COMMENTARY

OROS Medications Confounding Kidney Stone Diagnosis

James L. Schaller, MD, David Behar, MD

Disclosures

April 27, 2001

Introduction

The nondissolving carrier of osmotically controlled-release oral (OROS) pharmaceuticals may be misdiagnosed as kidney stones on x-ray. OROS is an osmotically controlled-release oral delivery system. Alza Corporation (Mountain View, California) is a pharmaceutical company developing new delivery technologies, including the OROS system. It is designed to provide once-daily dosing of a number of medications, eg, methylphenidate,[1] oxybutynin,[2] melatonin,[3] and metoprolol.[4] Brand-name medications using an OROS delivery include Concerta, Ditropan XL, Cardura XL (Germany), Covera-HS, and Alpress LP (France).

A 13-year-old male was treated for attention-deficit hyperactivity disorder and a previous bout of renal colic, passing stones at the age of 9. They were calcium based but could not be analyzed because of their small size and therefore went uncollected. He experienced severe pain late one evening, a "10" on a 0-10 scale. It localized to his periumbilical region, and then moved to his right lower quadrant. He was taken promptly to the pediatric hospital emergency room. After a history, exam, and flat plate x-ray, he was diagnosed as having 6 kidney stones, possibly requiring surgery.

The patient then voided urine with visible blood and was suddenly pain free. The attending referred the patient home with pain medication and requested he be seen the following week.

The youth was seen at another pediatric urology practice, which his mother brought him to because she was confused about his "need for surgery." A spiral CAT scan of the abdomen and the flat plate films were read by a radiologist and the pediatric urologist. They determined that the residual stones were actually "pills" located in the bowel. No surgery was needed. Any stone had already been passed and the "remaining stones" were "pills."

The patient was taking Concerta, an OROS form of methylphenidate. He took a 36-mg tablet in the early morning and two 18-mg tablets in the afternoon. According to the manufacturer, these usually remain in human intestines for 24-36 hours.[5]

Physicians evaluating abdominal radiographs for abdominal pain should be aware of the possibility that OROS medications may appear radio-opaque. It is not to be assumed that all OROS medications will have this feature, but clinicians should consider it a possibility.

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