Rifabutin is a semisynthetic rifamycin-class antibacterial active pharmaceutical ingredient used primarily in the treatment and prevention of Mycobacterium avium complex (MAC) infections and as part of certain tuberculosis treatment regimens. Rifabutin is identified by CAS No. 72559-06-9, molecular formula C₄₆H₆₂N₄O₁₁, and molecular weight 847.00 g/mol.
The current USP-NF monograph defines Rifabutin at 950–1020 µg/mg on the anhydrous basis, equivalent to 95.0–102.0% potency, and specifies a maximum water content of 2.5%.
Rifabutin is a semisynthetic derivative of rifamycin and belongs to the ansamycin antibiotic class. It inhibits bacterial DNA-dependent RNA polymerase and thereby interferes with bacterial RNA synthesis.
Rifabutin is described as a reddish-violet to violet-red powder. PubChem reports minimal water solubility, solubility in methanol and chloroform, and slight solubility in ethanol.
The substance has a highly complex ansamycin structure with multiple stereogenic centers and is chemically distinct from rifampicin/rifampin, although the compounds belong to the same rifamycin family.
| Parameter | Details |
|---|---|
| Product Name | Rifabutin |
| Synonyms | Ansamycin, LM-427, Mycobutin |
| CAS Number | 72559-06-9 |
| Molecular Formula | C₄₆H₆₂N₄O₁₁ |
| Molecular Weight | 847.00 g/mol |
| FDA UNII | 1W306TDA6S |
| ChEBI | CHEBI:45367 |
| DrugBank | DB00615 |
| ATC Code | J04AB04 |
| API Class | Rifamycin / Ansamycin antibiotic |
| Appearance | Reddish-violet / violet-red powder |
| Water Solubility | Minimally soluble |
| Ethanol Solubility | Slightly soluble |
| Methanol | Soluble |
| Chloroform | Highly soluble |
| Storage | Well-closed container; protected from light and excessive heat |
PubChem identifies CAS 72559-06-9, molecular formula C₄₆H₆₂N₄O₁₁ and molecular weight 847.00 g/mol.
Rifabutin is an antimycobacterial antibiotic used in pharmaceutical formulations for the management of Mycobacterium avium complex (MAC) infections. It is also used in selected multidrug regimens for tuberculosis and other mycobacterial infections.
Its mechanism involves inhibition of bacterial DNA-dependent RNA polymerase, resulting in suppression of RNA synthesis.
Rifabutin is particularly important where a rifamycin with a different drug-interaction profile from rifampicin may be clinically preferred.
Rifabutin has established pharmacopoeial quality requirements.
The USP monograph specifies:
The current USP revision also identifies individual impurities including 16-desacetylrifabutin, rifabutin 14R epimer, rifabutin N-oxide, rifabutin 21R epimer, didehydrorifabutin, rifabutin N-oxide open ring, and a specified unknown impurity, with individual limits ranging from 0.25% to 1.0%.
Commercial pharmaceutical-grade material is also commonly offered at ≥97.5% HPLC or >98% HPLC depending on the supplier's specification. These commercial purity values should not replace the USP potency specification.
Rifabutin API manufacturing requires controlled semisynthetic processing, purification and analytical characterization because of the molecule's complex rifamycin structure and multiple related substances.
A pharmaceutical-quality manufacturing program should control potency, water, N-isobutylpiperidone, specified degradation/related substances and total impurities in accordance with the applicable pharmacopoeial or approved product specification.
USP specifies that Rifabutin should be preserved in well-closed containers and protected from light and excessive heat.
Appropriate light-resistant packaging should therefore be used for pharmaceutical API storage. The validated stability condition of the actual manufactured batch should determine the final storage statement.
Typical documentation may include:
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 3.0% |
| Water Content | NMT 2.5% |