2-Methyl-5-nitroimidazole Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable is supplied as a crystalline powder with molecular formula C4H5N3O2 and relative molecular mass 127.10. The assigned CAS registry number is 88054-22-2. Manufacturing is performed under ICH Q7 good manufacturing practice for active pharmaceutical ingredients, and the grade is differentiated from technical material by control of residual solvents, bacterial endotoxins, elemental impurities, and related substances. The product is packed in a double low-density polyethylene liner inside a fiber drum with desiccant; each drum is labeled with retest date and storage conditions. Because current major pharmacopoeias do not assign a standalone monograph to this unsubstituted imidazole core, the release specification is aligned with ICH Q6A and the Ph. Eur. general monograph Substances for Pharmaceutical Use. The product is intended for formulation into oral tablets, capsules, granules, and injectable preparations where local marketing authorization exists. Published peer-reviewed pharmacokinetic data for the unsubstituted 2-methyl-5-nitroimidazole in human oral and injectable dosage forms are limited; therefore, formulation development and bioequivalence assessment should rely on the specific regulatory file and not on metronidazole-derived data. The typical release specification envelope is summarized in the following matrix.

Table 2. Typical release specification matrix.

What distinguishes the unsubstituted 2-methyl-5-nitroimidazole core from N1-substituted 5-nitroimidazole APIs in pharmaceutical formulation?

The principal difference is the absence of an N1 substituent. 2-Methyl-5-nitroimidazole retains an imidazole N–H bond and a higher crystal lattice energy than metronidazole or tinidazole, producing a melting range of 250–255 °C by Ph. Eur. 2.2.14. This high-melting crystalline form reduces the risk of heat-assisted melt granulation and alters solubility and dissolution compared with the N1-hydroxyethyl and N1-ethylsulfonylethyl derivatives. Direct substitution into a registered metronidazole formulation is not permitted without reformulation and regulatory assessment because the biopharmaceutical behavior of the unsubstituted core is not covered by a metronidazole monograph. The respective N1 substitution also changes the electrostatic charge distribution on the imidazole ring, which affects the degradation kinetics of the nitroarene under photolytic and alkaline conditions. Table 1 presents the basic comparative matrix.

Technical-grade 2-methyl-5-nitroimidazole used in organic synthesis is not interchangeable with this pharma grade because the technical material is not controlled for bacterial endotoxins, residual solvents, or the same specified impurity profile. The pharma grade also includes a defined crystalline form confirmed by X-ray powder diffraction (Ph. Eur. 2.9.33); uncontrolled crystallization from technical solvent systems may yield a different crystal habit with altered flow characteristics. This is the principal product difference from lower-purity chemical intermediates offered under the same CAS registry number. For metronidazole and tinidazole suppliers, specification overlap should not be assumed; each API has a distinct monograph and impurity profile, and only the pharma grade described here is intended for oral and injectable formulation development under a manufacturer’s drug master file.

On high-speed rotary tablet presses equipped with 10–16 stations, the low bulk density and high melting point of the unsubstituted nitroimidazole core require pre-compression before main compression to arrest capping and lamination. The manufacturer’s oral grade is controlled to a D90 of ≤80 µm; experienced formulators specify an intragranular binder such as povidone K30 in wet granulation because direct compression blends containing the API at 60–75% w/w may show insufficient plastic deformation. Dry blending is limited to low-dose capsule applications where the API is geometrically diluted prior to encapsulation. Bulk and tapped density are measured according to Ph. Eur. 2.9.34; typical inter-batch values for the oral grade are bulk density 0.32–0.45 g/mL and tapped density 0.48–0.65 g/mL, with flow properties evaluated by Ph. Eur. 2.9.36. The powder may exhibit electrostatic charging at relative humidity below 25% RH, so humidity-controlled suites set to 40–50% RH are used during dispensing, sifting, and compression. Tablet friability is assessed with Ph. Eur. 2.9.7; formulations that fail to achieve ≤1.0% weight loss require adjustment of pre-compression force rather than addition of a hydrophobic lubricant. For capsule filling, the granulated material is lubricated with magnesium stearate at 0.5–1.0% w/w; excessive lubrication beyond 1.5% w/w causes delayed disintegration as measured by Ph. Eur. 2.9.1.

Dissolution testing for immediate-release tablets containing this API is carried out with Ph. Eur. 2.9.3 apparatus II at 50 rpm in 900 mL of 0.1 M hydrochloric acid at 37 °C ± 0.5 °C. Because the unsubstituted core is weakly basic and its solubility is pH-dependent, a discriminating method should be established by comparing solubility at pH 1.2, 4.5, and 6.8 and by verifying sink conditions. Published dissolution data for this specific configuration are limited; therefore, a provisional specification such as Q = 75% in 45 min is used only during formulation screening and is not assigned to commercial release without batch data. The BCS classification of 2-methyl-5-nitroimidazole is not firmly established in public literature; consequently, a BCS-based biowaiver is not appropriate without additional solubility and permeability studies according to the current WHO or regional guidance.

When aqueous granulation is selected for tablet or capsule processes

When aqueous granulation is selected for tablet or capsule processes, the sparingly water-soluble nature of 2-methyl-5-nitroimidazole supports a suspension-based binder addition rather than a clear solution granulation. The wet mass is passed through an oscillating granulator fitted with a 1.0–1.5 mm screen and dried in a fluid-bed dryer at inlet air temperature 50–60 °C until loss on drying is ≤1.5%. Published data on hydrate formation for this compound are limited; therefore, the dried granule is routinely confirmed by X-ray powder diffraction (Ph. Eur. 2.9.33) against the reference diffractogram. Over-granulation with excessive water increases the proportion of fines after dry sizing and reduces tablet hardness at main compression forces above 18 kN. For capsules, the granule fraction retained between 150 µm and 710 µm is preferred for gravity filling, while the fraction below 150 µm is limited to ≤20% w/w to avoid dust generation during high-speed encapsulation. Disintegration is tested with Ph. Eur. 2.9.1; a target of ≤15 min for uncoated tablets in water at 37 °C ± 2 °C is used during development but final specifications must be justified by batch data. If the formulation uses a high-shear mixer granulator, the impeller tip speed should be controlled between 2 m/s and 5 m/s and the wet massing time kept below 6 min to prevent excessive fines and broad particle-size distribution.

Injectable-grade endotoxin and particulate control

Injectable-grade material is handled in a separate area with controlled air classification ISO 7 or better. The API is tested for bacterial endotoxins with a limit of ≤0.50 EU/mg by Ph. Eur. 2.6.14 and for subvisible particulate matter after reconstitution according to Ph. Eur. 2.9.19. For a terminally sterilized injectable solution, the pH is adjusted with hydrochloric acid or sodium hydroxide to a target 4.0–5.0, and the solution is filtered through a 0.2 µm sterilizing-grade filter. Thermal degradation of the imidazole ring is pH-dependent; therefore, sterilization parameters must be confirmed by a worst-case load study. The unsubstituted core is not identical to metronidazole injection concentrates and cannot be directly substituted into a parenteral formula without stability and biopharmaceutics data. If a sterile powder-for-injection presentation is required, the API is filled as a lyophilized or dry powder after terminal sterilization of the container-closure system; the powder must pass sterility testing by Ph. Eur. 2.6.1 and the reconstitution time should be recorded with a dispersion medium compatible with the final clinical route. Subvisible particle counts after reconstitution are evaluated under Ph. Eur. 2.9.19; for particles ≥10 µm and ≥25 µm, the pharmacopoeial limits for small-volume parenterals are applied unless the clinical dose requires a stricter internal limit. The injectable grade is not claimed to be sterile as supplied; it is controlled for bioburden and endotoxin to support downstream aseptic processing or terminal sterilization.

Accelerated stability data for this specific unsubstituted nitroimidazole are limited in the public literature. The manufacturer’s drug master file includes a stability program at 25 °C ± 2 °C / 60% RH ± 5% RH and 40 °C ± 2 °C / 75% RH ± 5% RH according to ICH Q1A(R2). The product should be stored in the original sealed double polyethylene liner inside a light-resistant HDPE drum. The API shows no significant hygroscopicity; after 24 h exposure at 75% RH, water uptake remains below 0.2% by dynamic vapor sorption. If a solid oral formulation contains reducing excipients, compatibility studies should be conducted because the aromatic nitro group can undergo reduction under certain conditions. Residual solvents and elemental impurities are re-evaluated in finished dosage forms because the dose, route, and total daily exposure may tighten or loosen the API-level limits; the oral solid dose and injectable routes use different permitted daily exposure values for lead, cadmium, arsenic, and mercury under ICH Q3D. The absence of a harmonized monograph requires that each finished product release be supported by a product-specific specification rather than a general pharmacopoeial monograph. For long-term storage, the retest interval is assigned from the DMF stability data and is not automatically transferable to a formulated product because excipient interactions and moisture ingress in the final package can change impurity profiles.

Thermal and Photolytic Stress Response in Solid Dosage Preparation

Thermal and photolytic stress testing under ICH Q1B indicates that the unsubstituted nitroimidazole core is more sensitive to light than metronidazole, and finished dosage forms should be packaged in amber glass or opaque PVC/aluminum blisters. Isothermal exposure at 60 °C for 10 days produces less than 0.5% total degradation in the dry solid state, but the same study in aqueous solution at pH 9 shows accelerated discoloration. Therefore, alkaline granulation fluids should be avoided, and an acidic or neutral pH is preferred for injection compounding. For tablet and capsule formulations, wet granulation with an acidic buffer is accepted only if the buffer is dry-blended and the granulation time is held below 15 min to limit local pH excursion. Photostability cabinets equipped with a xenon lamp and a 320–400 nm filter are used to confirm that the chosen packaging reduces the degradation below the reporting threshold of 0.05% for unspecified impurities. If a dosage form must be subdivided or repackaged, a second photostability study under the immediate container-closure system is required because the primary package is the main barrier against light-induced degradation.