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Therapeutic drug Monitoring - PowerPoint PPT Presentation


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Therapeutic drug Monitoring. What is therapeutic drug monitoring (TDM)? Individualization of drug doses by maintaining plasma/blood drug concentrations within a target range---- therapeutic range therapeutic window.

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Presentation Transcript
slide2

What is therapeutic drug monitoring (TDM)?

Individualization of drug doses by maintaining plasma/blood drug concentrations within a target range---- therapeutic range

therapeutic window.

Takes care of inter-individual variability.

slide3

Therapeutic Window

Therapeutic failure results when either the concentration is too low, ineffective therapy, or is too high, producing unacceptable toxicity. Between these limits of concentration lies a region associated with therapeutic success – regarded as a Therapeutic window.

slide4

Wide therapeutic window

A

B

Toxicity

Efficacy

Response

Drug concentration (log scale)

slide5

Narrow therapeutic window

Efficacy

Toxicity

Response

Drug concentration (log Scale)

slide6

Major sources of Variability:

  • Compliance
  • Age- neonates, children, elderly
  • Physiology- gender, pregnancy
  • Disease- Hepatic, renal, cardiovascular, respiratory
  • Drug interactions
  • Environmental influences on drug metabolism
  • Genetic polymorphisms
slide7

For which drugs is monitoring helpful?

  • Marked pharmacokinetic variability
  • Concentration related therapeutic and adverse effects
  • Narrow therapeutic index
  • Defined therapeutic (target) concentration range
  • Desired therapeutic effect difficult to monitor
slide8

TDM useful in 2 major situations:

  • Drugs used prophylactically to maintain absence of a condition--- seizures, cardiac arrhythmias. depressive/manic episodes, transplant rejection
  • To avoid serious toxicity--- Aminoglycoside antibiotics
slide9

Sampling and drug analysis:

Plasma/ serum; cyclosporin- whole blood.

Timing: least variable point in dosing interval– predose/trough concentration.

Wait for steady state to be achieved---at least 5 half-lives. Exceptions are there! Drugs with long half-life.

HPLC, GLC, Immunoassays- sensitivity, specificity.

slide10

Information required for interpretation:

  • Timing of sample in relation to last dose
  • Duration of treatment in with current dose
  • Age, gender
  • Other drug therapy
  • Relevant disease states
  • Reason for TDM- lack of effect, routine monitoring, suspected toxicity.
slide11

Plasma protein binding:

Free drug vs total drug concentration.

Importance of plasma protein binding.

Remember that only total drug concentration is measured but only the free drug is active!

slide12

Drugs commonly monitored:

Drug Therapeutic range (mg/L)

Amiodarone 1.0-2.5

Digoxin 0.5-2.1microgram/L

Quinidine 2.0-5.0

Theophylline 10-20

Phenytoin 10-20

Carbamazepine 5.0-12

Sodium valproate 50-100

Phenobarbitone 15-40

Gentamicin peak>5, trough<2

Amikacin peak>15, trough<5

Vancomycin peak20-40, trough<10

Lithium 0.6-1.2mmol/L

slide13

Target concentration intervention

ESTIMATE INITIAL DOSE

Target Dose

Loading Dose

Maintenance Dose

BEGIN THERAPY

ASSESS THERAPY

Patient Response

Drug Level

REFINE DOSE ESTIMATE

ADJUST DOSE