Drugs are formulated in three major dosage forms: solid, semisolid, and solid dosage forms. Of these three dosage forms, the most common is the solid dosage form, and some examples include tablets, granules, powders, and capsules, amongst many others. Interestingly, the types of solid dosage forms are formulated differently and are designed for different purposes.
While tablets are entirely composed of medication, capsules only contain medication inside the shell. Let’s talk more about capsules.
What are Capsules?
Capsules are formulated to contain drug products, which could be a powder, a solution, or suspension, a simple liquid, or a combination of miscible liquids in a shell. Capsule shells are usually made of gelatin, and depending on the composition, they can be soft or hard gelatin capsules.
Capsules, just like every other pharmaceutical, are subjected to different manufacturing practices and measures that are regulated by different regulatory agencies. The finished products also pass through several tests ensuring that they comply with compendial standards and requirements for unit dose capsules.
These tests guarantee that each batch of capsules is acceptable, in terms of quality, efficacy, and strength, for its intended use and marketing. However, while these many standards are put in place to ensure the quality, safety, and efficacy of these pharmaceuticals, there is no shortage of counterfeit drugs in the market.
Hence, we will discuss some quality control tests used to determine the quality and safety of capsules.
Simple Tests To Evaluate The Quality of Empty Capsules
1. Permeability and Sealing
One easy test carried out is the test of physical integrity. It is done by visual inspection. Soft gelatin capsules are checked for leakages and hard gelatin capsules are checked for any breakage or opened cap.
2. Potency and Impurity Content
Capsules are also tested for quality and potency. Not just that. They are also tested for the presence of impurities or any other related substances. Any other substance apart from what is stated on the label, or the presence of an identified substance at a level different from the predefined specifications is considered an impurity.
3. Weight Variation Test
The weight uniformity test of capsules is carried out to identify weight or content variation in a batch. There are recommended procedures for carrying out weight uniformity tests for both hard and soft gelatin capsules. Generally, any deviation from the specified range will render the batch unacceptable.
4. Uniformity of Content
Uniformity of content is usually carried when the content of the drug is specified in the monographs, and more importantly, if the capsule batch fails the weight uniformity test. There is no need for this test if the weight of the capsules is filled.
The monograph provides a complete guide on the specifications of virtually all drug products, and any variation from what’s specified would mean the batch does not pass the test.
5. Disintegration Time Test for Capsules
Disintegration tests are performed to determine the ease at which the capsule shell will release the drug content fully for dissolution, and absorption from the GI tract. There are standards and procedures for performing this test. Both soft and hard gelatin capsules follow the same steps and apparatus as stated in the official books.
The capsule is said to have passed the test if it fully disintegrates into a soft mass with no firm core and only some fragments of the shell. Anything other than that would mean the capsule has failed the test.
6. Dissolution Test for Capsules
Another key important test is the dissolution test. To begin with, the extent and rate of drug absorption and subsequently, physiological availability depends on the ability of the drug substance to dissolve at the site of absorption. The dissolution test measures both the extent and rate of capsule dissolution.
The test is usually performed between batches to ensure all the batches have similar dissolution characteristics. That is a very important quality control method to ensure that the characteristics shown by the capsule batch during clinical stages are retained and maintained.
The official compendium contains the procedures, apparatus, medium, and tests. The same procedures are used for uncoated and plain-coated tablets. Usually, the capsule shell should not interfere with the procedure, however, if it does, the content of the test capsules can be emptied, and the shell is dissolved in the medium, before proceeding with the chemical analysis.
7. Moisture Content
One of the easiest ways for capsules to lose their potency and degrade rapidly is the presence of moisture. The Karl Fisher titrimetry measures the water content of capsules to ensure the correlation of the water content with the degradation features of the drug.
8. Microbial Content
Microbes can degrade pharmaceutical products easily. Consuming contaminated products can also result in mild or severe infections depending on the strain of microbial contaminants. Hence, the microbial content of capsules is evaluated.
Microbial content tests are done to check for the presence of the prohibited strains of bacteria in the capsules. These tests are performed by incubating the capsules for a specified number of days and checking for microbial growth in the culture.
The procedures, culture medium, test duration, and aseptic conditions for successful assessment are stated in the compendium.
9. Shelf-life Test
Shelf-life tests are performed to evaluate how long the capsules can stay intact under normal use and storage conditions. The test also helps determine the usability and favorable conditions for the capsules.
10. Stability Testing of Capsules
Finally, stability tests for capsules are done to evaluate their physicochemical stability. These tests also help to recommend storage conditions, packaging materials, long-term usability, formulation components, and environmental factors that could negatively impact the drug substance.
Storing the drug outside the recommended conditions may result in the capsules getting degraded. Sometimes, stability tests and shelf-life tests are done together.
The efficacy, safety, and strength of capsules, and pharmaceuticals in general, lie in the fact that the drug content is potent, present in the right quantity, free of contaminants, and has favorable physicochemical properties. Anything that affects these parameters will result in the capsule becoming unwholesome and unfit for consumption. And in some cases, consuming such products can be deleterious to health.
Hence, reputable empty capsule manufacturers entrench these quality control standards in their operations to ensure capsules are safe, effective, and acceptable to consumers.