Quality Control Tests for Capsule Drug Products

Capsules are solid dosage forms in which the drug formulation in a powder, solution or suspension, a combination of miscible liquid, or a simple liquid formulation is enclosed in a shell.  Depending on the composition of the gelatin shell, the capsules can be hard or soft gelatin capsules. Hard gelatin capsules are typically used for powder or solid fills, whereas soft gelatin capsules are used for semisolid or liquid fills. Lately, hard capsules have also been used for liquid or semisolid fills.

In capsule formulation development and during filling of capsules, a number of quality control tests are performed to ensure that capsules produced meet the requirements as specified in official compendium and conventional requirements established by the industries over the years. These tests will be discussed in three stages: in-process testing, finished product testing and shelf-life testing.

Dissolution test for capsules

Drug absorption and physiological availability depend on the drug substance being in the dissolved state at the site of drug absorption. The rate and extent of dissolution of the drug from the capsule dosage form is tested by a dissolution test. This test provides means of quality control in ensuring that

1. different batches of the drug product have similar drug release characteristics and

2. that a given batch has similar dissolution as the batch of capsules that was shown initially to be clinically effective

The compendial dissolution test for capsules uses the same apparatus, dissolution medium, and test as that for uncoated and plain coated tablets. However, in instances in which the capsule shells interfere with the analysis, the contents of a specified number of capsules can be removed and the empty capsule shells dissolved in the dissolution medium before proceeding with the sampling and chemical analysis.

If the capsule floats on the surface of the dissolution fluid, a small, loose piece of nonreactive material, 

The capsules are tested to ensure lack of growth of bacteria and mould by microbiological tests. These tests are usually carried out by incubation of the capsule contents in a growth medium and counting the colonies formed after a predefined period of time. Selection of the growth medium and duration of the test, as well as maintenance of aseptic conditions during the testing, are critical to successful assessment of microbial contamination by this method.

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