Drug Elimination, Mechanisms, and Therapeutic Levels
Renal Drug Elimination
Renal elimination is the primary route for drug removal from the body, involving several kidney excretion mechanisms.
Enterohepatic Recirculation (Biliary Excretion)
Some drugs are excreted through bile, which is released into the duodenum to aid fat emulsification during digestion.
Pulmonary Elimination
The respiratory mucosa can eliminate volatile substances like anesthetics and alcohol.
Elimination Through Glands
Elimination can occur through glands, notably the mammary gland, which can affect infants.
Drug Molecule Characteristics and Elimination
Small, ionized, and lipid-soluble molecules readily cross membranes via passive diffusion.
Therapeutic Levels, Toxicity, and Therapeutic Range
Therapeutic Level
The minimal effective concentration at which a drug starts producing therapeutic effects.
Therapeutic Margin
The drug concentration range with a high probability of efficacy and minimal toxicity for most patients.
Toxic Level (Toxic Concentration)
The plasma concentration exceeding the level causing toxic effects.
Narrow Therapeutic Range and Risks
The interval between therapeutic and toxic drug levels is the therapeutic range. A wider range indicates a safer drug. Drugs with narrow ranges require monitoring to prevent toxicity.
Plasma Half-Life
The time taken for a drug’s plasma concentration to decrease by half, describing its duration of action.
Therapeutic Index
The ratio between the effective dose for 50% of the population (ED50) and the lethal dose for 50% of the population (LD50).
Safety and Therapeutic Index
A higher therapeutic index indicates a safer drug due to a lower risk of toxicity.
Agonists vs. Antagonists
Agonists
Drugs binding to a receptor and producing a similar response to the endogenous substance, potentially with greater or lesser magnitude.
Antagonists
Drugs binding to a receptor and blocking the action of the endogenous substance.
Enteric-Coated vs. Film-Coated Tablets
Enteric-Coated Tablets
Pass through the stomach unchanged, releasing the active substance in the intestine. Should not be crushed.
Film-Coated Tablets
Protect the active ingredient from light/moisture and ease swallowing.
Delayed-Release Tablets
Release the drug in the intestine, passing intact through the stomach. Oral forms are often enteric-coated.
Continuous-Release Oral Systems
Complex designs maintaining uniform and constant active substance release over extended periods (8, 12, 24, or 48 hours), achieving sustained therapeutic levels.