Differences in Adverse Event Reporting Rates of Therapeutic Failure Between Two Once-daily Extended-release...

Our study evaluated adverse events of therapeutic failure (and specifically reduced duration of action) with the use of a branded product, Osmotic Release Oral System (OROS) methylphenidate, which is approved for the treatment of attention deficit/hyperactivity disorder, and a generic product (methylphenidate, methylphenidate ER-C), which was approved for marketing in Canada based on bioequivalence to OROS methylphenidate. This study was initiated following reports that some US-marketed generic methylphenidate ER products had substantially higher reporting rates of therapeutic failure than did the referenced brands.

Through methodology similar to that used by the US Food and Drug Administration to investigate the issue with the US-marketed generic, reporting rates were calculated from cases of therapeutic failure identified in the Canadian Vigilance Adverse Reaction Online database for a 1-year period beginning 8 months after each product launch. Corresponding population exposure was estimated from the number of tablets dispensed. An in-depth analysis of narratives of individual case safety reports (ICSRs) with the use of the generic product was conducted in duplicate by 2 physicians to assess causality and to characterize the potential safety risk and clinical pattern of therapeutic failure. Similar secondary analyses were conducted on the US-marketed products.

Reporting rates of therapeutic failure with the use of methylphenidate ER-C (generic) and OROS methylphenidate (brand name) were 411.5 and 37.5 cases per 100,000 patient-years, respectively (reporting rate ratio, 10.99; 95% CI, 5.93-22.21). In-depth analysis of narratives of 230 ICSRs of therapeutic failure with the Canadian-marketed generic determined that all ICSRs were either probably (60 [26%]) or possibly (170 [74%]) causally related to methylphenidate ER-C. Clinical symptoms suggestive of overdose were present in 31 reports of loss of efficacy (13.5%) and occurred primarily in the morning, and premature loss of efficacy (shorter duration of action) was described in 98 cases (42.6%) and occurred primarily in the afternoon. Impacts on social functioning, such as disruption in work or school performance or adverse social behaviors, were found in 51 cases (22.2%).

The ~10-fold higher reporting rate of therapeutic failure with the generic product relative to its reference product in the present Canadian study resembles findings with US-marketed generic products. While these results should be interpreted with caution due to the limitations of spontaneous adverse event reporting, which may confound comparisons across products, similar findings nonetheless led the US Food and Drug Administration to declare in 2014 that 2 methylphenidate ER generic products in the United States were neither bioequivalent nor interchangeable with OROS methylphenidate-their reference product. Our results indicate a potential safety issue with the Canadian-marketed generic and suggest a need for further investigation by Health Canada.