Classification of Dosage Forms
A dosage form is the physical vehicle in which a drug substance is presented for administration to a...
A dosage form is the physical vehicle in which a drug substance is presented for administration to a patient. The choice of dosage form is dictated by numerous factors, including the physicochemical properties of the drug, the intended route of administration, the required onset and duration of action, patient population and compliance considerations, and manufacturing feasibility. Dosage forms are broadly classified according to their physical state and the route through which they are administered.
Solid dosage forms — tablets, capsules, powders, granules, and pellets — represent the most widely manufactured category, valued for their chemical stability, ease of accurate dosing, low manufacturing cost per unit, and convenience for the patient. They are administered principally by the oral route, though specialised solid forms exist for buccal, sublingual, and rectal administration. Liquid dosage forms, encompassing true solutions, suspensions, emulsions, syrups, and elixirs, offer the advantage of rapid onset and ease of swallowing for paediatric and geriatric patients, but present greater challenges in chemical and physical stability, microbial contamination control, and accurate dose measurement. Liquids may be formulated for oral, parenteral, nasal, or ophthalmic use depending on their composition.
Semi-solid dosage forms — creams, ointments, gels, pastes, and lotions — are designed predominantly for topical, rectal, or vaginal application, where localised action at or near the site of application is desired, although some semi-solids are engineered for systemic transdermal absorption. Parenteral dosage forms, including intravenous solutions, subcutaneous and intramuscular injections, and lyophilised powders for reconstitution, bypass the gastrointestinal tract entirely and are reserved for situations demanding rapid onset, complete bioavailability, or administration to patients unable to take oral medication; their manufacture is governed by the most stringent quality standards in the entire pharmaceutical industry owing to the requirement for sterility.
Beyond these conventional categories, the modern pharmaceutical landscape includes inhalation products — pressurised metered-dose inhalers, dry powder inhalers, nebuliser solutions, and soft mist inhalers — engineered for direct pulmonary deposition; transdermal systems such as matrix and reservoir patches that deliver drug continuously across the skin into systemic circulation; and implantable systems, including biodegradable rods and osmotic pumps, that provide sustained drug release over weeks to months following a single surgical or subcutaneous placement. Each of these specialised categories demands its own body of formulation science, discussed in detail in later chapters of this text.