Solid Dosage Forms — Tablets and Capsules

Tablets remain the most widely manufactured pharmaceutical dosage form, prized for their chemical stability, dose accuracy, low unit manufacturing cost, and...

Tablets remain the most widely manufactured pharmaceutical dosage form, prized for their chemical stability, dose accuracy, low unit manufacturing cost, and ease of patient handling. Tablet development begins, in accordance with QbD principles, with definition of the Quality Target Product Profile, typically specifying the dosage form as a film-coated oral tablet, the required dissolution performance — commonly not less than eighty per cent drug release within forty-five minutes under USP Apparatus II conditions at pH 6.8 — the content uniformity requirement expressed as an Acceptance Value of no more than fifteen under USP <905>, and a target shelf-life of at least twenty-four months under the relevant climatic storage conditions.

Excipient selection follows, guided by both the preformulation compatibility data and the functional role each excipient must fulfil: diluents to provide adequate bulk, binders to impart mechanical strength, disintegrants to promote rapid tablet breakup, lubricants to prevent adhesion to manufacturing equipment, and glidants to improve powder flow. The manufacturing process itself is typically achieved through either wet granulation, in which powders are agglomerated using a liquid binder to improve flow and compressibility, or direct compression, a simpler process suitable for drugs and excipients with inherently favourable flow and compaction properties; the choice between these routes is dictated largely by the physical characteristics established during preformulation.

Following granulation, the resulting blend is optimised, commonly through Design of Experiments, to balance flow, compressibility, and content uniformity, before proceeding to compression, where tablet hardness, thickness, and weight are controlled within tightly specified ranges. Many tablets subsequently undergo film coating, which may serve aesthetic, taste-masking, or functional purposes such as moisture protection or modified-release performance. The finished tablet is then subjected to comprehensive Critical Quality Attribute testing, encompassing hardness, friability, disintegration time, dissolution profile, content uniformity, and assay, each of which must satisfy the acceptance criteria established in the original Quality Target Product Profile.

Capsules, comprising a drug-containing fill enclosed within a hard or soft gelatin or hypromellose shell, offer certain advantages over tablets, including the ability to accommodate liquid or semi-solid fills for poorly soluble drugs, ease of swallowing for some patient populations, and the masking of unpleasant taste or odour without the need for a coating step. Hard capsules are typically filled with powder blends, granules, or pellets using volumetric or dosator filling technology, while soft gelatin capsules are formed and filled simultaneously, making them particularly well suited to the delivery of liquid lipid-based formulations such as those used for BCS Class II and IV drugs.