Back and neck pain sufferers who divide the most frequently prescribed muscle relaxant may be getting anywhere from half to one-and-a-half times the amount of medicine they believe they are taking, suggests a new study examining the practice of tablet splitting. This may place them at an increased risk of encountering side effects such as drowsiness and fatigue from too much medication, according to the study's primary investigator.

Researchers at the Ernest Mario School of Pharmacy at Rutgers, The State University of New Jersey, recently conducted a study to determine the level of weight variability of tablet fragments when the muscle relaxant cyclobenzaprine HCl 10 mg was split into halves with two commonly used devices - a tablet splitter and a kitchen knife. Initiation of the study followed anecdotal reports that patients given a prescription for branded Flexeril (cyclobenzaprine HCl) 5 mg tablets were being advised to split generic cyclobenzaprine HCl 10 mg tablets instead of taking the 5 mg tablet as prescribed by their physician.

Flexeril 5 mg, approved by the US FDA in February 2003, is comparable in efficacy to the 10 mg strength, but has been shown to be less sedating.

"Ideally, an evenly split 10 mg tablet should have 100 per cent of the half tablet weight and 5 mg of the medication," explained study investigator Thomas J. Cook, assistant professor, Department of Pharmaceutics. "In this study, the variance in estimated drug content due to uneven tablet splitting ranged anywhere from 50 to 150 per cent of the ideal targets, meaning a patient would have no guarantee of receiving a full half-dose consistently throughout the course of therapy."

According to its labeling, Flexeril 5 mg is recommended as a two-three week adjunct to rest and physical therapy for the relief of muscle spasm associated with acute, painful musculoskeletal conditions.

Since generic cyclobenzaprine HCl 10 mg tablets are not designed for splitting (tablets are not scored), there is an increased likelihood that they will split unevenly, crumble or shatter, according to Dr. Cook. "In this instance, the practice of pill splitting may put patients at risk of receiving too little or too much medication, either depriving them of the intended therapeutic benefit of the medication or exposing them to unintended side effects such as dizziness or tiredness. The best way to be confident that a patient consistently gets the intended amount of medication is to take the 5 mg tablet as prescribed."

The research is consistent with a study in the March/April 2002 issue of the Journal of the American Pharmacists Association (APhA) which found that tablet splitting generally resulted in a lack of uniformity, even when the tablets were scored. The APhA, along with The National Association of Boards of Pharmacy and the American Society of Consultant Pharmacists are among groups opposing mandated tablet splitting by patients.

The newly published "Tablet Splitting: Evaluating Appropriateness for Patients - Tool for pharmacists from the 2003-2004 APhA Strategic Directions Committee" appears in the May-June Journal of the American Pharmacists Association.