Pharmacology Part 4 Flashcards
What must a drug achieve to be safe?
Must reach a critical concentration in the plasma (MEC) but ideally be well bellow the concentration causing side effects (MTC)
What will an unsafe drug have?
Narrow therapeutic window
Define pharmacokinetics
mathematical analysis of all drug disposition factors (absorption, distribution, metabolism and excretion)
What is first-order kinetics?
the rate of elimination is directly proportional to drug concentration
For drugs that exhibit first order kinetics what will the administered dose do to Cp, Kel or t1/2?
Change Cp in direct proportion
Does not effect Kel or t1/2
What is clearance?
The volume of plasma cleared of drug in unit time
-applying only to drugs that exhibit 1st order kinetics
What does the rate of drug administered equal in the steady state?
The rate of drug elimination
What is the difference between dosing to steady state in Oral and IV drugs?
involves the same principles as continuous infusion, but plasma concentration fluctuates about an average steady state value (Css (average)) in oral
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 loading dose administered?
to decrease time to steady state for drugs with long half lives (e.g. digoxin, phenytoin)
What can alter Vd?
Disease (heart failure, liver disease)
What is half life?
The time for the concentration of the during in plasma (or the amount of drug in the body) to halve)
What is t 1/2 dependant on?
Vd and Cl
What is zero order kinetics?
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)
Which drugs are zero order?
Ethanol, phenytoin
