You know, capsules are a popular form of drug delivery in both the pharmaceutical and nutraceutical industries. Why? They are convenient.
Since capsules are quite common these days, knowing what goes into making a stable and effective capsule is vital.
In this article, we’ll break down the key ingredients that make up a capsule and why they matter.
What Is Capsule Formulation?
Capsule formulation is the art and science of putting different ingredients together to make a capsule, e.g, to make soft gelatin capsule.
You see, a single capsule is more than just the active ingredient. It’s a combination of different individual capsular ingredients.
To end up with an ideal capsule, you need the active pharmaceutical ingredient (API), the capsule shell materials, and a range of excipients. These excipients will improve the process of digestion, the stability of the drug, and how available the capsule content is for absorption.
Capsule formulation is important, as it determines if the patient will comply with the therapy regimen. The better involved you are in formulating every type of capsule, the better you can keep the API safe and improve the shelf life of the capsule, too.
Key Ingredients Used in Formulating a Capsule
As you earlier read, an ideal capsule must contain these three components: API, the excipients, and capsule shell materials. These three key components of a capsule are further explained.
1. The Active Pharmaceutical Ingredient (API)
The API is the core of the capsule. It’s the only reason why you are formulating the capsule in the first place. It’s the main ingredient responsible for whatever treatment effect you need to take the capsule for.
The active pharmaceutical ingredient is the component of the formed capsule that carries the intended therapeutic or nutritional benefit you desire. There’s no limit to what the active compound of a capsule could be. So, the API could be a drug, vitamin, mineral, herbal extract, or any other compound people take for a reason.
Now, it’s good you keep in mind that the dosage form, the solubility of the API in water or fat, and the absorption site you are targeting are important factors. These factors play a big role in how you formulate the APIs and other ingredients into the capsule.
A fun fact—most times, the active compound contributes less than 10% of the entire capsule’s content.
2. Excipients
Excipients in capsules are inert substances that help in processing, stabilizing, improving, and releasing the content in the capsule.
To give you a better understanding, think of the role of colors and flavors in the cake. Both ingredients don’t react, but their presence improves the overall taste and feel of the cake. When you choose excipients, you need to make sure that it can improve the effectiveness of the API.
The excipients used to formulate capsules are many. Common excipients used to make capsules include:
Fillers(Diluents)
Capsule fillers, which are also called bulking agents, are those parts of capsules that are used to “bulk up.” They bulk up the capsule content to a much preferred capsule volume and size. When you have an insufficient quantity of concentrated APIs and you want to make many more capsules than the API can make, then you use fillers to make up.
Some diluents used to make capsules are microcrystalline cellulose, lactose, and so on.
Binders (Adhesives)
As the name implies, binders in capsule formulation help to hold the capsule content together. Binders are more of a tablet thing, as they improve the uniformity of a tablet. However, in some capsules where you need cohesive blends for the oneness of the formulation, you need binders. Examples of binding agents are starch slurry, sodium CMC, and so on.
Disintegrants
Disintegrants are the capsule components that ensure that the capsule content breaks down and dissolves well in the patient’s digestive tract.
As a component, disintegrants make sure the active compound of the capsule is absorbed on time. They improve the bioavailability of the API. Common disintegrants are croscarmellose sodium, corn starch, sodium starch glycolate, crospovidone, etc.
Lubricants and Gliders
For capsule formulation, lubricants and Gliders serve different purposes. Lubricants reduce the friction and adhesion of powder content to the metal when you fill the capsule. Hence, lubricants make the manufacturing process faster and more efficient.
Some examples of common lubricants used in capsule formation are talc, glyceryl monostearate, magnesium stearate, etc.
Glidants, on the other hand, increase the “flow” of the content in the capsule. A good example of a glidant is micro-silica gel.
Most times, though, drug formulators may substitute some lubricants for glidants.
Wetting Agents
These are substances that increase the rate at which the capsule dissolves when it reaches its target absorption site. It increases the wettability of the active compound as the capsule travels down the digestive tract.
Examples of wetting agents include polysorbate 80, sodium lauryl sulfate, and so on.
Preservatives and Stabilizers
Preservatives and stabilizers are components that ensure the capsule stays longer, yet they are still safe for consumption. These excipients prevent the growth of microbes that can affect the potency of the API, oxidation, and degradation.
The extent of preservatives and stabilizers you use when you formulate a capsule depends on the nature of the API. When you have a natural product or herb as the API, you must be careful when choosing the agents you use to preserve the substance.
This is because natural capsule contents are more sensitive to changes caused by temperature change, light, and humidity. Artificial APIs are less likely to be affected by these factors.
Examples of common preservatives and stabilizers used for formulating capsules include ascorbic acid (which is an antioxidant), sodium benzoate, and butylated hydroxytoluene (BHT).
3. Capsule Shell Material
These are materials used to make the capsule shell that you see. Well, they are different shell types that you can use for your capsule. But, in your choice, the capsule shell material should contain an opacifier and a plasticizer.
An opacifier is a component of the shell material that makes it more opaque; that is, light doesn’t get through it.
When your capsule, be it a hard capsule or a soft gelatin capsule, has an opacifier, it reduces degradation of the capsule content caused by light. An excellent example of an opacifier is titanium dioxide.
A plasticizer, especially for gelatin capsules, makes the capsules more pliable and easier to handle. The most common ones used to form capsules are glycerin and sorbitol.
Common materials used to make capsule shells are:
- Gelatin is preferred for its availability, flexibility, and ease of production.
- HPMC (Hydroxypropyl Methylcellulose), which is a plant-based alternative to gelatin (which is animal-derived), does its best for vegans
- Pullulan or Starch-Based Polymers for special types of capsules.
Keep in mind that each of these capsule shells materials have its unique time of dissolution. They may have their preferences for some capsule content, too.
Ingredient Compatibility and Interaction Risks in Capsule Formulation
When formulating capsules, several factors ensure the success of this task. One aspect of capsule formulation you must always pay attention to is the compatibility of the various ingredients. This is because some compounds may:
- React with each other, reducing the potency or even causing the production of a toxic metabolite.
- Accelerate the degradation of another, or the API
- Cause physical instability (e.g., clumping, color change)
Before you take the bold step of formulating any capsule, you should carry out a thorough pre-formulation and stability testing study. That way, you’d avoid negative interactions that may compromise product quality or safety.
Conclusion
Formulating capsules is more than just stuffing ingredients you think will improve one’s health into a shell. Yes, it’s science. But it’s an art too.
Every capsule’s content plays a vital role in ensuring the API works as you intend it to. As you work around these capsule ingredients and their functions, you can create safer and more effective products. Consumers can make more informed choices. And, the pharmaceutical and nutraceutical industries will do better with trusted formulators, too.
FAQs
What Is the Most Important Ingredient in Capsule Formulation?
The most important ingredient in a formulated capsule is the active compound or API. This is because it delivers the primary health benefit. This is the reason why anyone would take the supplement in the first place.
However, other ingredients ensure the active ingredient works as it should.
Can Capsule Fillers Affect How Well a Supplement Works?
Well, it depends, as certain fillers can impact the absorption of the API. Some can even be dangerous, as they cause allergies to sensitive individuals.
Overall, your choice of capsule filler affects bioavailability, user experience, and, of course, the effectiveness of the capsule.
Are Vegan Capsules as Effective as Gelatin Capsules?
Yes. As long as you formulate the capsule well and make the right considerations, vegan capsules can be as effective as gelatin capsules. But there’ll be slight differences, though. However, these differences are okay given that the substances are different.
