Dosage Forms — Complete Overview

Figure: Commonly used routes of drug administration — Lippincott Illustrated Reviews: Pharmacology

Classification of Dosage Forms

1. Enteral (via the GI tract)

A. Oral

• Subject to first-pass hepatic metabolism
• Low gastric pH inactivates some drugs
• Food can significantly affect absorption
• Patient compliance is essential

B. Sublingual / Buccal

• Sublingual: Drug placed under the tongue (e.g., nitroglycerin, buprenorphine)
• Buccal: Drug placed between the cheek and gum (e.g., asenapine sublingual tablets)

C. Rectal

• ~50% of rectal venous drainage bypasses the portal circulation → reduces first-pass metabolism
• Useful when oral route is unavailable (vomiting, unconsciousness)
• Rectal absorption is often erratic and incomplete
• Many drugs irritate the rectal mucosa
• Clinical use: antiemetics (promethazine), antiepileptics (diazepam rectal gel), hydrocortisone enemas for ulcerative colitis

2. Parenteral (Injected — bypasses GI tract)

3. Topical & Transdermal

A. Topical (local effect)

B. Transdermal (systemic effect via skin)

Figure: A. Cross-section of a transdermal patch showing the drug reservoir, drug-release membrane, and diffusion into subcutaneous tissue. B. Nicotine transdermal patch applied to the arm.

• Skin thickness at application site
• Lipid solubility of the drug

C. Inhalation

• Drug delivered directly to the lungs → high local concentration at site of action
• Minimizes systemic side effects
• Used for asthma, COPD (bronchodilators: salbutamol, tiotropium; corticosteroids: budesonide, fluticasone, beclomethasone)

4. Special & Newer Dosage Forms

Pediatric Dosage Form Considerations

• Most pediatric drugs are given as elixirs or suspensions
• Elixirs are alcoholic solutions → drug molecules evenly dissolved → no shaking required
• Suspensions contain undissolved particles → must be shaken before each dose
  • Inadequate shaking of phenytoin suspension → underdosing early and toxicity late in therapy
• Calibrated medicine spoons or oral syringes should replace household teaspoons (measured volume varies 2.5–7.8 mL)
• Palatability is critical for adherence in children — bitter formulations may need flavored additives
• Dosing errors (10-fold decimal point errors) are a serious risk when doses are weight-calculated

Summary Comparison Table

• Lippincott Illustrated Reviews: Pharmacology, Chapters 1 (Routes of Administration)
• Katzung's Basic and Clinical Pharmacology, 16th Edition, Chapters on Pediatric Pharmacology and Corticosteroids
• Kaplan & Sadock's Comprehensive Textbook of Psychiatry (Antipsychotic Dosage Forms)

Additional Dosage Forms: Ampoules, Vials, Pessaries & More

1. Ampoules (Ampules)

• Made from neutral (borosilicate) glass to prevent chemical interaction with the drug
• Sealed by melting the glass neck — the seal is broken open just before use (snap-off or score-and-break type)
• Single-dose only — once opened, the entire contents must be used; cannot be re-sealed
• No preservatives needed (used immediately after opening)
• Protects light-sensitive or air-sensitive drugs (complete hermetic seal)
• The contents are withdrawn using a filter needle to prevent glass particle contamination

2. Vials

• Aqueous solution ready to inject
• Powder for reconstitution
• Concentrated solution for dilution before IV infusion

3. Pessaries (Vaginal Pessaries)

A. Pharmaceutical Pessary (Vaginal Suppository)

• Shape: torpedo-shaped, ovoid, or globular
• Base: typically cocoa butter, polyethylene glycol (PEG), or gelatin
• Mechanism: melts at 37°C → releases drug → absorbed by vaginal mucosa

B. Mechanical/Orthopaedic Pessary (Device)

Figure: Types of pessaries (1–23). 1. Hodge with knob; 2. Risser; 3. Smith; 12. Gellhorn rigid; 14. ring with support; 17. Inflatoball; 22. donut; 23. ring — Pfenninger and Fowler's Procedures for Primary Care

4. Lozenges / Troches / Pastilles

5. Linctus

• Used for coughs and sore throats
• Slow sipping allows drug to coat the pharyngeal mucosa
• Often contains glycerol, honey, or sugar base
• Examples: Simple linctus (glycerol base, demulcent), pholcodine linctus (cough suppressant), codeine linctus (cough suppressant/analgesic)

6. Gargle / Mouthwash

• Used for local antiseptic, anti-inflammatory, or anaesthetic effects in the mouth and throat
• Examples: Chlorhexidine mouthwash (antiseptic), benzydamine gargle (anti-inflammatory/analgesic), lidocaine "laryngeal gargle" via endoscope during bronchoscopy, alcohol-free antibacterial mouthwash for oral piercings

7. Other Less-Discussed Dosage Forms

Quick Reference Summary

DOSAGE FORM CONTAINERS:
├── Ampoule     — glass, hermetically sealed, single-dose, no preservative
├── Vial        — rubber-stoppered, single or multi-dose, may contain preservative
│   └── Lyophilized vial — powder + diluent for reconstitution
│
VAGINAL/LOCAL:
├── Pharmaceutical pessary — solid, dissolves vaginally (drug delivery)
├── Mechanical pessary     — silicone device for prolapse (not drug delivery)
│
ORAL MUCOSAL:
├── Lozenge / Troche / Pastille — slow oral dissolution
├── OTFC lozenge ("lollipop")   — transmucosal systemic absorption
│
LIQUID ORAL:
├── Linctus   — viscous, sipped slowly, coats throat
├── Gargle    — aqueous, held in throat
├── Mouthwash — swished and expectorated
│
SUSTAINED RELEASE (NOVEL):
├── Implant / Pellet — subcutaneous, months–years duration
├── IUD              — intrauterine, local hormonal release

• Lippincott Illustrated Reviews: Pharmacology (Routes and forms)
• Pfenninger and Fowler's Procedures for Primary Care, 3rd ed. (Pessary fitting)
• Tintinalli's Emergency Medicine (OTFC lozenge)
• Goodman & Gilman's The Pharmacological Basis of Therapeutics (Troches)
• Katzung's Basic and Clinical Pharmacology, 16th ed. (Pediatric and special dosage forms)