Abacavir
From DrugPedia: A Wikipedia for Drug discovery
Abacavir (ABC) is a nucleoside analog reverse transcriptase inhibitor (NRTI) used to treat HIV and AIDS. It is available under the trade name Ziagen (GlaxoSmithKline) 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, in 90% of patients, the risk of heart attack has increased.<ref>SFGate.com</ref>
[edit] History
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 will expire in the United States on 2009-12-26.
[edit] Indication
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.
[edit] Mechanism of action
ABC is an analog of guanosine (a purine). Its target is the viral reverse transcriptase enzyme.
[edit] Pharmacokinetics
Abacavir is given orally and has a high bioavailability (83%). It is metabolised primarily through alcohol dehydrogenase or gluconyl transferase. It is capable of crossing the blood-brain barrier.
[edit] Adverse reactions
Fatal hypersensitivity reactions have been associated with therapy with abacavir. Symptoms of hypersensitivity include fever, skin rash, fatigue, gastrointestinal symptoms such as nausea, vomiting, diarrhea or abdominal pain and respiratory symptoms such as pharyngitis, dyspnea, or cough. Hypersensitivity is strongly associated with HLA-B*5701<ref>Mallal S, Nolan D, Witt C, et al. (2002). "Association between the presence of HLA-B*5701, HLA-DR7 and HLA-DQ3 and hypersensitivity to HIV-1 reverse transcriptase inhibitor abacavir". Lancet 359: 727–32. doi:.</ref><ref>Hetherington S, Hughes AR, Mosteller M, et al. (2002). "Genetic variations in HLA-B region and hypersensitivity reactions to abacavir". Lancet 359: 1121–2. doi:.</ref> for which testing is now available in most western countries. There is a strong relationship with race: the prevalence of HLA-B*5701 in India is 20–50%, but is 0% in Japan; the prevalence is 5–7% in western Europe. Screening for the HLA-B*5701 has been convincingly shown to reduce the incidence of abacavir hypersensitivity reactions.<ref>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". Clin Infect Dis 43 (1): 99–102. doi:.</ref><ref>Zucman D, de Truchis P, Majerholc C, et al. (2007). "Prospective Screening for Human Leukocyte Antigen-B*5701 Avoids Abacavir Hypersensitivity Reaction in the Ethnically Mixed French HIV Population". J Acquir Immune Defic Syndr 45: 1. doi:. PMID 17356469.</ref>
A new FDA alert concerning abacavir and abacavir containing medications was issued on July 24, 2008. FDA informed that based on data from two studies they support a recommendation for pre-therapy screening for the presence of the HLA-B*5701 allele and the selection of alternative therapy in positive subjects. Genetic tests for HLA-B*5701 are available and all patients should be screened for the HLA-B*5701 allele before starting or restarting treatment with abacavir or abacavir containing medications. Development of clinically suspected abacavir HSR requires immediate and permanent discontinuation of abacavir therapy in all patients, including patients negative for HLA-B*5701.<ref name="fda08242008">http://www.fda.gov/cder/drug/InfoSheets/HCP/abacavirHCP.htm FDA abacavir alert web access July 29, 2008 </ref>
[edit] Cautions and Warnings
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 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.
[edit] Food Interactions
None known
[edit] Usual Dose
Adult (age 17 and over) :300mg 2 times a day Child (age 3 months - 16 years) 3.6mg per lb. of body weight twice a day, up to a maximum of 300mg in each dose.
[edit] Overdosage
Little is known about the effects of Abacavir overdose. Overdose victims should be taken to a hospital emergency room for treatment. Always bring the prescription bottle or container.
[edit] References
- Antiretroviral Therapy-Investigational NRTIs: HIV Clinical Management Vol. 3. Medscape Inc, 1998
- HIV Insite Antiretroviral Drug Database; UC Regents, 1999
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