Therapeutic Drug Information
Clinical
Biochemistry

From 16th April 2012, all drug results will be reported according to National Pathology Harmonisation Ranges where available (indicated by asterisk *)

Please note:  ALL drug concentrations (except lithium) are reported in MASS UNITS
Salicylate and paracetamol are reported in mg/L.
Ethanol will be reported in both mg/L and mmol/L
Lithium is reported in mmol/L

Previous therapeutic ranges used prior to this date can be viewed here.

Measurement of the concentration of a therapeutic drug in serum/plasma can serve as a useful aid in patient management. The aim of this analytical service is to help physicians tailor drug therapy to individual needs so that the beneficial effects of drugs are optimised and toxicity is minimised. Measurement of drug levels may be of value in assessment of compliance, therapeutic control, and confirmation of clinical toxity. Individual drug pharmacokinetics may be influenced by many factors. For advice concerning interpretation or for drug assays not included in the table below, please contact the Duty Biochemist or Medical Staff.
Drug Therapeutic Range Units Half life Sampling Time Time to
Steady
state
Carbamazepine * 4.0 - 12.0 mg/L 12 hrs pre-dose 2 - 6 days
Cyclosporin A See CYA therapeutic ranges ug/L 2 - 6 hrs pre-dose 2 -3 days
Digoxin * 0.5 - 2.0
(0.5 - 1.0 target in heart failure)
ug/L 36 - 48 hrs pre-dose (or at least 6hrs post-dose) 5 - 7 days
Lamotrigine 3.0 - 15.0 mg/L 20 - 30 hrs pre-dose 4 - 15 days
Lithium * 0.40 - 1.00 mmol/L 18 - 36 hrs pre-dose (ideally 12h pre-doses) 3 - 7 days
Phenobarbitone * 10.0 - 40.0 mg/L 96 hrs pre-dose 10 - 25 days
Phenytoin * 5.0 - 20.0 mg/L 7 - 42 hrs pre-dose 7 - 35 days
Tacrolimus Renal transplant: 10 - 20
Auto-immune disease: 5 - 15
pre-dose (trough) samples
Values >20 may be associated
with nephrotoxicity, glucose
intolerance etc.
ug/L 4 - 33 hrs pre-dose (trough) 2 days
Theophylline * 10.0 - 20.0 mg/L 3 -13 hrs pre-dose (or see below) 2 -3 days
sampling time: oral dosing - pre and/or 2-4 hrs post dose
infusion - sampling >6 hrs into a 24hr infusion
 
Valproic acid * None (toxic effects at >100 mg/L 8 - 20 hrs pre-dose 2 - 4 days

Please note:  Toxic effects for some drugs may be observed at the upper limit of therapeutic levels.
The time of sampling realtive to the dose should be specified

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