Height-Based Versus Weight-Based Dosing Regimen for Radium 223

SAN FRANCISCO—Researchers make a strong case for height-base dosing regimen when the intervention is designed only to treat the skeleton—as is the case with the radiopharmaceutical, radium 223.

 6 - Thomas A. Longo, MDThomas Andrew Longo, MD, from the University of Nebraska Medical Center in Omaha, presented the results at the 2014 Genitourinary Cancers Symposium, and colleagues conducted a study looking at the safety profile of radium 223 in the context of a height-based dosing regimen, rather than the weight-based dosing regimen in which it is currently dosed.

Radium 223 dichloride—a newly-approved targeted alpha emitter that is able to bind to materials in the bone and emit radiation directly to bone tumors—was recently approved for use in patients with symptomatic bone metastasis from castration-resistant prostate cancer (CRPC). Other presentations at the symposium highlighted the radiopharmaceutical’s long-term safety and ability to extend survival in this population.

The current study—a retrospective, observational study of all patients receiving radium 223 at a designated urology cancer treatment center—30 discreet patients received a total of 58 doses. Weight-based doses were administered at 50 kilobecquerels (kBq) per kilogram; each dose was then recalculated based upon the patient’s height.

The lowest dose received based on height was 17.39 kBq/cm and the highest dose was 40.7 kBq/cm with an average dose of 27.4 kBq/cm. Radium 223 at these doses was also well tolerated: there were eight grade 1 toxicities, and the side effect profile did not show any trends across the different levels of dosing regarding the number or grade of toxicity (with a greater number occurring below the median dose).

“A height based dosing regimen may be more appropriate for a drug designed to treat only the skeleton,” the investigators concluded. “In our population, we administered a wide variety of doses when administered by height. Higher doses appear to be well tolerated, and the optimal dose has yet to be determined. We propose future studies with height-based dosing escalation to look at the safety and efficacy.”

Source: Longo TA, McDonald M, Mehr SH, et al. Consideration of height-based rather than weight-based dosing as a more appropriate method of treating with radium-223. Abstract presented at 2014 Genitourinary Cancers Symposium; San Francisco, California. January 31, 2014.