Capsules are solid unit dosage form of medicament in which the drug(s) is enclosed in a practically tasteless, hard or soft soluble container or shell made up of a suitable form of gelatin.
In other word, Capsules are solid dosage forms in which one or more drugs and inert substances are enclosed within a small shell or container generally prepared from a suitable form of gelatin.
Capsules are available in two types:
1. Hard Gelatin Capsules
2. Soft Gelatin Capsules
Hard gelatin capsules are used for filling the solid substances whereas soft gelatin capsules are used for filling the liquids and semisolids.
Advantage
1. Easy to handle and carry
2. Capsules are much economical
3. They are attractive in appearance
4. Better bioavailability and faster onset of action than tablets
5. More stable and have longer shelf life than liquid dosage form
6. Capsules are tasteless, odorless and can easily be administered
7. Have “prescribing flexibility” as a variety of dosage strengths are available
8. The capsule shells can be opacified with titanium dioxide or colored substances, to give protection from light.
9. Packaging and shipping can be done by the manufacturers at a lower cost and less breakage than liquid dosage forms
Disadvantage
1. Hygroscopic drugs not suitable for filling into capsules as they absorb water present in capsule shell. As a result, the shell became very brittle & ultimately lead to crumble into pieces.
2. The concentrated solutions which require previous dilution are unsuitable for capsules because if administered as such lead to stomach irritation
3. Capsules are not suitable for effervescent or deliquescent materials. Efflorescence softens the capsule and deliquescent can dry the capsule shell and make it brittle.
Gelatin
Gelatin is heterogeneous product derived by hydrolytic extraction of animal’s collagen.
Types of Gelatin
There are two basic types of gelatin;
1. Type A
2. Type B
These types are described below;
Type A
Gelatin is mainly derived from pork skin by acid treatment. This process exhibits an iso electric point at pH 9.
Type B
Gelatin is derived from bones and animal skin by alkaline treatment. This process exhibits an iso electric point at pH 4.7.
Why gelatin is the major component of the capsule!
Gelatin is the major component of the capsule. The reason for this is that gelatin possesses five basic properties. They are;
1. Non-toxic
2. It is a good film-forming material
3. Soluble in biological fluids at body temperature
4. Solutions of high concentration, 40% w/v, are mobile at 50°C
5 A solution in water changes from a sol to a gel at temperatures only a few degrees above ambient.
General Characteristics of Gelatin
1. Bloom value
It is a measurement of the gelling power and the strength of the resulting gel. Gelatin generally falls between 50 and 300 bloom strength.
2. Gelling power
It is the key function of gelatin. The gelling power varies depending on the grade of gelatin. It’s measured in terms of bloom value.
The higher the bloom value, the greater the ability to form gel.
3. Viscosity
In general the higher the bloom, the greater the viscosity. Beef bone grades tend to have higher viscosity.
Viscosity is determined by measuring the flow time of a 6.67% solution of gelatin through a U-tube viscometer at 60 °C.
Viscosity measurement is given in millipoise units and varies between 20 and 70mps.
4. Foamability
In general pigskin grades tend to have better foaming properties. Gelatin lowers the surface tension, allowing for the incorporation of air, and stabilizes the foam once aerated.
5. Melting point
Lower melting point gelatins dissolve faster in the mouth, therefore releasing the flavors more quickly for an instant taste sensation.
Lower bloom grades tend to have lower melting points.
6. Color and odor
The gelatin should be as clear as possible and without odor in the solution. Clarity is measured using a turbidimeter.
7. Conductivity
It is a key parameter in photographic applications and grades of the highest purity with minimal or no conductivity are required.
De-ionized grades have an advantage because of their low conductivity.
8. pH
pH is measured using a pH meter on a 1% solution. The pH of gelatin used for capsules ranges from 4 to 6.8.
Preparation of Gelatin
Hard gelatin and soft gelatin capsules are the main two oral dosage forms in the pharmaceutical and nutraceutical sectors, and with each developed for a distinct purpose. Hard gelatin capsules are two-piece units which consist of a body and a cap. They are commonly used to encapsulate the dry components such as powders, granules, or pellets. These capsules are constructed of gelatin, water, and few plasticizers, which results in a hard structure. Hard gelatin capsules have some advantage such as, they are inexpensive, easy to fill, and provide accurate dosing. They are perfect for solid formulations and shield the drug or other contents from light, air, and humidity. However, they are not suited for liquids unless they have been transformed into a solid or semi-solid state.
Soft gelatin capsules, on the other hand, are one-piece, hermetically sealed capsules that have a higher plasticizer content, which makes them elastic and soft. Softgels are mainly used to encapsulate the semi-liquid formulations, liquids, oils, and suspensions. They are especially useful for preventing the deterioration of delicate components and increasing the bioavailability of medications that are not very water soluble. They are visually pleasing, easy to swallow, and tamper-evident. In contrast to firm gelatin capsules, their production method is more intricate and costly because specialized equipment is used for both capsule manufacture and filling at the same time.
The primary distinction between these two is their applications. The hard gelatin capsules are better for solid or semi-solid compositions, whilst soft gelatin capsules are best for liquid or oil-based compounds. The decision between the two is determined by the criteria such as the nature of the drug, its stability, and desired release profile. Both forms of the capsules are versatile and plays an important role in the successfully delivery of drugs, catering to a variety of therapeutic requirements and consumer preferences.
To explore the fascinating differences in greater detail, check out the linked article; “Hard and Soft Gelatin Capsules: A Comprehensive Guide”