It was developed in the late 1980s and approved for medical use in the mid-1990s, becoming one of the first effective drugs targeting the HIV protease enzyme. Its history is notable for its ability to suppress viral replication and improve immune function in patients with HIV, but also for challenges related to adherence due to frequent dosing and potential nephrotoxicity. Indinavir was approved in the United States in 1996 and has been included in multiple combination antiretroviral therapies (cART). Its development included accelerated approval programs, enabling early clinical use and monitoring of efficacy and safety in HIV-infected patients.
Brand Names
Indinavir is marketed under several brand names depending on formulation and region:
Crixivan – the most widely known oral capsule formulation
Indinavir sulfate – generic formulations in some countries
MECHANISM OF ACTION
Indinavir is a protease inhibitor that targets the HIV-1 protease enzyme, which is essential for the cleavage of viral polyproteins into functional proteins. By inhibiting this enzyme, Indinavir prevents the maturation of viral particles, resulting in the production of immature, non-infectious HIV virions.
PHARMACOKINETICS
Absorption
Indinavir is well absorbed orally, with peak plasma concentrations occurring approximately 1–2 hours after a single dose when taken on an empty stomach. Its oral bioavailability is reduced by high-fat meals, so it is generally recommended to take Indinavir either 1 hour before or 2 hours after meals to ensure optimal absorption.
Distribution
Indinavir is widely distributed throughout the body after absorption. It is approximately 60% protein-bound in plasma, which influences its free, active concentration. The drug readily penetrates lymphatic tissue, the gastrointestinal tract, and genital secretions, which are key sites of HIV replication.
Metabolism
Indinavir is extensively metabolized in the liver, primarily via the cytochrome P450 enzyme CYP3A4. Hepatic metabolism converts Indinavir into several inactive metabolites, which are then excreted in the urine and feces.
Elimination
Indinavir is primarily eliminated via the kidneys, with approximately 20% of the administered dose excreted unchanged in urine. The majority of the drug is metabolized hepatically and excreted as inactive metabolites in both urine and feces.
PHARMACODYNAMICS
Indinavir exerts its antiretroviral effects by selectively inhibiting the HIV-1 protease enzyme, which is essential for cleaving viral polyproteins into functional structural and enzymatic proteins. This inhibition prevents the maturation of new viral particles, leading to the production of immature, non-infectious virions.
ADMINISTRATION
Indinavir is administered orally as capsules, usually taken every 8 hours due to its short half-life. To maximize absorption, it should be taken on an empty stomach, either 1 hour before or 2 hours after meals. Patients are advised to maintain adequate hydration to reduce the risk of kidney stones, a known adverse effect. Indinavir is typically used as part of combination antiretroviral therapy (cART), and strict adherence to the dosing schedule and hydration guidelines is essential to ensure therapeutic effectiveness and safety.
DOSAGE AND STRENGTH
Indinavir is typically administered to adults at a dose of 800 mg orally every 8 hours as part of combination antiretroviral therapy. In regimens boosted with ritonavir, the dose may be reduced to 400 mg every 12 hours due to increased plasma concentrations. Indinavir is available in capsules of 100 mg and 200 mg, with tablets of 400 mg available in some regions.
DRUG INTERACTIONS
Indinavir has significant potential for drug interactions due to its metabolism by CYP3A4. Drugs that inhibit CYP3A4, such as ketoconazole, ritonavir, or clarithromycin, can increase Indinavir plasma levels, raising the risk of toxicity, including kidney stones and hyperbilirubinemia. Conversely, CYP3A4 inducers like rifampin, phenytoin, or carbamazepine can reduce drug levels, decreasing antiviral efficacy and increasing the risk of HIV resistance.
FOOD INTERACTIONS
Indinavir absorption is significantly affected by food, with high-fat or large meals reducing bioavailability. For optimal absorption, the drug should be taken on an empty stomach, typically 1 hour before or 2 hours after eating. Patients are also advised to maintain adequate hydration to reduce the risk of kidney stones, a known adverse effect.
CONTRAINDICATIONS
Indinavir is contraindicated in patients with a known hypersensitivity to Indinavir or any component of the formulation. It should not be used in patients with severe renal impairment without careful monitoring, as the drug can exacerbate renal complications. Caution is required in individuals with hepatic impairment, history of kidney stones, or other conditions that predispose to nephrolithiasis. Indinavir is also contraindicated in patients taking strong CYP3A4 inducers or inhibitors that cannot be safely managed, due to the risk of subtherapeutic levels or toxicity.
Side Effects
Kidney stones (nephrolithiasis)
Increased bilirubin levels (hyperbilirubinemia)
Nausea and vomiting
Diarrhea
Headache
OVER DOSAGE
Overdose of Indinavir is uncommon, but when it occurs it mainly leads to an exaggeration of its known toxic effects. Patients may present with severe nausea, vomiting, abdominal pain, dizziness, and dehydration. One of the most important concerns is renal toxicity, as excess drug can increase the risk of crystal formation in the urinary tract, potentially leading to flank pain, hematuria, and even acute kidney injury.
TOXICITY
Indinavir toxicity primarily affects the renal and hepatic systems. Overdose or prolonged high plasma concentrations can lead to severe nephrolithiasis, crystalluria, acute kidney injury, and hyperbilirubinemia. Hepatic toxicity, including elevated liver enzymes and rare cases of hepatotoxicity, may occur, especially in patients with preexisting liver disease. Other systemic effects can include hyperglycemia, lipid abnormalities, and gastrointestinal disturbances.
