Viva Flashcards
Define pharmacokineties
what the body does to a drug
define pharmacodynamics
what the drug does to the body
what is clearance?
the volume of plasma cleared of a drug per unit of time
what is half-life?
time taken for drug concentration to decline to half it’s original value
what is half-life of a drug dependent on?
volume of distribution
clearance
what is volume of distribution?
the volume into which a drug will distribute into
- high if lipid soluble
- lower if water soluble
what are first order kinetics?
refer to drugs where clearance is proportional to plasma concentration
- most drugs
what are zero order kinetics?
clearance is not always proportion to plasma concentration
occurs at saturation of metabolism (constant rate of elimination regardless of plasma level due to all enzymes used)
e.g. phenytoin, salicylates, ethanol
what is bioavailability?
% reaching systemic circulation
100% in IV
when is a loading dose needed?
loading doses are used to reduce the time needed to reach a steady state of drug level
good if short or long half life
examples are phenytoin, digoxin, amiodarone, theophylline
what is first pass metabolism?
inactivation of drug prior to systemic circulation in gut wall + liver
e.g. propranolol, verapamil, morphine, nitrates
how are drugs excreted?
either:
- phase 1 metabolism -> renal excretion
- phase 2 metabolism -> renal excretion
what is phase 1 metabolism?
Creation of reactive, polar functional groups
- Oxidation: usually by CyP450 system
- Reduction and hydrolysis
what is phase 2 metabolism?
Production of polar compounds for renal elimination
- Either the drug or its phase 1 metabolite
- Conjugation reactions
- Glucuronidation, sulfonation, acetylation, methyl
describe cytochromeP450 system
Most important system of phase 1 metabolism
> 11 subtypes
CyP3A4 - Most important subtype
≥ 30% of drugs: CCBs, β-B, statins, benzos
CyP2D6 - Second most important
≥20% of drugs: antidepressants, some β-B,
opiates
what drugs are affected by varying acetylation?
Fast vs. slow acetylators (↑↑ fast in Japan vs. Europe)
Affects: isoniazid, hydralazine and dapsone
what are the allergy types in relation to medications?
1 - allergy/anaphylaxis, IgE
2 - cytotoxic Ab resulting in haemolysis e.g. penicillin, methyldopa, oral hypoglycaemics
3 - immune complex - serum sickness, penicillins
4 - cell-mediated (T), topical treatments
classification of adverse drug reactions?
A - common, predictable, dose-related, consequence of known pharmacology
B - rare, idiosyncratic, not dose related, include pharmacogenetic + allergy
Long term ADR - dependence, addiction, withdrawal, adaptive changes (tardive dyskinesia)
delayed ADR - carcinogenesis, teratogenesis
p450 inducers
Phenytoin Carbamazepine Barbiturates Rifampicin Alcohol (chronic) Griseofulvin St. John’s Wart
p450 inhibitors
Valproate INH Protease inhibitors Cipro, Cimetidine Erythromycin + clarithromycin Omeprazole Grapefruit juice Fluconazole / Fluoxetine
