Dosage Forms Deep Dive
Understanding dosage forms is essential for pharmacy technicians. Different dosage forms serve different purposes - from controlling drug release to targeting specific body sites to accommodating patients who cannot swallow tablets. This guide covers the major dosage forms tested on the CPHT exam.
Solid Oral Dosage Forms
| Dosage Form | Description | Key Points |
|---|---|---|
| Tablet (tab) | Compressed powder into a solid form | Most common oral dosage form. May be scored for splitting. |
| Capsule (cap) | Drug contained within a gelatin or vegetarian shell | Can be hard-shell (two pieces) or soft-gel (one piece, liquid-filled). |
| Enteric-coated (EC) tablet | Tablet with a coating that resists dissolution in stomach acid | Dissolves in the alkaline environment of the small intestine. Do not crush or chew. |
| Extended-release (ER/XR/XL/CR/SR/LA) | Formulated to release drug slowly over time | Provides longer duration of action and less frequent dosing. Do not crush, chew, or split unless specifically designed for it. |
| Delayed-release (DR) | Drug release is delayed until a certain condition is met (e.g., reaching the intestine) | Similar to enteric-coated. Do not crush. |
| Orally disintegrating tablet (ODT) | Dissolves rapidly on the tongue without water | Useful for patients who have difficulty swallowing. Place on the tongue and allow to dissolve. |
| Sublingual tablet (SL) | Placed under the tongue for rapid absorption through oral mucosa | Do not swallow whole. Example: nitroglycerin SL tablets. |
| Buccal tablet | Placed between the cheek and gum for absorption through oral mucosa | Do not chew or swallow. |
| Chewable tablet | Designed to be chewed before swallowing | Must be chewed for proper effect. Flavored for palatability. |
| Effervescent tablet | Dissolves in water to produce a fizzy solution | Must be dissolved in water before drinking. Contains sodium bicarbonate and citric acid. |
| Lozenge / Troche | Dissolves slowly in the mouth for local or systemic effect | Do not chew or swallow whole. |
| Powder | Finely divided drug particles | May be mixed with food or liquid before administration. |
| Granules | Larger aggregates of powder particles | May be sprinkled on food or dissolved in liquid. |
Liquid Dosage Forms
| Dosage Form | Description | Key Points |
|---|---|---|
| Solution | Drug completely dissolved in a solvent | Clear liquid. Dose is uniform throughout. |
| Suspension | Fine drug particles dispersed (not dissolved) in a liquid | Must "shake well" before each use. Particles settle over time. |
| Emulsion | Mixture of two immiscible liquids (oil and water) stabilized by an emulsifying agent | Can be oil-in-water (o/w) or water-in-oil (w/o). |
| Elixir | Clear, sweetened, hydroalcoholic solution | Contains alcohol. May not be suitable for pediatric patients or those avoiding alcohol. |
| Syrup | Concentrated, sweetened aqueous solution | Sugar-based. Sugar-free versions available for diabetic patients. |
| Tincture | Alcoholic or hydroalcoholic solution of a drug | Higher alcohol content than elixirs. Example: iodine tincture. |
| Spirit | Alcoholic solution of a volatile substance | Example: spirit of peppermint. |
Injectable Dosage Forms
| Route | Description | Key Points |
|---|---|---|
| Intravenous (IV) | Directly into a vein | Fastest onset. Drug bypasses absorption. Must be sterile and typically pyrogen-free. |
| Intramuscular (IM) | Into the muscle tissue | Slower absorption than IV. Common sites: deltoid, vastus lateralis, ventrogluteal. |
| Subcutaneous (SubQ) | Into the fatty tissue beneath the skin | Slower absorption than IM. Common for insulin, heparin, and some vaccines. |
| Intradermal (ID) | Into the dermis (top layer of skin) | Used for TB skin tests and allergy testing. Very small volumes (0.1 mL). |
| Intrathecal | Into the spinal canal | Specialized; used for certain chemotherapy and pain management. |
Topical and Transdermal Dosage Forms
| Dosage Form | Description | Key Points |
|---|---|---|
| Cream | Semisolid emulsion (oil-in-water or water-in-oil) | Spreads easily, absorbs well. Vanishes into the skin. Generally preferred for moist or weeping areas. |
| Ointment | Semisolid preparation (oil-based) | Greasy, occlusive, provides a moisture barrier. Better for dry skin conditions. |
| Gel | Semisolid system in which a liquid phase is constrained within a polymer network | Clear or translucent. Non-greasy. |
| Lotion | Liquid preparation for topical application | Spreads easily over large areas. Less occlusive than creams or ointments. |
| Paste | Thick semisolid with a high proportion of powder | Provides a protective barrier. Absorbs moisture. |
| Transdermal patch | Adhesive patch that delivers drug through the skin into systemic circulation | Provides sustained drug delivery. Examples: fentanyl, nicotine, estradiol patches. |
Ophthalmic, Otic, and Nasal Forms
| Dosage Form | Route | Key Points |
|---|---|---|
| Ophthalmic solution | Eye drops | Must be sterile. One drop approximately 0.05 mL. |
| Ophthalmic suspension | Eye drops | Must be sterile. Shake before use. |
| Ophthalmic ointment | Applied to lower eyelid | Must be sterile. May cause temporary blurred vision. |
| Otic solution | Ear drops | Not required to be sterile (the ear canal is not sterile). Do NOT use ophthalmic preparations in the ear unless labeled for dual use. |
| Nasal spray | Intranasal | Can be for local (decongestants) or systemic effect (sumatriptan nasal spray). |
Important: Ophthalmic preparations can generally be used in the ear, but otic preparations should NEVER be used in the eye (they may not be sterile and may contain irritating ingredients).
Rectal and Vaginal Dosage Forms
| Dosage Form | Description | Key Points |
|---|---|---|
| Suppository | Solid dosage form that melts or dissolves at body temperature | Rectal or vaginal. Used when oral route is not feasible (nausea, unconsciousness). |
| Enema | Liquid preparation administered rectally | Can be for local effect (constipation) or systemic absorption. |
| Vaginal cream / tablet / ring | Various forms for vaginal administration | Typically for local effect (antifungal, hormonal). |
Inhalation Dosage Forms
| Device | Description | Key Points |
|---|---|---|
| MDI (Metered-Dose Inhaler) | Pressurized canister that delivers a measured dose of aerosolized medication | Requires coordination of breathing and actuation. A spacer can improve delivery. |
| DPI (Dry Powder Inhaler) | Device that delivers medication as a dry powder | Breath-activated - no coordination needed. Must inhale quickly and deeply. |
| Nebulizer | Device that converts liquid medication into a fine mist for inhalation | Used for patients who cannot use MDIs or DPIs (young children, elderly, severe respiratory distress). |
Key Rules About Dosage Forms
- Never crush: Enteric-coated, extended-release, sustained-release, controlled-release, or delayed-release tablets. Crushing destroys the release mechanism and can cause dose dumping (releasing the full dose at once).
- Shake well: All suspensions must be shaken well before each use to ensure uniform distribution of particles.
- Store properly: Some dosage forms have specific storage requirements (e.g., suppositories may need refrigeration, nitroglycerin SL tablets must be kept in the original glass container).
- Route matters: Never substitute an otic preparation for an ophthalmic one. Always verify the intended route before dispensing.
Exam Tips
- Know which dosage forms should NOT be crushed (EC, ER, XR, XL, CR, SR, LA, DR).
- Understand the difference between a solution (dissolved) and a suspension (dispersed, needs shaking).
- Elixirs contain alcohol; syrups are sugar-based aqueous solutions.
- Ophthalmic preparations are sterile; otic preparations are not always sterile.
- Know the difference between cream (emulsion, absorbs) and ointment (oil-based, occlusive).
- Transdermal patches provide sustained systemic drug delivery through the skin.
- MDIs require coordination; DPIs are breath-activated; nebulizers turn liquid into mist.