Types of Dosage Forms in Pharmaceutical Industry
The term Dosage form is rather recent and appears to be replacing the expression Pharmaceutical preparation. A dosage form of a drug is a product designed for administration to the body in the diagnosis or treatment of disease. Giving a proper dosage form to a drug is needed for administration of drug safely to the body without any destruction to drug or any harmful effect to body. Destruction to drug here means that some drugs become inactive or get destructs when given orally due to gastric acid. Sometimes some drugs affect gastric lining or mucosa and are not intended for oral use hence it should be changed to other dosage form, for example Injections. One drug may have more than one dosage form for different route of administration. Knowledge of these is essential for successful prescription writing and achieving the maximal therapeutic response from a drug. Let us consider some of the most important dosage forms.
The vehicles or solvents are used for the purpose of:
- Dissolving and rendering drugs more palatable
- To provide extended release and/or extended drug action
- To protect the drug from external influences eg. Moisture, temperature variation
Waters, syrups and elixirs are important vehicles.
Waters are aqueous solutions of volatile substances, usually volatile oils. They are excellent solvents for saline drugs such as salicylates. They are used as vehicles in prescriptions intended for digestive disorders. Typical waters are peppermint, cinnamon and spearmint.
Syrups are solutions of flavouring or medicinal substances in a nearly saturated solution of sucrose in water. Members of flavouring syrups are cheery, tolu etc. flavouring agents are mainly used to mask nauseating medicines.
Elixirs are hydroalcoholic solutions of medicinal substances sweetened and flavoured. Aromatic elixir, simple elixir, orange elixir is the main solvent of this class. Elixirs are excellent solvents for many drugs and mask the disagreeable odours and tastes of many substances dissolved in them for example phenobarbital elixir.
The aqueous solutions can be divided into two categories.
The first is the class of dosage form known as a solution and is intended for oral use. The second is the class known as an injection and is intended for parenteral use, ie., to be injected under the skin or into the muscles or veins.
Injections are a class of sterile liquids or suspensions which are packaged in containers (sealed glass ampoules or vials) which will maintain the sterility and are intended for parenteral administration.
In the pharmacopeia, “The sterile preparations for parenteral use are grouped in five distinct classes, defined as follows:
- Solutions of medicaments suitable for injection, referred to by titles of the form, Injection
- Dry solids which, upon the addition of suitable solvents, yield solutions conforming in all respects to the requirements for injections and which are distinguished by titles of the form, for injection
- Solids which are suspended in a suitable fluid medium and which are not to be injected intravenously or into the spinal canal, distinguished by titles of the form, Sterile Suspension.
- Dry solids which, upon the addition of suitable solvents, yield preparations conforming in all respects to the requirements for Sterile suspensions and which are distinguished by titles of the form, Sterile for Suspension
- Emulsions of fluids in fluid media, suitable for parenteral administration, which are not to be injected into the spinal canal and which are distinguished by titles of the form, Sterile Emulsion
The aqueous suspensions are classified as emulsions and mixtures. Emulsions are suspensions of insoluble liquid substances; while mixtures are dispersions of insoluble solid substances. In each class as a rule a protective colloid is added to increase stability.
Emulsions contain fixed oil suspended in water with an emulsifying agent added. The oil is dispersed through the aqueous solution of the emulsifying agent. The oil particles are small and because they are coated, they are not disagreeable to the taste. Emulsified oils are more easily digested than undispersed oils. For example, cod liver emulsion and mineral oil emulsion.
Mixtures: any solid material suspended in a liquid is designated as a mixture. Chalk mixture is a member of this class. Milk of magnesia and aluminium hydroxide gel may be considered mixtures. Dense mixtures of precipitates and supernatant fluid such as these preparations are magmas.
Spirits and essences are alcoholic solutions of volatile medicaments, usually volatile oils. Spirits are often prepared simply by diluting 10 volumes of oil with 90 volumes of alcohol. Very popular household remedies are peppermint spirit, lemon spirit, and aromatic ammonia spirit.
These preparations are high in alcoholic content and must be diluted with water before ingested.
Extractive preparations are made from vegetable drugs. Extractive preparations, as the name suggests, contain the extracted medicinal virtues from leaves, bark, roots, or other parts of the plant. The solvent which is called menstrum, is alcohol or a mixture of alcohol and water. There are three dosage forms in this class of extractive preparations.
Tinctures are alcoholic or hydroalcoholic extractive preparations of vegetable drugs. When made from potent drugs they represent 10 percent of the drug from which they are prepared. When the drug is non-potent, the tincture is prepared at twice the strength, or 20 percent.
Fluidextracts are alcoholic or hydroalcoholic extractive preparations of vegetable drugs, prepared as such strength that 1 ml of the fluid extract represent 1 gm. of the dried drug.
Extratcs may be obtained by evaporating the solvent from tinctures or fluidextracts. They are plastic in character or may be completely dried and powdered for example Belladonna extract, cascara extract.
SOLID DOSAGE FORMS
Powders. Many medicinal substances are insoluble in the pharmaceutical solvents water, alcohol, and glycerin. Materials of this kind are administered in their pulverulent form. These are called powders. Powders may be mixed with sodium bicarbonate and tartaric acid and citric acids. When mixed with water, the mixed powder effervesces and charges the water with carbon dioxide, giving the dosage form palatability; such a powder is called an effervescent powder. The dose of effervescent powder may be compressed into a tablet. Powders can be used internally or externally. External powders are applied locally as dusting powders.
Capsules. Powders may be packed into hard gelatin capsules. The resulting dosage form is called a capsule. These are tasteless, readily swallowed, and rapidly disintegrate in the stomach, where they discharge their contents. These are available in various sizes and are most popular dosage forms.
Delayed action capsules. A useful dosage form for drug whose drug particles are coated with an agent that provides intermittent release of the drug in the gastrointestinal tract. After ingestion some of the particles disintegrate immediately, others after 2 to 4 hours, and still others after 6 to 8 hours. This dosage form provides uniform medication over a period of 10-12 hours.
Tablets. Powders may be subjected to mechanical pressures and compressed into small discoid shapes known as tablets. Most compressed tablets contain a tablet filler composed of some inert binding material. Dried starch is frequently added, when comes in contact with water it swells, causing the tablet to disintegrate immediately. Tablets may be coated with gelatin, sugar or other coatings suitable for improving their taste.
Pills. When powdered drugs are mixed with adhesive substances like glucose or honey, they may be kneaded into a firm and adhesive mass. This may be cut into desirable weights and moulded into spherical or avoid forms called pills. These become hard upon drying.
SKIN AND MUCOUS MEMBRANE DOSAGE FORMS
The dosage forms intended for application to the skin or mucous membranes may be divided into liniments, lotions, ointments, creams, suppositories.
Liniments are liquid preparations applied to the skin by rubbing and producing heat. They consist of one or more active ingredients and a liniment base or vehicle. The base is generally a bland of fixed oil or alcohol. The massage of the skin is an important feature of liniment therapy. Camphor liniment, camphor and soap liniment are popular.
Lotions liquid preparations applied to the skin without rubbing. The base is usually aqueous. Glycerine and suspending agents are frequently used. After application, fluid is permitted to evaporate from the skin, leaving a film of the dissolved or suspended ingredients. Calamine lotion is best example.
Ointments are semi-solid, grease-like substances intended for local application to the skin. They may be applied to the mucous membrane also. There are ointment bases which are miscible with water. One of these is hydrophilic ointment. Most ointments are applied as local agents to serve as astringents, antiseptics, and protective.
Suppositories are solid preparations for administration to body cavities. There are rectal, vaginal and urethral suppositories. The most common are oil of theobroma (cacao butter) and glycerinated gelatin. Theobroma is fixed oil which is solid at room temperature but which melts at body temperature. They usually weigh 2 gm. Rectal suppositories may be used to elicit systemic effects of their active ingredients. The rectal dose is usually double the oral dose. Vaginal suppositories contain glycerinated gelatin as a base and are usually conical or spherical in shape, they weigh from 4 to 10 gm.