Term
Where does tubular secretion take place
name important drugs which are secreated here?
what can be done to reduce secretion? 

Definition
1. Proximal convulated tubule
penicillin & methotrexate



Term

Definition
+ probenecid competes with penicillin for its binding sites thus allows duration of penicillin to be longer
+ competes with uric acid, thus more will be excreted  useful in treatment of GOUT (which is excess uric acid) 


Term
Clearance (CL)
if drug is protein bound? 

Definition
CL = rate of elimination (k) x volume of distribution (vd or plasma conc)
CL is usually constant for first order drugs
with no active secretion or renal absorption CL=GFR
protein bound drugs CL= GFR x free fraction 


Term

Definition
Rate of elimination is directly proportional to the plasma concentration of the drug. (varies with dose). thus SATURATION DOES NOT OCCUR!
A constant fraction (instead of amount) of a drug is being eliminated per unit time
Example : 200mg….100mg….50mg…25mg…12.5mg…6.25mg…
…3.127mg….1.551mg
MOST DRUGS! 


Term

Definition
•Rate of elimination is independent of plasma concentration of the drug. Constant with the any dose
•Also called as saturable or Capacity limited or nonlinear or Michelis –menten ellimination



Term
Drugs that follow zero order kinetics 

Definition
Ethanol, Aspirin and Phenytoin in very high dose follow zero order kinetics . Otherwise in normal dose they follow first order kinetics
A constant amount of drug is being eliminated per unit time
Example: In each hour 25mg of drug A is eliminated 200mg….175mg….150mg…125mg….



Term

Definition
• Time required to reduce the plasma concentration of the drug to its half of its original value
•Half life is constant for the drugs which follow first order kinetics
•But it varies for drugs which follow zero order kinetics



Term
t 1/2 calculation
how many half lives does it take for a drug to be completely eliminated? 

Definition
t1/2 =0.693 x Vd/CL
it takes 45 half lives for a drug to be completely eliminated



Term

Definition
On continuous steady administration of a drug, plasma concentration will rise fast at first then more slowly and reach a plateau, where
rate of administration = rate of elimination (usually takes 45 half lives)



Term
Dose of Drug in relation to Css 

Definition
the dose not affect the time at which it takes to reach the Css, it will always be 45 half lives,
however the dose does affect the plasma conc 


Term

Definition
To maintain the required plasma concentration over a long period of time



Term

Definition
Single or a few quickly repeated doses given in the beginning to achieve target plasma level rapidly



Term
What is the calculation for maintenance dose? 

Definition
Maintainance dose= CL x Css
Bioavailability(F)



Term
What is the calculation for loading dose? 

Definition
Loading dose= Vd x Css
Bioavailability(F)


