1- Therapeutic Drug Monitoring & Clinical Questions

Define therapeutic drug monitoring

the use of serum drug concentrations as an adjunct to decision-making that leads to increased efficacy & decreased toxicity

What is the assumption of TDM?

drug concentration in serum/plasma correlates with the drug concentration at the site of action

Identify indications for concentration monitoring

• drug with narrow therapeutic window

• effect cannot be easily quantified clinically or is not timely

• dose-response varies widely

• drug-drug interactions

• significant change in factors affecting Vd or CL

• overdose suspected

• compliance

Define therapeutic range

the serum concentration between which the desired response is most likely to occur

• below which increased probability of inadequate response

• above which increased probability of toxic response

What is total serum concentration?

free + bound

• measure total if the response and total concentration are proportional to the free concentration at the site of action

• protein binding must remain relatively constant

What is free serum concentration?

free

• phenytoin

• valproic acid

Identify factors affecting concentration monitoring

• internal patient variables

• external patient variables

What are internal patient variables?

• disease state

• development

• concurrent drug therapy

• nutrition

What are external patient variables?

• medication administration (timing, compliance)

• drug delivery (routes, techniques)

• sample collection

• lab limitations