Learning Objects : Lifelong Application

RLO: Introduction to drug clearance

Resources

Title/link	Description
RLO: Half-life of drugs	Explains the half-life of drugs and its relationship with volume of distribution and clearance.
RLO: The kidneys and drug excretion	The role of the kidneys in the excretion of drugs.
RLO: The physiology of the kidneys	Introduction to the physiology of the kidney, examining the processes by which the kidneys filter blood, control body pH and eliminate the waste products of metabolism from the body.
RLO: The liver and drug metabolism	The role of the liver in the metabolism of drugs.
RLO: The physiology of the liver	Introduction to the physiology of the liver, examining its role in filtering blood, metabolism, nutrient extraction and homeostasis.

Glossary

Alkalinise: To make more alkaline, less acidic. In terms of alkalinisation of the urine, this can be done to promote the excretion of drugs which are weak acids.

Aspirin: A non-steroidal anti-inflammatory drug which exists as a weak acid.

Atenolol: A cardioselective beta adrenoreceptor antagonist which is polar in nature and cleared almost exclusively by the kidneys.

Bile: A fluid secreted by the liver, stored in the gall bladder and released into the duodenum to aid the emulsification of fats. Bile can also contain drugs which have been metabolised in the liver.

Clearance: The rate of drug elimination divided by the plasma concentration of the drug.

Cytochrome P450: Drug metabolising enzymes that are embedded in the smooth endoplasmic reticulum of liver cells.

Elimination: The irreversible loss of drug from the body.

Excretion: The removal of drug from the body.

Furosemide: A loop diuretic which is polar in nature and cleared almost exclusively by the kidneys.

Genetic polymorphisms: Changes in the genetic code which occur in a population and result in the production of enzymes, particularly cytochrome P450 enzymes, which may as a result be more or less active than the norm.

Glomerular filtration: One of three processes which are critical for renal clearance. Involves the filtration of 20% of renal plasma flow through the glomerular capillaries, thus allowing drug molecules to diffuse into the glomerular filtrate.

Half-life: The time taken for the plasma concentration of a drug to reduce by 50%.

Hepatocyte: A liver cell.

Ionised: Charged or polar in nature (not lipid soluble).

Metabolism: The enzymatic conversion of one chemical entity to another in order to make it less lipid soluble, hence easier to excrete.

Passive diffusion: One of three processes which are critical for renal clearance. Involves the reabsorption of water and drug molecules across the tubule membranes and back into the plasma.

Steady state: Steady state is said to have been reached when the concentration of the drug in the plasma does not drop below therapeutic levels between doses. Steady state is usually achieved after 4/5 half-lives of the drug.

Tubular secretion: One of three processes which are critical for renal clearance. Involves the transfer of drug molecules to the tubular lumen by two independent, non-selective carrier systems.