Dosage forms of drugs / Classification dosage forms of drugs / Dosage forms of drugs pharmacology

 Dosage forms of drugs

Dosage form is a product suitable for administration of a drug to a patient. Every active ingredient (drug) has to be formulated by adding other substances (excipients, diluents, preservatives,vehicles, etc.) according to a specific recipe and packaged into a specific ‘dosage form’ such as tablet, elixir, ointment, injection vial, etc. which is then administered to the subject. The dosage form provides body to the drug, demarkates single doses, protects the active ingredient(s), and makes it suitable for administration in various ways. The important dosage forms are briefly described below

Solid dosage forms 

 1. Powders 

The drug is in a dry and finely pulverised state. If the drug is for oral administration, each dose has to be wrapped separately or packed in sachets; therefore this dosage form is inconvenient and unpopular except when the quantity is several grams, e.g. oral rehydration salts. Powders for topical application (dusting powders) are supplied as bulk powders in metallic or plastic containers with holes for sprinkling. Effervescent powders contain granulated sod. bicarbonate and citric or tartaric acid. They react when dissolved in water to liberate CO2 causing bubbling. 

 2. Tablets

 The drug is powdered or granulated, mixed with binding agents, and other excipients, and compressed/moulded into discoid, oblong or other shapes suitable for swallowing. The tablet may be plain or sugar coated or film coated. Other specialized types of tablets are: 

•  Chewable tablets—can be chewed and swallowed, ingredients must be pleasent tasting. 

•  Dispersible tablets—the tablet is dropped in a small quantity of water, wherein it disperses quickly; the solution is then gulped. 

•  Sublingual tablets—put under the tongue, the drug is rapidly absorbed from the mouth. 

•  Enteric coated tablet—the tablet is coated with a material that does not dissolve in the acidic medium of the stomach; the tablet disintegrates only on reaching the duodenum. 

•  Sustained/Extended release tablets—These contain drug particles which are coated to  dissolve at different rates. The active ingredient is made available for absorption over a longer period of time. The duration of action of short acting (2-6 hours) drugs can be extended to 12 hours or more.

•  Controlled release tablets—A semipermeable membrane controls the release of the drug – prolonging its duration of action.

 3. Pills

 These are archaic dosage forms in which the drug powder is mixed with honey/syrup to make a sticky mass. This is then rolled into spherical/oval bodies meant to be swallowed. The term is often loosely applied to tablets as well. SECTION 1 

 4. Capsules 

These are water soluble cylindrical containers made of gelatin which are filled with powdered or liquid medicament. The container dissolves on swallowing so that the drug is released in the stomach. Soft gelatine capsules dissolve very rapidly and generally contain liquid medicament. Enteric coated capsules are designed to dissolve only on reaching the ileum. Spansules are extended release capsules which are packed with granules of the drug having different coatings to dissolve over a range of time periods. 

 5. Lozenges 

These are tablet-like bodies of various shapes containing the drug along with a suitable gum, sweetening and flavouring agents. They are to be retained in the mouth and allowed to dissolve slowly, providing the drug for local action in the mouth and throat.

 6. Suppositories

 These are conical bullet- shaped dosage forms for insertion into the anal canal, in which the drug is mixed with a mouldable f irm base that melts at body temperature and releases the contained drug. Oval or suitably shaped bodies for vaginal insertion are called ‘pessaries’, while elongated pencil-like cones meant for insertion into male or female urethra are called bougies.

 Liquid dosage forms 

 1. Aqueous solutions 

They contain the drug dissolved in water, and may be meant fororal, topical or parenteral administration. Oral drug solutions often contain sweetening and flavouring agents. Preservatives have to be mostly added because shelf-life of watery solutions is short. 

 2. Suspensions 

are dispersion of insoluble drugs in water with the help of a suspending agent. Emulsions are uniform mixtures of two immiscible liquids (mostly oil and water) in which droplets of one (dispersed phase) are suspended in the other (continuous phase) with the help of an amphiphilic emulsifying agent. Milk is a naturally occurring emulsion. Both suspensions and emulsions tend to settle down on keeping; should be shaken thoroughly before use. 

 3. Elixirs

 are hydro-alcoholic solutions of drugs, usually sweetened with syrup and flavoured by fruit extracts. Syrups have higher concentration of sugar and are thicker in consistency. Drugs that deteriorate in aqueous medium can be dispensed as ‘dry syrups’ which is reconstituted by adding water and shaking. The reconstituted syrup must be used within a few days. Linctus is a viscous syrupy liquid meant to be licked slowly for soothing the throat. It generally has menthol to impart cooling sensation, and an antitussive. 

 4. Drops 

These are relatively more concentrated solutions of medicaments meant for oral ingestion or external application to eye, nose or ear canal. Oral drops are the preferred dosage form for infants and young children. Eye/ nasal drops should be isotonic. Eye drops need sterilization. Drops are supplied in vials with a nozzle or alongwith a dropper for accurate dosing. 

 5. Lotions

 These are solutions, suspensions or emulsions meant for external application to the skin without rubbing. They generally have soothing, cooling, protective or emollient property and are better suited than creams or ointments for hairy skin. Liniments are similar preparations which generally contain counterirritants, and are to be rubbed on the skin to relieve pain and cause rubefaction.

 6. Injections

 These are sterile solutions or suspensions in aqueous or oily medium for subcutaneous or intramuscular administration. Only aqueous solutions (not suspensions) are suitable for intravenous (i.v.) injection, because particles in suspension and oils injected i.v. can cause embolism. Injections are supplied in sealed glass ampoules or air tight rubber capped vials. Ampoules are broken just before injection, and usually contain a single dose. Drug from the vial is sucked in a syringe by piercing the rubber cap. Vials may be single or multi-dose. Drugs which are unstable in solution are supplied as dry powder vials. Sterile solvent is injected in the vial just before it is to be administered, and the dissolved/suspended drug is then sucked out into the syringe. Some drugs like insulin are also supplied in prefilled syringes and pen injectors. Large volume i.v. infusions are marketed in glass/polypropylene bottles.

 Semisolid dosage forms

 1. Ointments 

These are greasy semisolid preparations meant for external application to the skin, eye, nasal mucosa, ear or anal canal. The drug is incorporated in an oily base, such as soft or hard paraffin, wool fat, bee’s wax, etc. Ointments are not suitable for oozing surfaces, because they are more occlusive and donot allow evaporation of water. Rather they are good for dry, chronic lesions. Creams are similar to ointment but the base is a water in oil emulsion. The medicament is better absorbed into the skin from creams than from ointments, and creams are cosmetically more acceptable than ointments. 

 2. Pastes 

These are nongreasy preparations of thick consistency containing hydrophilic adhesive powders such as starch, prepared chalk, aluminium/magnesium hydroxide, zinc oxide, carboxy methylcellulose, etc. which swell by absorbing water. Pastes may contain viscous nonoily liquids like glycerol or propylene glycol. Pastes can be applied to inflamed or excoriated skin, oozing surfaces 

and mucous membranes. Toothpastes are items of personal hygiene, and medicated toothpastes are extensively used in dentistry. 

 3. Gels

 The medicament is incorporated in a viscous colloidal solution of gelatin or similar material and is usually dispensed in collapsible tubes. They are meant for external application to the skin or mucosa and provide longer duration contact, but are nongreasy and washable with water. Gels are suitable for application to hairy skin, and are commonly applied to oral ulcers because they are better retained than aqueous solutions.

 Inhalations 

Drugs which are gases or volatile liquids can be administered by inhalation carried into air or oxygen with the help of a mouth piece, face mask, hood or endotracheal tube. Nonvolatile liquids and fine particle solids can be aerosolized using a metered dose inhaler, jet nebulizer, rotahaler or spinhaler for inhalation through the mouth. Pressurized metered dose inhalers (PMDIs) are hand-held devices which use a propellant, mostly hydrofluoroalkane (HFA), and deliver a specified dose of the drug in aerosol form per actuation. Jet nebulizers produce a mist of the drug solution generated by pressurized air or oxygen. Rotahaler is also a portable device in which a capsule (rotacap) containing very fine powder of the drug is punctured during actuation and the released particles are aerosolized by the inspiratory airflow of the patient. A propellant can also be used in some spin halers. Efficacy of the aerosolized drug depends on the particle size: 1–5 mm diameter particles deposit on the bronchioles and effectively deliver the drug. Larger particles settle on the oropharynx, while <1 mm particles donot settle anywhere and are exhaled out.