Table of Contents

Kinetics Problems

PROBLEM 1

Consider the effect on free drug concentration of an increase in protein binding of 1% for 3 drugs whose protein bindings are 95%, 80% and 50%.

Would there be any difference if the change in protein binding occured in minutes versus over 2 weeks?

PROBLEM 2

A 50 kilogram woman ingests 5000 mg of controlled release theophylline. The average Vd for theophylline is 0.5 litres/kg.

  1. What is the likely peak concentration if it is fully absorbed?
  2. Theophylline is metabolised by P450 enzymes. What is the likely impact of this dose on theophylline’s metabolism and elimination?
  3. The half-life was calculated using 2 levels 6 hours apart. The half-life appeared to be 10 hours. What factors may contribute to this result. What are some of the potential sources of error in such a calculation?