In the manufacture of pharmaceuticals, encapsulation refers to a range of dosage forms—techniques used to enclose medicines—in a relatively stable shell known as a capsule, allowing them to, for example, be taken orally or be used as suppositories. The two main types of capsules are:
- Hard-shelled capsules, which are typically made using gelatin and contain dry, powdered ingredients or miniature pellets made by e.g. processes of extrusion or spheronisation. These are made in two halves: a lower-diameter "body" that is filled and then sealed using a higher-diameter "cap".
- Soft-shelled capsules, primarily used for oils and for active ingredients that are dissolved or suspended in oil.
Both of these classes of capsules are made from aqueous solutions of gelling agents like:
- Animal protein, mainly gelatin;
- Plant polysaccharides or their derivatives like carrageenans and modified forms of starch and cellulose.
Other ingredients can be added to the gelling agent solution like plasticizers such as glycerin or sorbitol to decrease the capsule's hardness, coloring agents, preservatives, disintegrants, lubricants and surface treatment.
Since their inception, capsules have been viewed by consumers as the most efficient method of taking medication. For this reason, producers of drugs such as OTC analgesics wanting to emphasize the strength of their product developed the "caplet" or "capsule-shaped tablet" in order to tie this positive association to more efficiently-produced tablet pills. After the 1982 Tylenol tampering murders, capsules experienced a minor fall in popularity as tablets were seen as more resistant to tampering.
Single-piece gel encapsulation ("soft capsules")
In 1834, Mothes and Dublanc were granted a patent for a method to produce a single-piece gelatin capsule that was sealed with a drop of gelatin solution. They used individual iron moulds for their process, filling the capsules individually with a medicine dropper. Later on, methods were developed that used sets of plates with pockets to form the capsules. Although some companies still use this method, the equipment is not produced commercially any more. All modern soft-gel encapsulation uses variations of a process developed by R.P. Scherer in 1933. His innovation was to use a rotary die to produce the capsules, with the filling taking place by blow molding. This method reduced wastage, and was the first process to yield capsules with highly repeatable dosage.
The current owner of the RPScherer technology is Catalent Pharma Solutions, the world's largest manufacturer of prescription pharmaceutical softgels.
Softgels can be an effective delivery system for oral drugs, especially poorly soluble drugs. This is because the fill can contain liquid ingredients that help increase solubility or permeability of the drug across the membranes in the body. Liquid ingredients are difficult to include in any other solid dosage form such as a tablet. Softgels are also highly suited to potent drugs (for example, where the dose is <100 µg), where the highly reproducible filling process helps ensure each softgel has the same drug content, and because the operators are not exposed to any drug dust during the manufacturing process.
In 1949, the Lederle Laboratories division of the American Cyanamid Company developed the "Accogel" process, allowing powders to be accurately filled into soft gelatin capsules.
Two-piece gel encapsulation ("hard capsules")
James Murdock of London patented the two-piece telescoping gelatin capsule in 1847. The capsules are made in two parts by dipping metal pins in the gelling agent solution. The capsules are supplied as closed units to the pharmaceutical manufacturer. Before use, the two halves are separated, the capsule is filled with powder or more normally pellets made by the process of Extrusion & Spheronization (either by placing a compressed slug of powder into one half of the capsule, or by filling one half of the capsule with loose powder) and the other half of the capsule is pressed on. With the compressed slug method, weight varies less between capsules. However, the machinery required to manufacture them is more complex.
The process of encapsulation of hard gelatin capsules can be done on manual, semi-automatic and automatic machines. Softgels are filled at the same time as they are produced and sealed on the rotary die of a fully automatic machine.
Standard sizes of two-piece capsules
|Size||Volume (ml)[A]||Locked length (mm)[A]||External diameter (mm)[A]|
- Sims, Calvin (1986-02-15). "Despite "mystique" of capsules, many drugs work in other forms". New York Times.
- "History of dosage forms and basic preparations". Encyclopedia of Pharmaceutical Technology 7. Informa Health Care. 1998. pp. 304–306. ISBN 0-8247-2806-8.
- Bill Bennett and Graham Cole (2003). Pharmaceutical Production, an Engineering Guide. IChemE. pp. 126–129. ISBN 0-85295-440-9.
- L. Lachman, H.A. Lieberman, J.L. Kanig (1986). The Theory and Practice of Industrial Pharmacy (Third ed.). Lea & Febiger, Philadelphia. ISBN 0-8121-0977-5.