Term
Where does tubular secretion take place
name important drugs which are secreated here?
what can be done to reduce secretion? |
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Definition
1. Proximal convulated tubule
penicillin & methotrexate
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Term
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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) |
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Term
Clearance (CL)
if drug is protein bound? |
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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 |
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Term
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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! |
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Term
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Definition
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•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
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Term
| Drugs that follow zero order kinetics |
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Definition
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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….
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Term
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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
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Term
t 1/2 calculation
how many half lives does it take for a drug to be completely eliminated? |
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Definition
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t1/2 =0.693 x Vd/CL
it takes 4-5 half lives for a drug to be completely eliminated
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Term
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Definition
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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 4-5 half lives)
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Term
| Dose of Drug in relation to Css |
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Definition
the dose not affect the time at which it takes to reach the Css, it will always be 4-5 half lives,
however the dose does affect the plasma conc |
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Term
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Definition
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To maintain the required plasma concentration over a long period of time
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Term
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Definition
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Single or a few quickly repeated doses given in the beginning to achieve target plasma level rapidly
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Term
| What is the calculation for maintenance dose? |
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Definition
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Maintainance dose= CL x Css
Bioavailability(F)
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Term
| What is the calculation for loading dose? |
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Definition
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Loading dose= Vd x Css
Bioavailability(F)
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