Routes of Drug Administration

Enteral Route

• Enteral route involves administration of drugs through the gastrointestinal tract
• Includes oral, sublingual, buccal, and rectal routes

Oral Route

• Most common and convenient route of administration
• Advantages: easy, safe, economical, and preferred by patients
• Disadvantages: limited absorption, affected by food, unsuitable for uncooperative or unconscious patients, and first-pass effect
• Solid dosage forms:
  • Tablets: hard-compressed units consisting of active ingredients and excipients
  • Chewable tablets: can be chewed before swallowing
  • Capsules: gelatin containers filled with medication (hard gelatin and soft gelatin)

Sublingual/Buccal Route

• Absorption pattern depends on physico-chemical properties of drugs
• Advantages: bypasses first-pass effect, bypasses stomach acid, and immediate pharmacological effects
• Disadvantages: limited to certain types of drugs, limited to small doses, and may lose part of the drug dose if swallowed

Rectal Route

• Partially bypasses first-pass effect, bypasses stomach acid, and ideal for drugs that cause vomiting
• Advantages: suitable for unconscious patients, bypasses digestive enzymes, and ideal for high-molecular-weight proteins and peptide drugs
• Disadvantages: may irritate rectal mucosa and not a well-accepted route

Parenteral Route

• Includes intravenous, intramuscular, and subcutaneous routes
• Injections act rapidly, with 100% bioavailability, and can be used for drugs that are poorly absorbed or ineffective when given orally

Intravenous (IV) Route

• Advantages: immediate effects, ideal for large volumes, suitable for irritating substances, and valuable in emergency situations
• Disadvantages: unsuitable for oily or poorly absorbed substances, bolus injection may result in adverse effects, and strict aseptic techniques needed

Subcutaneous (SC) Route

• Depends on drug diluents: aqueous solutions for prompt absorption and depot preparations for slow and sustained absorption
• Advantages: suitable for slow-release drugs and ideal for poorly soluble suspensions
• Disadvantages: pain or necrosis if drug is irritating and unsuitable for large volumes

Other Routes

• Inhalation route:
  • Advantages: rapid absorption, ideal for gases, effective for patients with respiratory problems, and fewer systemic side effects
  • Disadvantages: systemic absorption may occur, addictive, and patients may have difficulty regulating dose
• Intranasal route:
  • Advantages: rapid onset of action, bypasses first-pass metabolism, and suitable for local and systemic effects
  • Disadvantages: limited volume, continuous and frequent administration may irritate nasal epithelium
• Intrathecal/Intraventricular route:
  • Advantages: drugs can bypass blood-brain barrier, local effects, and fewer systemic side effects
  • Disadvantages: can cause direct irritation of meninges
• Topical route:
  • Advantages: easy, non-invasive, and local effect
  • Disadvantages: most drugs have high molecular weight, poorly lipid-soluble, and very slow absorption
• Transdermal route:
  • Advantages: slow and sustained, bypasses first-pass effect, convenient, and painless
  • Disadvantages: some patients are allergic to patches, drug must be highly lipophilic, and may cause delayed delivery of drug to site of action

Selection of Suitable Route of Administration

• Depends on:
  • Physio-chemical properties of the drug (solubility, stability, pH, irritation)
  • Site of desired drug action (local, systemic)
  • Rapidity of desired response (fast or slow response)
  • Rate and extent of absorption from different routes
  • Effect of digestive juices and first-pass metabolism
  • State of patient (conscious, vomiting)