What is a Dosage Form?

A dosage form (DF) refers to how a drug should be consumed or administered in order to appropriately deliver a medication. It can be classified according to its route, which includes oral, inhaled, intravenous, topical, and suppository routes. The chosen route of administration (ROA) typically depends on the medical condition of a patient and the efficiency of drug delivery through that particular route.

In pharmacology, the dosage form of a drug is important in determining whether it will reach effective concentrations in the bloodstream. For instance, penicillin has very low oral bioavailability due to first-pass hepatic metabolism. This means that when penicillin is taken orally, it is absorbed through the intestinal mucosa but is extensively metabolized by the liver. An insufficient amount of penicillin reaches the target organ, for instance, the heart for rheumatic fever. Hence, the dosage form of penicillin is neither as a pill nor as a tablet, but as an intravenous injection.

Penicillin is an effective antibiotic, and giving it as an intravenous injection is often inconvenient, so it was modified to produce amoxicillin, which has high oral bioavailability. Amoxicillin has oral forms, and it is given as capsules for adults or as syrup for children. The high oral bioavailability of paracetamol also explains why its preferred dosage form is oral.

Oral dosage forms include pills, tablets, capsules, liquid solution or suspension, and pastes. Some drugs are in the form of specialty tablets, and one example is sublingual nitroglycerin tablets, which have to be put under the tongue in order to relieve chest pains or angina. Inhaled dosage forms include nebulizers, inhalers, aerosols, vaporizers, and smoked substances. Salbutamol, a short-acting bronchodilator, is often given in nebulized form to patients who are having asthma attacks. Corticosteroids, such as budeson, fluticasone, and mometasone, are administered in inhalers for people who have persistent allergic rhinitis, uncontrolled asthma, or chronic obstructive pulmonary disease.

Parenteral injections are preferred for drugs that have to reach the bloodstream in the quickest amount of time. The dosage forms for these drugs include intradermal (ID), intramuscular (IM), intraosseus (IR), intraperitoneal (IP), intravenous (IV), and subcutaneous (SC). For instance, the bacillus Calmette–Guérin (BCG) vaccine, which is designed to prevent complicated forms of tuberculosis, is administered ID. Live attenuated vaccines are generally delivered IM. Parenteral nutrition is delivered IV, and insulin is delivered SC.

Topical dosage forms include creams, gels, lotions, ointments, otic drops, ophthalmic drops, and skin patches. In general, topical forms are preferred for conditions that are limited to one organ, such as topical corticosteroids for allergic dermatitis, eye drops for bacterial conjunctivitis, and eardrops for acute otitis media. Laxatives, such as bisacodyl, may be used in the form of rectal suppository, while antifungal drugs for candidiasis may be delivered in the form of vaginal suppository.