Abacavir Sulfate Tablets

Name: Abacavir Sulfate Tablets

Adverse Reactions

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)] .
  • Lactic acidosis and severe hepatomegaly with steatosis [see Boxed Warning, Warnings and Precautions (5.2)] .
  • Immune reconstitution syndrome [see Warnings and Precautions (5.3)] .
  • Fat redistribution [see Warnings and Precautions (5.4)] .
  • Myocardial infarction [see Warnings and Precautions (5.5)] .

Clinical Trials Experience in Adult Subjects

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 [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 sulfate

Therapy-Naïve Adults: Treatment-emergent clinical adverse reactions (rated by the investigator as moderate or severe) with a greater than or equal to 5% frequency during therapy with abacavir sulfate 300 mg twice daily, lamivudine 150 mg twice daily, and efavirenz 600 mg daily compared with zidovudine 300 mg twice daily, lamivudine 150 mg twice daily, and efavirenz 600 mg daily from CNA30024 are listed in Table 2.

Table 2. Treatment-Emergent (All Causality) Adverse Reactions of at Least Moderate Intensity (Grades 2-4, Greater than or Equal to 5% Frequency) in Therapy-Naive Adults (CNA30024*) through 48 Weeks of Treatment
* Ten (3%) cases of suspected drug hypersensitivity were reclassified as not being due to abacavir following unblinding. † This trial used double-blind ascertainment of suspected hypersensitivity reactions. During the blinded portion of the trial, suspected hypersensitivity to abacavir was reported by investigators in 9% of 324 subjects in the abacavir group and 3% of 325 subjects in the zidovudine group.
Adverse Reaction
Abacavir sulfate plus Lamivudine plus Efavirenz
(n = 324)
Zidovudine plus Lamivudine plus Efavirenz
(n = 325)
Dreams/sleep disorders
10%
10%
Drug hypersensitivity
9%
<1%†
Headaches/migraine
7%
11%
Nausea
7%
11%
Fatigue/malaise
7%
10%
Diarrhea
7%
6%
Rashes
6%
12%
Abdominal pain/gastritis/ gastrointestinal signs and symptoms
6%
8%
Depressive disorders
6%
6%
Dizziness
6%
6%
Musculoskeletal pain
6%
5%
Bronchitis
4%
5%
Vomiting
2%
9%

Treatment-emergent clinical adverse reactions (rated by the investigator as moderate or severe) with a greater than or equal to 5% frequency during therapy with abacavir sulfate 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 3.

Table 3. Treatment-Emergent (All Causality) Adverse Reactions of at Least Moderate Intensity (Grades 2-4, Greater than or Equal to 5% Frequency) in Therapy-Naive Adults (CNA3005) through 48 Weeks of Treatment
Adverse Reaction
Abacavir sulfate plus Lamivudine/Zidovudine
(n = 262)
Indinavir plus Lamivudine/Zidovudine
(n = 264)
Nausea
19%
17%
Headache
13%
9%
Malaise and fatigue
12%
12%
Nausea and vomiting
10%
10%
Hypersensitivity reaction
8%
2%
Diarrhea
7%
5%
Fever and/or chills
6%
3%
Depressive disorders
6%
4%
Musculoskeletal pain
5%
7%
Skin rashes
5%
4%
Ear/nose/throat infections
5%
4%
Viral respiratory infections
5%
5%
Anxiety
5%
3%
Renal signs/symptoms
<1%
5%
Pain (non-site-specific)
<1%
5%

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

Abacavir sulfate Once Daily versus Abacavir sulfate Twice Daily (CNA30021): Treatment-emergent clinical adverse reactions (rated by the investigator as at least moderate) with a greater than or equal to 5% frequency during therapy with abacavir sulfate 600 mg once daily or abacavir sulfate 300 mg twice daily, both in combination with lamivudine 300 mg once daily and efavirenz 600 mg once daily from CNA30021, were similar. For hypersensitivity reactions, subjects receiving abacavir sulfate once daily showed a rate of 9% in comparison with a rate of 7% for subjects receiving abacavir sulfate twice daily. However, subjects receiving abacavir sulfate 600 mg once daily experienced a significantly higher incidence of severe drug hypersensitivity reactions and severe diarrhea compared with subjects who received abacavir sulfate 300 mg twice daily. Five percent (5%) of subjects receiving abacavir sulfate 600 mg once daily had severe drug hypersensitivity reactions compared with 2% of subjects receiving abacavir sulfate 300 mg twice daily. Two percent (2%) of subjects receiving abacavir sulfate 600 mg once daily had severe diarrhea while none of the subjects receiving abacavir sulfate 300 mg twice daily had this event.

Laboratory Abnormalities: Laboratory abnormalities (Grades 3-4) in therapy-naive adults during therapy with abacavir sulfate 300 mg twice daily, lamivudine 150 mg twice daily, and efavirenz 600 mg daily compared with zidovudine 300 mg twice daily, lamivudine 150 mg twice daily, and efavirenz 600 mg daily from CNA30024 are listed in Table 4.

Table 4. Laboratory Abnormalities (Grades 3-4) in Therapy-Naive Adults (CNA30024) through 48 Weeks of Treatment

ULN = Upper limit of normal

n = Number of subjects assessed.

Grade ¾
Laboratory Abnormalities
Abacavir sulfate plus Lamivudine plus Efavirenz
(n = 324)
Zidovudine plus Lamivudine plus Efavirenz
(n = 325)
Elevated CPK (>4 X ULN)
8%
8%
Elevated ALT (>5 X ULN)
6%
6%
Elevated AST (>5 X ULN)
6%
5%
Hypertriglyceridemia (>750 mg/dL)
6%
5%
Hyperamylasemia (>2 X ULN)
4%
5%
Neutropenia (ANC <750/ mm3)
2%
4%
Anemia (Hgb ≤6.9 gm/dL)
<1%
2%
Thrombocytopenia (Platelets <50,000/ mm3)
1%
<1%
Leukopenia (WBC ≤1,500/ mm3)
<1%
2%

Laboratory abnormalities in CNA3005 are listed in Table 5.

Table 5. Treatment-Emergent Laboratory Abnormalities (Grades 3-4) in CNA3005

ULN = Upper limit of normal

n = Number of subjects assessed.

Grade 3/4
Laboratory Abnormalities
Abacavir sulfate plus Lamivudine/Zidovudine
(n = 262)
Indinavir plus Lamivudine/Zidovudine
(n = 264)
Elevated CPK (>4 x ULN)
18 (7%)
18 (7%)
ALT (>5.0 x ULN)
16 (6%)
16 (6%)
Neutropenia (<750/mm3)
13 (5%)
13 (5%)
Hypertriglyceridemia (>750 mg/dL)
5 (2%)
3 (1%)
Hyperamylasemia (>2.0 x ULN)
5 (2%)
1 (<1%)
Hyperglycemia (>13.9 mmol/L)
2 (<1%)
2 (<1%)
Anemia (Hgb  6.9 g/dL)
0 (0%)
3 (1%)

The frequencies of treatment-emergent laboratory abnormalities were comparable between treatment groups in CNA30021.

Clinical Trials Experience in Pediatric Subjects

Therapy-Experienced Pediatric Subjects (Twice-Daily Dosing)

Treatment-emergent clinical adverse reactions (rated by the investigator as moderate or severe) with a greater than or equal to 5% frequency during therapy with abacavir sulfate 8 mg per kg twice daily, lamivudine 4 mg per kg twice daily, and zidovudine 180 mg per m2 twice daily compared with lamivudine 4 mg per kg twice daily and zidovudine 180 mg per m2 twice daily from CNA3006 are listed in Table 6.

Table 6. Treatment-Emergent (All Causality) Adverse Reactions of at Least Moderate Intensity (Grades 2-4, Greater than or Equal to 5% Frequency) in Therapy-Experienced Pediatric Subjects (CNA3006) through 16 Weeks of Treatment
Adverse Reaction
Abacavir sulfate plus Lamivudine plus Zidovudine
(n = 102)
Lamivudine plus Zidovudine
(n = 103)
Fever and/or chills
9%
7%
Nausea and vomiting
9%
2%
Skin rashes
7%
1%
Ear/nose/throat infections
5%
1%
Pneumonia
4%
5%
Headache
1%
5%

Laboratory Abnormalities: In CNA3006, laboratory abnormalities (anemia, neutropenia, liver function test abnormalities, and CPK elevations) were observed with similar frequencies as in a trial of therapy-naive adults (CNA30024). Mild elevations of blood glucose were more frequent in pediatric subjects receiving abacavir sulfate (CNA3006) as compared with adult subjects (CNA30024).

Other Adverse Events

In addition to adverse reactions and laboratory abnormalities reported in Tables 2, 3, 4, 5 and 6, other adverse reactions observed in the expanded access program were pancreatitis and increased GGT.

Additional pediatric use information for patients aged 3 months and above is approved for ViiV Healthcare Company's ZIAGEN® (abacavir sulfate) tablets and oral solution. However, due to ViiV Healthcare Company's marketing exclusivity rights, this drug product is not labeled with that pediatric information.

Postmarketing Experience

The following adverse reactions have been identified during postmarketing use of abacavir sulfate. 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 exposures.

Body as a Whole

Redistribution/accumulation of body fat.

Cardiovascular

Myocardial infarction.

Hepatic

Lactic acidosis and hepatic steatosis [see Warnings and Precautions (5.2)].

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)].

Drug Interactions

Methadone

In a trial of 11 HIV-1-infected subjects receiving methadone-maintenance therapy with 600 mg of abacavir sulfate twice daily (twice the currently recommended dose), oral methadone clearance increased [see Clinical Pharmacology (12.3)]. This alteration will not result in a methadone dose modification in the majority of patients; however, an increased methadone dose may be required in a small number of patients.

Abacavir Sulfate Tablets Description

Abacavir sulfate is a synthetic carbocyclic nucleoside analogue with inhibitory activity against HIV-1. The chemical name of abacavir sulfate is (1S,cis)-4-[2-amino-6- (cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol sulfate (salt) (2:1). Abacavir sulfate is the enantiomer with 1S, 4R absolute configuration on the cyclopentene ring. It has a molecular formula of (C14H18N6O)2•H2SO4 and a molecular weight of 670.76 g per mol. It has the following structural formula:

Abacavir sulfate is a white to off-white solid and is soluble in water.

Abacavir tablets USP 300 mg are for oral administration. Each tablet contains abacavir sulfate equivalent to 300 mg of abacavir as active ingredient and the following inactive ingredients: microcrystalline cellulose, sodium starch glycolate, corn starch, hypromellose, magnesium stearate, colloidal silicon dioxide and opadry yellow 15C52843 (consist of hypromellose, titanium dioxide, polyethylene glycol, iron oxide yellow, polysorbate 80).

In vivo, abacavir sulfate dissociates to its free base, abacavir. Dosages are expressed in terms of abacavir.

Abacavir Sulfate Tablets - Clinical Pharmacology

Mechanism of Action

Abacavir is an antiretroviral agent [see Microbiology (12.4)].

Pharmacokinetics

Pharmacokinetics in Adults

The pharmacokinetic properties of abacavir were independent of dose over the range of 300 to 1,200 mg per day.

Absorption and Bioavailability: Following oral administration, abacavir is rapidly absorbed and extensively distributed. The geometric mean absolute bioavailability of the tablet was 83%. Plasma abacavir AUC was similar following administration of the oral solution or tablets. After oral administration of 300 mg twice daily in 20 subjects, the steady-state peak serum abacavir concentration (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. After oral administration of a single dose of 600 mg of abacavir in 20 subjects, Cmax was 4.26 ± 1.19 mcg per mL (mean ± SD) and AUC∞ was 11.95 ± 2.51 mcg•hour per mL.

Distribution: The apparent volume of distribution after IV administration of abacavir was 0.86 ± 0.15 L per kg, suggesting that abacavir distributes into extravascular space. In 3 subjects, the CSF AUC(0-6 h) to plasma abacavir AUC(0-6 h) ratio ranged from 27% to 33%.

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.

Metabolism and Elimination: In humans, abacavir is not significantly metabolized by cytochrome P450 enzymes. 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. The metabolites do not have antiviral activity. In vitro experiments reveal that abacavir does not inhibit human CYP3A4, CYP2D6, or CYP2C9 activity at clinically relevant concentrations.

Elimination of abacavir was quantified in a mass balance trial following administration of a 600-mg dose of 14C-abacavir: 99% of the radioactivity was recovered, 1.2% was excreted in the urine as abacavir, 30% as the 5 -carboxylic acid metabolite, 36% as the 5 -glucuronide metabolite, and 15% as unidentified minor metabolites in the urine. Fecal elimination accounted for 16% of the dose.

In single-dose trials, the observed elimination half-life (t1/2) was 1.54 ± 0.63 hours. After intravenous administration, total clearance was 0.80 ± 0.24 L per hour per kg (mean ± SD).

Effects of Food on Oral Absorption

Bioavailability of abacavir tablets was assessed in the fasting and fed states with no significant difference in systemic exposure (AUC∞); therefore, abacavir tablets may be administered with or without food. Systemic exposure to abacavir was comparable after administration of abacavir oral solution and abacavir tablets. Therefore, these products may be used interchangeably.

Specific Populations

Renal Impairment: The pharmacokinetic properties of abacavir sulfate have not been determined in patients with impaired renal function. Renal excretion of unchanged abacavir is a minor route of elimination in humans.

Hepatic Impairment: The pharmacokinetics of abacavir have been studied in subjects with mild hepatic impairment (Child-Pugh Class A). Results showed that there was a mean increase of 89% in the abacavir AUC, and an increase of 58% in the half-life of abacavir after a single dose of 600 mg of abacavir. The AUCs of the metabolites were not modified by mild liver disease; however, the rates of formation and elimination of the metabolites were decreased [see Contraindications (4), Use in Specific Populations (8.6)].

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.

Pediatric Patients: The pharmacokinetics of abacavir have been studied after either single or repeat doses of abacavir sulfate in pediatric subjects. Subjects receiving abacavir oral solution according to the recommended dosage regimen achieved plasma concentrations of abacavir similar to adults. Subjects receiving abacavir oral tablets achieved higher plasma concentrations of abacavir than subjects receiving oral solution.

Additional pediatric use information for patients aged 3 months and above is approved for ViiV Healthcare Company's ZIAGEN® (abacavir sulfate) tablets and oral solution. However, due to ViiV Healthcare Company's marketing exclusivity rights, this drug product is not labeled with that pediatric information.

Geriatric Patients: The pharmacokinetics of abacavir sulfate have not been studied in subjects older than 65 years.

Gender: A population pharmacokinetic analysis in HIV-1-infected male (n = 304) and female (n = 67) subjects showed no gender differences in abacavir AUC normalized for lean body weight.

Race: There are no significant or clinically relevant racial differences between blacks and whites in abacavir pharmacokinetics.

Drug Interactions

In human liver microsomes, abacavir did not inhibit cytochrome P450 isoforms (2C9, 2D6, 3A4). Based on these data, it is unlikely that clinically significant drug interactions will occur between abacavir and drugs metabolized through these pathways.

Lamivudine and/or Zidovudine: Fifteen HIV-1-infected subjects were enrolled in a crossover-designed drug interaction 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. Due to the common metabolic pathways of abacavir and ethanol via alcohol dehydrogenase, the pharmacokinetic interaction between abacavir and ethanol was studied in 24 HIV-1-infected male subjects. Each subjects received the following treatments on separate occasions: a single 600-mg dose of abacavir, 0.7 g per kg ethanol (equivalent to 5 alcoholic drinks), and abacavir 600 mg plus 0.7 g per kg ethanol. Coadministration of ethanol and abacavir resulted in a 41% increase in abacavir AUC∞ and a 26% increase in abacavir t1/2. Abacavir had no effect on the pharmacokinetic properties of ethanol, so no clinically significant interaction is expected in men. This interaction has not been studied in females.

Methadone: In a trial of 11 HIV-infected subjects receiving methadone-maintenance therapy (40 mg and 90 mg daily), with 600 mg of abacavir sulfate twice daily (twice the currently recommended dose), oral methadone clearance increased 22% (90% CI: 6% to 42%). This alteration will not result in a methadone dose modification in the majority of patients; however, an increased methadone dose may be required in a small number of patients [see Drug Interactions (7)]. The addition of methadone had no clinically significant effect on the pharmacokinetic properties of abacavir.

Microbiology

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.

Antiviral Activity

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. The antiviral activity of abacavir in cell culture was not antagonized when combined with the nucleoside reverse transcriptase inhibitors (NRTIs) didanosine, emtricitabine, lamivudine, stavudine, tenofovir, zalcitabine or zidovudine, the non-nucleoside reverse transcriptase inhibitor (NNRTI) nevirapine, or the protease inhibitor (PI) amprenavir. Ribavirin (50 microM) used in the treatment of chronic HCV infection had no effect on the anti–HIV-1 activity of abacavir in cell culture.

Resistance

HIV-1 isolates with reduced susceptibility to abacavir have been selected in cell culture. Genotypic analysis of isolates selected in cell culture and recovered from abacavir-treated subjects demonstrated that amino acid substitutions K65R, L74V, Y115F, and M184V/I emerged in HIV-1 RT. M184V or I substitutions resulted in 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.

Thirty-nine percent (7 of 18) of the isolates from subjects who experienced virologic failure in the abacavir once-daily arm had a greater than 2.5-fold mean decrease in abacavir susceptibility with a median-fold decrease of 1.3 (range: 0.5 to 11) compared with 29% (5 of 17) of the failure isolates in the twice-daily arm with a median-fold decrease of 0.92 (range: 0.7 to 13).

Cross-Resistance

Cross-resistance has been observed among NRTIs. Isolates containing abacavir resistance-associated substitutions, namely, K65R, L74V, Y115F, and M184V, exhibited cross-resistance to didanosine, emtricitabine, lamivudine, and tenofovir in cell culture and in subjects. An increasing number of thymidine analogue mutation substitutions (TAMs: M41L, D67N, K70R, L210W, T215Y/F, K219E/R/H/Q/N) is associated with a progressive reduction in abacavir susceptibility.

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