Ziagen (Abacavir)

Abacavir Succinate

Abacavir Sulfate

Adverse Effects

The most significant adverse effects associated with antiretroviral regimens containing abacavir are severe hypersensitivity reactions, sometimes fatal, that may occur in up to 9% of patients given abacavir, especially (but not exclusively) during the first 6 weeks of treatment, or during intermittent therapy.

Symptoms of hypersensitivity often include fever, rash, cough, dyspnoea, lethargy, malaise, headache, myalgia, and gastrointestinal disturbances, particularly nausea and vomiting, diarrhoea, and abdominal pain. Anaphylaxis has occurred. Caution is needed as hypersensitivity may be misdiagnosed as influenza, respiratory disease, or gastroenteritis.

Erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis have occurred rarely. O ther adverse effects associated with abacavir include pancreatitis and raised liver enzyme values.

Lactic acidosis, sometimes fatal and usually associated with severe hepatomegaly and steatosis, has been reported in patients receiving NRTIs. Immune reconstitution syndrome (an inflammatory immune response resulting in clinical deterioration) has been reported during the initial phase of treatment with combination antiretroviral therapy, including abacavir, in HIV-infected patients with severe immune deficiency.

Accumulation or redistribution of body fat (lipodystrophy) 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, including abacavir.

Metabolic abnormalities such as hypertriglyceridaemia, hypercholesterolaemia, insulin resistance, hyperglycaemia, and hyperlactataemia have also been reported. NRTIs have also been associated with mitochondrial dysfunction such as abnormal behaviour, anaemia, convulsions, hyperlipasaemia, hypertonia, and neutropenia.

Elevated creatine phosphokinase, myalgia, myositis, and rarely rhabdomyolysis have been reported, particularly when nucleoside analogues have been given with HIV-protease inhibitors. Osteonecrosis has been reported, particularly in patients with advanced HIV disease or long-term exposure to combination antiretroviral therapy.

Effects on the heart

For the possible risk of myocardial infarction in patients taking abacavir.

Effects on the skin

Stevens-Johnson syndrome occurring in a patient receiving antiretroviral therapy with abacavir, lamivu-dine, and zidovudine was probably associated with abacavir. Resolution occurred upon stopping antiretroviral therapy and the condition did not recur upon rechallenge with an alternative regimen also containing lamivudine and zidovudine.

Hypersensitivity

Reviews of hypersensitivity associated with abacavir.

Precautions

Patients considered to be at increased risk for an abacavir hypersensitivity reaction are those that carry the human leucocyte antigen (HLA) HLA-B(*)5701 allele; screening patients for HLA-B(*)5701 allele before starting treatment with abacavir has been shown to reduce the risk of hypersensitivity reactions. Routine screening of all patients before starting treatment with an abacavir-containing product is therefore recommended.

Abacavir should be stopped immediately if symptoms associated with hypersensitivity occur and should never be restarted in patients who have stopped therapy due to a hypersensitivity reaction.

Patients should be closely monitored for signs of hypersensitivity during the first 2 months of treatment, although hypersensitivity reactions can occur at any time.

Patients restarting therapy after an interruption are at particular risk even if they have not previously had symptoms of hypersensitivity. Since intermittent therapy may increase the risk of hypersensitivity developing, patients should be advised of the importance of regular dosing.

Abacavir should not be used in patients with moderate to severe hepatic impairment, and should be used with caution and reduced doses in those with lesser degrees of impairment and those with risk factors for liver disease. Treatment should be stopped if liver function deteriorates rapidly or if hepatomegaly or unexplained metabolic acidosis develop. Abacavir should be avoided in patients with end-stage renal disease.

Interactions

Use of alcohol with abacavir may result in decreased elimination of abacavir and consequent increases in exposure. Abacavir increases the systemic clearance of oral methadone and patients should be monitored for signs of withdrawal symptoms. The dose of methadone may need to be increased in some patients.

Antiviral Action

Abacavir is converted intracellularly in stages to its active form carbovir triphosphate. This halts the DNA synthesis of retroviruses, including HIV, through competitive inhibition of reverse transcriptase and incorporation into viral DNA.

Pharmacokinetics

Abacavir is rapidly absorbed after oral doses with a bio-availability of about 80%. Absorption is delayed slightly by food but the extent is unaffected. Abacavir crosses the blood-brain barrier. It is about 50% bound to plasma proteins.

The elimination half-life is about 1.5 hours after a single dose. Abacavir undergoes intracellular metabolism to the active antiviral metabolite carbovir triphosphate. Elimination is via hepatic metabolism primarily by alcohol dehydrogenase and by glucuronidation and the metabolites are excreted mainly in the urine. There is no significant metabolism by hepatic cytochrome P450 isoenzymes.

Uses and Administration

Abacavir is a nucleoside reverse transcriptase inhibitor with antiretroviral activity against HIV. It is used in the treatment of HIV infection and AIDS. Viral resistance emerges rapidly when abacavir is used alone, and it is therefore used with other antiretrovirals. Abacavir is given orally as the sulfate but doses are expressed in terms of the base; 1.17 g of abacavir sulfate is equivalent to about 1 g of abacavir.

The adult dose is 300 mg twice daily or 600 mg once daily. For details of doses in children, see below. Doses should be reduced in patients with hepatic impairment (see below). Fixed-dose combination products have been developed in order to improve patient adherence and avoid monotherapy, thereby decreasing the risk of acquired drug resistance. Products containing abacavir in combination with lamivudine and with lamivudine and zidovudine are available in some countries.

Administration in children

For the treatment of HIV infection in children 3 months of age and older, abacavir may be given orally as a tablet or solution with other antiretroviral drugs. Doses are based on body-weight:

• 14 to 21 kg: 150 mg (half a tablet) twice daily
• 22to29kg: 150 mg (half atableflin the morning and300 mg (1 tablet) in the evening
• 30 kg or more: 300 mg (1 tablet) twice daily or
• the solution may be given in a dose of 8 mg/kg twice daily to a maximum dose of 300 mg twice daily

Administration in hepatic impairment

Abacavir should not be used in patients with moderate to severe hepatic impairment although reduced oral doses of 200 mg twice daily may be given to patients with mild impairment (Child-Pugh score 5 to 6).

Preparations

Proprietary Preparations

Country	Medications
Argentina	Filabac; Finecil; Plusabcir; Zepril; Ziagenavir
Australia	Ziagen
Austria	Ziagen
Belgium	Ziagen
Brazil	Ziagenavir
Canada	Ziagen
Chile	Ziagen
Czech Republic	Ziagen
Denmark	Ziagen
Finland	Ziagen
France	Ziagen
Germany	Kivexa; Ziagen
Greece	Ziagen
Hong Kong	Ziagen
Hungary	Ziagen
India	Abamune
Ireland	Ziagen
Israel	Ziagen
Italy	Ziagen
Mexico	Ziagenavir
The Netherlands	Ziagen
Norway	Ziagen
New Zealand	Ziagen
Poland	Ziagen
Portugal	Ziagen
Russia	Ziagen
South Africa	Ziagen
Singapore	Ziagen
Spain	Ziagen
Sweden	Ziagen
Switzerland	Ziagen

Multi-ingredient

Country	Medications
Argentina	Kivexa; Tricivir; Trivudin
Australia	Kivexa; Trizivir
Austria	Trizivir
Belgium	Kivexa; Trizivir
Canada	Kivexa; Trizivir
Chile	Kivexa; Tricivir
Czech Republic	Kivexa; Trizivir
Denmark	Kivexa; Trizivir
Finland	Kivexa; Trizivir
France	Kivexa; Trizivir
Germany	Trizivir
Greece	Kivexa; Trizivir
Hong Kong	Trizivir
Hungary	Kivexa; Trizivir
Ireland	Kivexa; Trizivir
Israel	Trizivir
Italy	Kivexa; Trizivir
Mexico	Kivexa; Trizivir
The Netherlands	Kivexa; Trizivir
Norway	Kivexa; Trizivir
New Zealand	Kivexa; Trizivir
Poland	Kivexa; Trizivir
Portugal	Kivexa; Trizivir
Russia	Trizivir
South Africa	Trizivar
Singapore	Trizivir
Spain	Kivexa; Trizivir
Sweden	Kivexa; Trizivir
Switzerland	Trizivir
UK	Kivexa; Trizivir
USA	Epzicom; Trizivir
Venezuela	Trizivir