Canterbury DHB

Context

Drug-specific Therapeutic Drug Monitoring (TDM) information

Drugs with TDM

Drug

For more information see the Clinical Pharmacology website

Half life*

Time to steady state*

Ideal time for blood sample and tube colour**

Sample time and tube

amikacin

 

3 hours

 

 

N/A

 

Seek pharmacist advice.

Green.

amiodarone

 

8 weeks

N/A

 

Any time.

Green, red, or purple.

amitriptyline

15 hours

(30 hours nortriptyline)

7 days

Just before a dose (and at least 12 hours after a dose). Trough (12 to 24 hours after last dose).

Green or red.

azathioprine (and 6 mercaptopurine)

azathioprine 1 hour

6-TGN 5 days

6-MMP 5 days

4 weeks

Any time.

Purple.

carbamazepine#

15 hours

3 days

Trough (12 to 24 hours after last dose).

Purple.

ciclosporin

12 hours

3 days

Trough (8 to 18 hours after last dose) or peak (1.8 to 2.2 hours after last dose).

Purple.

clomipramine

28 hours

7 days

Trough (12 to 24 hours after last dose).

Green or red.

clozapine

12 hours

Norclozapine: 13 hours

3 days

Trough (12 to 24 hours after last dose).

Green or red.

desipramine

20 hours

5 days

Trough (12 to 24 hours after last dose).

Green or red.

digoxin

36 hours

7 days

Trough (12 to 24 hours after last dose).

Green.

dosulepin

22 hours

5 days

Trough (12 to 24 hours after last dose).

Red.

flecainide

14 hours

3 days

Trough (16 to 24 hours after last dose).

Green or red.

gentamicin

3 hours

N/A.

2 samples needed. First sample 30 minutes after end of infusion. For second sample, see guidelines. Record exact times on blood form.

Green or red.

itraconazole

35 hours

Hydroxitraconazole: 12 hours

 

7 days

Trough (12 to 24 hours after last dose).

Red.

lamotrigine

24 hours

 

5 days

Trough (12 to 24 hours after last dose).

Green or red.

lithium

22 hours

5 days

Trough (12 to 24 hours after last dose).

Red.

metformin

5 hours

1 day

Trough (12 hours after last dose).

Purple or red.

methadone

30 hours

7 days

Trough (12 to 24 hours after last dose).

Red.

methotrexate

8 hours

Not applicable

See departmental guidelines.

Red.

mianserin

13 hours

3 days

Trough (16 to 24 hours after last dose).

Red.

mycophenolate

Mycophenolic acid 16 hours

4 days

Trough (8 to 18 hours after last dose).

Green.

nortriptyline

30 hours

7 days

Trough (12 to 24 hours after last dose).

Red.

olanzapine

33 hours

7 days

Trough (12 to 24 hours after last dose).

Red.

perhexiline+

 

15 hours

Hydroxyperhexiline: no data

3 days

Trough (12 to 24 hours after last dose).

Green.

phenobarbital#

4 days

3 weeks

Trough (12 to 24 hours after last dose).

Green or red.

phenytoin#+

 

24 hours

5 days

Trough (12 to 24 hours after last dose).

Green or red.

tacrolimus

10 hours

3 days

Trough (8 to 18 hours after last dose).

Purple.

theophylline

8 hours

3 days

Trough (8 to 18 hours after last dose).

Green.

tobramycin

3 hours

Refer to guidelines

2 samples needed. First sample 30 minutes after end of infusion. For second sample, see guidelines. Record exact times on blood form.

Green.

topiramate

21 hours

5 days

Trough (8 to 18 hours after last dose).

Red.

valproate sodium

12 hours

3 days

Trough (8 to 18 hours after last dose).

Green or red.

vancomycin

6 hours

Refer to dosing guidelines

Seek pharmacist advice.

Green or red.

voriconazole#

6 hours

3 days

Trough (8 to 18 hours after last dose).

Green or red.

*Time to steady state and half life are often longer in patients, e.g. frail elderly.

**Use non-gel tubes.

# Because of autoinduction, concentrations taken before 4 weeks may not reflect steady state.

+ Saturable metabolism at therapeutic doses. Careful dose-titration required.

For other drugs that Canterbury Health Laboratories measures, see Test Manager.

Information about this Canterbury DHB document (93304):

Document Owner:

Not assigned (see Who's Who)

Last Updated:

December 2020 (Therapeutic Drug Monitoring (TDM))

Next Review Due:

December 2022

Keywords:

Note: Only the electronic version is controlled. Once printed, this is no longer a controlled document.

Topic Code: 93304