Abacavir Sulfate

Class and Category

Pharmacologic class: Nucleoside reverse transcriptase inhibitor (NRTI)

Therapeutic class: Antiretroviral

Indications and Dosages

As an adjunct to treating human immunodeficiency virus (HIV) infection

ORAL SOLUTION, TABLETS

• Adults: 600 mg once daily or 300 mg twice daily in combination with other antiretroviral agents.
• Children, infants 3 months of age and over: 16 mg/kg once daily or 8 mg/kg twice daily in combination with other antiretroviral agents. Maximum: 600 mg daily.
• DOSAGE ADJUSTMENT: For patients with mild hepatic impairment, the dosage is reduced to 200 mg twice daily and only an oral solution is used to ensure accurate dosage.

Mechanism of Action

Blocks an HIV enzyme called reverse transcriptase, which is responsible for starting or increasing the speed of a chemical reaction. By blocking this enzyme, HIV is prevented from multiplying.

Contraindications

Hypersensitivity to abacavir or its components, moderate or severe hepatic impairment, presence of HLA-B*5701 allele

Interactions

DRUGS

methadone: Possibly increased methadone clearance

Adverse Reactions

• CNS: Anxiety, chills, depression, dizziness, fatigue, fever, headache, lethargy, malaise, migraines, paresthesia, sleep disorders
• CV: Edema, elevated triglyceride levels, hypotension, MI
• EENT: Conjunctivitis, ENT infections, mouth ulcerations, pharyngitis
• ENDO: Cushingoid appearance, fat redistribution, hyperglycemia
• GI: Abdominal pain, diarrhea, elevated liver enzymes, gastritis, hyperamylasemia, liver failure, nausea, pancreatitis, severe hepatomegaly with steatosis, vomiting
• GU: Renal dysfunction, renal failure
• HEME: Anemia, neutropenia, leukopenia, thrombocytopenia
• MS: Achiness, arthralgia, elevated CPK levels, musculoskeletal pain, myalgia, myolysis
• RESP: Adult respiratory distress syndrome, bronchitis, cough, dyspnea, pneumonia, respiratory failure, viral respiratory infections
• SKIN: Erythema multiforme, rash, Stevens-Johnson syndrome, toxic epidermal necrolysis
• Other: Anaphylaxis, lactic acidosis, lymphadenopathy, multiorgan failure, nonspecific pain

Childbearing Considerations

PREGNANCY

It is not known if the drug can cause fetal harm although it does cross the placental barrier. Use with caution only if the benefit to the mother outweighs the potential risk to the fetus.

LACTATION

• The drug is present in breast milk. 
• The Centers for Disease Control and Prevention recommends that HIV-1 infected mothers not breastfeed to avoid risking postnatal transmission of HIV-1 infection in HIV-negative infants or developing vial resistance in HIV- positive infants. They also do not recommend breastfeeding because of potential drug-induced adverse reactions in the infant.

Nursing Considerations

• Check to be sure the patient has been screened for the HLA-B*5701 allele prior to initiating abacavir therapy because carriers of this allele are at greater risk of developing serious and sometimes fatal hypersensitivity reactions to abacavir. Know that a past medical history of an allergic reaction to abacavir, including any abacavir-containing product, is a contraindication for the use of abacavir therapy.
• Use caution when administering abacavir to patients with known risk factors for liver disease.
• Use cautiously in patients with coronary artery disease, because an increase in myocardial infarctions has occurred within 6 months of initiating abacavir therapy.
• Be aware that a scored tablet is available for pediatric patients weighing 14 kg or more, provided the child can swallow tablets.

WARNING Monitor the patient closely for any hypersensitivity reaction. If present, notify the prescriber immediately and expect the drug to be discontinued, especially if a hypersensitivity reaction cannot be ruled out. Obesity, prolonged nucleoside exposure, and being a woman have been identified as risk factors. Know that a hypersensitivity reaction to abacavir usually presents with at least two of the following signs or symptoms:

constitutional symptoms (achiness, fatigue, generalized malaise), fever, GI symptoms (abdominal pain, diarrhea, nausea, vomiting), rash, or respiratory symptoms (cough, dyspnea, pharyngitis). Other signs and symptoms that may be present include arthralgia, edema, headache, lethargy, myalgia, myolysis, and paresthesia. Know that adult respiratory distress syndrome, anaphylaxis, hypotension, renal failure, and respiratory failure have also occurred in association with an abacavir-induced hypersensitivity reaction, and death has occurred.

• Monitor the patient’s liver enzymes periodically, as ordered, and monitor the patient for any signs and symptoms of lactic acidosis or liver dysfunction such as severe hepatomegaly with steatosis, which may become life-threatening. Be aware that incidence is higher in women and in the presence of obesity. If present, notify the prescriber, and expect abacavir therapy to be discontinued even in the absence of marked transaminase elevations.
• Be aware that immune reconstitution syndrome has occurred in patients treated with combination antiretroviral therapy, including abacavir. The inflammatory response predisposes susceptible patients to opportunistic infections such as cytomegalovirus infection, Mycobacterium avium infection, Pneumocystis jiroveci pneumonia, or tuberculosis. Autoimmune disorders such as Graves’ disease, Guillain–Barré syndrome, or polymyositis have also occurred. Report sudden or unusual adverse reactions to the prescriber.
• Observe the patient for redistribution of body fat, including breast enlargement, central obesity, development of buffalo hump, facial wasting, and peripheral wasting, which may produce a cushingoid-type appearance.

PATIENT TEACHING

• Instruct patient/parents/caregiver to administer drug exactly as prescribed. If a dose is missed, have the patient take it as soon as it is remembered. Stress importance of not doubling the next dose or taking more than the prescribed dose.

WARNING Review the warning card and medication guide with the patient/parents/caregiver on how to recognize a hypersensitivity reaction. Stress the importance of stopping abacavir at the first sign of a hypersensitivity reaction and notifying the prescriber.

• Instruct patient/parents/caregiver on the signs and symptoms of lactic acidosis and liver dysfunction. Advise patient to stop taking abacavir if present and notify the prescriber.
• Advise patient/parents/caregiver to inform prescriber of any signs or symptoms of an infection, as well as any unusual, persistent severe, or unusual adverse reactions.
• Instruct a mother not to breastfeed while she is receiving abacavir therapy.
• Warn patient that fat distribution may occur with abacavir therapy.
• Tell women of childbearing age to report a known or suspected pregnancy. Provide patient with information on pregnancy exposure registry, if pregnancy occurs.