Phenobarbital Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable is the free acid form of 5-ethyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trione, CAS 50-06-6, molecular formula C₁₂H₁₂N₂O₃, relative molecular mass 232.24 g mol^-1. The product descriptor functions as the model identifier and specifies a compendial-grade active pharmaceutical ingredient supplied as a white or almost white crystalline powder for solid oral dosage forms and, when supported by route-specific endotoxin, particulate matter, sterility, and stability data, sterile injectable presentations. It is not interchangeable with reagent-grade phenobarbital, technical intermediates, or the sodium salt derivative, because those products lack the full pharmacopeial release specification, residual solvent control, elemental impurity limits, controlled particle-size distribution, and GMP documentation required for pharmaceutical manufacturing.

The API is manufactured and released under GMP expectations established in 21 CFR 210, 21 CFR 211, and ICH Q7. The certificate of analysis includes lot-specific values for assay, related substances, loss on drying, residue on ignition, elemental impurities, residual solvents, particle size, and microbial quality. The grade designation does not assign a proprietary model number; the supplier’s certificate of analysis defines the release version by compendial monograph, edition, and intended route of administration. Because the product descriptor includes tablet, capsule, granule, injection, oral, and injectable uses, the release specification for a given lot must be selected by the most stringent route unless the receiving manufacturer verifies all parameters.

What compendial limits and in-process controls define this grade?

Release against the current USP/NF and Ph. Eur. Phenobarbital monographs requires conformance to identity, assay, melting range, loss on drying, residue on ignition, related substances, and residual solvent standards. The assay range and drying limits are harmonized across many pharmacopeial regions, but residual solvent and impurity acceptance criteria can differ by monograph edition. Elemental impurities are controlled under ICH Q3D and USP 232/USP 233; microbial quality for nonsterile oral applications is controlled under USP 61 and USP 62.

Because the product descriptor includes multiple routes, a single API lot can be used for both oral solid and injectable processing only when the manufacturer has verified injectable-specific controls. Blending, sampling, and environmental controls in the API facility must prevent endotoxin introduction. For injectable applications, the absence of a bacterial endotoxin result from the supplier is not affirmative evidence of suitability; the finished product manufacturer must establish a route-appropriate endotoxin limit under USP 85 and validate the depyrogenation and sterile processing train.

Direct compression performance of the free acid form is governed by particle-size distribution, bulk density, tapped density, and the derived compressibility index and Hausner ratio under USP 1174. A compressibility index below 25% is classified as passable and is normally needed to maintain weight uniformity on rotary tablet presses with forced feeders. Above 30%, flow is classified as poor, and bridge or rathole formation can occur in transfer hoppers and bin blenders. Production-scale batch records for brittle, low-moisture APIs show that capping and lamination are commonly attributed to excessive fines or insufficient precompression; the specific compression force threshold is formulation-dependent and must be established during process development. Where the API lot has a high fines fraction, blending time is restricted to prevent over-blending and demixing. In bin blenders of 600 L to 1200 L working capacity, baffle geometry, fill level, and transfer-line free-fall distance are adjusted to maintain blend uniformity.

Granulation is used when direct compression is not feasible. In wet granulation, the free acid API is pre-blended with microcrystalline cellulose and crospovidone before addition of a povidone solution in a high-shear granulator. Granulation endpoint is controlled by impeller power consumption and torque; fluid-bed drying is performed at inlet air temperatures supported by ICH Q1A stability data to limit hydrolytic degradation. High-shear granulation with sodium bicarbonate, sodium carbonate, or other alkaline agents should be avoided because ionization of the free acid can alter granule dissolution, compressibility, and tablet hardness. Dry milling after granulation is controlled by laser diffraction under USP 429; D10, D50, and D90 values are reported in the certificate of analysis or development report when a specific particle-size distribution is required for content uniformity or dissolution control.

When terminal sterilization or sterile filtration is required for injection

For injectable presentations, the API must meet bacterial endotoxin limits defined by dose, route, and the administered volume under USP 85. Particulate matter in the final product is controlled under USP 788 for subvisible particles, and sterility of the finished product is demonstrated by USP 71. The manufacturing process uses a sterility assurance level of 10^-6. For a free acid API with very slight aqueous solubility, the injectable formulation is prepared by pH adjustment to form the sodium salt in situ or by use of a non-aqueous vehicle. pH measurement follows USP 791; the target pH is established by solubility and stability studies. Sterile filtration through a 0.22 µm membrane is common for formulations that are not suitable for terminal steam sterilization. Aseptic filling is conducted in a ISO 14644-1 Class 5 environment with Grade A conditions under EudraLex Volume 4 Annex 1. Autoclave cycles may be considered only where thermal stability data demonstrate absence of impurity increase and pH drift.

Endotoxin control in the API synthesis requires depyrogenated equipment, water-for-injection rinses for product-contact surfaces, and controlled bioburden before crystallization. The oral solid grade is not automatically acceptable for injection merely because the same chemical entity and assay are present; the supplier and receiving manufacturer must define separate acceptance criteria for endotoxin, bioburden, extraneous particles, and container-closure residues. Published development reports for phenobarbital free acid in terminal sterilization of aqueous injection vehicles are limited; therefore, terminal sterilization of the specific formulation cannot be assumed and must be validated experimentally.

Compendial identity, residual solvent limits, and controlled substance handling

Residual solvent control is governed by ICH Q3C and USP 467. Class 1 solvents are controlled at levels such as benzene 2 ppm, carbon tetrachloride 4 ppm, and 1,2-dichloroethane 5 ppm. Class 2 solvents are limited according to the permitted daily exposure, and Class 3 solvents are controlled to general limits appropriate to the manufacturing route. The API should not be stored or processed near strong oxidizers, strong acids, or strong bases; alkaline hydrolysis of the barbituric acid ring may occur at high pH and generate degradation products that alter assay and related substance profiles. Storage in tight, light-resistant containers at controlled room temperature 20–25 °C with USP 659 allowances for excursions to 15–30 °C is required. Moisture exposure from condensation or prolonged open handling changes powder flow and can reduce blend uniformity in solid dosage processing.

Phenobarbital is controlled under the US Controlled Substances Act Schedule IV and the Single Convention on Psychotropic Substances Schedule IV. Imports, exports, storage, distribution, and recordkeeping require security controls and documentation under 21 CFR 1304, 21 CFR 1305, and 21 CFR 1312. These regulatory requirements are independent of pharmacopeial quality and must be included in site master files and supplier quality agreements. The API should be handled only by qualified personnel under controlled substance procedures; inventory reconciliation and periodic stock audits are part of GMP and controlled substance compliance.

Differences from other products are route-dependent and chemical-form-dependent. Phenobarbital sodium, CAS 57-30-7, is the water-soluble salt used for aqueous injections and oral solutions. The free acid product is not directly interchangeable with the sodium salt on a weight basis because the salt form has a different relative molecular mass, dissolution rate, hygroscopicity, and particle-size behavior. Reagent-grade phenobarbital may be supplied without GMP release, without full related-substance testing, and with higher heavy metal content; it is unsuitable for pharmaceutical manufacturing. Technical intermediates may contain process impurities not controlled by a pharmacopeial monograph. The descriptor Phenobarbital Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable therefore identifies a controlled, compendial-grade free acid with multi-route potential. It does not guarantee that every lot is automatically suitable for every route; the receiving manufacturer must verify route-specific attributes and validate each finished dosage form.

On production-scale rotary tablet presses, capping and lamination have been observed when poor powder compressibility is combined with inadequate precompression; this is a common failure mode for brittle, low-moisture APIs with compressibility index above 30%. Batch-to-batch variability in particle-size distribution after milling can shift fill volume in dosator capsule machines, so supplier certificates of analysis should include D10, D50, and D90 values by laser diffraction under USP 429. High-shear granulation with alkaline binders should be avoided because conversion of part of the free acid to the sodium salt alters dissolution, compactibility, and granule hardness. These processing boundaries define the practical limits of the product across tablet, capsule, granule, and injection applications and must be controlled through supplier quality agreements, route-specific release, and process validation rather than assumed from the API grade designation alone.