Abacavir belongs to a class of medications called nucleoside reverse transcriptase inhibitors (NRTI). Reverse transcriptase is a part of the human immunodeficiency virus (HIV) which is required to infect cells and make more of the virus. Abacavir prevents reverse transcriptase from working properly. Abacavir is used in combination with other medications to reduce the HIV in your blood. HIV is the virus responsible for acquired immune deficiency syndrome (AIDS). HIV infection destroys CD4 (T) cells, which are important to the immune system. The immune system helps fight infections.

Abacavir does not cure AIDS and does not prevent it from being spread to others. It is used in combination with other anti-HIV medications to slow further growth or reproduction of HIV and it seems to slow down the destruction of the immune system.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose for adults, adolescents, and children who weigh at least 25 kg is 600 mg daily. This may be taken as 300 mg taken twice a day or 600 mg taken once a day.

The recommended dose for children older than 3 months, and who weigh less than 25 kg is based on body weight. The usual dose is 8 mg per kilogram of body weight taken 2 times a day, up to a maximum dose of 300 mg taken twice daily. Alternatively, a once daily dose of 16 mg per kg of body weight may be taken, up to a maximum of 600 mg once daily.

Abacavir may be taken with food or on an empty stomach. It must be taken in combination with other medications to treat HIV infection.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store both the tablet and the liquid forms of this medication at room temperature, and keep them out of the reach of children.

Each yellow, modified-capsule-shaped, scored, biconvex, film-coated tablet engraved with "APO" on one side and "AB" bisect "300" on the other side contains abacavir sulfate equivalent to 300 mg of abacavir. Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, hydroxy propylmethyl cellulose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, titanium dioxide, and yellow iron oxide.

Do not take abacavir if you:

• are allergic to abacavir or any ingredients of the medication
• have the HLA-B*5701 gene variation
• have moderately-to-severely reduced liver function

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• fever
• headache
• lack of energy
• loss of appetite
• nausea
• rash (without any other symptoms)
• unusual tiredness or weakness
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• signs of autoimmune disorder or immune reconstitution inflammatory syndrome (e.g., high temperature, redness, rash, fatigue, joint pain, numbness, tingling or weakness, rapid or pounding heartbeat, yellowing of eyes or skin, muscle weakness)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• severe skin rash, including skin blistering and peeling (possibly with headache, fever, coughing, or aching before the rash begins)
• signs of a serious allergic reaction including two or more of the following sets of symptoms:
• fever
• skin rash
• nausea, vomiting, diarrhea, or abdominal pain
• severe tiredness, achiness, or general ill feeling
• sore throat, shortness of breath, or coughing
• signs of lactic acidosis (muscle pain, nausea and vomiting, weakness, abdominal pain, difficulty breathing, rapid breathing, loss of appetite)
• signs of a heart attack (e.g., chest pain or pressure, pain extending through shoulder and arm, nausea and vomiting, sweating)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Allergic reactions: At the time of receiving this medication, make sure you are given a leaflet and warning card that will help you to recognize the signs and symptoms of allergy to abacavir. Abacavir can cause a severe allergic reaction, which may be life-threatening, and should be treated as a medical emergency. The symptoms usually appear within the first 6 weeks of treatment, but may occur at any time while you are taking the medication. People who suffer an allergic reaction to abacavir should never take the medication again. Some people are at higher risk of this allergic reaction. Your doctor can perform a blood test to see if you are at greater risk. If you have 2 or more of the following sets of symptoms, you may be experiencing a serious allergic reaction:

• fever
• nausea, vomiting, diarrhea, or abdominal pain
• severe tiredness, aches, or generally feeling ill
• skin rash
• sore throat, shortness of breath, or coughing

Autoimmune conditions: Like other HIV medications, abacavir can cause other serious and possibly life-threatening autoimmune conditions, including autoimmune liver disease, thyroid disease, muscle disorders (polymyositis), or Guillain-Barre syndrome. Your doctor will order blood tests to monitor for changes that could signal the development of one of these conditions. If you experience any unusual or unexpected effects, contact your doctor to have these effects checked out.

Cholesterol: Abacavir can cause increases in cholesterol and other lipids in the blood. If you are at any increased risk of developing increased blood lipids, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Diabetes: Abacavir may cause an increase in blood sugar levels (may cause a loss of blood glucose control) and glucose tolerance may change. If you have diabetes, you may need to monitor your blood sugar more frequently while using this medication.

Fructose: Abacavir oral solution contains sorbitol, which gets changed to fructose in the body. If you have hereditary fructose intolerance, the oral solution is not recommended.  

Heart attack: The use of abacavir is associated with an increased risk of heart attack. Due to this increased risk, if you have any of the following conditions or risk factors, tell your doctor about them:

• diseases that increase your risk of heart disease, such as high blood pressure and diabetes
• heart problems
• smoking

Immune reconstitution inflammatory syndrome: This medication may cause immune reconstitution syndrome, where signs and symptoms of inflammation from previous infections appear. These symptoms occur soon after starting anti-HIV medication and can vary. They are thought to occur as a result of the immune system improving and being able to fight infections that have been present without symptoms (such as pneumonia, herpes, or tuberculosis). Report any new symptoms to your doctor immediately.

Lactic acidosis and enlarged liver: This medication can cause a rare but serious condition called lactic acidosis, together with an enlarged fatty liver. You may be more likely to experience these problems if you are female, obese, have known risk factors for liver disease, or have been taking medications such as abacavir for a long time. If you experience weakness, loss of appetite, sudden unexplained weight loss, abdominal pain, and difficulty breathing or rapid breathing, contact your doctor immediately or seek immediate medical attention.

Liver function: Abacavir is removed from the body by the liver. As a result, liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. People with moderately-to-severely reduced liver function should not take abacavir. If you have liver disease or decreased liver function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Abacavir may also cause liver problems. If you experience symptoms of liver problems (e.g., abdominal pain, persistent vomiting, feeling unwell, fever, itching, yellowing of the skin and eyes, dark urine), contact your doctor immediately.

Stopping the medication: If you stop taking this medication, your HIV infection could get worse. Take the medication exactly as prescribed by your doctor, and do not stop taking the medication without checking with your doctor first.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication may pass into breast milk and affect your baby. Since HIV can be transmitted by breast milk, women who have HIV infection should not breast-feed because of the risk of passing HIV to a baby who does not have the infection.

Children: The safety and effectiveness of this medication have not been established for children less than 3 months of age.

Seniors: Seniors are more likely to have reduced kidney, liver, and heart function, putting them at increased likelihood of experiencing side effects. They may require lower doses. The safety and effectiveness of once-daily doses of abacavir have not been studied for people more than 65 years of age and should therefore be avoided.

There may be an interaction between abacavir and any of the following:

• alcohol
• cladribine
• methadone
• orlistat
• protease inhibitors (e.g., atazanavir, lopinavir, ritonavir)
• retinoids (medications that are chemically related to vitamin A; e.g., isotretinoin)
• riociguat

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.