Pharmacology - Pharmacokinetic
- Created by: Sophie
- Created on: 16-01-13 15:44
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- Pharmacokinetics
- Drug Elimination
- The irreversible loss of drug from the body
- Occurs by 2 processes; metabolism + excretion
- Metabolism consists of anabolism + catabolism
- Most drugs leave the body via the kidneys, lungs or hepatobiliarysystem
- Drug Metabolism
- Enzymatic modification of drug molecule
- New molecules may be:
- Active; change in pharmacology, toxicology, duration
- Inactive
- New molecules may be:
- Involves 2 kinds of reaction; Phase 1 and Phase 2
- Phase 1 reactions are catabolic
- Phase 2 reactions are anabolic/ synthetic
- Enzymatic modification of drug molecule
- Excretion
- Elimination of drug and metabolites from the body
- Excretion through kidneys, GI tract, lungs, sweat, tears, mil
- Renal excretion:
- 1. Glomerular Filtration
- Allow molecules of <20000 to pass
- Most drugs are potentially filterable
- Filtratability affected by binding of drug to plasma proteins; only unbound are filtratable
- 2. Tubular Secretion
- Renal tubules contain transporter proteins that pump drugs across membranes
- Many drugs are pumped across membrane by same transporter
- Gives potential for drug interactions due to competition
- Active transport will pump drugs that are bound to plasma proteins
- Binding of drugs to plasma proteins is reversible
- 3. Diffusion across Renal Tubule
- Glomerular filtrate is concentrated in renal tubule
- Reabsorption of water
- Increase in drug
- Non-polar drug = drug reabsorption by increasing conc. gradient
- Polar drug = little reabsorption, drug is excreted in urine eg. penicillin
- Non-polar drug = drug reabsorption by increasing conc. gradient
- Increase in drug
- Ion trapping in Renal Tubule
- Ionisation of weak acids + weak ases changes with pH
- Degree of ionisation can change the rate of drug excretion
- Alkaline urine increases excretion of weak acids
- Acidic urine increases excretion of weak bases
- Alkaline urine increases excretion of weak acids
- 1. Glomerular Filtration
- Biliary Excretion
- Liver cells transport drugs from plasma into bile
- Bile is excreted into intestine
- Involves active transport
- Uncharged drug eg. digoxin
- Unconjugated drug eg. morphine as glucuronide
- Uncharged drug eg. digoxin
- Liver cells transport drugs from plasma into bile
- Quantitative
- Why study pharmacokinetics?
- To determine dose and frequency of admin.
- To explain diff. in response to a drug
- To study:
- 1. Inject a small dose
- 2. Measure disappearancefrom plasma at various times
- 3. Use resulting data to determine Vd and eliminations rate
- Kel = Kexc + Kmet
- Why study pharmacokinetics?
- Drug Elimination
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