Fred is taking 1000mg penicillin, which has a short half life of 1.5h. Doses occur at six hour intervals. How much penicillin is in his bloodstream six hours after his first dose?
Select one:
A. 62.5mg
B. 31.25mg
C. 125mg
D. 250mg
Answer A.62.5mg
Half life = 1.5 hours
Time given = 6 hours = 6/1.5 = 4 (four)half lifes
Half life of a drug is the time taken for the plasma level of drug to reduce by 50% .
After first half life ,drug level = 1000*50% = 500
After second half life ,drug level = 500*50/100 = 250
After third half life, drug level = 250*50/100 = 125
After fourth half life ,drug level = 125*50/100 = 62.5
Hence after 6 hours ,4 half lifes, penicillin in bloodstream would be 62.5mg
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