First order kinetics and Zero order kinetics

Views:
 
Category: Education
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

First order kinetics and Zero order kinetics:

First order kinetics and Zero order kinetics Dr. Meena Atray Professor Department of Pharmacology R.N. T. Medical College, Udaipur

Slide 2:

Rate and pattern of drug elimination follow three type of elimination First order kinetics– Most of the drugs follow first order kinetics Zero order kinetics– Alcohol obeys zero order kinetics Mixed order kinetics

Difference between first order kinetics and zero order kinetics:

Difference between first order kinetics and zero order kinetics First order kinetics Constant fraction of drug is eliminated at constant interval Clearance remains constant Rate of elimination vary with plasma concentration Nearly complete elimination in 4-5 half lives 1 st half life-50%, 2 nd t1/2- 50+ 25 = 75% 3 rd t1/2- 50+ 25 +12.5= 87.5% 4 th t1/2- 50+ 25 +12.5 + 6.25= 93.75 5 th t1/2- 50+ 25 +12.5 + 6.25+ 3.125= 96.875% If dose is doubled, the duration is prolonged for one half life Zero order kinetics Constant quantity of drug is eliminated at constant interval Clearance is never constant Rate of elimination remains constant No relation with half life If dose is doubled, the duration is prolonged for so many times, not related to half life

Slide 4:

First order kinetics Zero order kinetics On arithmetic scale On log scale

Slide 5:

Plateau Principle Drugs which follow first order kinetics follow plateau principle

Mixed order kinetics Michaelis Menten kinetics:

Mixed order kinetics Michaelis Menten kinetics Few drugs like phenytoin , warfarin , theophylline follow first order kinetics at low dose Changes to zero order kinetics at high dose because metabolizing enzymes or the elimination process get saturated Results in increase in plasma concentration disproportionately with increase in dose Half life changes with dose Needs proper monitoring and maintenance of dose

authorStream Live Help