Drug Level Sampling Times

Drug	Ideal Sampling Time1	Minimum resampling interval2
AMINOGLYCOSIDES (Gentamicin and Tobramycin)	Conventional Dosing (e.g. 3x day) Trough:  <30 minutes before dose Peak:      1 hour after IM injection or 1 hour after start IV infusion	1 day
	Once daily dosing (ODD) Trough:  18 hours after dose (or refer to specific ODD guidelines / contact Pharmacy for time of trough.) Peak:      1 hour after start IV infusion	A sample can be taken on the first dose.
CARBAMAZEPINE (Tegretol)	Immediately before an oral dose	Initiation of therapy: 2-4 weeks. Chronic therapy: 4 days.
DIGOXIN	At least 6-8 hours after OR immediately before an IV or oral dose	7 days
LITHIUM	At 12 hours after dose	Check weekly until stable, then 2-3 monthly.
PHENYTOIN (Dilantin)	> 6 hours post dose OR immediately before an oral dose	Dose dependent, 2-4 weeks.
THEOPHYLLINE (Nuelin, Aminophylline)	ORAL (slow release preparation) 4-8 hours after dose OR Immediately before a dose IV (continuous infusion) sample at 12 and 24 hours	2 days
VALPROATE SODIUM (Epilim, Valproic acid)	> 6 hours post dose OR immediately before an oral dose	3 days
VANCOMYCIN	Trough: Immediately before an IV dose Peak:     Not necessary	1-2 days

1.     Ideal Sampling Time: This should be adhered to wherever possible.  Drug levels taken at these times provide more meaningful information and this facilitates the interpretation of results.

2.     Minimum resampling intervals:  This is the earliest time a drug level should be measured following initiation of therapy or a change of dosage (unless therapeutic failure or toxicity is suspected). These times are based on the average time to steady state.

References:

Abbott package insert.

Tietz, "Textbook of Clinical Chemistry and Molecular Diagnostics", 5th edition.

Medicine - Therapeutic Monitoring - IVTG002 HBDHB IV & Therapeutic Guidelines, July 2019.