A drug Y takes 6 hours to reach its 50% steady state plasma concentration when given IV. what is the elimination half-life of the drug Y?

A. 4 h

B. 6 h

C. 12 h

D. 24 h

answer is B 6hrs

The THUMB rules for time to steady-state plasma concentration

• it takes 4–5 t ½ to  reach clinical steady-state plasma concentration
• at one half life it reaches  50% of steady-state plasma concentration
• from the question 6hrs required for 50%  steady-state plasma concentration which is equal to its half life, so half life of drug is 6hrs

Steady concentration plasma concentration is achieved when a constant amount of drug is added every half life

• 1st t1/2       50%
• 2nd t1/2     (50+25) 75%
• 3rd t1/2      (50+25+12.5) 87.5%
• 4th t1/2      (50+25+12.5+6.25) 93.75%
• 5th  t1/2      (50+25+12.5+6.25+ 3.125) 96.97%

so from above concept

• at one half life it reaches  50% of steady-state plasma concentration
• from the question 6hrs required for 50%  steady-state plasma concentration which is equal to its half life, so half life of drug is 6hrs

For more MCQs and concepts  become pro member by clicking below

https://drpharmacologist.testpress.in/products/pro-members/