Depending on the nature of the capsule shell., Capsules may be classified mainly as either hard or soft. Other types of capsules are Modified release & Enteric Capsules.

  1. Hard Gelatin Capsule
  2. Soft Gelatin Capsule
  3. Modified Release Capsule
  4. Enteric Capsule

Types of Capsules

Types, Capsules, Hard, Soft, Modified, Enteric, gelatin
Types of Capsules

Also Capsule can be classified on following basis

Classification, Capsules, Gelatin, Hard, Soft, HPMC, Dry filled, Liquid Filled
Classification of Capsules

1. Hard gelatin capsules

Hard gelatin capsule is composed of two pieces (cap & body) in the form of cylinders closed at one end; the shorter piece called the ‘cap’ and the longer piece, called the ‘body,. Cap cover body part of capsule & body holds drug substance.

Capsule, Cap, body, hard, gelatin
Hard Gelatin capsule
Hard gelatin capsule structure

Size of Capsule

The two-piece hard gelatin capsule (for human use) is available in a range of sizes; from largest to smallest, these sizes are 000, 00, 0, 1, 2, 3, 4, 5. 

Size of capsule Volume (mL)weight (m=V  d (in gm))
0001.37 
000.95 
00.68 
10.50 
20.37 
30.30 
40.21 
50.13 
Size of capsule for human use

Note:

The approximate capacity for capsules from 000 to 5 ranges from 600 to 30 mg, depending on the densities of the powdered drug materials

Manufacturing of Hard Gelatin Capsule

Hard gelatin capsule are manufactured in one operation & filled in a completely separate operation.

Hard gelatin capsule mainly composed of gelatin and purified water. Some colored hard gelatin capsules also contain a small amount of Titanium dioxide and colorants.

 NameGelatinWaterTitanium dioxideColorant
 Transparent85%15%//
 Opaque83-84%15%0.5-1.8%0.2-0.5%
Composition of Hard Gelatin capsule shell
I. Shell composition of Hard Gelatin Capsule
IngredientUses
Gelatin often used a combination of  pork skin & bone gelatin to get desired property of the gelatin shell
Colorant Dye, pigments & (Iron oxides)- commonly used (Iron < 15ppm)
Opaquing AgentsTiO­2 (titanium dioxide)- use to render shell opaque & to provide protection against light or to conceal the contents of the capsule
Preservativesmethyl-paraben & propyl-paraben & SO2 (Sulphur dioxide)– to prevent decomposition during manufacturing
WaterPurified water De-ionised water used to prepare gelatin solution for the preparation of dipping solution.
PlasticizersGlycerin USP, Sorbitol USP (more common for soft gelatin capsules)
Compositions of Capsule shell
II. Shell manufacturing

Automatic machines are used for hard capsule production consists of mechanisms for automatically dipping, spinning, drying, stripping, trimming, and joining the capsules.

Hard, Manufacturings, Capsule, Gelatin, Shell, Spinning, Drying, Stripping, Cutting, Joining, Dipping,
Steps in two-piece Hard Gelatin capsule Manufacturing

Steps involved in Hard Gelatin capsule Manufacturing

1. Dipping:

One hundred and fifty pairs of these pins are dipped, into a gelatin sol (about 12 seconds)of controlled viscosity at 50 oC temp. to form caps and bodies simultaneously.

2. Spinning/rotation

The pins are usually rotated to distribute the gelatin uniformly.

3. Drying

The pins are moved through a controlled air drying & precisely controlled removal of water

4. Stripping

The capsules are stripped from the pins by bronze jaws and

5. Trimming

Stripped Capsules are trimmed to length by stationary knives.

6. Joining

After being trimmed to exact length, the cap and body sections are joined and ejected from the machine.

Note: Thickness of the capsule wall is controlled by the viscosity of the gelatin solution and the speed and time of dipping.

III. Moisture Content
  • Moisture can diffuse through the gelatin wall/film.
  • Finished Hard gelatin capsules – optimum 13-16% moisture content (12-15% Lackman)
  • If Moisture content   less than< 12% – shell become brittle and suffer dimensional changes.
  • If Moisture content of Shell more than 18% – shell become too soft & Result in a loss of mechanical strength.
  • size variation in empty capsules aa result of moisture content variation.
IV. Storage of Empty Hard Gelatin Capsule
  • Should storage at – 40-60%  RH/relative humidity & Temp= 100 oF

Types of dosage forms for filling into hard capsules

SolidSemi-solidLiquid
Powder
Pellets
Granules
Tablets
Capsules
Pastes
Thermosofting mixture
Thixotropic mixture
Non aqueous solutions
Oil liquids
Type of Material for filling into Hard Gelatin Capsules

Powder filling in the hard gelatin capsule

  1. Loading of empty capsule shell in filling machine
  2. Rectification of the capsule shell
  3. Separation of the body & cap.
  4. Filling the body with formulation
  5. Joining of the body & cap
  6. Ejection of the filled capsule
  7. Finishing – Dusting & Polishing –
    • Pan polishing
    • Cloth dusting
    •  Brushing

Soft Gelatin Capsule:

The soft gelatin capsule (SGC) was invented by Mothes, a French pharmacist, in 1833. It is One piece, hermetically sealed of gelatin shell containing, liquid, a suspension or a semisolid.

The composition of soft gelatin capsules is similar to that of hard gelatin capsules, except that the different moisture proportion & Plasticizers. Usually, plasticizers will be added to keep capsules’ elasticity and stability, including Glycerol, Sorbitol etc. It may contain preservative to prevent the fungal growth.

HPMC capsules

HPMC Capsule is mainly composed of HPMC and purified water. HPMC is a kind of cellulose obtained by the hydrolysis of plants and is made by etherification.

HPMC capsules are stable at low humidity levels, have low moisture content (3–8%), and low static charge. These natural HPMC capsules are suitable for highly reactive molecules (because they have no cross-linking reactions). Compared to hard gelatin, HPMC is more suitable for moisture-sensitive products, hygroscopic products, and for low relative-humidity applications.

Because HPMC is derived from plants, it is a vegetarian capsule (herbal product).

Type of Capsule

Modified Release Capsule

Both hard or soft gel capsules can be chemically modified to alter the release of the active ingredient(s). If the drug is water-soluble and in a hard capsule and a fast release is desired, the excipients should be hydrophilic and neutral whereas for slow release of water soluble drugs the excipients will slow the release. Rapid release from capsules can also be obtained by piercing the outer film with small holes or incorporating a small quantity of citric acid and sodium bicarbonate to assist in opening the capsule by evolution of carbon dioxide.

A small concentration (up to 1%) of sodium lauryl sulfate may be added to the gel of a soft capsule to enhance penetration of water and speed dissolution. If slow release from a soft capsule is required, polymer or alginates may be added.

Enteric Coated Capsules

Enteric Coated Capsules do not belong to a certain type of capsules. They are made by applying an enteric coating to other common capsules. Enteric Coated Capsules are mainly made to meet the needs of releasing medication in the intestine.

Its general principle works like that, with the coating process, the enteric capsule only can be dissolved by the alkaline liquid in the intestinal tract.

Starch capsules

Starch capsules are made from potato starch. Their dissolution is pH independent, and they are suitable for enteric coating. The moisture content of starch capsules ranges between 12–14% w/w, with more than 30% being tightly bound. 

Pullulan capsules

These vegetarian capsules are made from tapioca, which is naturally fermented into pullulan. They provide a high barrier to oxygen.

Pullulan is a water-soluble mucopolysaccharide, a mature food additive

Polyvinl acetate (PVA) capsules

Capsules made from PVA can be used for filling insoluble drugs dissolved in polyethylene glycol (PEG) 400. PEG 400 when used as single vehicle is not compatible with other hard capsules. The oxygen permeability of PVA is low, resulting in a high barrier to oxygen.

Liquid-filled hard capsules

Two-piece hard capsules made of either gelatin or HPMC can be used for filling and band sealing non-aqueous liquid, paste, suspension, hot melts, and other vehicles that melt up to 70 °C and flow easily. LFHC can also be filled with tablets, pellets, or other capsules as combination fill. LFHC can be used for moisture-sensitive drugs. These can be a cost-effective alternative to some soft gelatin capsule products and can also enhance bioavailability and improve product stability. Liquid encapsulation technology helps overcome many problems associated with the use of softgel capsules including high cost, waste, cross-contamination, migration of the drug into the capsule shell, and issues with low bioavailability. Liquid-filled and semi-solid capsules by their nature are resistant to crushing and powdering and therefore provide a good basis for developing an abuse-resistant formulation. These capsules can also be enteric coated. HPMC hard capsules do not become brittle when they lose water.


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