Chemical structure of abacavir
|Systematic (IUPAC) name|
|Pregnancy cat.||B3 (AU) C (US)|
|Legal status||POM (UK) ℞-only (US)|
|Routes||Oral (solution or tablets)|
|Half-life||1.54 ± 0.63 h|
|Excretion||Renal (1.2% abacavir, 30% 5'-carboxylic acid metabolite, 36% 5'-glucuronide metabolite, 15% unidentified minor metabolites). Fecal (16%)|
|Mol. mass||286.332 g/mol|
|Melt. point||165 °C (329 °F)|
|(what is this?)|
Abacavir (ABC) i// is a nucleoside analog reverse transcriptase inhibitor (NRTI) used to treat HIV and AIDS. It is available under the trade name Ziagen (ViiV Healthcare) and in the combination formulations Trizivir (abacavir, zidovudine and lamivudine) and Kivexa/Epzicom (abacavir and lamivudine). It has been well tolerated: the main side effect is hypersensitivity, which can be severe, and in rare cases, fatal. Genetic testing can indicate whether an individual will be hypersensitive; over 90% of patients can safely take abacavir. However, in a separate study, the risk of heart attack increased by nearly 90%.
Viral strains that are resistant to zidovudine (AZT) or lamivudine (3TC) are generally sensitive to abacavir (ABC), whereas some strains that are resistant to AZT and 3TC are not as sensitive to abacavir.
Abacavir tablets and oral solution, in combination with other antiretroviral agents, are indicated for the treatment of HIV-1 infection.
Abacavir should always be used in combination with other antiretroviral agents. Abacavir should not be added as a single agent when antiretroviral regimens are changed due to loss of virologic response.
Common reactions include nausea, headache, fatigue, vomiting, hypersensitivity reaction, diarrhea, fever/chills, depression, rash, anxiety, URI, ALT, AST elevated, hypertriglyceridemia, and lipodystrophy.
Patients with liver disease should be cautious about using abacavir because of the possibility that it can aggravate the condition. The use of nucleoside drugs such as abacavir can very rarely cause lactic acidosis. Resistance to abacavir has developed in laboratory versions of HIV which are also resistant to other HIV-specific antiretrovirals such as lamivudine, didanosine and zalcitabine. HIV strains that are resistant to protease inhibitors are not likely to be resistant to abacavir.
Redistribution or accumulation of body fat, lipodystrophy, may occur in people taking antiviral medications giving rise to central obesity, facial, arm, leg, and/ or buttock wasting, breast enlargement, and fat accumulation at the base of the neck (buffalo hump).
Abacavir is contraindicated for use in infants under 3 months of age.
Little is known about the effects of Abacavir overdose. Overdose victims should be taken to a hospital emergency room for treatment.
Abacavir hypersensitivity syndrome
Hypersensitivity to abacavir is strongly associated with a single-nucleotide polymorphism at the human leukocyte antigen B*5701 locus. There is an association between the prevalence of HLA-B*5701 and ancestry. The prevalence of the allele is estimated to be 3.4 to 5.8% on average in populations of European ancestry, 17.6% in Indian Americans, 3.0% in Hispanic Americans, and 1.2% in Chinese Americans. There is significant variability in the prevalence of HLA-B*5701 among African populations. In African Americans, the prevalence is estimated to be 1.0% on average, 0% in the Yoruba from Nigeria, 3.3% in the Luhya from Kenya, and 13.6% in the Masai from Kenya, although the average values are derived from highly variable frequencies within sample groups.
Common symptoms of abacavir hypersensitivity syndrome include fever, malaise, nausea, and diarrhea; some patients may also develop a skin rash. Symptoms of AHS typically manifest within six weeks of treatment using abacavir, although they may be confused with symptoms of HIV, immune restoration disease, hypersensitivity syndromes associated with other drugs, or infection. The FDA released an alert concerning abacavir and abacavir-containing medications on July 24, 2008. It recommends pre-therapy screening for the HLA-B*5701 allele, and the use of alternative therapy in subjects with this allele. Genetic testing for the HLA-B*5701 allele is recommended before starting or restarting treatment with abacavir or abacavir-containing medications.
Skin-patch testing may also be used to determine whether an individual will experience a hypersensitivity reaction to abacavir, although some patients susceptible to developing AHS may not react to the patch test.
The development of suspected hypersensitivity reactions to abacavir requires immediate and permanent discontinuation of abacavir therapy in all patients, including patients who do not possess the HLA-B*5701 allele. On March 1, 2011, the FDA informed the public about an ongoing safety review of abacavir and a possible increased risk of heart attack associated with the drug.
The mechanism underlying abacavir hypersensitivity syndrome is related to the change in the HLA-B*5701 protein product. Abacavir binds with high specificity to the HLA-B*5701 protein, changing the shape and chemistry of the antigen-binding cleft. This results in a change in immunological tolerance and the subsequent activation of abacavir-specific cytotoxic T cells, which produce a systemic reaction known as abacavir hypersensitivity syndrome.
Mechanism of action
Abacavir was approved by the Food and Drug Administration (FDA) on December 18, 1998 and is thus the fifteenth approved antiretroviral drug in the United States. Its patent expired in the United States on 2009-12-26.
- Mallal, S., Phillips, E., Carosi, G. et al. (2008). "HLA-B*5701 screening for hypersensitivity to abacavir". New England Journal of Medicine 358: 568–579.
- Rauch, A., Nolan, D., Martin, A. et al. (2006). "Prospective genetic screening decreases the incidence of abacavir hypersensitivity reactions in the Western Australian HIV cohort study". Clinical Infectious Diseases 43: 99–102.
- Heatherington et al. (2002). "Genetic variations in HLA-B region and hypersensitivity reactions to abacavir". Lancet 359: 1121–1122.
- Mallal et al. (2002). "Association between presence of HLA*B5701, HLA-DR7, and HLA-DQ3 and hypersensitivity to HIV-1 reverse-transcriptase inhibitor abacavir". Lancet 359: 727–732.
- Rotimi, C.N.; Jorde, L.B. (2010). "Ancestry and disease in the age of genomic medicine". New England Journal of Medicine 363: 1551–1558.
- Phillips, E., Mallal, S. (2009). "Successful translation of pharmacogenetics into the clinic". Molecular Diagnosis & Therapy 13: 1–9.
- Phillips, E., Mallal S. (2007). "Drug hypersensitivity in HIV". Current Opinion in Allergy and Clinical Immunology 7: 324–330.
- http://www.fda.gov/drugs/drugsafety/postmarketdrugsafetyinformationforpatientsandproviders/ucm123927.htm Accessed November 29, 2013.
- Shear, N.H., Milpied, B., Bruynzeel, D.P. et al. (2008). "A review of drug patch testing and implications for HIV clinicians". AIDS 22: 999–1007.
- http://www.drugs.com/fda/abacavir-ongoing-safety-review-possible-increased-risk-heart-attack-12914.html Accessed November 29, 2013.
- Illing PT et al. 2012, Nature, doi:10.1038/nature11147