abacavir primarily in combination with medications known to be associated with SJS and TEN, respectively. Because of the overlap of clinical signs and symptoms between hypersensitivity to abacavir and SJS and TEN, and the possibility of multiple drug sensitivities in some patients, abacavir should be discontinued and not restarted in such cases. There have also been reports of erythema multiforme with abacavir use [see ADVERSE REACTIONS (6.1)].

Abacavir, Lamivudine, and/or Zidovudine

Body as a Whole:

Redistribution/accumulation of body fat [see WARNINGS AND PRECAUTIONS (5.8)].

Cardiovascular:

Cardiomyopathy.

Digestive:

Stomatitis.

Endocrine and Metabolic:

Gynecomastia.

Gastrointestinal:

Anorexia and/or decreased appetite, abdominal pain, dyspepsia, oral mucosal pigmentation.

General:

Vasculitis, weakness.

Hemic and Lymphatic:

Aplastic anemia, anemia (including pure red cell aplasia and severe anemias progressing on therapy), lymphadenopathy, splenomegaly, thrombocytopenia.

Hepatic:

Lactic acidosis and hepatic steatosis [see WARNINGS AND PRECAUTIONS (5.4)], elevated bilirubin, elevated transaminases, posttreatment exacerbations of hepatitis B [see WARNINGS AND PRECAUTIONS (5.5)].

Hypersensitivity:

Sensitization reactions (including anaphylaxis), urticaria.

Musculoskeletal:

Arthralgia, myalgia, muscle weakness, rhabdomyolysis.

Nervous:

Dizziness, paresthesia, peripheral neuropathy, seizures.

Psychiatric:

Insomnia and other sleep disorders.

Respiratory:

Abnormal breath sounds/wheezing.

Skin:

Alopecia, erythema multiforme, Stevens-Johnson syndrome.

There is no known specific treatment for overdose with abacavir, lamivudine and zidovudine tablets. If overdose occurs, the patient should be monitored and standard supportive treatment applied as required.

Abacavir

It is not known whether abacavir can be removed by peritoneal dialysis or hemodialysis.

Lamivudine

Because a negligible amount of lamivudine was removed via (4-hour) hemodialysis, continuous ambulatory peritoneal dialysis, and automated peritoneal dialysis, it is not known if continuous hemodialysis would provide clinical benefit in a lamivudine overdose event.

Zidovudine

Acute overdoses of zidovudine have been reported in pediatric patients and adults. These involved exposures up to 50 grams. No specific symptoms or signs have been identified following acute overdosage with zidovudine apart from those listed as adverse events such as fatigue, headache, vomiting, and occasional reports of hematological disturbances. Patients recovered without permanent sequelae. Hemodialysis and peritoneal dialysis appear to have a negligible effect on the removal of zidovudine, while elimination of its primary metabolite, 3′- azido-3′-deoxy-5′-O-β-D-glucopyranuronosylthymidine (GZDV), is enhanced.

Mechanism of Action

Abacavir, lamivudine and zidovudine tablet is an antiretroviral agent [see Microbiology (12.4)].

Pharmacokinetics

Pharmacokinetics in Adults

In a single-dose, 3-way crossover bioavailability trial of 1 abacavir, lamivudine and zidovudine 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 abacavir, lamivudine and zidovudine 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 to 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.

Effect of Food on Absorption of Abacavir, Lamivudine and Zidovudine Tablets

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 abacavir, lamivudine and zidovudine tablets 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 (2.2)].

Specific Populations

Renal Impairment: 

Abacavir, Lamivudine and Zidovudine Tablets 

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: 

Abacavir, Lamivudine and Zidovudine Tablets 

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 

Abacavir pharmacokinetics were studied in 25 pregnant women during the last trimester of pregnancy receiving abacavir 300 mg twice daily. Abacavir exposure (AUC) during pregnancy was similar to those in postpartum and in HIV-infected non-pregnant historical controls. Consistent with passive diffusion of abacavir across the placenta, abacavir concentrations in neonatal plasma cord samples at birth were essentially equal to those in maternal plasma at delivery.

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.

Drug Interactions

The drug interaction trials described were conducted with abacavir, lamivudine or zidovudine as single entities; no drug interaction trials have been conducted using abacavir, lamivudine and zidovudine tablets. 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.

Other Interactions

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 (7.1)]. 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 (5.6)].

The effects of other coadministered drugs on abacavir, lamivudine, or zidovudine are provided in Table 4.

Microbiology

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.

Antiviral Activity

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 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 0.003 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 was 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).

Resistance

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 analogue 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

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.

The following trial was conducted with the individual components of abacavir, lamivudine and zidovudine tablet [see CLINICAL PHARMACOLOGY (12.3)].

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.

Treatment response by plasma HIV-1 RNA strata is shown in Table 6.

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.

Mild liver dysfunction (Child-Pugh A): Not recommended; individual components should be used.
Moderate or severe liver dysfunction (Child-Pugh B or C): Contraindicated

US BOXED WARNINGS:
-HYPERSENSITIVITY REACTIONS: Serious and sometimes fatal hypersensitivity reactions (with multiple organ involvement) reported with abacavir. Patients with the human leukocyte antigen subtype B*5701 (HLA-B*5701) allele are at higher risk of abacavir hypersensitivity reactions; however, such reactions have occurred in patients without the HLA-B*5701 allele. This drug is contraindicated in patients with prior hypersensitivity reaction to abacavir and in HLA-B*5701-positive patients. All patients should be screened for the HLA-B*5701 allele before starting or restarting treatment with this drug (unless HLA-B*5701 allele assessment previously documented). Regardless of HLA-B*5701 status, this drug should be discontinued without delay if hypersensitivity reaction is suspected, even if other diagnoses are possible. After hypersensitivity reaction to this drug, NEVER restart this or any other abacavir-containing product as more severe symptoms (including death) can occur within hours. Similar severe reactions also reported after restarting abacavir-containing products in patients with no history of abacavir hypersensitivity.
-HEMATOLOGIC TOXICITY: Zidovudine has been associated with hematologic toxicity (including neutropenia and severe anemia), especially in patients with advanced HIV-1 disease.
-MYOPATHY: Prolonged zidovudine use has been associated with symptomatic myopathy.
-LACTIC ACIDOSIS AND SEVERE HEPATOMEGALY WITH STEATOSIS: Lactic acidosis and severe hepatomegaly with steatosis (including fatalities) reported with use of nucleoside analogs and other antiretrovirals. This drug should be discontinued if clinical or laboratory findings suggest lactic acidosis or pronounced hepatotoxicity.
-EXACERBATIONS OF HEPATITIS B: Severe acute exacerbations of hepatitis B reported in patients coinfected with HBV and HIV-1 after stopping lamivudine. Hepatic function of coinfected patients should be closely monitored with clinical and laboratory follow-up for at least several months after stopping this drug. If appropriate, initiation/resumption of antihepatitis B therapy may be necessary.

This drug is not recommended for use in pediatric patients weighing less than 40 kg.

Consult WARNINGS section for additional precautions.