Error Alert
Institute for Safe Medication Practices, Horsham, PA
Methadone overdose has been linked to mistaken use of concentrated oral solution and scanning the wrong barcode. When prescribing methadone oral solution, it is critical that pharmacists confirm that the most appropriate concentration of the product based on the patient’s dose is used.
Background
In a case that illustrates the issues with methadone dosing, an elderly patient was admitted to the hospital for pain management and was to continue her home regimen of methadone oral solution 2.5 mg twice daily. During order entry, the physician was presented with a selection of methadone products, including 10 mg tablets, 1 mg/mL oral solution, and 10 mg/mL concentrated oral solution. The physician did not see the 1 mg/mL oral solution choice and selected the 10 mg/mL oral solution. This required a volume of 0.25 mL per dose, which is difficult to measure. A pharmacist verified the order but did not think to call the prescriber to change the concentration of methadone to 1 mg/mL.
For methadone maintenance, the pharmacy prepared batches of oral syringes (10 mg/mL), each containing 6 mL (60 mg of methadone total per syringe) to meet the needs of patients requiring higher doses. A barcoded label was affixed to each batched oral syringe. When dispensed, the batched syringe would be placed in a bag with an attached label stating the patient’s dose and volume. An erroneous dispense code allowed a barcode to be printed on this patient-specific label. The process called for nurses to scan the barcode on the oral syringe (not on the patient-specific label affixed to the bag). The barcode system would then alert the nurse to administer the correct volume and dose from the batched oral syringe.
In this case, instead of scanning the barcode on the syringe label, the nurse scanned the barcode on the patient-specific label on the outer bag, which indicated the correct patient dose of 2.5 mg. Thus, the nurse was not alerted to administer just 0.25 mL of the syringe. The nurse administered the full 6 mL (60 mg) of the concentrated oral solution.
The evening nurse, who was undergoing orientation, also administered a full 6-mL syringe for the second dose of the day. Instead of the intended 5 mg total daily dose, the patient received 120 mg of methadone that day—a 24-fold overdose. When a nurse preceptor asked about wasting the remainder of the oral methadone, the orientee said she had administered the entire syringe of medication. The patient was transferred to the ICU, started on a naloxone drip, and was monitored.
Safe practice recommendations
When prescribing methadone oral solution, the order entry system, not the prescriber, should automatically select the most appropriate concentration of the product based on the patient’s dose. For example, if the dose is 10 mg or less, the system would default to a 1 mg/mL oral solution; if the dose is greater than 10 mg, the system would default to a 10 mg/mL concentration.
Particularly for an infrequently prescribed, high-alert medication like methadone oral solution, pharmacy-prepared oral syringes in patient-specific doses should be dispensed for inpatients, as nurses are often accustomed to believing that one syringe equals one dose. This would also reduce the amount of waste and the risk of diversion. The same is true for other oral high-alert medications in cups, oral syringes, and bottles of tablets. Whenever possible, one package should equal one dose.
If products must be batched, the barcode on the batched product should be the only available barcode for nurses to scan at the bedside. Thus, if the patient’s dose is different than the amount in the batched container, the barcode system should alert the nurse to administer a partial dose. Also, be sure the standard dose of the batched product is as close as possible to commonly prescribed doses in your facility.