therapeutic drug monitoring

Question 1

why is TDM IMPORTANT

Answer 1

Avoid toxicity
Optimize dose & improve efficacy
Assist in diagnosis
Assess adherence

Question 2

When is TDM indicated

Answer 2

enhance efficacy

minimize toxicity

Question 3

what makes a drug suitable for TDM

Answer 3

High inter-patient variability in plasma concentrations

Narrow therapeutic range

Good correlation between plasma concentrations and clinical effects

Pharmacological effect persists and is dependent on the plasma concentration

Availability of cost effective, accurate drug assays with rapid turnaround time and a small blood volume requirement

Question 4

which drugs are monitored

Answer 4

gentamicin
vancomycin
phenytoin, carbamazepine
digoxin
theophylline

Question 5

factors that affect PK

Answer 5

Age 
Weight 
Sex
Genetics
Disease
Drug interactions

Question 6

phenytoin

Answer 6

zero order kinetics
small doses can lead to toxicity
difficult to interpret pharmacokinetics

Question 7

how to interpret results

Answer 7

time of sample collection
time of last dose 
dose regimen
indication for drug monitoring
avoid drawing blood before absorption

Question 8

protein binding

Answer 8

Acidic drugs bind largely to albumin

Basic drugs bind mainly to α-1-acid glycoprotein, albumin and -lipoproteins

Question 9

how do we interpret concentration

Answer 9

lower:
Incorrect dose

Patient non compliance

Rapid elimination

Timing of sample

Higher:
Error in dosage regimen

Decreased renal/hepatic function
Slow elimination

Question 10

phenytoin toxicity

Answer 10

less than 10
rare side effects 
10-20mg 
nystagmus
30-40
ataxia
slurred speech
tremor 
nausea
vomiting 
40-50
lethargy
confusing 
hyperactivity 
less than 50 mg 
coma 
seizures