This article throws light upon the six main formulations of drugs for oral use. They are: 1. Powders 2. Pills 3. Tablets 4. Bolus 5. Capsules 6. Suppositories.
1. Powders:
Powders are solid dosage of medicament in finely divided form for internal and external use and are available in crystalline or amorphous form. The particle size of powders is significant in their dissolution and bioavailability. Micronization (conversion of coarse particles into fine particles) leads to significantly higher absorption due to increase in surface area. Powders have more surface area, so they are rapidly dissolved.
The advantages of powders are that they are/more stable (dry powders are stable at room temperature for 3 years) than other dosage forms and chances of incompatibility in powders are less. Powders are generally administered in a gelatin capsule.
The gelatin capsule has to be dissolved for release of active ingredient which is in the form of powder to be released in the GI fluid for absorption. A large number of drugs are administered in the form of powder, for example multivitamins and minerals in the form of powder are packaged in a capsule.
2. Pills:
Pills are spheric, globular or lenticular masses, each containing a definite dose of medicinal substances intended to be swallowed whole. They are made up of powdered drugs with a sticky substance (excipient) like honey, glucose, glycerin, or tragacanth. The pills must be firm, smooth and round.
3. Tablets:
Flattened pills are termed as tablets. These are prepared by compressing or moulding a drug or a mixture with or without excipient.
Coating of tablets is done:
(i) To prevent exposure of medicament to atmospheric effect
(ii) To make the tablet more elegant
(iii) To improve unpleasant taste and odour of the drug
(iv) To produce sustained release preparations
(v) To prevent disintegration in the stomach.
Various methods of coating are:
(i) Sugar coating – acacia, sugar, syrup is coated on the tablet
(ii) Film coating – polymer dissolved in some organic solvent is sprayed over tablet. After drying they form a permanent film
(iii) Enteric coating – some drugs are required to disintegrate in the intestine, and need to pass the stomach as such without any absorption, such preparations require enteric coating. Cellulose acetate, phthalate, fatty acids, waxes etc. are used as adjuvant. Whereas solutions represent a state of maximum dispersion, compressed tablets have the closest proximity to particles.
Complexities in dissolution and bioavailability are generally inversely proportional to the degree of dispersion. Bioavailability from tablets is less. Tablets have smaller surface area, have to be broken down into smaller particles (micronization) for proper dissolution.
Factors responsible for breakdown of tablets into coarse and subsequently into finer particles include parameters as the concentrations of binder, disintegrant, and lubricant; the hydrophobicity of the drug and the adjuvants; the compression force applied; storage conditions etc.
The coatings on tablets add to the rate limiting factor, coatings need to be disrupted and dissolved before the disintegration and dissolution of tablet begins. Dissolution and bioavailability of tablets varies with different composition. Most of the drugs meant for oral administration are formulated in the form of tablets.
4. Bolus:
Boluses are solid preparations of cylindrical shape and rounded ends containing active ingredients. The consistency of bolus mass is such that the shapes do not change on storage.
Their method of preparation is similar to that employed in making a pill mass. They are mainly intended for large animals. On an average they weigh 30-40 gm. Their size parameter is one and a half inch to two and a half inch in length and half inch to three quarters an inch in diameter, e.g. Aloe’s bolus.
5. Capsules:
Capsules are gelatin shells used for administration of drugs. A common way of administering powder is by incorporating it into gelatin capsule. They may be hard or soft. Hard capsules are made of gelatin, 8 parts; sugar, 8 parts; acacia, 1 part; and water, 8 parts.
Their manufacturing consists of dipping suitable molds into a special healed gelatin mass. Upon drying, the adhesive gelatin mixture solidifies, forming the capsule. Soft capsules are generally ovoid or spherical in shape and are made from gelatin softened with some substance, such as glycerin. Usually liquid drugs are filled and their open ends sealed with a drop of molten capsule mass.
Rectal Preparations:
Rectal Preparations (solid or liquid form) are preferred for drugs that cause nausea or any other ailment in which drugs cannot be administered orally. The rate of release of the drug from rectal preparation is dependent on the nature of the base composition and the solubility of the drug involved. It also has an -advantage that it does not undergo first pass metabolism.
Some drugs are administered rectally either in suppository or solution form, e.g., retention enema. The solutions yield better absorption provided that they are retained for a sufficient length of time in the rectum. The suppositories are the most commonly used dosage forms for local and systemic effect.
6. Suppositories:
Suppositories are soft medicinal masses of various weights and shapes intended for insertion into body orifices (rectum, vagina, nasal cavities). Their melting temperature is slightly below the body temperature, so that after insertion, the masses melt and the medicament is liberated. The vehicles employed are oil or theobroma, glycerinated gelatin, or sodium stearate.
The various suppositories are:
(i) Anal suppositories
(ii) Vaginal suppositories (pessaries)
(iii) Uretheral suppositories
(iv) Nasal suppositories (bougies).