Introduction
A capsule consists of a dose of drug enclosed in a water-soluble shell or envelope.
Although capsules are predominantly used for oral medication, suppositories, consisting of the drug and a suitable dispersion medium enclosed in a flexible gelatine shell are available.
There are two types of capsule, the hard variety which is intended for the administration of particulate solids and the soft or flexible used for liquids or pastes.
As the shell takes several minutes to dissolve, the taste of unpalatable drugs is effectively masked. Officially, capsules may be spherical (perles), ovoid or cylindrical with hemispherical ends – only the last of these descriptions applies to hard capsules.
The shell may include an antimicrobial preservative can be coloured as an acid to identification and may be rendered opaque by dyes or fillers if the drug e.g. some vitamins and chlorodiazepoxide, is photosensitive.
For official preparations, dihents may not be added to the medicament unless this is specifically permitted in the relevant monograph: a similar restriction also applies to the use of coloured shells for capsules described in the codex.
It is possible to coat capsules with cellulose acetate phthalate or a mixture of stearic acid and butyl stearate if enteric action is required, but it is more usual in these circumstances for formulate if possible as an enteric coated tablet.
Types of Capsules
There are two main types of Capsules. These are Hard shell/gelatin capsules and Soft Shell/gelatin Capsules.
1. Hard Capsules
These are made by filling the drug as powder, granules or pellets into a preformed cylindrical shell or body, the contents being retained by a shorter shell or cap fitted over the body.
Hard capsules provide an alternative to powder cachets and tablets for the administration of solid medicaments.
They are at least as durable as tablets and correct formulation permits the rapid release and absorption of drug in the g.i.t.
Hard capsules shells are made by dipping mould into a gelatine solution, the film on the mould dries the shell cut to length and then stripped from the mould.
The shells are made in a range of 8 sizes to accommodate 50 to 1000mg degree of drug but for veterinary preparations, three larger shells are available for 5 to 30g dose for large scale production the capsules are sorted and positioned body downwards and sucked into holes in upper and lower rings which when separated, retain the cap and body respectively.
The lower ring is then presented to a head which fills the body cavity.
Subsequently the rings are recombined, the body pushed into the cap, the capsule ejected and any dust adhering to the outer capsule surface removed.
In Semi-automatic equipment the rings are separated, transferred to the filling head and recombined by hand, but with fully automatic machines, these operations are accomplished by mechanical means.
Moisture will be absorbed from the environment via the capsule wall if the medicament is more hygroscopic than the shell and for this reason such substances should not be dispersed in capsules.
Care must be taken to ensure the efficient mixing of minor constituents with other drugs of diluents.
The weight of drug in both tablets and capsules is governed by the volume available for filling and the bulk density of the drug formulation under production conditions, while for low weight variation the powder must flow in a reproducible manner.
Hard capsules are second to tablets in importance as a visit dose form. They owe their popularity to the following:
- They obscure the taste and odour of unpleasant drugs
- They are attractive in appearance
- They are slippery when moist and, hence easy to swallow with a draught of water
- If properly stored, the shells contain 12-15 of moisture which gives flexibility and consequently very considerable resistance to mechanical stress.
- Less adjuncts are necessary than for tablets
- The content are usually in fine powder, combined with adjunct provides rapid and uniform release of medicament in the g.i.t
- The shells can be pacified (with titanium dioxide) or coloured, to give protection from light.
- The shells are made to very fine limit, hence the cap and base fit well and give substantial protection against air and moisture
- The shells are physiologically inert and easily and quickly digested in the g.i.t. presentation of a drug in capsules allows quicker submission of a new drug for clinical trials, because fever development problems are involved. Also, it is easier to vary the dose.
Capsule shells may contain preservative such as benzoic acid. Para-hydroxy-benzoic acid ester or sulphur dioxide.
They are available in eight sizes, identified by numbers ranging from 000 (largess) to 5
Capsule No: 000 00 0 1 2 3 4 5
Content (Mg): 950 650 450 300 250 200 150 100.
Some capsule types have identations by which the cap is tucked to the base when pressed home fully.
Certain manufacturers of filled capsules apply a gelatine band around the junction to improve resistance to gases and moisture General Aspects of preparation.
(a) Normally the minimum weight in a capsule should not be less than 100mg
(b) The transparent capsules, commonly used for extemporaneous dispensing, look better if completely full
(c) Generally, diluents are used only when the amount of medicament is below 100mg.
Commercial capsules sometimes contain lubricant such as aluminium stearate or colloidal silicon dioxide to assist filling by improving flow properties and wetting agents, to increase drug release from non-wettable insoluble materials.
The inclusion of adjuncts in official capsules is permitted only if they are innocuous, have no adverse effect on therapeutic efficiency and do not interfere with assays and tests.
2. Soft Capsules
Like the variety, gelatine soft capsules are made from gelatine and water but with the addition of polyhydric alcohol, such as glycerol or sorbitol to make them flexible.
Sorbitol is less hydroscopic then glycerol. They usually contain preservative such as naphthol.
Soft capsules are available in a variety of shapes and sizes e.g. spherical (0.05 to 5ml), ovoid (0.05 to 7ml), cylindrical (0.15 to 25ml) tubes (0.5 to 30ml) and pear shaped (0.3 to 5ml), small spherical forms are sometimes called “perles”.
They are most suitable for liquids and semi liquids and are widely used in spherical halibut liver oil, vitamins A and D are minimum vitamins.
Liquid therapeutic agents with unpleasant taste and/or colours are conveniently administered in soft capsules e.g. the sedative, ethclorvynol; the anticonvulsant, paramethadione; and the anthelmintics tetrachloroethylene and male fern.
Substances insoluble in water but soluble in vegetable oil may also be present in this form, e.g., the synthetic sex hormones, chlorotrianisene, which is dissolved in maize oil.
Opthalmic ointments are frequently packed in unit-dose, tube-shaped capsules and occasionally medicaments for rectal administration are supplied in the pear-shaped form.
Soft capsule shells mat be coloured, to provide protection from light (e.g. phytomenadione capsules which are brown), or enteric-coated, when action in the intestine is required (e.g. male form).
They are unsuitable for preparation containing an appreciable amount of a solvent that either dissolves gelation (e.g. water) or can diffuse from the capsule via the moisture in the shell (e.g. alcohol).
Soft capsules are made by dipping metal formers or “olives” into a molten aqueous base containing glycerine and gelatine (glycogelatine)
NATURE OF SOFT GELATINE SHELLS
Soft gelatine capsules are made of gelatine to which glycerine or polyhydric alcohol such as sorbital has been added.
Soft gelation capsules, may have a preservative, such as methyporaben and propylparaben, to retard microbial growth. Soft gelatine capsules may be oblong, oval, or round.
They may be a single colour or two-tone and imprinted with identifying markings.
CONTENTS OF SOFT GELATINE CAPSULES
The capsule shell is basically composed of gelatine, plasticizer and water.
It may contain additional ingredients such as preservative, colouring or opecifying agents, flavourings, sugar, acids and medicaments to achieve desired effects.
CONTENTS:
Water:
Not more than 45% l/m
The ratio by weight of water to dry gelatine can vary form 0.7 to 1.3 (water) to 1.0 (dry gelatine) depending on the viscosity of the gelatine being used.
Plasticizer
Used to make the soft gel shell elastic and pliable. Ratio used is between 0.3 to 1.8 for soft to hand shell on dry basis.
Colour
Used in shell has to be darker than colour of encapsulating material; may be natural or synthetic.
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