Ritonavir belongs to the class of antiretroviral medications called protease inhibitors (PIs). Ritonavir is used in combination with other HIV medications to treat the infection caused by the human immunodeficiency virus (HIV) for adults and children more than 2 years old. 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.

Ritonavir works by blocking the action of protease, an enzyme that the virus needs to multiply. Ritonavir does not cure AIDS and does not prevent it from being spread to others. It does slow further growth or reproduction of HIV when used in combination with other medications, and it seems to slow down the destruction of the immune system. This may help to delay the development of problems that are related to AIDS or HIV infection.

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 adult dose of ritonavir is 600 mg taken 2 times daily. For children 2 to 16 years old, the dosage is based on body size. The recommended dose of ritonavir is 400 mg per square metre (m²) of body surface area (to a maximum of 600 mg per dose) as calculated by the doctor. Ritonavir is taken in combination with other anti-HIV medications.

The doctor may start the medication at a lower dose and increase it to the recommended dose so that side effects are minimized.

Many things can affect the dose of 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.

Ritonavir should be taken with meals if possible. Tablets should be swallowed whole and not crushed or chewed.

If you are using ritonavir solution, use a calibrated delivery device to ensure an accurate dose. If you use the dosage cup provided with the medication, clean the cup with hot water and dish soap immediately after taking a dose to remove any medication residue. Make sure your measuring device is dry before using it for the next dose.

Shake the solution well before measuring a dose. To help cover the taste of the medication, ritonavir solution may be mixed with chocolate milk or a liquid nutritional supplement. If you mix the medication with chocolate milk, take the dose within 1 hour of preparing it.

It is important to take this medication 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.

If you forget many doses in a row, talk to your doctor about how to resume dosing.

Ritonavir tablets and solution should be stored at room temperature. Keep them in their original containers. Do not refrigerate the solution and avoid exposure of the medication to excessive heat.

Keep this and all medication out of the reach of children.

Each white-to-off-white, film-coated, ovaloid tablet, debossed with "I" on one side and "100" on the other side, contains 100 mg of ritonavir. Nonmedicinal ingredients: calcium hydrogen phosphate anhydrous, calcium hydrogen phosphate dihydrate, copovidone, maize starch, mannitol, microcrystalline cellulose, silicified microcrystalline cellulose (Prosolv SMCC 50), silicified microcrystalline cellulose (Prosolv SMCC 90), powdered cellulose, sodium stearyl fumarate, and sorbitan laurate; film coating: Aquarius Prime BAP 118010 (titanium oxide, talc, polyethylene glycol, and polysorbate).

Do not use this medication if you:

• are allergic to ritonavir or any ingredients of this medication
• are taking any of the following medications:
• alfuzosin
• amiodarone
• astemizole
• cisapride
• colchicine
• dihydroergotamine
• dronedarone
• ergonovine
• ergotamine
• flecainide
• fusidic acid
• lovastatin
• lurasidone
• methylergonovine
• midazolam taken by mouth
• pimozide
• propafenone
• quinidine
• rivaroxaban
• salmeterol
• sildenafil
• simvastatin
• St. John's wort
• terfenadine
• triazolam
• vardenafil
• venetoclax
• voriconazole

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.

• abdominal pain
• change in sense of taste
• diarrhea
• dizziness
• fatigue
• headache
• loss of appetite
• nausea
• rash
• sleepiness
• vomiting
• weakness

Although most of the 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:

• increased cholesterol or triglycerides (fats in the blood)
• numbness or tingling feeling in the hands or feet
• numbness or tingling feeling around the mouth
• signs of bleeding (e.g., unusual bleeding or bruising, bleeding gums, unexplained nosebleeds)
• signs of diabetes or increased blood sugar, e.g.:
• cuts that don't heal
• fruity mouth odour
• increased thirst
• increased urination
• signs of infection (e.g., fever or chills, sore throat, cough)
• signs of liver problems, e.g.:
• dark urine
• diarrhea
• loss of appetite
• nausea
• pale stools
• vomiting
• weight loss
• yellowing of the skin or whites of the eyes

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

• chest pain
• signs of a serious allergic reaction, e.g.:
• abdominal cramps
• difficulty breathing
• nausea and vomiting
• swelling of the face and throat
• signs of a severe skin reaction, e.g.:
• a rash combined with fever or discomfort
• a rash covering a large area of the body
• a rash that spreads quickly
• blistering
• peeling
• signs of pancreatitis, e.g.:
• abdominal pain on the upper left side
• back pain
• chills
• fever
• nausea
• rapid heartbeat
• swollen abdomen

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.

Birth control: Birth control pills may be less effective while taking this medication. Talk to your doctor or pharmacist about forms of birth control that may be more reliable.

Diabetes: Ritonavir can cause diabetes or increase blood sugar levels. If you have diabetes, 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 required.

If you experience symptoms of diabetes, such as frequent urination or increased thirst, or a fruity odour to your breath, contact your doctor.

Heart conditions: Ritonavir may cause unusual heart rhythms. If you have heart disease or abnormal heart rhythms, 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.

Hemophilia: Ritonavir may put people with hemophilia at a higher risk of bleeding. If you have hemophilia, 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.

Hepatitis B or C: People who have hepatitis B or hepatitis C are more likely to experience decreased liver function and side effects involving the liver when they are taking ritonavir. If you have hepatitis B or C, 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.

If you experience symptoms of worsening liver function such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Immune reconstitution 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.

Liver function: Ritonavir is removed from the body by the liver and may cause liver problems. 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.

Ritonavir can also cause decreased liver function. 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.

Pancreatitis (inflammation of the pancreas): Ritonavir may cause or worsen pancreatitis. If you have a history of or are at risk for developing pancreatitis, you should be closely monitored by your doctor while taking this medication. If you develop signs of pancreatitis (e.g., upper left abdominal pain, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen), contact your doctor.

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. The oral solution should not be used during pregnancy due to the alcohol and propylene glycol content.

Breast-feeding: Ritonavir passes into breast milk. Breast-feeding is not recommended by HIV-positive women since the virus can be transmitted through breast milk.

Children: The safety and effectiveness of this medication have not been established for children under the age of 2 years.

Seniors: There is an increased risk of liver, kidney, or heart problems for seniors taking ritonavir. Your doctor should closely monitor you for these problems while you are taking ritonavir.

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

• abiraterone
• aliskiren
• almotriptan
• alpha-blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
• amiodarone
• anticancer medications (e.g., cabazitaxel, docetaxel, doxorubicin; etoposide, ifosfamide, irinotecan, vincristine)
• antipsychotics (e.g., aripiprazole, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apixaban
• aprepitant
• atomoxetine
• atovaquone
• "azole" antifungals (fluconazole, itraconazole, voriconazole)
• benzodiazepines (e.g., alprazolam, diazepam, lorazepam, midazolam)
• birth control pills
• bosentan
• bromocriptine
• buprenorphine
• bupropion
• buspirone
• calcitriol
• calcium channel blockers (e.g., amlodipine, nifedipine, verapamil)
• canagliflozin
• cannabis
• carvedilol
• cetirizine
• chloroquine
• cobicistat
• colchicine
• conivaptan
• corticosteroids (e.g., budesonide, dexamethasone, fluticasone, methylprednisolone, prednisone)
• cyclosporine
• dabigatran
• dantrolene
• dapsone
• darifenacin
• deferasirox
• dextromethorphan
• digoxin
• dipyridamole
• disopyramide
• disulfiram
• domperidone
• dronedarone
• dutasteride
• edoxaban
• enzalutamide
• eplerenone
• ergot derivatives (e.g., dihydroergotamine, ergotamine, ergonovine, methylergonovine)
• estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
• everolimus
• flecainide
• flutamide
• fusidic acid
• garlic
• "gliptin" diabetes medications (e.g., linagliptin, saxagliptin, sitagliptin)
• grazoprevir
• guanfacine
• hepatitis C antivirals (e.g., asunaprevir, daclatasvir, elbasvir, velpatasvir)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delavirdine, efavirenz, etravirine, nevirapine)
• other HIV protease inhibitors (e.g., atazanavir, indinavir, saquinavir)
• insulin
• lidocaine
• lomitapide
• loperamide
• losartan
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• maraviroc
• mefloquine
• metoprolol
• metronidazole
• mexiletine
• mifepristone
• mirabegron
• mirtazapine
• modafinil
• montelukast
• narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone)
• nefazodone
• nitrates (e.g., isosorbide mononitrate, isosorbide dinitrate)
• phenobarbital
• phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pioglitazone
• prasugrel
• praziquantel
• primaquine
• procainamide
• progestins (e.g., dienogest, levonorgestrel, medroxyprogesterone, norethindrone)
• propafenone
• propranolol
• proton pump inhibitors (e.g., lansoprazole, omeprazole)
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, norfloxacin, ofloxacin)
• ranitidine
• repaglinide
• rifabutin
• rifampin
• riociguat
• rivaroxaban
• romidepsin
• rosiglitazone
• salmeterol
• seizure medications (e.g., carbamazepine, gabapentin, levetiracetam, phenytoin, topiramate)
• selective serotonin reuptake inhibitors (e.g., fluoxetine, paroxetine, sertraline)
• serotonin antagonists (anti-emetic medications; e.g., granisetron, ondansetron)
• serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., desvenlafaxine, duloxetine, venlafaxine)
• solifenacin
• sotalol
• "statin" cholesterol-lowering medications (e.g., atorvastatin, lovastatin, simvastatin)
• St. John's wort
• tacrolimus
• tamoxifen
• tetrabenazine
• tetracycline
• theophylline
• ticagrelor
• ticlopidine
• tolterodine
• tolvaptan
• tramadol
• trazodone
• tretinoin
• tricyclic antidepressants (e.g., amitriptyline, desipramine, nortriptyline)
• trimethoprim
• tyrosine kinase inhibitors (e.g., bosutinib, dasatinib, imatinib, nilotinib)
• ulipristal
• warfarin
• zolpidem
• zopiclone

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.