Young male Kallu is brought to the hospital with Severe asthama. PharmacoKinetics of theophylline include the following parameters:Vd=35L ;CL=48ml/min;half life is 8hrs.if an intravenous infusion of theophylline is staed at a rate of 0.48mg/min,how long will it take to reach 93.75% of the final steady stare
Correct Answer: Approximately 32hrs
Description: Ref-Katzung 10/e p52 For a drug following first order kinetics,rise in plasma concentration as well as fall in plasma concentraton is similar.when the steady state is attained and the drug administration is stopped.it will be eliminated from the body.50% will be eliminated in one half life 75% in second half life and 87.5%(50+25+12.5%) in third half life and 93.75% (50+25+12.6+6.5%) in four half lives. When constant i.v. is administered, plasma concentration increases in the same manner.in one half life,it is 50% of the steady state and to reach 93.75% of steady state ,4half loves will be required As the half life of this drug is 8hrs, approximately 32hrs will be taken
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