Pharmacokinetics (AS) Flashcards
What is pharmacokinetics?
quantitative description of changes in conc of drug in body over time after dosing
ADME
interaction between fluoxetine and amitriptyline
- fluoxetine increases plasma concentration of amitriptyline
- fluoxetine inhibits metabolism of amitriptyline and inc its plasma conc
-> pharmacokinetic interaction
interaction between fluoxetine and tramadol
- serotonin syndrome can occur
- both inc availability of serotonin
- happens without change in the conc of either drug
-> pharmacodynamic interaction
drugs that need regular pharmacokinetic monitoring
theophylline lithium methotrexate ciclosporin cardioselective agents (digoxin) aminoglycosides (gentamicin) anti-convulsants (phenytoin)
TDM
therapeutic drug monitoring
why to indicidualise dosage regimens
- therapeutic index of drug is small
- standard dose doesn’t always produce expected results
- signs of toxicity may be hard to recognise
- metabolites may be effective AND toxic
- inter-patient variability factors
- disease states can alter patients’ PD parameters
- social habits can alter parameters
- protein binding
- non-compliance
- overdoses
- route of admin
- drug interactions
drug that smoking effects
theophylline
factors that affact absorption of drugs
- pH/surface tension
- food/mucus/other drugs
- emptying time
- motility
- disease
- posture (maybe)
- brand substitution
factors that affect distribution of drug
- perfusion (blood supply)
- binding (to R/plasma proteins)
- membrane (can drug cross?)
- drug (physiochem properties)
What does k stand for?
elimination rate constant
- > FRACTION of drug eliminated per unit time
- > unit = minute-1 or hr-1
What does K=0.25 per hour mean?
25% is eliminated from the body per hour
What does V stand for?
volume of distribution
-> hypothetical vomume of fluid in which the total amount of drug in the body would need to be distributed to give a conc equal to the conc measured in plasma
What does high vol of distribution mean?
- drug distributes better to the peripheries
- need large vol to contain the total amount of drug
- distributes everywhere
- will need go give a high dose of drug to get the plasma conc
How to calculate dose based on vol of distcibution?
conc required x V
vol of distribution for drug that binds tightly to tissues
high V
- small proportion found in plasma
