13. Capsules in Pharmaceutics: Types, Composition, Manufacturing & Uses

INTRODUCTION TO CAPSULES

Capsules are solid dosage forms in which a drug (or a combination of drugs) is enclosed within a small shell made of gelatin or a suitable gelatin substitute. They are one of the most widely prescribed oral dosage forms because they are easy to swallow, mask the unpleasant taste or odour of drugs, and allow precise, unit-based dosing. Capsules can accommodate powders, granules, pellets, semi-solids, or liquids, making them one of the most versatile dosage forms taught in Pharmaceutics. For D.Pharmacy students, understanding capsules is essential not only for theory exams but also for practical knowledge required in community and hospital pharmacy practice, where capsule-based medicines are dispensed daily.

Types of Capsules

Capsules are broadly classified into two categories based on the physical nature of their shell:

• Hard Gelatin Capsules (HGC)
• Soft Gelatin Capsules (SGC), also called Softgels

Both types serve the same basic purpose — safe and convenient drug delivery — but differ significantly in composition, manufacturing, and the types of formulations they can hold. Let’s look at each in detail.

Hard Gelatin Capsules (HGC)

Hard gelatin capsules are the most commonly used capsules in pharmacy practice. They consist of two telescoping parts — the body (longer, narrower section) and the cap (shorter, wider section) — which fit together to enclose the drug. HGCs are ideal for dry powders, capsule-within-capsule formulations, pellets, granules, and low-viscosity, non-aqueous liquids that do not dissolve gelatin.

Composition of Hard Gelatin Capsules

• Gelatin – obtained from collagen of animal bones, skin, and connective tissue (Type A from pork skin, Type B from bovine bone)
• Plasticizers – such as sorbitol, added in small amounts to control shell flexibility
• Colourants – synthetic or natural dyes used for brand identification and to reduce photodegradation
• Preservatives – such as parabens, to prevent microbial growth during storage
• Opacifiers – e.g., titanium dioxide, used to protect light-sensitive drugs

Manufacturing Process of Hard Gelatin Capsule Shells

Empty HGC shells are manufactured industrially by the dipping process, which follows a defined sequence of steps:

• Dipping – Stainless steel pins are dipped into a temperature-controlled gelatin solution
• Rotation – Pins are rotated to spread the gelatin film evenly and remove air bubbles
• Drying – Coated pins pass through a drying kiln with controlled temperature and humidity
• Stripping – Dried shells are stripped off the pins
• Trimming – Shells are cut to the required length
• Joining – Cap and body sections are joined together to form the finished capsule

Advantages of Hard Gelatin Capsules

• Easy to swallow due to smooth, slippery surface
• Effectively masks unpleasant taste and smell of the drug
• Flexible dosage form – can hold powder, pellets, granules, or mini-tablets
• Visually appealing, brandable, and available in multiple colours/sizes
• Simple, economical, and suited to large-scale manufacturing

Disadvantages of Hard Gelatin Capsules

• Not suitable for highly aqueous liquids, as these can dissolve or soften the shell
• Moisture-sensitive – the shell may become soft and sticky in high humidity, or brittle in very dry conditions
• Generally costlier to produce than compressed tablets

Sizes of Hard Gelatin Capsules

Hard gelatin capsules for human use are manufactured in eight standard sizes, ranging from 000 (largest) to 5 (smallest). Larger sizes such as 10, 11, and 12 exist mainly for veterinary applications. Size selection depends on the bulk density and dose of the fill material — a pharmacist or formulator selects the smallest capsule size that can comfortably accommodate the required fill weight.

Soft Gelatin Capsules (Softgels)

Soft gelatin capsules are one-piece, elastic, hermetically sealed capsules that contain liquids, oils, suspensions, or semi-solids. Because the shell is thicker and more plasticized than HGC shells, softgels dissolve quickly in the stomach, which often improves the bioavailability of poorly water-soluble drugs.

Composition of Soft Gelatin Capsules

• Gelatin – base shell-forming material
• Plasticizers – glycerin, sorbitol, in higher concentration than HGC for elasticity
• Water – present in higher content compared to hard gelatin shells
• Preservatives – to prevent microbial contamination
• Colourants and Opacifiers – for identification and light protection

Manufacturing Process: Rotary Die Process

Softgels are manufactured mainly by the Rotary Die Process, developed by Robert Scherer. The basic steps are:

• Molten gelatin mass is cast into two continuous ribbons
• The liquid or semi-solid fill material is metered precisely between the two ribbons
• The ribbons pass between rotating dies that simultaneously shape, fill, and seal the capsule
• Sealed capsules are cut from the ribbon and tumble-dried to remove excess solvent
• Capsules undergo final drying, polishing, and inspection

Advantages of Soft Gelatin Capsules

• Ideal for oils, oil-soluble drugs, and liquid formulations
• Improves absorption and bioavailability of poorly soluble drugs
• Elegant appearance and easy to swallow
• Hermetically sealed, offering better protection from oxidation and moisture
• Highly accurate and uniform dosing, since fill is metered by volume

Disadvantages of Soft Gelatin Capsules

• More expensive to manufacture than hard capsules
• May absorb atmospheric moisture and become sticky or distorted
• Requires specialized rotary die machinery, unlike simple hand-filling of HGCs

Differences Between Hard and Soft Gelatin Capsules

Hard Gelatin Capsules	Soft Gelatin Capsules
Two-piece capsule (body + cap)	One-piece, sealed capsule
Used for powders, granules, and pellets	Used for oils, liquids, and semi-solids
Less flexible, more rigid shell	Soft and elastic shell
Lower plasticizer content	Higher plasticizer content
Made by dipping process	Made by rotary die process
Lower cost, easier manufacturing	Higher cost, specialized equipment needed

Storage Requirements

Since gelatin is highly sensitive to environmental conditions, capsules must be protected from excess humidity, heat, and light throughout their shelf life. Recommended storage conditions are:

• Hard gelatin capsules: 15–25°C with 35–55% relative humidity
• Soft gelatin capsules: 15–30°C with relative humidity below 50%

Both types are typically dispensed in tightly closed, moisture-resistant containers, often with a desiccant, to preserve shell integrity until the time of use.

Applications of Capsules

Capsules are widely used across several categories of pharmaceutical and healthcare products:

• Prescription medicines across therapeutic categories
• Over-the-counter (OTC) supplements
• Herbal and Ayurvedic preparations
• Nutritional oils, such as fish oil and vitamin E
• Drugs with a strong unpleasant taste or odour

👩‍🏫 Teacher’s Insight

In my experience teaching Pharmaceutics, students often lose easy marks by mixing up HGC and SGC manufacturing processes in exams — remember it simply as “Dipping for Hard, Rotary Die for Soft.” Another frequent confusion is capsule size ranking: students assume a higher number means a bigger capsule, when it’s actually the opposite — size 000 is the largest, size 5 is the smallest. A quick trick to remember this: think of it like clothing sizes counting down to “extra small.”

From a practical pharmacy standpoint, always check capsules for signs of moisture damage — softening, stickiness, or shell distortion — before dispensing, especially during monsoon season when humidity levels rise sharply in most parts of India. This is a common viva/practical question examiners like to ask because it connects theory directly to real dispensing practice.

Frequently Asked Questions (FAQs)

Q1. What is the main difference between hard and soft gelatin capsules?
Hard gelatin capsules are two-piece shells mainly used for solid fills like powders and pellets, while soft gelatin capsules are one-piece, sealed shells used for liquids, oils, and semi-solids.

Q2. Which capsule size is the largest?
Size 000 is the largest standard capsule size for human use, while size 5 is the smallest.

Q3. What is gelatin derived from?
Gelatin is derived from collagen found in animal bones, skin, and connective tissue, primarily from bovine or porcine sources.

Q4. Why are soft gelatin capsules used for oily drugs?
Because their sealed, one-piece shell can safely hold oils and liquids without leakage, and it also improves the bioavailability of poorly water-soluble drugs.

Q5. What manufacturing method is used for soft gelatin capsules?
Soft gelatin capsules are primarily manufactured using the Rotary Die Process, which forms, fills, and seals the capsule in a single continuous operation.

Q6. Why should capsules be stored away from humidity?
Gelatin shells are hygroscopic; excess humidity can make them soft, sticky, or misshapen, while very dry conditions can make them brittle and prone to cracking.

References

• Aulton, M.E., Aulton’s Pharmaceutics: The Design and Manufacture of Medicines, Churchill Livingstone.
• Ansel, H.C., Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems, Lippincott Williams & Wilkins.
• Indian Pharmacopoeia, Government of India, Ministry of Health and Family Welfare.
• Cooper and Gunn’s Dispensing for Pharmaceutical Students, CBS Publishers.