United States of America. The ISMP has received two reports in the last month of errors in the dosing of nortriptyline (Pamelor, Aventyl and others). In each case, the antidepressant was used to treat neuropathic pain syndromes.

Case 1. A 61-year old male patient was hospitalized for treatment of hyperglycaemia and had recently been started on nortriptyline for diabetic neuropathy of the lower limbs. The dose was slowly being increased - prior to admission he was receiving 20 mg daily at bedtime. Although the patient’s medical history was correctly noted, a senior resident mistakenly ordered nortriptyline 200 mg at bedtime. The patient received two doses and was extremely sedated and orthostatic on the third day when the error was finally recognized.

Case 2. A similar report was received a week later. The pain service of a teaching hospital had prescribed 10 mg of nortriptyline for a patient at bedtime for neuropathic pain. A physician from another service accidentally wrote a discharge prescription for nortriptyline 100 mg at bedtime and a community pharmacist dispensed that amount. Without knowing the patient’s history and prior drug therapy, the community pharmacist had no way of knowing that the 100 mg dose was wrong. The patient received five days of therapy and needed to be hospitalized. The error was discovered upon admission.

Nortriptyline and other tricyclic antidepressant drugs are not being used as frequently as in the past. Many pharmacists and physicians are not familiar with their proper dose ranges.

Selective serotonin reuptake inhibitors such as fluoxetine (Prozac), sertraline (Zoloft), and paroxetine (Paxil) and newer antidepressants, including venlafaxine (Effexor), nefazodone (Serzone) and mirtazapine (Remeron) are now the first-line agents used to treat depression.

The dose range for nortriptyline may be 10 mg to 150 mg for the treatment of depression or various pain syndromes. A dosage of more than 150 mg of nortriptyline is not recommended for any reason. Therefore the maximum dose warning feature in the hospital’s computer system should be set at this level. Wherever possible, pharmacy or nursing staff should review discharge prescriptions with an up-to-date list of the patient’s medications, patients should be encouraged to learn the names, doses and purposes of all their medications so that they can communicate this information to health care providers and even their pharmacist.

Reference: ISMP Medication Safety Alert! Vol. 3, Issue 17, 26 August 1998.