pharmacokinetics 4 Flashcards
how is drug cleared from the body
drug in to plasma conc and site of action to effect and out
what is drug clearance
The sum of all the drug-eliminating processes, principally determined by hepatic metabolism and renal excretion
also defined as theoretical volume of fluid from which a drug is completely removed in a given period of time
what do kidneys do for excretion
excreted in urine
either
excretion unchanged or metabolised then excreted
Components of renal excretion
Glomerular filtration - Glomerulus
Secretion – Proximal Convoluted tubule
Reabsorption - Distal Convoluted tubule
other excretory methods
Bile (faeces) Sweat Exhaled air Saliva Breast milk
causes of low drug clearance
Normal variation Renal impairment Liver impairment Enzyme inhibition Genetic poor metabolizer Neonate Old age
causes of high drug clearance
Normal variation
Increased renal blood flow
Genetic hypermetabolism
Enzyme induction
what is half life
Time for the concentration of drug in plasma to halve
what does half life provide information on
Time course of drug elimination
Time course of drug accumulation
Choice of dose interval
what is a steady state
drug conc varies in a steady state - about the mean
what is a loading dose
plasma vol to interstitial fluid to intracellular fluid volume - give large first dose then lower maintenance dose
PO top up after LO to keep between min toxic conc and minimum effective conc
IV stays at same conc as given constantly after LO
determined by vol of distribution
how is dosing of drugs calculated
half life= vol of dist/clearance
what is maintenance dose
determined by the clearance
what is dose interval
Dose interval is determined by the half life
when is plasma concentration of a drug negligible
5t1/2
