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Critical values for therapeutic drug levels.

The concept of critical values for drug levels was developed by Daniel M. Baer, MD, professor emeritus of laboratory medicine, Oregon Health Sciences University, Portland, OR, and first published in the April 1982 issue of MLO. This table is an expanded version of that publication and newly revised by Diane M. Lyle, PharmD, BCPS, Critical Care Clinical Pharmacy Specialist, Portland VA Medical Center. Dr. Baer is a member of MLO's Editorial Board and editor of MLO's "Tips from the Clinical Experts" department.
Drug Indication Therapeutic range

Acetaminophen Analgesic 5-20 mcg/mL

Amikacin Antimicrobial Peak: 15-30 mcg/mL
 Trough: < 10 mcg/mL

Amiodarone Antiarrhythmic 0.5-2mcg/mL

Amitriptyline Antidepressant/analgesic 125-250ng/mL
 (neuropathic pain)

Carbamazepine Antiepileptic/mood 4-12mcg/mL

Cyclosporins Immunosuppressant 100-400mcg/mL

Digoxin Inotrope, AV node blocker 0.8-1.2 ng/mL *

Doxepin Antidepressant 110-250ng/mL

Ethosuximide Antiepileptic 40-100 mcg/mL

Flecainide Antiarrhythmic 0.2-1.0 mcg/mL

Flucytosine Antifungal Not established

Gentamicin, Antimicrobial Peaks
Tobramycin 4-8mcg/mL. - standard
 8-12mcg/mL-once daily

 < 1.0 mcg/mL-standard
 < 0.5 mcg/mL-once daily

Imipramine Antidepressant >180-240ng/mL

Lamotrigine Antiepileptic/mood 1-4 mcg/mL

Lidocaine Antiarrhythmic 1.5-5mcg/mL

Lithium Mood stabilizer Acute: 1-1.6 mEq/L

Nortriptyline Antidepressant/analgesic 50-150ng/mL
 (neuropathic pain)

Phenobarbital Antiepileptic 15-40mcg/mL

Phenytoin Antiepileptic 10-20mcg/mL

Primidone Antiepileptic 5-12mcg/mL

Procainamide Antiarrhythmic PA:4-8mcg/mL (NAPA:
(PA) 10-20mcg/mL)

Protriptyline Antidepressant 70-250ng/mL

Quinidine Antiarrhythmic 2-5mcg/mL

Salicylate Analgesic/anti-inflammatory 10-30 mg/L

Sirolimus Immunosuppressant 5-15ng/mL

Tacrolimus Immunosuppressant 5-20 ng/mL

Theophylline Bronchodilator 5-20mcg/mL

Valproic acid Antiepileptic/mood 50-125mcg/mL

Vancomycin Antimicrobial Trough concentrations:
 General: 10-15mcg/mL
 Pneumonia: 15-20mcg/mL

Voriconazole Antifungal >0.25-1000 mcg/mL

Drug Critical Value Clinical

 Efficacy Toxicity

Acetaminophen >200 mcg/mL *drawn 4 UNCLR YES
 hours after ingestion

Amikacin Trough >10mcg/mL YES YES

Amiodarone >2.5mcg/mL UNCLR YES

Amitriptyline >500ng/mL UNCLR YES

Carbamazepine >20 mcg/mL YES YES

Cyclosporins >500mcg/mL YES YES

Digoxin >2.0ng/mL UNCLR YES

Doxepin >500ng/mL UNCLR YES

Ethosuximide > 200 mcg/mL YES YES

Flecainide > 1.0mcg/mL UNCLR YES

Flucytosine > 100-200 mcg/mL NO YES

Tobramycin Trough >2mcg/mL YES YES

Imipramine Not clear(>500nq/mL) YES YES

Lamotrigine >20mcg/mL UNCLR UNCLR

Lidocaine >60mcg/mL YES YES

Lithium > 2.0mEg/L YES YES

 potentially fatal

Nortriptyline >500ng/mL UNCLR YES

Phenobarbital > 60 mcg/mL YES YES

Phenytoin > 40 mcg/mL YES YES

Primidone >24mcg/mL YES YES
(metabolite: > l0mcg/mL YES(NO) YES
NAPA) (>40mcg/mL| (YES)

Protriptyline >500ng/mL UNCLR YES

Quinidine >6mcg/mL YES YES

Salicylate >40mg/dL NO YES -

Sirolimus >15ng/mL YES YES

Tacrolimus >25ng/mL NO YES

Theophylline >25mcg/mL UNCLR YES

Valproic acid >200mcg/mL YES * As YES

Vancomycin Trough >20mcg/mL UNCLR * UNCLR

 * Daily dose may
 correlate more
 with toxicity than

Voriconazole >6mcg/mL UNCLR YES

Drug Comments

Acetaminophen Determination of if a concentration
 is toxic is dependent upon when it
 is drawn in relation to the time of
 ingestion of the dose. Multiple
 serum concentrations will be needed
 to monitor improvement and removal
 of drug.

Amikacin Peak: 1 hour after end of infusion
 Trough: before next dose

Amiodarone Trough concentration Concentrations
 more accurate with chronic treatment
 (due to long half life of drug)

Amitriptyline Trough concentration Life
 threatening cardiac toxicity and/or
 seizures with concentration [greater
 than] 1000 ng/mL

Carbamazepine Trough concentrations preferred
 Correlate serum concentration with
 clinical presentation.

Cyclosporine Specific goal concentration
 dependent upon clinical situation.
 For concentrations drawn with
 intravenous therapy, blood should be
 drawn from site other than that
 where drug is infusing.
 (cyclosporine adheres to plastic)

Digoxin Concentrations should be drawn
 [greater than] 8 hours after last
 * Concentrations [greater than]
 1.5 in heart failure patients may be
 associated with higher mortality.
 Consult assay instructions for
 potential interfering factors.

Doxepin Trough concentration

Ethosuximide Trough concentration

Flecainide Midpoint or trough concentration
 Monitoring recommended when given
 concurrently with medications that
 may decrease metabolism (increase

Flucytosine Concentration should be a peak drawn
 2 hours post dose.

Gentamicin, Goal concentration (peak and trough)
Tobramycin dependent upon dosing method. Peak:
 1 hour after end of infusion Trough:
 before next dose

Imipramine Concentration= imipramine +

Lamotrigine Trough concentration.
 High concentrations generally associated
 with increased

Lidocaine Concentration can be drawn at any
 point (from separate IV line)

Lithium Serum concentrations may increase in
 presence of hyponatremia.
 Concentration: 12 hours after dose

Nortriptyhline Trough concentration

Phenobarbital Trough or mid interval

Phenytoin Toxicity may occur at lower
 concentrations in presence of
 hypoalbuminemia.Consider free

Primidone Metabolized to Phenobarbital

Procainamide (PA) Use as an antiarrhythmic decreasing
(metabolite: NAPA) NAPA concentrations increase in
 renal insufficiency/failure
 Mid-point or trough concentration

Protriptyline Trough concentration

Quinidine Midpoint or trough concentration

Salicylate Serum concentration should be used
 in conjuction with clinical
 presentation to make decision on
 therapy. Multiple serum
 concentrations will be necessary to
 monitor improvement and removal of

Sirolimus Trough concentration Whole blood

Tacrolimus Trough: 12 hours after given dose.
 Whole blood samples

Theophylline Pulmonary literature suggest that
 concentrations 5-15mg/L may be as
 efficacious with less toxicity.
 Trough or mid-interval concentration
 depending upon drug formulation.

Valproic acid Toxicity may occur at lower
 concentrations in presence of
 hypoalbuminemia. Consider free
 valproic acid. Trough concentration

Vancomycin Monitoring of peaks no longer
 recommended. Goal trough
 concentration dependent upon
 * Only trough concentrations of
 15-20mcg/mL for pneumonia have
 been proven to correlate. Trough:
 before next dose

Voriconazole Trough concentration preferred.
 Steady state trough achieved after 7
 days of therapy.

UNCLR = unclear

Ranges are approximate and may vary with laboratory and/or assay.

Proper interpretation of therapeutic drug concentrations requires that
the specimen be drawn at an appropriate time in relation to drug
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Article Details
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Publication:Medical Laboratory Observer
Article Type:Statistical table
Geographic Code:4EUUK
Date:Aug 1, 2008
Previous Article:Table of reference intervals.
Next Article:Cut-off and toxicity levels for drugs-of-abuse testing.

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