Abacavir + Lamivudine is a fixed-dose combination tablet containing two antiretroviral medicines, abacavir (as abacavir sulfate) and lamivudine, both belonging to the nucleoside reverse transcriptase inhibitor (NRTI) class [2][3]. It is used, together with at least one other antiretroviral medicine, to treat HIV-1 infection in adults and children weighing 25 kg or more [1]. Combining two NRTIs into a single tablet means one pill covers two parts of a multi-drug HIV treatment plan instead of two separate tablets. Abacavir + Lamivudine is never used on its own; it is always one part of a larger antiretroviral regimen prescribed by a doctor [1].

HIV-1 infection is treated with a combination of antiretroviral medicines that act at different steps of the virus's life cycle. Abacavir + Lamivudine supplies two of these medicines, abacavir and lamivudine, in a single tablet. Both belong to the nucleoside reverse transcriptase inhibitor (NRTI) class, meaning they are built to resemble the natural building blocks (nucleosides) that HIV's reverse transcriptase enzyme uses to copy the virus's genetic material [2][3]. Once inside a cell, abacavir and lamivudine are converted by the body's own enzymes into their active triphosphate forms, carbovir triphosphate and lamivudine triphosphate, which are built into the growing viral DNA chain and stop it from lengthening any further, so the virus cannot keep copying itself [1].

Before anyone starts this combination, the prescribing information calls for a blood test to check for the HLA-B5701 gene variant, because carrying this gene raises the chance of a serious, sometimes fatal, hypersensitivity reaction to abacavir [1]. People who have already had a hypersensitivity reaction to abacavir, or who test positive for HLA-B5701, should not take this combination [1].

Because this is a fixed 600 mg abacavir / 300 mg lamivudine tablet, the two doses inside it cannot be adjusted separately. It is not recommended for people with a creatinine clearance below 30 mL per minute (creatinine clearance is a lab measure of how well the kidneys are filtering blood), or for those with moderate to severe liver impairment, since these patients may need lower doses of one or both components than the combination tablet can provide [1]. Lamivudine also acts against the hepatitis B virus, so anyone who has both HIV and hepatitis B needs closer monitoring, particularly around the time this medicine is started or stopped [1].

Abacavir + Lamivudine is meant to be taken long-term, once daily, as part of an HIV treatment plan rather than as a short course, and it works only when taken exactly as prescribed alongside the other medicines in the regimen [1].

Each Abacavir + Lamivudine tablet contains 600 mg of abacavir (as abacavir sulfate) and 300 mg of lamivudine [1]. Abacavir sulfate is a synthetic carbocyclic nucleoside analogue, and lamivudine is a synthetic nucleoside analogue described as the (-)enantiomer of a dideoxy analogue of cytidine. Both are HIV-1 reverse transcriptase inhibitors [1].

Abacavir + Lamivudine, in combination with other antiretroviral agents, is indicated for the treatment of human immunodeficiency virus type 1 (HIV-1) infection [1]. It is prescribed as part of a combination regimen, not as a stand-alone treatment for HIV [1]. The fixed-dose tablet is intended for adults and pediatric patients who weigh at least 25 kg; children below this weight need the individual abacavir and lamivudine components dosed separately by their doctor [1].

1. Two NRTIs in one tablet - combines abacavir and lamivudine, so one pill covers two components of a multi-drug HIV-1 treatment plan [1].
2. Once-daily dosing - adults and children weighing 25 kg or more take one tablet a day along with the rest of the regimen [1].
3. Flexible with meals - can be taken with or without food, fitting around different daily routines [2][3].
4. Established drug class - abacavir and lamivudine are both nucleoside reverse transcriptase inhibitors, a class used for many years as part of HIV combination therapy [2][3].
5. Additional activity against hepatitis B - lamivudine also suppresses hepatitis B virus replication, which is relevant for people living with both HIV and hepatitis B, managed specifically by their doctor [1].

Common Side Effects (Usually Mild)

• Headache [2]
• Tiredness [2]
• Nausea and vomiting [2]
• Difficulty falling asleep or staying asleep [2]

Serious Side Effects (Seek Urgent Medical Attention)

• Signs of a hypersensitivity reaction: fever; rash; nausea, vomiting, diarrhea, or stomach pain; unusual tiredness; sore throat, cough, or shortness of breath. This reaction can be fatal, can occur with or without the HLA-B*5701 gene variant, and this medicine must never be taken again if it happens [1][2].
• This combination carries a known class warning for nucleoside reverse transcriptase inhibitors (NRTIs) called lactic acidosis (a build-up of acid in the blood) with severe hepatomegaly (an enlarged liver) with steatosis (a fatty liver), which has been reported with this combination and can be fatal. Signs include unusual weakness, dizziness or lightheadedness, fast or irregular heartbeat, muscle pain, stomach pain with nausea and vomiting, shortness of breath, feeling unusually cold especially in the arms or legs, yellowing of the skin or eyes, dark yellow or brown urine, pale-colored stools, or pain in the upper right part of the stomach [1][3].
• Severe skin reaction: hives, itching, blistering or peeling skin, or difficulty swallowing or breathing [2].
• Worsening of hepatitis B, including after this medicine is stopped, in people who have both HIV and hepatitis B [1].

• The standard dose described in the prescribing information for adults and children weighing 25 kg or more is one tablet by mouth, once daily, taken together with at least one other antiretroviral medicine as prescribed by a doctor [1].
• Swallow the tablet whole with a glass of plain water; do not crush, split, or chew it.
• Take it at around the same time every day so the interval between doses stays consistent [3].
• It does not need to be taken on an empty stomach; food does not change how much lamivudine is absorbed, and abacavir can be taken with or without food [2][3].
• Keep taking Abacavir + Lamivudine every day, even when feeling well, unless a doctor advises stopping; missed doses can allow HIV to multiply and increase the chance of drug resistance.
• Do not stop this medicine without talking to a doctor first, particularly for anyone who also has hepatitis B, since stopping lamivudine suddenly can cause a serious flare-up of hepatitis B [1].
• Complete the full course exactly as prescribed as part of the larger antiretroviral regimen; do not stop or interrupt it without medical advice [1].
• Limit alcohol around dosing, since alcohol slows how the body clears abacavir and raises abacavir levels in the blood [1].

Abacavir is converted inside cells to its active form, carbovir triphosphate, which resembles one of the natural building blocks (deoxyguanosine triphosphate) that HIV's reverse transcriptase enzyme needs. Carbovir triphosphate blocks this enzyme both by competing with the natural building block and by being built into the viral DNA chain itself, which stops the chain from growing any further [1].

Lamivudine works in a similar way. It is converted inside cells to lamivudine triphosphate, which is also built into the growing viral DNA chain by HIV's reverse transcriptase enzyme and then stops the chain from lengthening any further [1].

Because both drugs interrupt the same enzyme at the same step, but resemble different natural building blocks, combining them as part of a larger regimen creates two separate obstacles for the reverse transcriptase enzyme instead of one. Lamivudine's triphosphate form also blocks the reverse transcriptase enzyme of the hepatitis B virus, which is why lamivudine has activity against hepatitis B as well as HIV [1].

• Take the tablet at the same time every day, with or without food [2][3].
• Do not stop this medicine without medical advice, especially for anyone who also has hepatitis B [1].
• Keep a record of the HLA-B*5701 test result and share it with any new doctor or pharmacist.
• Watch for fever, rash, or stomach upset appearing together; these can be early hypersensitivity symptoms that need same-day medical attention [1][2].
• Keep every lab-monitoring appointment scheduled for kidney, liver, and viral load checks.
• Limit alcohol, since it can raise abacavir levels in the blood [1].

Store Abacavir + Lamivudine tablets at 20 to 25 degrees C (68 to 77 degrees F); brief excursions between 15 and 30 degrees C (59 to 86 degrees F) are permitted [1]. Keep the tablets in their original, tightly closed container, away from excess heat and moisture, and out of the sight and reach of children [1][2].

Food does not change how much lamivudine the body absorbs, and abacavir can be taken with or without food [2][3]. Alcohol is the main dietary factor to watch: a standard alcohol dose reduced how quickly abacavir is cleared from the body and raised abacavir blood levels by about 41 percent in one study, so alcohol use is worth discussing with a doctor [1].

• Methadone - Some patients on methadone maintenance may need their methadone dose adjusted when taking abacavir [1].
• Sorbitol-containing medicines - Sorbitol, an ingredient in some liquid medicines, reduces lamivudine levels in the blood in a dose-dependent way; regular, long-term use of sorbitol-containing products together with this combination should be avoided where possible [1].
• Ribavirin - In laboratory studies, ribavirin reduced the ability of both lamivudine and abacavir to act against HIV by 2- to 6-fold [1].

Every other prescription medicine, over-the-counter product, and supplement taken alongside Abacavir + Lamivudine should be reviewed by a doctor or pharmacist, since not every possible interaction can be listed here.

• Hepatitis B co-infection - In people who have both HIV-1 and hepatitis B, stopping lamivudine (including as part of this combination) has been linked to severe flare-ups of hepatitis B. Liver function needs close monitoring for several months after this medicine is stopped in these patients [1].
• Kidney disease - Not recommended when creatinine clearance is below 30 mL per minute; closer monitoring is needed between 30 and 49 mL per minute [1].
• Liver disease - Contraindicated in moderate to severe liver impairment (Child-Pugh Class B or C) [1].
• Heart disease - Some observational studies have linked abacavir to a higher risk of heart attack, while meta-analyses of randomized controlled trials have not found this excess risk, so the evidence is not conclusive. Doctors are advised to factor in a patient's underlying heart disease risk, such as high blood pressure, high cholesterol, diabetes, and smoking, when prescribing abacavir-containing regimens [4].

The usual dose described in the prescribing information for adults and children weighing 25 kg or more is one tablet (600 mg abacavir / 300 mg lamivudine) once daily, taken together with at least one other antiretroviral medicine [1]. Children weighing less than 25 kg need the individual components dosed by weight rather than this fixed-dose tablet [1]. The dose actually prescribed by a doctor should always be followed exactly, without self-adjustment.

There is no specific antidote for an Abacavir + Lamivudine overdose. Treatment is supportive. It is not known whether abacavir is removed from the body by dialysis, while only a negligible amount of lamivudine is removed by hemodialysis, so dialysis is not expected to meaningfully clear either drug from the body [1]. Suspected overdose needs emergency medical attention right away.

Take the missed dose as soon as it is remembered. If it is almost time for the next dose, skip the missed one and continue with the regular schedule; two doses should never be taken together to make up for a missed one [1][2][3]. Frequent missed doses should be reported to a doctor, since missed doses can allow HIV to multiply and increase the chance of drug resistance.

Seek urgent medical attention for:

• Fever, rash, nausea, vomiting, diarrhea, stomach pain, unusual tiredness, sore throat, cough, or shortness of breath appearing together, which may signal a hypersensitivity reaction [1][2].
• Unusual weakness, dizziness, fast or irregular heartbeat, muscle pain, breathing trouble, feeling unusually cold, yellowing of the skin or eyes, or dark urine, which may signal lactic acidosis or a liver problem [1][3].
• Hives, itching, blistering, or peeling skin, or difficulty swallowing or breathing [2].
• Any worsening of symptoms in a person with hepatitis B who has recently stopped this medicine [1].
• Doses that keep getting missed, so a doctor can help find a workable routine.

Any new or worsening symptom while taking Abacavir + Lamivudine is worth reporting to a doctor promptly, even if it does not appear on this list.