Abacavir, also known by the abbreviation ABC, is a nucleoside reverse transcriptase inhibitor (NRTI) used to treat HIV-1 infection. It is never used alone; doctors always prescribe it together with other antiretroviral medicines as part of a combination regimen, sometimes as a single co-formulated tablet with drugs such as lamivudine or dolutegravir. Abacavir slows down the ability of HIV to make copies of itself, helping keep the amount of virus in the blood low. Before starting Abacavir, doctors test patients for a gene variant called HLA-B*5701, because carrying it raises the risk of a serious hypersensitivity reaction to the drug.

Abacavir belongs to the nucleoside reverse transcriptase inhibitor (NRTI) class of antiretroviral medicines and is a guanosine analogue, meaning it is a lab-made copy of guanosine, one of the natural building blocks the body normally uses to build DNA. Inside the body it is converted into its active form, carbovir triphosphate (the activated form of the drug that actually does the work inside cells), which blocks the HIV enzyme reverse transcriptase by competing with the virus's natural building blocks and getting incorporated into the growing viral DNA chain, stopping the chain from being completed. Because HIV cannot replicate without this enzyme, viral copying slows down considerably.

Abacavir is approved for HIV-1 infection in adults and in children older than 3 months, always combined with other antiretroviral agents rather than used by itself. It is manufactured as film-coated tablets and as an oral solution, giving flexibility for adults and for younger children who cannot swallow tablets.

The single most important safety consideration with Abacavir is a serious, sometimes fatal, hypersensitivity reaction that is strongly linked to a genetic marker called HLA-B5701. Because of this, screening for the HLA-B5701 allele before the first dose is standard practice, and the medicine is contraindicated in anyone who tests positive for it or who has had a hypersensitivity reaction to it before. Abacavir also carries warnings for lactic acidosis and severe enlargement of the liver with fatty change, effects that have been reported with this class of nucleoside analogue drugs. Because of this safety profile, Abacavir is prescribed and monitored only under medical supervision, with regular blood tests to track liver function and overall response to treatment.

Abacavir is indicated for:

• Treatment of HIV-1 infection in adults, always combined with other antiretroviral medicines as part of a complete regimen.
• Treatment of HIV-1 infection in children older than 3 months, dosed by weight and combined with other antiretroviral agents.
• Use within single-tablet combination regimens, where it is co-formulated with other antiretrovirals such as lamivudine or dolutegravir to simplify a patient's daily regimen.

Abacavir is never prescribed as a stand-alone treatment for HIV-1; it works only as one component of a multi-drug antiretroviral combination.

1. Blocks HIV replication: As an NRTI, Abacavir interferes with the reverse transcriptase enzyme HIV needs to copy its genetic material, helping to reduce the amount of virus in the blood when used in combination therapy.
2. Flexible once-daily or twice-daily dosing: Abacavir can be given as 600 mg once a day or as 300 mg twice a day, giving doctors options that fit a patient's routine.
3. Available in tablet and liquid forms: A film-coated tablet and a 20 mg/mL oral solution mean the medicine can be used across a wide age range, including children older than 3 months.
4. Fits into single-tablet regimens: Abacavir is commonly co-formulated with other antiretrovirals, such as lamivudine and dolutegravir, into single combination tablets that reduce the number of pills a patient has to take.
5. No dose change needed for kidney disease: Abacavir does not require dose adjustment in patients with reduced kidney function and is described as well tolerated in this group, making it a practical option for people with existing renal impairment.

Common Side Effects (Usually Mild and May Lessen With Continued Use)

• Nausea
• Headache
• Fatigue
• Sleep disturbances
• In children: fever, rash, and gastrointestinal symptoms have been reported more often than in adults

Serious Side Effects (Seek Urgent Medical Attention)

• Signs of a hypersensitivity reaction: fever and rash together with any of the following - nausea, vomiting, diarrhoea or abdominal pain; generalised tiredness or body ache; shortness of breath, cough, or sore throat
• Severe hypersensitivity reactions that have involved anaphylaxis (a sudden, severe, whole-body allergic reaction that can be life-threatening), liver failure, kidney failure, or respiratory failure
• Symptoms consistent with lactic acidosis or severe liver enlargement with fatty change (hepatomegaly with steatosis), which have been reported, including fatal cases, with this class of nucleoside analogue medicines. The label lists these warning symptoms to watch for: feeling very weak or unusually tired, unexplained muscle pain, trouble breathing, nausea and vomiting with stomach pain, feeling cold especially in the arms and legs, feeling dizzy or light-headed, and a fast or irregular heartbeat

• Abacavir tablets are film-coated and are meant to be swallowed whole with water; they should not be crushed, chewed, or broken unless a doctor or pharmacist has specifically said this is safe for a particular product.
• The oral solution is measured using the dosing device supplied with the medicine, not an ordinary kitchen spoon, so that each dose is accurate.
• Abacavir is always taken as one part of a complete antiretroviral combination; the other prescribed medicines in the regimen must be taken alongside it, not in place of it.
• The full course, as prescribed, should be completed and continued exactly as advised, since HIV treatment works by keeping the virus suppressed on an ongoing basis.
• Any change to the regimen, including stopping the medicine, should only happen after discussing it with the treating doctor.
• Abacavir tablets or solution are swallowed with plain water and can be taken with or without food, since food has not been shown to have a clinically relevant effect on how the drug is absorbed.
• Whichever schedule a doctor prescribes, once daily or twice daily, it helps to take each dose at the same time every day so that the medicine keeps working evenly through the regimen.

Abacavir is a nucleoside reverse transcriptase inhibitor (NRTI) and a guanosine analogue. Once inside cells, it is converted through several enzymatic steps into its active form, carbovir triphosphate. This active form competes with the body's natural nucleotide building blocks for incorporation into the DNA that HIV's reverse transcriptase enzyme is building from the virus's RNA. When carbovir triphosphate is used instead of the natural building block, it stops the DNA chain from growing any further. Because the virus cannot complete this step, it cannot finish copying itself, which slows the spread of infection to new cells. The active metabolite has a half-life of more than 20 hours inside cells, which is part of why once-daily dosing is possible even though the parent drug itself clears from plasma more quickly.

• Get the HLA-B*5701 test done before the first dose if it has not already been performed.
• Keep taking the medicine at the same time each day, with or without food.
• Learn the early signs of a hypersensitivity reaction (fever, rash, nausea, tiredness, breathing trouble) so they can be recognised quickly.
• Never restart Abacavir after a suspected hypersensitivity reaction without the treating doctor's involvement.
• Keep all other prescribed antiretroviral medicines going alongside Abacavir; do not stop any of them without medical advice.
• Attend scheduled blood tests, since these track liver function and overall treatment response.
• Ask a doctor before combining Abacavir with any new medicine, including over-the-counter products.

Store Abacavir at room temperature, between 20°C and 25°C (68°F to 77°F). Keep it away from excess light and moisture, in its original container, and out of the sight and reach of children and pets.

Food has not been shown to have a clinically relevant effect on Abacavir absorption, so it can be taken with or without meals. Alcohol is the notable exception: drinking alcohol while taking Abacavir raises Abacavir blood levels (a documented 41% increase in total exposure), so alcohol use should be discussed with the prescribing doctor rather than treated as an ordinary dietary choice.

• Methadone: Abacavir can lower methadone levels in the body, and some patients may need an increased methadone dose; this should be managed by the prescribing doctor.
• Alcohol/ethanol: Co-administration increases Abacavir's total exposure (AUC) by about 41% and extends its half-life by about 26%, though Abacavir does not appear to change how alcohol itself is processed.
• Ribavirin: In laboratory (cell culture) studies, ribavirin did not change Abacavir's anti-HIV-1 activity.
• Abacavir should only be combined with other medicines, including other HIV drugs, herbal products, and over-the-counter medicines, under the guidance of the treating doctor, since it is always used as part of a multi-drug antiretroviral regimen.

• **Prior hypersensitivity or HLA-B*5701 positive status:** Abacavir must not be used in anyone who has previously had a hypersensitivity reaction to it or who tests positive for the HLA-B*5701 allele.
• Moderate to severe liver impairment: Abacavir is contraindicated in this group; mild liver impairment requires a reduced dose under medical supervision.
• Cardiovascular risk factors: Abacavir-containing regimens should be used with caution in people with a high risk of cardiovascular disease, and this should be discussed with the treating doctor.
• Kidney disease: No specific dose change is required, and Abacavir is described as generally well tolerated in patients with renal impairment, even though its pharmacokinetics have not been formally studied in this group.

Product labelling describes an adult dose of 600 mg once daily or 300 mg twice daily, always taken as part of a combined antiretroviral regimen. In patients with mild liver impairment, this is reduced to 200 mg twice daily. Children older than 3 months are given a lower, weight-based dose decided individually by their doctor. The exact dose, timing, and any adjustment always depend on what the prescribing doctor has decided for a specific patient, and the label-directed dose should never be changed without medical advice.

There is no known specific treatment for an Abacavir overdose. If an overdose is suspected, the person should be monitored and given standard supportive medical care as needed. Anyone who may have taken more Abacavir than prescribed should contact a doctor, go to the nearest emergency department, or call a poison control helpline right away.

If a dose is missed, take it as soon as it is remembered on the same day. If it is almost time for the next scheduled dose, skip the missed one and continue with the regular schedule. Do not take two doses together to make up for a missed one. Missing doses regularly can allow HIV to become harder to treat, so a missed dose pattern should be discussed with the treating doctor.

Contact a doctor immediately, or seek emergency care, if any of the following occur:

• Fever and rash appearing together, especially with nausea, vomiting, diarrhoea, abdominal pain, unusual tiredness, body ache, shortness of breath, cough, or sore throat, since these can be signs of a hypersensitivity reaction
• Any hypersensitivity symptoms that have occurred before while taking Abacavir; the medicine should never be restarted after such a reaction without the doctor's involvement, since restarting can cause more severe symptoms, including death, within hours
• Signs of lactic acidosis or severe liver problems: feeling very weak or unusually tired, unexplained muscle pain, trouble breathing, nausea and vomiting with stomach pain, feeling cold especially in the arms and legs, feeling dizzy or light-headed, or a fast or irregular heartbeat
• Signs of serious liver problems or unexplained severe illness
• Any new or worsening symptom that feels serious after starting Abacavir