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Drug For more information see the Clinical Pharmacology website |
Half-life* |
Time to steady state* |
Ideal time for blood sample |
amikacin |
3 hours |
N/A |
Seek pharmacist advice. |
amiodarone |
8 weeks |
N/A |
Collect pre-dose. |
amitriptyline |
15 hours (30 hours nortriptyline) |
7 days |
Trough (12 to 24 hours after last dose). |
azathioprine (and 6 mercaptopurine) |
azathioprine 1 hour 6-TGN 5 days 6-MMP 5 days |
4 weeks |
Any time. |
carbamazepine# |
15 hours |
3 days |
Trough immediately prior to next dose. |
ciclosporin |
12 hours |
3 days |
Trough (8 to 18 hours after last dose) or peak (1.8 to 2.2 hours after last dose). |
clomipramine |
28 hours |
7 days |
Trough (12 to 24 hours after last dose). |
clozapine |
12 hours norclozapine: 13 hours |
3 days |
Trough (12 to 24 hours after last dose). |
desipramine |
20 hours |
5 days |
Trough (12 to 24 hours after last dose). |
digoxin |
36 hours |
7 days |
Trough (12 to 24 hours after last dose). |
dabigatran |
15 hours |
3 days |
Trough (pre-dose) |
dosulepin |
22 hours |
5 days |
Trough (12 to 24 hours after last dose). |
flecainide |
14 hours |
3 days |
Trough (16 to 24 hours after last dose). |
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. |
itraconazole |
35 hours hydroxitraconazole: 12 hours |
7 days |
Trough (12 to 24 hours after last dose). |
lamotrigine |
24 hours |
5 days |
Trough (12 to 24 hours after last dose). |
lithium |
22 hours |
5 days |
Trough (12 to 24 hours after last dose). |
metformin |
5 hours |
1 day |
Collect sample pre-dose. |
methadone |
30 hours |
7 days |
Immediately pre-dose and/or 2.5-4 hours post-dose. |
methotrexate |
8 hours |
Not applicable |
See departmental guidelines. |
mianserin |
13 hours |
3 days |
Trough (16 to 24 hours after last dose). |
mycophenolate |
mycophenolic acid 16 hours |
4 days |
Trough (8 to 18 hours after last dose). |
nortriptyline |
30 hours |
7 days |
Take sample 18 hours after dose. Give dose, dose time, interval and collection time. |
olanzapine |
33 hours |
7 days |
Trough (12 to 24 hours after last dose). |
perhexiline+
|
15 hours hydroxyperhexiline: no data |
3 days |
Trough (12 to 24 hours after last dose). |
phenobarbital# |
4 days |
3 weeks |
Trough (immediately pre-dose) |
phenytoin#+
|
24 hours |
5 days |
Trough (immediately pre-dose) |
rivaroxaban |
7 hours |
2 days |
Trough (pre-dose) |
tacrolimus |
10 hours |
3 days |
Trough (8 to 18 hours after last dose). |
theophylline |
8 hours |
3 days |
Trough (8 to 18 hours after last dose). |
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. |
topiramate |
21 hours |
5 days |
Trough (8 to 18 hours after last dose). |
valproate sodium |
12 hours |
3 days |
Trough (8 to 18 hours after last dose). |
vancomycin |
6 hours |
Refer to dosing guidelines |
2 samples needed. First sample 30 minutes after end of infusion. See PinkBook guidelines for timing of second dose. |
voriconazole# |
6 hours |
3 days |
Trough (8 to 18 hours after last dose). |
*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.
Topic Code: 93304
