Critical values ofr therapuetuic drug levels.

Critical values ofr therapuetuic drug levels
The concept of critical vlaues for drug levels was developed by Daniel
M. Baer, MD, professor emertius 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
newly revised this year by Sue Millar, PharmD. Dr. Baer is a member of
MLO's Editorial Board and editor of MLO's "Tips from the Clinical
Expets" department.
Drug                                   Therapeutic range
ANTIBIOTICS (Specimen collection
depends on the the dosing protocol
followed. Consult the hospital
pharmacy).
Gentamycin                             6-10 mcg/mL peak
Tobramycin                             6-10 mcg/mL peak
Amikacin                               15-30 mcg/mL peak
                                       [less than]10mcg/mL trough
Vancomycin                             20-40 mcg/mL peak
                                       5-15 mcg/mL trough
ANALGESICS (Specimen collection:
For toxic ingestion, draw sample
at any time, noting times of
ingestion and sample collection.
Usually two samples, several hours
apart, acted to determine half-life.)
Acetaminophen                          5-20 mcg/mL
Salicylate                             10-20 mg/dL
ANTIEPILEPTICS (Specimen
collection: Trough, before next
dose. Several samples should be
drawn at the same time each day.)
Carbamazepine *                        4-12 mcg/mL
Ehtosuximide                           40-100 mcg/mL
Phenobarbitol                          15-40 mcg/mL
Phenytoin                              10-20 mcg/mL
Primidone                              5-12 mcg/mL
Valproic acid                          50-100 mcg/mL
ANTIDEPRESSANTS
Lithium specimen collection: 12
hours after dose
Lithium (acute)                        1.0-1.6 mEq/L
Lithium (chronic)                      0.5-1.0 mEq/L
Specimen collection: Trough, before
next dose
Amitriptyline                          120-125 ng/mL *
Imipramine                             150-300 ng/mL
Nortriptyline                          50-150 ng/mL
Protriptyline                          70-240 ng/mL
Doxepin                                150-300 ng/mL *
OTHER DRUGS
Cyclosporin                            150-400 ng/mL
                                       100-200 mcg/mL
Theophylline                           10-20 mcg/mL
Digoxin                                0.5-2.0 ng/mL
Drug                                   Critical value
ANTIBIOTICS (Specimen collection
depends on the the dosing protocol
followed. Consult the hospital
pharmacy).
Gentamycin                             [greater than] 12 mcg/mL peak
Tobramycin                             [greater than] 12 mcg/mL peak
Amikacin                               [greater than] 10 mcg/mL trough
Vancomycin                             60-80 mcg/mL peak
ANALGESICS (Specimen collection:
For toxic ingestion, draw sample
at any time, noting times of
ingestion and sample collection.
Usually two samples, several hours
apart, acted to determine half-life.)
Acetaminophen                          150 mcg/mL
Salicylate                             [greater than] 30 mg/dL
ANTIEPILEPTICS (Specimen
collection: Trough, before next
dose. Several samples should be
drawn at the same time each day.)
Carbamazepine *                        [greater than] 20 mcg/mL
Ehtosuximide                           [greater than] 200 mcg/mL
Phenobarbitol                          [greater than] 60 mcg/mL
Phenytoin                              [greater than] 40 mcg/mL
Primidone                              [greater than] 24 mcg/mL
Valproic acid                          [greater than] 200 mcg/mL
ANTIDEPRESSANTS
Lithium specimen collection: 12
hours after dose
Lithium (acute)                        [greater than] 2.0 mEq/L
Lithium (chronic)
Specimen collection: Trough, before
next dose
Amitriptyline                          400 ng/mL *
Imipramine                             400 ng/mL
Nortriptyline                          200 ng/mL
Protriptyline                          400 ng/mL
Doxepin                                400 ng/mL *
OTHER DRUGS
Cyclosporin
Theophylline                           [greater than]25 mcg/mL
Digoxin                                2.5 ng/mL
Drug                                 Comment
ANTIBIOTICS (Specimen collection
depends on the the dosing protocol
followed. Consult the hospital
pharmacy).
Gentamycin                           These values correlatee only with
                                     standard dosing, not pulse or
                                     single daily dosing.
Tobramycin                           Toxicity is related to trough
                                     concentrations and time spent at
                                     that concentration.
                                     Several methods for single daily
                                     dosing exist. Depending on the
                                     method, timing of drawing levels
                                     and desired levels will vary.
Amikacin
Vancomycin                           Draw peak 2-3 hrs after infusion
                                     ends. Peak concentrations not
                                     correlated with clinical efficacy.
                                     Toxicity is correlated with very
                                     high levels (60-80) mcg/mL) or
                                     duration of therapy.
                                     Draw trough immediately before
                                     next dose.
ANALGESICS (Specimen collection:
For toxic ingestion, draw sample
at any time, noting times of
ingestion and sample collection.
Usually two samples, several hours
apart, acted to determine
half-life.)
Acetaminophen                        To be measured 4 hours after the
Salicylate                           last dose.
ANTIEPILEPTICS (Specimen
collection: Trough, before next
dose. Several samples should be
drawn at the same time each day.)
Carbamazepine *                      Toxicity is usually clinically
                                     evident. Serious toxicity is
                                     likely
                                     at twice the upper therapeutic
                                     level.
Ehtosuximide
Phenobarbitol
Phenytoin
Primidone
Valproic acid
ANTIDEPRESSANTS
Lithium specimen collection: 12
hours after dose
Lithium (acute)                      Level over 5 mEq/L are potentially
                                     lethal.
Lithium (chronic)
Specimen collection: Trough,
before
next dose
Amitriptyline                        Life-threatening cardiac toxicity
                                     or seizures are seen if
                                     concentration is over 1,000 ng/mL
Imipramine
Nortriptyline
Protriptyline
Doxepin
OTHER DRUGS
Cyclosporin                          Monoclonal immunoassay. Sampling
                                     at
                                     a few time points may provide more
                                     cost-effective monitoring. Levels
                                     will vary based on whether taken
                                     from whole blood, serum, or
                                     plasma.
                                     High-performance liquid
                                     chromatography.
Theophylline                         Above this concentration, 75% of
                                     patients have toxic symtpoms.
                                     Serious toxicity causes seizures
                                     that can be fatal. Draw sample at
                                     peak. Different theophylline timed
                                     release medications have peaks at
                                     different times. Medication
                                     package
                                     insert should be consulted. Serial
                                     measurements should be collected
                                     at the same time each day.
Digoxin                              Eighty-seven percent of patients
                                     with greater than 2 ng/mL digoxin
                                     have toxic symptoms.
(*) 4-8 if patient is on multiple antiepileptic drugs
(*) Parent drug plus demethylated metabolite Proper interpretation of
therapeutic drug concentrations requires that the specimen be drawn at
an appropriate time in relation to drug administration.