C1
What is Saturation kinetics?
Switching from first to zero order kinetics at higher doses due to saturation of the drug eliminating pathways
What is the relation between rate of elimination and plasma concentration in first order kinetics and zero order kinetics
Directly proportional in first order
Remains fixed in zero order
What determines the rate of elimination in flow dependent elimination?
Rate of elimination determined by rate of drug delivery to the organ- Blood flow to clearing organ
Define Clearance of a drug
What is the equation to define clearance of a drug?
Theoretical volume of plasma that is completely removed of the drug per unit time & unit - ml/min
Rate of elimination/ Plasma concentration of a drug
What is plasma half life?
What is the equation for calculating t1/2?
Time taken for the plasma concentration to be reduced to half the original value
t1/2= ln2/ k
What is the equation that describes the fixed rate of elimination in zero order kinetics
Michealis Menton equation
Rate of elimination= Vmax X C/ Km+ C
What is Steady state plasma concentration?
Plasma concentration at which rate of drug administration = Rate of drug elimination
How long does it take to reach steady state for a drug with first order kinetics and zero order kinetics?
4 to 5 half lives
Principle -Plateau principle
Steady state cannot be achieved in zero order kinetics
How is half life related to (i)clearance of a drug (ii) vol of distribution
t1/2 =0.693 X Vd/Cl
How long does it take for a drug with first order kinetics of elimination to be removed from the body
Four to Five t1/2
How does t1/2 change in first and zero order kinetics
first - no change- remains constant
zero- prolonged as dose continued
You want to increase the elimination of a weakly acidic drug by altering the urinary pH based on the principle of ion trapping. What should be done - reduce or increase pH?
Alkalize urine with alkalinising agent like sodium bicarbonate
Drug conjugate eliminated in bile is deconjugated by enteric bacteria & released into the gut. This can get absorbed into biliary circulation. This is called
Enterohepatic cycling
If breast milk has lower pH than plasma, which drugs get concentrated - acidic or basic
Basic
By the phenomenon of ion trapping
How will you calculate CL using AUC
Dose/ AUC in first order
Dose (single/few quickly repeated) at the beginning of therapy is? and is it dependent on Vd or CL?
Loading dose, Vd
Dose that is repeated at specified intervals? and is it dependent on Vd or CL?
Maintainence dose, CL
What is the laboratory measurement of the plasma drug concentration called and why you should measure the plasma concentration ?
Therapeutic drug monitoring
Phenytoin is an antiepileptic. Do you think TDM is needed
Yes
Saturation kinetics- dose adjustment to prevent toxicity
Check compliance
Smaller frequent dose is better than larger intermittent doses. Why?
To avoid large fluctuations in plasma concentrations