Drug Elimination Pathways and Therapeutic Concepts
Drug Elimination Pathways
Renal elimination is the main route of drug elimination, occurring through several kidney excretion mechanisms.
Enterohepatic Recirculation (Biliary Excretion)
Some drugs are excreted through the bile, which is released into the duodenum to emulsify fats during digestion.
Pulmonary Elimination
The respiratory mucosa can eliminate substances, especially volatile ones, such as volatile anesthetics and alcohol.
Elimination Through Glands
Elimination through glands, particularly the mammary gland, is important due to its potential impact on infants.
Molecular Characteristics and Elimination
Small, ionized, and lipid-soluble molecules easily cross membranes through passive diffusion, facilitating their elimination.
Therapeutic Levels and Ranges
Therapeutic Level
The minimal effective concentration above which a drug begins to exert its therapeutic effect.
Therapeutic Margin
The range of drug concentrations within which there is a high probability of achieving efficacy with minimal toxicity in most patients.
Toxic Level (Toxic Concentration)
The plasma concentration above which the drug causes toxic effects.
Therapeutic Range and Risks
The therapeutic range is the interval between the therapeutic level and the toxicity level of a drug. A wider interval indicates a safer drug. Drugs with a narrow therapeutic range require careful monitoring to prevent adverse effects.
Plasma Half-Life
Plasma half-life describes the duration of action of most drugs. It is the time it takes for a drug’s plasma concentration to decrease by half.
Therapeutic Index
The therapeutic index expresses the relationship between the effective dose for 50% of the population and the lethal dose for 50% of the population.
Drug Safety and Therapeutic Index
A drug with a higher therapeutic index is safer because there is a lower chance of causing toxic effects.
Agonists vs. Antagonists
Agonists
When an agonist binds to a receptor, it leads to the same type of response as the endogenous substance that usually binds to that receptor. The agonist can elicit a response of greater or lesser magnitude than the original substance.
Antagonists
When an antagonist binds to the receptor, it prevents the endogenous substance from developing its action. It blocks the binding site and does not trigger the expected action.
Tablet Types
Enteric-Coated Tablets
- Pass through the stomach unchanged.
- Release the active substance in the intestine.
- Should not be crushed.
Film-Coated Tablets
- Protect the active ingredient from light and moisture.
- Facilitate swallowing.
Delayed-Release Tablets
Delayed-release tablets begin drug release in the intestine after passing intact through the stomach. These oral forms are often enteric-coated.
Continuous Release Oral Systems
These systems have a more complex design and maintain a uniform and constant release of the active ingredient over 8, 12, 24, or even 48 hours, achieving sustained therapeutic levels.