The overall dropout rate for oncology phase I trials is only 8%, according to a study by Cutting Edge Information. However, dropout rates tend to rise as the number of required visits increases.

The study, Phase I Clinical Trials: Optimizing Cost-Drivers for Clinical Pharmacology Programs, found the average number of patients enrolled for these trials across all therapeutic areas is 47.2.

Surveyed companies reported as few as 15 patients enrolled in their phase I trials. However, "one interviewed executive conducting a diabetes trial reported 200 enrolled patients, many more than any other trial," said Ryan McGuire, research team leader at Cutting Edge Information. "Though the diabetes trial had the highest patient enrollment, its total costs are 2.5 times less than the overall average. Patient recruitment was likely easy for this therapeutic area, and the trial required only four patient visits."

The next highest number of patients came from an oncology clinical trial. Initial patient enrollment ranged from 15 to 106, much higher than the average for phase I trials. Across other therapeutic areas, including cardiovascular, gastroenterology and women's health, average enrollment was generally between 20 and 40 patients.

The study reveals the average number of patients completing phase I trials by therapeutic area. Oncology trials align with the average dropout rate at 8%. Central nervous system/neurology trial results show a dropout rate at 7%. Women's health trials appear to have a high average dropout rate at 16%—double this study's overall average.