From the April 2006 issue

Health professionals should be concerned about the number of mix-ups reported to ISMP and USP involving expressions of volume, specifically confusion between milliliter and teaspoonful. When these errors appear on pharmacy-generated labels, patients receive 5-fold overdoses or underdoses if undetected. In one report, a pharmacist labeled a prescription for ZITHROMAX (azithromycin) suspension with the directions to give “2 1/2 teaspoonsful daily” (equivalent to 12.5 mL) instead of 2.5 mL daily. The entire content of the bottle was administered according to the labeled instructions, and the child developed diarrhea. In another case, an 8-month-old child was dispensed ZANTAC (ranitidine) syrup to treat gastroesophageal reflux disease. The pharmacy label incorrectly instructed the parent to administer “0.5 teaspoonful three times daily” (equivalent to 2.5 mL) instead of 0.5 mL three times daily. The overdose was administered for two weeks and the child experienced tremors, excessive blinking and the inability to sleep. These reactions resolved after the medication was discontinued. Similar mix-ups between teaspoonful and mL have also involved drugs such as amoxicillin, amoxicillin/clavulanic acid, fluoxetine, citalopram and fluconazole. To prevent the teaspoonful-mL confusion, volume expression on prescriptions and pharmacy labels must be standardized. Doses for oral liquids should be expressed only in metric weights and Volumes (i.e., mg and mL). This would also eliminate potential confusion between teaspoon and tablespoon. Prescribers should include the calculated dose by metric weight, not just the metric volume; the use of teaspoon and tablespoon should be avoided. Remove non-metric volume expressions such as teaspoon from computer systems. This should include any mnemonics or defaults used to generate prescriptions and labels. Double check the directions that appear on the pharmacy label against the original prescription. Take steps to ensure that patients have an appropriate device to measure volume in milliliters when a prescription for an oral liquid medication is dispensed. Coach patients how to use these devices and ask patients to demonstrate their understanding of the instruction. See our November 2005 (available at: www.ismp.org/Newsletters/ambulatory/archives/200511_1.asp) and February 2006 (available at: www.ismp.org/Newsletters/ambulatory/archives/200602_3.asp) issues for more recommendations on providing appropriate measuring devices to patients.