Pharmacology Chapter: Routes of Drug Administration

Routes of Drug Administration

• Presented by Dr. Mariam Ashraf Amin, Pharmacology and Toxicology department, Faculty of Pharmacy (2024-2025)
• Drug administration has two main categories: enteral and parenteral.

Enteral Routes

• Enteral routes are related to the gastrointestinal tract (GIT).
• This includes: oral, sublingual, buccal, and rectal administration.

Oral Route

• Advantages: easy, economical, self-administered, and safe due to potential for overdose management.
• Disadvantages: slow absorption (limiting in emergencies), destruction by digestive fluids, interactions with food, and unsuitable for unconscious/uncooperative/severely ill patients or if vomiting/convulsions occur.
• Dosage forms: oral drops, suspension, tablets, effervescent sachets (enterically coated, sustained release), colored, effervescent, chewing tablets, and lozenges.

Sublingual Route

• Advantages: rapid onset, suitable for emergencies (angina/hypertension), bypasses first-pass metabolism (high bioavailability), and excess dose can be expelled.
• Disadvantages: not suitable for all drugs (e.g., nitrates/captopril).

Rectal Route

• Advantages: suitable for patients unable to take oral drugs (e.g., unconscious/vomiting). 50% of drug bypasses the liver, offers localized or systemic effects (depending on drug), and avoids gastric irritation.
• Disadvantages: not suitable for diarrhea, inconvenient/unacceptable by many patients.
• Dosage forms: suppositories and enemas.

Parenteral Routes

• Parenteral routes bypass the GIT, involving injections, topical application, and inhalation.

Injections

• Advantages and Disadvantages of different types of injection are discussed (Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), and Intrathecal)

• IV: rapid onset, suitable for emergencies, maintains drug in active form, and high bioavailability. Disadvantages include expense, aseptic conditions are needed, difficulty in self-administration, pain, need for patent vein, and difficulty eliminating the drug if toxicity occurs.

• IM: suitable for moderate-volume drugs and irritant drugs. Disadvantages include not suitable for anticoagulants, lower volume given (4-5 ml), expense, need aseptic condition, and pain.

• SC: suitable for suspensions and oily solutions, provides slow duration of action, suitable for hormones. Disadvantages include slow onset, not suitable for irritant/large volumes.

• Intrathecal/Intra-thecal: high concentration in CSF suitable for treating CNS disorders, diagnosing CNS disorders and injecting antibiotics. Need highly specialized physician and special precaution for avoiding infection/spinal nerve injury.

Inhalational Routes

• Advantages: suitable for volatile compounds (gases), allows for local/systemic effects, avoids first-pass metabolism, rapid onset (similar to IV) and self-administered.
• Disadvantages: not used for irritant drugs, difficult to adjust dose, and may need special inhaler apparatus.
• Used for bronchial asthma and volatile anesthetics.

Topical/Local Administration

• Advantages: local high concentrations of drug, bypasses first-pass metabolism (transdermal), localized effects.
• Disadvantages: some systemic absorption can occur; unsuitable for highly lipid-soluble drugs.
• Dosage forms: drops, creams, ointments, lotions, transdermal patches.

First-Pass Metabolism

• Metabolism that occurs as drugs are absorbed from the Gastrointestinal tract before reaching systemic circulation.
• Hepatic first-pass: Drugs absorbed from the GIT are carried first in portal circulation to the liver.
• Intestinal first-pass: due to intestinal mucosal metabolism affecting drugs e.g., nitroglycerin, propranolol, isoprenaline, and tyramine.
• First-pass metabolism can be avoided or reduced by sublingual, parenteral, or partially by rectal administration.