Medications with delayed- or extended-release formulations can play a vital role in improving adherence to drug therapy. These unique dosage formulations avoid the need for multiple daily doses of a medication due to their delayed or sustained delivery of a total daily dose steadily throughout the day. This is convenient for patients, may reduce certain side effects, and, on occasion, even allows use for different indications. However, the nomenclature used for long-acting dosage forms is often confusing, and errors may occur when the same drug has several oral dosage forms with different release rates.
The practice of adding “suffixes” or “modifiers” (e.g., Depakote ER or Cardizem CD) to medication names is used by manufacturers to maintain brand awareness while signifying that the formulation is different from the immediate-release version of the product. However, there is no standardization of the terms for the many different kinds of long-acting formulations. As a result, there are many inconsistencies, allowing different suffixes to be used for an identical formulation by two different manufacturers or even similar suffixes for dissimilar formulations. In short, the nomenclature used for these formulations often fails to provide appropriate “cues” regarding proper use of a dosage form.1
In addition to lack of standards, another problem is that health professionals have been known to communicate drug names that have suffixes, but omit the suffix. This occasionally results in patients getting the immediate-release version and thus, an entire day’s dose at one time, sometimes with adverse effects. Practitioners have also been known to include suffixes that do not exist for the specified product.2 Additional contributing factors reported to PA-PSRS include similar packaging, overlapping dosages, and storage of the products next to each other. These factors combine to allow confusion, inefficiencies, and medication errors at various stages in the medication use system.
In an analysis of 402 prescribing errors, Lesar3 found that the most common type of error was failure to specify the controlled-release formulation (280 cases, 69.7%). The Institute for Safe Medication Practices (ISMP) has received reports of confusion between Abbott’s DEPAKOTE ER (divalproex sodium extended release) and DEPAKOTE (divalproex sodium delayed release).4 Additional examples include GLUCOTROL and GLUCOTROL XL as well as GLUCOPHAGE and GLUCOPHAGE XR.
The most common examples of this type of error reported to PA-PSRS include mix-ups between products such as:
- ADDERALL and ADDERALL XR
- EFFEXOR and EFFEXOR XR
- VICODIN and VICODIN ES
Additional examples include:
- AUGMENTIN and AUGMENTIN XR
- CARDIZEM and CARDIZEM CD
- CIPRO and CIPRO XR
- DEPAKOTE and DEPAKOTE ER
- DETROL and DETROL LA
- LOPRESSOR and LOPRESSOR XL (the XL formulation is Toprol XL)
- RYTHMOL and RYTHMOL SR
- SENOKOT and SENOKOT S
- SINEMENT and SINEMENT CR
- verapamil and verapamil SR
The confusion multiplies when there are two or more “extended” release formulations for the same products, which are not therapeutically equivalent or “substitutable.” Some products have numerous suffixes to differentiate formulations of the same drug. For example, suffixes for various diltiazem products include SR, CD, XR, XT, and LA. ISMP also has received reports where pharmacists dispensed METADATE ER instead of METADATE CD. Similarly, ISMP has received a report where a prescription for METADATE CD 20 mg was dispensed as METADATE ER 20 mg. The pharmacists involved in these errors weren’t aware that the METADATE CD product existed.5 PA-PSRS has received reports noting confusion between medications such as the once-a-day formulation WELLBUTRIN XL (bupropion extended-release) and WELLBUTRIN SR (buproprion sustained-release), which is indicated for twice-daily dosing. Wellbutrin mix-ups are especially likely since both the SR and XL formulations are available in 150 mg tablet strengths, and it’s not unusual for the SR formulation to be prescribed once daily.
Drug name suffixes are confusing enough without coining them on our own. One report to ISMP involved a physician assistant that wrote a prescription for a patient, which was misread by both the pharmacist and technician as VICODIN ES (hydrocodone 7.5 mg/ acetaminophen 750 mg). However, on closer inspection, the suffix looked more like RS. The pharmacist called the physician assistant and learned that he had used “RS” to mean “regular strength.” VICODIN (hydrocodone 5 mg/acetaminophen 500 mg) was then dispensed.6
In order to improve the landscape when suffixes are used and reduce the risk of errors, nomenclature standards would help to diminish confusion between various formulations of the same drug.7 Standard suffixes or descriptive phrases might be incorporated directly into the drug name, or a unique brand name might be needed to designate a different formulation property, as was done with NEORAL (cyclosporine modified) and SANDIMMUNE (cyclosporine). FDA is aware of these problems and will be examining ways to improve trademark nomenclature.
Being mindful of the potential for this type of confusion when prescribing, storing, dispensing, and administrating such medications is just the first step in prevention. Other preventive strategies to consider include:
- Selectively building flags into computer systems and marking drug containers to warn staff about the differences where a high risk of error exists or when a mix-up might be very serious.
- Designing computer mnemonics to separate the different formulations on computer screens used during order entry.
- Storing similarly named drugs separately and using auxiliary labels to differentiate the products in medication storage areas.
- Verifying new prescriptions for any of these medications where prescriber confusion among suffixes has been reported.
- When communicating orders orally, using the full words “extended release” or “sustained release,” not abbreviations, especially for those medications that are available as an immediate release formulation.
- Involving patients also may help. When prescribing and dispensing one of these medications, practitioners may want to inform patients of the potential for confusion between the various formulations and suffixes.
- Cohen MR, ed. Medication Errors. Causes, Preventions and Risk Management. Sudbury (MA): Jones and Bartlett Publishers; 2000.
- ISMP Medication Safety Alert! Community Pharmacy/Ambulatory Edition. 15 Jul 2004;(9)14.
- Lesar TS. Medication errors related to dosage formulation issues. Medscape Pharmacists 2001. Available on Internet: http://www.medscape.com/viewarticle/408579_print
- ISMP Medication Safety Alert! 7 Feb 2001;(6)3.
- ISMP Medication Safety Alert!. 28 Nov 2001;(6)24.
- ISMP Medication Safety Alert! [online]. 15 Nov 2004;(9)14.
- Cohen MR. Medication error reports. Hosp Pharm. 1990;25:747-8.