Drug Delivery: Enteral Route

Enteral administration includes oral, sublingual, and buccal routes. Oral administration involves swallowing a pill; sublingual delivery places the drug under the tongue, while buccal intake positions it between the gums and cheek. Oral is the most prevalent, safe, economical, and convenient method for drug delivery.

Enteric-coated drugs release only in the intestine, preventing denaturation or inactivation of acid-sensitive drugs like omeprazole while shielding the stomach from irritants like aspirin. This coating protects drugs from destruction by gastric secretions and reduces gastric irritation, ensuring the drug reaches the small intestine intact for proper absorption.

Sublingual and buccal routes enable direct drug diffusion into the bloodstream, bypassing the gastrointestinal tract and the first-pass effect in the liver. The venous drainage from the mouth leads directly to the superior vena cava, protecting the drug from premature metabolism and ensuring rapid effectiveness upon reaching the heart and arterial system.

Gastric emptying is affected by food caloric content, fluid volume, osmolality, temperature, pH, diurnal and interindividual variation, metabolic state, and ambient temperature. Estrogen also affects gastric emptying in women; emptying is slower for premenopausal women and those on estrogen replacement therapy, influencing overall drug absorption rates.

Controlled-release preparations employ special coatings for gradual drug release, ensuring prolonged action and reducing dosage frequency. They maintain overnight therapeutic effects, decrease undesired effects, and are particularly suitable for drugs with short half-lives or specific patient groups receiving antiepileptic or antipsychotic agents.

Although weak acids are better absorbed from the stomach and weak bases from the intestine, the large surface area of the small intestine allows for a greater drug absorption rate than the stomach. Most drugs are absorbed by passive diffusion, favoring nonionized, lipophilic forms that cross intestinal membranes more efficiently.

Sublingual nitroglycerin is used in the management of angina, providing rapid relief by bypassing first-pass metabolism and hepatic inactivation. Buccal midazolam is employed in the emergency treatment of epileptic seizures in children, allowing quick absorption and therapeutic action without requiring intravenous administration or gastrointestinal processing.