Ritonavir is a synthetic HIV-1 protease inhibitor and antiretroviral active pharmaceutical ingredient. It is also widely used as a pharmacokinetic enhancer because of its potent inhibition of CYP3A-mediated drug metabolism. This pharmacokinetic-boosting property is particularly important when Ritonavir is administered with other antiviral agents.
Ritonavir has the molecular formula C₃₇H₄₈N₆O₅S₂ and a molecular weight of 720.94 g/mol. Its CAS Registry Number is 155213-67-5, and its FDA UNII is O3J8G9O825.
The current USP-NF monograph defines Ritonavir as containing 97.0–102.0%, calculated on the anhydrous basis.
Ritonavir is a structurally complex peptidomimetic molecule containing two thiazole rings, phenyl groups, multiple amide functionalities and several stereogenic centers. The API is produced as a defined stereochemical form, making stereochemical control an important part of its manufacturing and analytical quality strategy.
USP describes Ritonavir as a white-to-light-tan powder, while current U.S. labeling describes Ritonavir USP as white to almost white powder. It is freely soluble in methanol and methylene chloride, very slightly soluble in acetonitrile, and practically insoluble in water.
Ritonavir also exhibits polymorphism, making solid-state characterization important for pharmaceutical-grade API manufacture. WHO documentation notes that Ritonavir is described in the International Pharmacopoeia, Ph. Eur. and USP and has multiple crystal forms.
| Property | Details |
|---|---|
| API Name | Ritonavir |
| CAS Number | 155213-67-5 |
| Molecular Formula | C₃₇H₄₈N₆O₅S₂ |
| Molecular Weight | 720.94 g/mol |
| PubChem CID | 392622 |
| FDA UNII | O3J8G9O825 |
| ChEBI ID | CHEBI:45409 |
| API Type | Synthetic small-molecule API |
| Pharmacological Class | HIV protease inhibitor |
| Therapeutic Class | Antiretroviral |
| Physical Form | White to light-tan / almost white powder |
| USP Assay | 97.0–102.0%, anhydrous basis |
| Water Solubility | Practically insoluble |
| Methanol Solubility | Freely soluble |
| Methylene Chloride Solubility | Freely soluble |
Chemical identity and molecular information are supported by PubChem and USP.
Ritonavir is used in antiretroviral therapy and is particularly important as a pharmacokinetic enhancer for other antiviral medicines.
As an HIV protease inhibitor, Ritonavir inhibits the HIV protease enzyme required for processing viral polyproteins into mature functional proteins. However, at currently used low doses in combination regimens, its strong CYP3A inhibition is frequently exploited to increase systemic exposure to co-administered antiviral agents.
Ritonavir is included in several combination antiviral products. It is also used with nirmatrelvir in the treatment of COVID-19 in eligible patients under applicable regulatory indications. PubChem identifies Ritonavir as an HIV protease inhibitor and notes its use in combination with other antiviral agents.
Ritonavir inhibits the HIV-1 protease enzyme, interfering with the cleavage of viral precursor polyproteins required for the production of mature infectious HIV particles.
Ritonavir also strongly inhibits CYP3A-mediated metabolism. This property can reduce the metabolism of co-administered drugs that are CYP3A substrates and thereby increase their plasma concentrations and duration of exposure.
This dual pharmacological profile explains the continuing importance of Ritonavir both as an antiretroviral agent and as a pharmacokinetic enhancer.
Ritonavir has an established USP-NF drug-substance monograph with detailed analytical requirements.
The current USP monograph specifies:
The USP assay uses liquid chromatography with UV detection at 240 nm. The monograph specifies system suitability requirements including column efficiency of NLT 5000 theoretical plates, tailing factor 0.8–1.2, and relative standard deviation NMT 2.0% for the assay system.
The current USP impurity section establishes NMT 0.1% for any other individual impurity and NMT 1.0% for total impurities, while several named Ritonavir-related impurities have specific limits of 0.1%, 0.2% or 0.3%.
Ritonavir is manufactured through a controlled multi-step synthetic process requiring careful control of stereochemistry, intermediates, reaction conditions and process-related impurities.
The molecule contains multiple stereogenic centers, and selective production of the desired stereoisomer is important to API quality. WHO documentation specifically notes that Ritonavir has four chiral centres and that its manufacture stereoselectively produces the desired stereoisomer.
Manufacturing controls should include qualified raw materials, controlled reaction conditions, impurity monitoring, purification, crystallization, drying and appropriate solid-state characterization.
Ritonavir is a crystalline solid with a molecular weight of 720.94 g/mol. It is practically insoluble in water but has substantially greater solubility in organic solvents such as methanol and methylene chloride.
Ritonavir is also known to exhibit polymorphism. Solid-state form can therefore be relevant to API manufacturing, storage and pharmaceutical formulation. X-ray diffraction is included in the established USP identification approach for the drug substance when used for solid dosage forms.
The USP monograph specifies that Ritonavir should be preserved in tight, light-resistant containers and stored between 5°C and 30°C.
Pharmaceutical-grade API should be packaged in suitable containers that protect the material from light, contamination and unsuitable environmental exposure. Packaging should maintain batch identification and traceability throughout storage and transportation.
Pharmaceutical-grade Ritonavir API can be supported by appropriate quality and regulatory documentation, including:
Ritonavir is a highly established antiretroviral API with detailed pharmacopoeial requirements for identity, assay, impurities, water and solid-state quality.
A quality-focused Ritonavir API manufacturer in India should maintain appropriate stereochemical control, validated chromatographic methods, impurity management and solid-state characterization.
The USP-NF monograph provides particularly useful benchmarks, including the 97.0–102.0% anhydrous-basis assay, NMT 0.2% residue on ignition, NMT 0.5% water, NMT 0.1% any other individual impurity, and NMT 1.0% total impurities.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 97.0–102.0% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 0.5% |