Solid Dosage Forms: Capsules

Capsules are a significant solid dosage form in which drug mixtures are enclosed in a stable outer shell.
Similar to tablets, capsules incorporate excipients which can vary depending on the intended release profile and stability requirements.
The capsule shell is typically soluble and is made from an aqueous solution of gelling agents, including gelatin (derived from animal protein) and carrageenans (derived from plant polysaccharides).
In terms of physical characteristics, capsule shells can be classified as either hard or soft.
- The hard-shell capsules are commonly employed for dry powdered ingredients, ensuring protection and stability during storage.
- Conversely, soft-shell capsules are generally designed for liquid formulations, encapsulating oils or drugs dissolved in oil, making them ideal for substances that require enhanced solubility or stability upon ingestion.
Regardless of whether a capsule has a hard or soft shell, it is crucial that the shell is inert to its contents to prevent any potential interaction that could affect the drug's efficacy or safety.
Another essential requirement for this dosage form is the dissolution of the capsule shell upon administration.
The dissolution must occur in a controlled manner to effectively release the active pharmaceutical ingredient (API) for absorption in the gastrointestinal tract.
In certain cases, formulations containing water-insoluble drugs can greatly benefit from soft-gel formulations.
These formulations can lead to improved absorption and bioavailability parameters.
Drugs like temazepam and ibuprofen have demonstrated enhanced pharmacokinetic properties when administered in soft-gel capsules, highlighting the importance of formulation strategy in achieving desired therapeutic outcomes.