9. Pharmacokinetics Flashcards
How do you calculate bioavailability using a plasma drug concentration against time graph?
Area under curve of the oral dose/area under curve of the injected dose x100
Define oral bioavailability?
The proportion of a dose that reaches the systemic circulation in an unchanged form
What is the therapeutic ratio calculated as?
Max tolerated dose/minimum effective dose
LD50/ED50
What is the first pass effect?
Substances absorbed in the ilium enter the venous blood which drains into the hepatic portal vein which goes to the liver. The liver will then metabolise most of the drug on the first pass.
What is drug distribution?
The theoretical volume into which a drug has been distributed assuming this occurs instantaneously
How do you calculate drug distribution?
Amount given/plasma concentration at time 0(via extrapolation)
Which drug, the object (class I) or the precipitant (class II) displaces which?
Precipitant drugs displace the object drug, this raises levels of the object drug
When given simultaneously with precipitant drugs, is the object drug given at a lower, higher or the same value as the number of albumin binding sites for it?
The object drug is given at a lower dose than the number of albumin binding sites
If warfarin is used as an object drug, what precipitant drugs would displace it from binding sites?
Sulphonamide
Aspirin
Phenytoin
What is first order pharmacokinetics?
Where metabolism of the drug is proportional to its concentration
Constant half life
What is zero order pharmacokinetics?
Dangerous
The elimination enzyme is saturated so decline in concentration is constant regardless of concentration
Why are 0 order kinetics responses dangerous?
Suddenly escalates as elimination mechanisms saturate e.g alcohol
What does a drug have to be to be filtered through the glomerular shaft and reabsorbed?
Unbound
Unionised
Aspirin, a weak acid, in alkaline urine will be more or less reabsorbed?
Less will be reabsorbed as it is charged hence in aspirin overdose, alkaline diuresis is used
Name a drug that is a weak base
Amphetamine
