Therapeutic Drug Monitoring (TDM) Request



                

TDM: Plasma drug concentrations measured to determine whether therapeutic or toxic concentration has been produced

Indicated to:

  • confirm effective doses
  • monitor compliance
  • investigate possible toxicity
  • monitor drugs with narrow therapeutic range


Beneficial for:

  • Extreme age (extremely young or old)
  • Altered pharmacokinetics (renally, hepatically impaired, burns and ICU patients)
  • Not responding to therapy as expected after adequate doses have been given
  • Exhibit adverse effects at normal dosages

Importance of sampling time:
  • Accuracy crucial to ensure that drug distribution at steady state
  • Large errors in interpretation can occur if sampling time is wrongly stated
  • Except to check for toxicity, send sample for monitoring only after the drug level achieved steady state.


Electronic Therapeutic Drug Monitoring Request:

Effective from 7 January 2019 onwards, all TDM requests from wards and clinics MUST be submitted via electronic through LMD order, iPesakit system. Blood samples are to be sent to Laboratory Medicine Division, Pathology Department as usual. 

Please ensure electronic TDM request form is filled completely prior submission. Electronic requests and blood samples have to be submitted to Laboratory Medicine Division before 4.00 pm on working days. Any blood sample which comes after 4.00 pm will be refrigerated and processed on the following day (except weekends and public holidays). Recommendation pertaining drug doses by pharmacists will only be made after getting the results of the analysed samples.


Please refer to the attached manual for your reference:



Drugs Available for TDM in UMMC

Drugs

Time to steady state

Sample collection time

Amikacin

10-15 H1,2

Renally impaired: prolonged

Trough: immediately before next dose

Peak:

1 H after dose (IM)

0.5-1 H after end of infusion (IV)

Gentamicin

10-15 H1,2

Trough: immediately before next dose

Peak:

1 H after dose (IM)

0.5-1 H after end of infusion (IV)

Vancomycin

30-35 H1

Trough: immediately before next dose

Peak: 2 H after dose

Phenytoin

5 days if dosed at 300mg/day2

Trough: immediately before next dose

Phenobarbitone

Adult: 2-3 weeks1

Paeds: 8 days1

Trough: immediately before next dose

Valproic Acid

Adult: 50-60 H1

Paeds: 30-40 H1

Trough: immediately before next dose

Carbamazepine

2-4 days (assuming autoinduction has completed)

Trough: immediately before next dose

Digoxin

7 days (without LD)1

24 H (with LD)1

Trough: immediately before next dose

Random: at least 8 H post-dose

Theophylline

24 H1

Trough: immediately before next dose

Reference:

  1. Michael E. Winter, Basic Clinical Pharmacokinetics, 4th Edition (2004)

  2. Larry A. Bauer, Applied Clinical Pharmacokinetics, 2nd Edition (2008)


Updated: 11 Feb 2019

 Contacts

Ext 2926

 Links

Download Clinical Pharmacokinetics Pharmacy Handbook

Clinical Pharmacokinetics Pharmacy Handbook