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Ritonavir for HIV


Ritonavir slows the progress of HIV infection. It is one of a number of medicines that you will need to take regularly.

It has been associated with some side-effects. Your doctor will discuss these with you before you start treatment.

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About ritonavir for HIV

Type of medicine

A protease inhibitor (PI) antiretroviral medicine

Used for

Human immunodeficiency virus (HIV) infection in adults and in children aged over 2 years

Also called

Combination brand: Kaletra® (ritonavir with lopinavir)

Available as

Tablets, sachets of powder for oral suspension

Ritonavir is an antiretroviral medicine. It is prescribed for human immunodeficiency virus (HIV) infection. It slows the progress of HIV infection, but it is not a cure. HIV destroys cells in the body, called CD4 T cells. These cells are a type of white blood cell and are important because they are involved in protecting your body from infection. If left untreated, the HIV infection weakens your immune system so that your body cannot defend itself against bacteria, viruses and other germs. Ritonavir slows down the progress of HIV infection by reducing the amount of virus in your body. It does this by stopping the production of a protein that the virus needs to copy (replicate) itself.

Ritonavir will be prescribed for you by a doctor who is a specialist. It belongs to a group of antiretroviral medicines known as protease inhibitors (PIs). It is given alongside a number of other antiretroviral medicines, as part of a combination therapy. It is often prescribed to boost the action of these other antiretroviral medicines - when it is given like this, it is referred to as 'low-dose' ritonavir. Taking three or more antiretroviral medicines at the same time is more effective than taking one alone. Taking a combination of different medicines also reduces the risk that the virus will become resistant to any individual medicine. One brand of ritonavir (called Kaletra®) also contains another antiretroviral medicine called lopinavir. There is more information available about this brand in a separate medicine leaflet called Lopinavir with ritonavir for HIV.

It is vital to take your antiretroviral medicines exactly as prescribed in order to maintain success and to help to prevent the virus from becoming resistant to the medicines. These medicines are usually taken for life.

Ritonavir is also available in combination with nirmatrelvir in a medicine called Paxlovid®. It is used for the treatment of COVID-19 disease. For more information on this read our leaflet called Paxlovid tablets for COVID-19 disease.

Before taking ritonavir

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking ritonavir it is important that your doctor knows:

  • If you are pregnant, trying for a baby or breastfeeding.

  • If you have diabetes (diabetes mellitus).

  • If you are being treated for low levels of thyroid hormone (hypothyroidism).

  • If you have a heart problem or have been told you have a heart rhythm disorder.

  • If you have liver inflammation (called hepatitis), or any other liver problem.

  • If you have inflammation of the pancreas (pancreatitis).

  • If you have either haemophilia or porphyria, which are both rare inherited blood disorders.

  • If you are taking any other medicines. This includes any medicines which are available to buy without a prescription, as well as herbal and complementary medicines.

  • If you have ever had an allergic reaction to a medicine.

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How to take ritonavir

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about ritonavir, and it will also provide you with a full list of the side-effects which you could experience from taking it.

  • Take ritonavir exactly as your doctor tells you to - the directions will be printed on the label of the pack to remind you about what the doctor said to you. Depending upon which other medicines you are taking, you may be prescribed a 'high dose' of ritonavir (adult dose: six tablets twice daily), or a 'low dose' (adult dose: 1-2 tablets once or twice daily). If you are prescribed high-dose ritonavir, you will be given three tablets twice a day for three days to start with, and then your dose will be increased over the next two weeks to the maintenance dose of six tablets twice a day. Twice-daily doses should ideally be taken 12 hours apart, so take the first dose in the morning and the other in the evening.

  • If ritonavir is being prescribed for your child, the dose prescribed will depend upon your child's weight and height. Your doctor will advise you about how much you should give for each dose.

  • Tablets should be swallowed with a drink of water. Do not crush or break the tablet before you swallow - it should be swallowed whole. If you have any difficulties swallowing tablets, let your doctor know about this, as either the sachets or liquid medicine could be more suitable for you.

  • Take ritonavir after a meal or with a snack, and try to take your doses at the same times of day each day, as this will help you to remember to take it regularly.

  • If you (or your child) are using powder sachets, open the sachet and pour the 100 mg of ritonavir powder from the sachet on to soft food (such as apple sauce or vanilla pudding). Swallow the mixture within two hours. Alternatively the powder from the sachet can be mixed with 9.4 ml of liquid (water, chocolate milk, or infant formula) in the mixing cup provided. If you do this, make sure you mix the solution well, allow the bubbles to disappear, and then measure out your dose using the dosing syringe provided. Wash and dry the mixing cup and syringe after each use.

  • If you forget to take a dose, take it as soon as you remember (unless it is nearly time for your next dose, in which case do not take the forgotten dose but take the next dose when it is due). Do not take two doses together to make up for a missed dose.

Getting the most from your treatment

  • Keep your regular appointments with your doctor so that your progress can be monitored. You will need to have regular blood tests.

  • It is important that you continue to take antiretroviral treatment regularly. This will help to prevent the HIV from becoming resistant to the medicines you are taking. Even if you miss only a small number of doses, the virus can become resistant to treatment.

  • If you develop any infection soon after you start this treatment, let your doctor know. As a result of taking ritonavir, your immune system may start fighting an infection which was present before you started the treatment, but which you may not have been aware of.

  • Follow carefully any advice your doctor gives to you about making lifestyle changes to reduce any risk of damage to your heart and blood vessels. These can include stopping smoking, eating healthily and taking regular exercise.

  • Some people taking antiretroviral medicines develop changes to the way body fat is distributed in the body. This can result in changes to body image. Your doctor will discuss the possibility of this with you.

  • Although treatment with antiretroviral medicines may reduce the risk of you passing HIV to others through sexual contact, it does not stop it. It is important that you use condoms.

  • It is not uncommon for people with HIV to feel low or even depressed, especially soon after the diagnosis has been made and treatment has been started. If you have any feelings of depression, or any distressing thoughts about harming yourself then you should speak with your doctor straightaway.

  • Some people who have taken antiretroviral medicines (particularly over a long time) have developed a condition called osteonecrosis. This is a bone disease where bone tissue dies because there is a reduced blood supply to it. It leads to joint pains and stiffness, and can cause difficulties in movement. If you notice any of these symptoms, speak with your doctor.

  • If you buy any medicines, check with a pharmacist that they are suitable to take with your other medicines. This is because some medicines interfere with ritonavir, and vice versa. This can mean either that the ritonavir does not work properly, or that it increases the risk of side-effects from the other medicines. In particular, do not take St John's wort while you are on ritonavir.

  • If you have diabetes you may need to check your blood sugar (glucose) more frequently, as this medicine can affect the levels of sugar in your blood. Your doctor will advise you about this.

  • If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

  • Treatment for HIV is usually lifelong. Continue to take this medicine regularly for as long as your doctor tells you to, even if you feel well. This is to keep your immune system healthy.

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Can ritonavir cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with ritonavir. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common ritonavir side-effects (these affect more than 1 in 10 people)

What can I do if I experience this?


Drink plenty of water to replace lost fluids. If this continues or becomes severe, let your doctor know

Feeling sick (nausea) or being sick (vomiting), tummy (abdominal) pain, indigestion

Make sure you remember to take your doses after food. Stick to simple meals - avoid fatty or spicy food

Headache, muscle and back pain

Ask your doctor or pharmacist to recommend a suitable painkiller

Feeling dizzy, tired or weary

Do not drive and do not use tools or machines while affected. If this continues, speak with your doctor

Itchy rash, feeling hot and flushed, changes in the way things taste, tingling sensations, cough, and throat infections

If any of these become troublesome, speak with your doctor

Important: some people taking ritonavir have developed inflammation of the pancreas (pancreatitis) - the most common signs of this are persistent stomach pain, feeling sick (nausea) or being sick (vomiting), high temperature (fever), and feeling generally unwell. Let your doctor know straightaway if you develop these symptoms.

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

How to store ritonavir

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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