University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

451

Pages:

2
Author:

Mariam A. A.

Pharmacokinetics Absorption • • • • Movement of the drug from the site of administration to circulation and then to the targeted site All drugs expect those that are administrated intravenously need to cross at least one cell membrane Movement across cell membrane - Passive diffusion: ✓ Cross the membrane from an area of high concentration to an area of low concentration ✓ Used for small molecules, lipid soluble and non-polar molecules - Facilitated diffusion: ✓ Movement across the membrane through transport proteins such as channels and carrier proteins ✓ Used for polar and large molecules - Active: ✓ Involves carrier proteins that use ATP to pump medications into the cell ✓ Used for medications that need to move against their concentration gradient - Bulk transport ✓ Use endocytosis ✓ Used for large molecules Factors affecting rate and extend of absorption - Available surface area: for example, the villi found within the small intestine - pH Distribution • • • Factors that influence rate of distribution: - Blood circulation and Blood prefusion ✓ More blood flow -> drugs more rapidly distributed to these areas, such as brain, liver and kidney ✓ Less blood flow to areas such as adipose tissues and skin - pH difference between plasma and tissue - molecular size: preferably MW 100 – 1000) - plasma binding ✓ only unbound fractions are able to diffuse through tissues - binding to other tissues such as fat drugs will some extent be metabolised in the liver before passing to the systemic circulation - GIT-> portal vein -> Liver -> heart -> distribution BBB - No fenestrations and endothelial cells are tightly packed together -> prevents unwanted things from passing - Capillaries and brain tissues are formed by connective tissue - Problematic for drugs like penicillin that cannot pass through Metabolism • • • • • • • Occurs in hepatocytes Metabolised to be activated -> desired effect Metabolised to be inactivated -> excretion Produces two effects: - Termination and inactivation of drug activity - Drugs converted into water soluble molecules Involves Phase I and II - Both may occur - Only one - I may occur before II - II may occur before I Phase I - Non-polar & lipid soluble coveted by CYP450 into polar and soluble metabolites - Done through reactions of oxidation, hydrolysis, and reduction Phase II - Conjugation reactions: meds joined with another compounds - These reactions include methylation, sulfation, acetylation and glutathionylation - Create very polar molecules that cannot diffuse through the cell membrane - Trapped in urine and eliminated in the kidneys Elimination • • • Involves: - Metabolism - Excretion Filtered through the glamorous - > proximal convoluted tube -> distal convoluted tube - As it goes though the convoluted tube: ✓ If non-polar: passively diffused back into circulation ✓ If polar: gets trapped in tubular fluid -> eliminated from body in the form of urine Other routes for elimination - Faeces - Bile - Through lungs