It is an inhibitor of the enzyme human immunodeficiency virus protease which is required for the proteolytic cleavage of the viral polyprotein precursors into the individual functional proteins found in infectious HIV.

Ritonavir is a peptide analogue. It reversibly binds to the catalytic site of HIV encoded aspartyl protease enzyme which is involved in the degradation of poly protein into structural protein and subsequent maturation of virus particle. Binding of Ritonavir to the enzyme results in immature noninfectious viral progeny.

Pharmacokinetics
Absorption: It is rapidly absorbed after oral administration. Distribution: It is distributed as protein bound form. Metabolism: It undergoes metabolism in the liver. Excretion: It is excreted primarily through faeces and small amount through urine.

Half Life
3- 5 hours

Adverse Effects
1. Diarrhoea
2. Anorexia
3. Nausea
4. Vomiting
5. Abdominal pain
6. Paresthesia
7. Rash
8. Dizziness
9. Headache
10.Thrombocytopenia
11. Taste disturbances

ContraIndications
Hypersensitivity to Ritonavir

Special Precautions
1. Hepatic dysfunction
2. Diabetes mellitus
3. Haemophilia
4. Patient with high cholesterol and triglycerides level

Pregnancy
Use with caution

Breast Feeding
Contraindicated

Elderly
Use with caution

Children
Use with caution
Below 12: Contraindicated

Interactions
Analgesics: Plasma concentration of dextroprop-oxyphene, pethidine and piroxicam increased (risk of toxicity-avoid concomitant use); plasma concentrations of other opioid analgesics (except methadone) and other NSAIDs possibly increased; plasma concentration of methadone reduced.
Anti-arrhythmics: Increased plasma concentration of amiodarone, flecainide, propafenone and quinidine (increased risk of ventricular arrhythmias-avoid concomitant use); possibly increased risk of arrhythmias with disopyramide and mexiletine.
Antibacterials: Plasma concentration of rifabutin increased by ritonavir (risk of uveitis-avoid concomitant use); plasma concentration of clarithromycin and possibly other macrolides increased.
Anticoagulants: Plasma concentration of warfarin and other anticoagulants possibly increased  by ritonavir.
Antidepressants: Plasma concentration of SSRIs and tricyclics possibly increased; plasma concentration reduced by St John s wort (avoid concomitant use).
Antidiabetics: Plasma concentration of tolbutamide possibly increased.
Antiepileptics: Plasma concentration of carbamazepine possibly increased.
Antifungals: Plasma concentration of ketoconazole and possibly other imidazoles and triazoles increased.
Antihistaminics: Increased risk of arrhythmias with terfenadine - avoid concomitant use.
Antipsychotics: Increased plasma concentration of pimozide (risk of ventricular arrhythmias); increased plasma concentration of clozapine.
Other antivirals: Combination with nelflnavir may lead to increased plasma concentration of either drug; ritonavir increases plasma concentration of indinavir and saquinavir; increased risk of toxicity with efavirenz (monitor liver function tests).
Anxiolytics and Hypnotics: Plasma concentration of alprazolam, clorazepate, diazepam, flurazepam, midazolam and zolpidem increased.
Ergotamine and Ergometrine: Risk of ergotism-avoid concomitant use.
5HT1 Agonists: Plasma concentration of eletriptan increased (avoid concomitant use).
Lipid-regulating Drugs: Increased risk of myopathy with simvastatin.
Oestrogens and Progestogens: metabolism accelerated by ritonavir (contraceptive effect of combined oral contraceptives reduced).
Theophylline: Metabolism accelerated by ritonavir  (reduced plasma-theophylline concentration).

Indications
HIV infection

Dosage
Adult 1.2 g / day in 2 divided dose; given with other antiretroviral agents.

Storage
Keep at 2 - 8 degree C for long term storage. If the drug is used with in 1 month then it can be store at 15 - 30 degree C in a tightly closed container. Protect away from heat and light. Keep out of the reach of Children.

Missed Dose
Take the missed dose as soon as noticed and if it is the time to take the next dose then skip the missed dose.

Over Dose
Give supportive measures and treatment. Induce emesis or gastric lavage has to be done followed by charcoal administration.