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About drug elimination


Q. What do you know about drug elimination? What are the routes of excretion of drugs?

Ans: Drug elimination: It is the Pharmacokinetics Process by which drugs after being partly or
wholly converted to water soluble metabolites and in some cases in unchanged forms are removed from the body.
Routes of drug excretion:
(1) Major process:
a) Kidney Frusemide, Pethidine
b) Hepato-billiary process —> Tetracycline, Chloramphenicol
c) Gastro-intestinal --> Antacid, Ba504
d) Pulmonary -4 Alcohol, inhalation anaesthetics
(2) Miror Process:
a) Skin/Sweat gland —> Vit-C, Fe, griseofulvin
b) Saliva --> Morphine, Caffeine
c) Breastmilk —> Morphine, Phenobarbitone
d) Vagina --> Metronidazol
e) Hair, nail -4 As, Hg
f) Tear —4 Rifampicin


Q: Name the factors that modify drug excretion through kidney.

Factors that modify drug excretion through kidney:
A. Factors related to drug:
a) Molecular size of the drug: M.W.>300 dalton cross the glomerular capillary with difficulty.
b) PH of the drug: Acidic drug in acidic urine —4 Less ionization —>Less excretion.
c) Concentration of drug: Increase conc. —3 Increase excretion.
d) Ionization of drug: More polar drug —3 more excretion.
e) Plasma protein binding of drug: Protein binding reduces the amount of drug to be filtered.
B. Factors related to kidney:
a) GFR: Increase GFR-4 Increase excretion
b) Impaired renal function: Excretion is less.
c) Renal blood flow: Increase flow —> Increase excretion.

Q: Define first order kinetics and zero order kinetics/Describe drug elimination process.
First order kinetics: A fixed percentage of drugs are eliminated per unit of time. Example: "A" is a 100 mg drug 10% is excreted in one hour.
1st hour 10 mg is eliminated.
2'd hour -3 9 mg is eliminated (10% from 90 gm= 9 mg) 3rd hour --> 8.1 mg is eliminated (10% from 81 mg= 8.1 mg)

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