Blood concentrations of amitriptyline may be used by clinicians to monitor concentrations during therapy. Clinician can also use the concentrations to evaluated potential toxicity and test patient compliance.
Amitriptyline is a tricyclic antidepressant that acts primarily as a serotonin-norepinephrine reuptake inhibitor, with strong actions on the serotonin transporter, and moderate effects on the norepinephrine transporter. The relative blood levels of Amitriptyline and Nortriptyline are highly variable among patients. Amitriptyline is the drug of choice in treatment of depression when the side effect of mild sedation is desirable. Nortriptyline is used when its stimulatory side effect is considered to be of clinical advantage.
Amitriptyline displays major cardiac toxicity when the concentration of Amitriptyline and Nortriptyline is in excess of 1,000 mg/L, characterized by QRS widening leading to ventricular tachycardia and asystole. In some patients, toxicity may manifest at lower concentrations.
Nortriptyline is unique among the antidepressants in that its blood level exhibits the classical therapeutic window effect; blood concentrations above or below the therapeutic window correlate with poor clinical response.
Like Amitriptyline, Nortriptyline can cause major cardiac toxicity when the concentration is in excess of 500 mg/L, characterized by QRS widening leading to ventricular tachycardia and asystole. In some patients, toxicity may manifest at lower concentrations.
Amitriptyline: 30 – 150 ug/L
Nortriptyline: 50 – 150 ug/L
Serum specimen in a plain (red topped) tube.
SST samples can NOT be used.
Nortriptyline: Toxicology Laboratory
Amitriptyline: Llandough Hospital