Question

Which one is the correct equation to calculate the fraction of unbound drug in plasma?

(a) Concentration of unbound drug in plasma / total plasma concentration of drug

(b) Total plasma concentration of drug / Concentration of unbound drug in plasma

(c) 1/Concentration of unbound drug in plasma

(d) 1/total plasma concentration of drug

I had been asked this question in a job interview.

The question is from Drugs Excretion in division Prodrugs & Excretion of Drugs of Drug Biotechnology

Answer 1

Right choice is (a) Concentration of unbound drug in plasma / total plasma concentration of drug

Best explanation: The fraction of drug bound to plasma proteins can be calculated by the equation fu = Cu/C. Here fu is fraction of unbound drug and Cu is the concentration of unbound drug in plasma and C is the total plasma concentration of the drug.