OIA1013 DRUG EXCRETION

Overview of Drug Excretion

Definition and Importance of Excretion

Excretion is the process of removing drugs from the body, either as unchanged substances or as metabolites.

It is crucial for maintaining homeostasis and preventing drug accumulation, which can lead to toxicity.

The primary excretory organs involved are the kidneys and liver, which play significant roles in drug metabolism and elimination.

Routes of Excretion

Various routes exist for drug excretion, including urine, bile, sweat, saliva, tears, milk, and stool.

Each route has specific mechanisms and implications for drug elimination, affecting therapeutic outcomes.

Renal Excretion Mechanisms

Overview of Renal Excretion

The kidneys are responsible for the majority of drug excretion, filtering blood and producing urine.

Drug excretion involves three main processes: glomerular filtration, tubular secretion, and passive reabsorption.

Glomerular Filtration

Glomerular filtration allows substances with a molecular weight less than 30,000 to pass into the renal tubule.

Approximately 1200 mL of blood is filtered per minute, with about 10% being plasma water.

Tubular Secretion

Active transport mechanisms in the proximal tubule move drugs from the bloodstream into the tubular fluid.

Two main secretory processes exist: one for weak acids (negatively charged) and another for weak bases (positively charged).

Passive Reabsorption

In the loop of Henle, most of the filtered fluid is reabsorbed, with only 1-2 mL excreted as urine.

Unionized, lipid-soluble metabolites are reabsorbed, while ionized, lipid-insoluble metabolites are excreted.

Biliary and Other Routes of Excretion

Biliary Excretion

The liver excretes some drugs into bile, which are then eliminated in feces.

Enterohepatic recycling can occur, where drugs are reabsorbed from the gut after being excreted into bile.

Other Excretion Routes

Pulmonary excretion is significant for gases and volatile compounds, such as anesthetics.

Minor routes include sweat, tears, saliva, and breast milk, which can lead to drug exposure in infants.

Factors Influencing Drug Elimination

Drug Interactions and Age

Drug interactions can significantly affect excretion rates, with enzyme inhibitors and inducers altering drug metabolism.

Age-related changes in renal and liver function can impact drug clearance, particularly in neonates and the elderly.

Genetic and Disease Factors

Genetic polymorphisms in drug-metabolizing enzymes can lead to variations in drug metabolism among individuals.

Diseases affecting liver or kidney function can hinder drug excretion, leading to increased toxicity and altered pharmacokinetics.

Discussion questions

1/6

What are the primary routes of drug excretion in the human body, and how do they differ in terms of their mechanisms?

Difficulty: Easy

2/6

How does urine pH influence the excretion of drugs, particularly in cases of poisoning?

Difficulty: Medium

3/6

Discuss the impact of age on drug metabolism and excretion, particularly in neonates and the elderly.

Difficulty: Medium

4/6

What role do genetic polymorphisms play in drug metabolism, and how can they affect patient treatment outcomes?

Difficulty: Hard

5/6

Analyze the significance of renal excretion processes, including glomerular filtration, tubular secretion, and passive reabsorption.

Difficulty: Hard

6/6

How do disease states, such as liver cirrhosis or chronic kidney disease, influence drug elimination and potential toxicity?

Difficulty: Hard