Drug Emlimination Flashcards
(21 cards)
What is the MEC?
The minimum effective concentration - the critical concentration in the plasma for a drug to achieve an effecr
What is the MTC?
The maximum tolerate concentration - the maximum concentration in the plasma before significant unwanted effects happen
In terms of therapeutic window and ratio what would a safe drug have?
A safe drug would have a large therapeutic window and a high therapeutic ratio - examples are penicillins and benzodiazepines
In terms of therapeutic window and ratio what would an unsafe drug have?
An unsafe drug would have a small therapeutic window and a small therapeutic ration - examples are barbiturates and cardiac glycosides
What is pharmacokinetics?
the mathematical analysis of all drug disposition factors (absorption, distribution, metabolism and excretion)
What is first order kinetics?
where the rate of elimination is directly proportional to drug concentration
most drugs exhibit first order kinetics
What is half life of a drug?
The time taken for Ct to fall buy 50%
It is inversely related to Kel
T(1/) = 0.69/Kel
If a drug exhibits first order kinetics, what does the dose administer change and not change/affect?
The dose administered change Cp in direct proportion
The dose administered does not affect Kel or T(1/2)
E.g double the dose, the Cp changes but the half life is the same.
What is clearance?
‘The volume of plasma cleared of drug in unit time’
‘A constant relating the rate of elimination to plasma concentration’
Applies only to the drugs that exhibit first order kinetics
What does Cl determine?
The maintenance dose rate (the dose per unit time required to maintain a given plasma concentration)
At a steady state what does rate of drug administration =?
rate of drug administration = rate of drug elimination
For drugs that exhibit first order kinetics, the stead state plasma concentration (Css) is _________ related to the infusion rate?
For drugs that exhibit first order kinetics, the stead state plasma concentration (Css) is linearly related to the infusion rate?
When is the Css reached?
After 5 half lives approx
The time to reach Css is determined by __, but not the ____ rate?
The time to reach Css is determined by t½, but not the infusion rate
How is drug dosing to a steady state in oral different to IV?
The plasma concentration fluctuates about an average steady state value
What is the volume of distribution?
‘The volume into which a drug appears to be distributed with a concentration equal to that of plasma’
What is the loading dose?
an initial higher dose of a drug given at the beginning of a course of treatment before stepping down to a lower maintenance dose
Why is the loading dose employed?
TO decrease the time to steady state for drugs with a long half life such as digixoin
What does half life give an index of?
the time course of drug accumulation
the time course of drug elimination
choice of dose interval
What is the equation that links, half life, clearance and Vd?
T(1/2) = (0.693 x Vd) / Cl
What is zero order elimination?
A few drugs of clinical significance (e.g. ethanol, phenytoin) are initially eliminated at a constant rate, rather than at a rate that is proportional to their concentration (this can occur, for example, when the plasma concentration of a drug is greater than the Km of an enzyme that metabolises it)
