Investigating levothyroxine errors

Nurse Practitioner, Mar 2001 by Cohen, Hedy, Smetzer, Judy, Cohen, Michael

Safe Prescribing

Over the years, medication errors with levothyroxine have been reported. Some have resulted in serious patient harm and even death. To better understand the causes of these errors, the Food and Drug Administration's Office of Postmarketing Drug Risk Assessment (OPDRA) recently reviewed reported incidents.

Most errors involved confusion between Lanoxin (digoxin) and levothyroxine, especially before the brand name Levoxine was changed to Levoxyl. Nevertheless, the generic name levothyroxine can resemble Lanoxin, especially when orders are poorly handwritten. The risk of an error is also heightened because both drugs are prescribed for chronic use, have a similar daily dosing regimen, and have overlapping dosage strengths of 0. 125 mg. Some of the errors involved dispensing and administering an incorrect dose of levothyroxine, most often a tenfold overdose after a decimal point had been misinterpreted.

Abbreviations used during the prescribing process have also played a role. For example, a prescription for Synthroid (levothyroxine) "QD" was misinterpreted as "QID In another case, the abbreviations "mcg" and "mg" were confused with each other, and a patient who had been taking Synthroid 25 mcg orally each day received a fatal intravenous dose of Synthroid 0.25 mg (250 mcg) prior to surgery.

Manufacturer labeling states that the product, a lyophilized powder of 200 or 500 mcg, is supplied in a 10-ml vial. This refers to the size of the glass vial, but the product should be reconstituted with 5 ml of diluent, resulting in a final concentration of approximately 40 or 100 mcg per ml. In one case, although only 5 rrd of diluent was used, the pharmacist miscalculated using 10 ml as the final volume, yielding an incorrect concentration of 50 mcg per ml. The patient received 1 ml (100 mcg), not the correct dose of 0.5 ml (50 mcg).

To reduce the risk of error, prescribers should print all orders for Lanoxin and levothyroxine and include the purpose for each drug on all prescriptions. Both the mg dose and the mcg conversion should be listed in all levothyroxine orders, such as "levothyroxine 100 mcg (0. 1 mg)" or "Synthroid 0.1 mg (100 mcg).' A leading zero should always be written for doses less than I mg to avoid misinterpreting a dose of "Synthroid.025 mg" as "Synthroid 0.25 mg." Trailing zeros (for example, Synthroid 25.0 mcg) should never be used. Prescribers should instruct patients to verify the drug and dose when in the hospital and with the pharmacist when their prescription is dispensed.

The authors of Safe Prescribing are the following staff from the Institute for Safe Medication Practices (ISMP): Hedy Cohen, RN, BSN, vice-president nursing; Judy Smetzer, RN, BSN, director, risk management; and Micheal Cohen, RPh, MS, FASHP, president. ISMP, a nonprofit organization, derives its reports from the USP Medication Errors Reporting Program. To report medication errors, call the USP at 1-800-23-ERROR (233-7767). To contact ISMP, call 215-947-7797 or e-mail ismpinfo@ismp.org.