lamivudine/abacavir (Rx)

Contraindications

Patients who have the HLA-B*5701 allele

Prior hypersensitivity to abacavir or lamivudine

Moderate or severe hepatic impairment

Cautions

Review medical history for hypersensitivity to abacavir before administration; discontinue at first signs of hypersensitivity

Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, reported with nucleoside analogues, including abacavir and lamivudine (components of the combination product); a majority of these cases have been in women; female gender and obesity may be risk factors; suspend dosing in those who develops clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity

Exacerbation of hepatitis B may occur on discontinuation

Immune reconstitution syndrome reported with combination ART; during the initial treatment phase, patients whose immune systems respond may develop an inflammatory response to indolent or residual opportunistic infections (eg, Mycobacterium avium infection, cytomegalovirus, Pneumocystis jirovecii pneumonia [PCP], or tuberculosis); autoimmune disorders (eg, Grave disease, polymyositis, and Guillain-Barré syndrome) have also been reported

Use has been associated with increased risk of myocardial infarction in observational studies, but not in a meta-analysis of 26 randomized trials; caution with risks for coronary heart disease and minimizing modifiable risk factors, including smoking, hypertension, and hyperlipidemia, prior to use

Concomitant administration of emtricitabine with lamivudine-containing products not recommended

Hepatic decompensation, some fatal, reported in HIV-1/HCV co-infected patients receiving combination antiretroviral therapy and interferon alfa with or without ribavirin; discontinue therapy as medically appropriate and consider dose reduction or discontinuation of interferon alfa, ribavirin, or both

Pregnancy

If pregnant woman exposed to abacavir, report to the Antiretroviral Pregnancy Registry 1-800-258-4263

Abacavir

• Based on prospective reports to APR of exposures to abacavir during pregnancy resulting in live births (including over 1,300 exposed in the first trimester and over 1,300 exposed in the second/third trimester), there was no difference between overall risk of birth defects for abacavir compared with the background birth defect rate of 2.7% in the U.S. reference population of the MACDP
• The prevalence of defects in live births was 3.2% (95% CI: 2.3% to 4.3%) following first-trimester exposure to abacavir-containing regimens and 2.9% (95% CI: 2.1% to 4.0%) following second/third trimester exposure to abacavir-containing regimens

Lamivudine

• Based on prospective reports to APR of exposures to lamivudine during pregnancy resulting in live births (including over 5,300 exposed in first trimester and over 7,400 exposed in second/third trimester), there was no difference between overall risk of birth defects for lamivudine compared with background birth defect rate of 2.7% in U.S. reference population of MACDP
• The prevalence of birth defects in live births was 3.1% (95% CI: 2.7% to 3.6%) following first-trimester exposure to lamivudine-containing regimens and 2.9% (95% CI: 2.5%, 3.3%) following second/third-trimester exposure to lamivudine- containing regimens

Lactation

Abacavir and lamivudine are present in human milk; there is no information on effects of abacavir and lamivudine on breastfed infant or effects of drug on milk production; because of potential for (1) HIV-1 transmission (in HIV-negative infants), (2) developing viral resistance (in HIV-positive infants), and (3) serious adverse reactions in breastfed infant, instruct mothers not to breastfeed if they are receiving therapy

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Pharmacogenomics

Patients who carry the HLA-B*5701 allele are at high risk for experiencing a hypersensitivity reaction

Prior to initiating therapy with abacavir, screening for the HLA-B*5701 allele is recommended

For HLA-B*5701-positive patients, treatment with an abacavir-containing regimen is not recommended

Genetic testing laboratories

• The following companies provide genetic testing for HLA variants
• Kashi Clinical Laboratories (www.kashilab.com)
• LabCorp (http://www.labcorp.com/)
• Specialty Laboratories (http://www.specialtylabs.com)
• Quest (http://www.questdialgnotics.com)

Mechanism of Action

Lamivudine: NRTI; following phosphorylation, inhibits HIV reverse transcriptase by viral DNA chain termination; cytosine analog

Abacavir: NRTI; following phosphorylation, inhibits HIV reverse transcriptase by inhibiting viral replication; guanosine analogue