Medical devices can range in complexity from a simple tongue depressor to a sophisticated CT (computed tomography) x-ray system. Most of the devices reach the market through FDA’s premarket notification (or 510(k)) review process. Under its 510(k) authority, FDA may determine that a device is substantially equivalent to a device already on the market and therefore not likely to pose a significant increase in risk to public safety. When evaluating 510(k) applications, FDA makes a determination regarding whether the new device is as safe and effective as a legally marketed predicate device. Performance data (bench, animal, or clinical) are required in most 510(k) applications, but clinical data are needed in less than 10 percent of applications. An alternative mode of entry into the market is through the premarket approval (PMA) process. PMA review is more stringent and typically longer than 510(k) review. For PMAs, FDA determines the safety and effectiveness of the device based on information provided by the applicant. Nonclinical data are included as appropriate. However the answers to the fundamental questions of safety and effectiveness are determined from data derived from clinical trials. FDA also regulates research conducted to determine the safety and effectiveness of unapproved devices. FDA approval is required only for “significant risk” devices. Applicants submit applications for such devices to obtain an investigational device exemption (IDE) from regulatory requirements and approval to conduct clinical research. For an IDE, unlike PMAs and 510(k)s, it is the proposed clinical study that is being assessed—not just the device. Modifications of medical devices, including any expansion of their labeled uses, are also subject to FDA regulation. Applications to modify a device that entered the market through a PMA are generally linked to the original PMA application and are called PMA supplements. In contrast, modifications to a 510(k) device are submitted as new 510(k) applications. References may be made to previous 510(k) applications. FDA uses several measures of duration to report the amount of time spent reviewing applications. In this letter, we use only three of those measures. The first is simply the time that elapses between FDA’s receipt of an application and its final decision on it (total elapsed time). The second measure is the time that FDA has the application under its review process (FDA time). This includes both the time the application is under active review and the time it is in the FDA review queue. The amount of time FDA’s review process has been suspended, waiting for additional information from the applicant, is our third measure (non-FDA time). Our measures of review time are not intended to be used to assess the agency’s compliance with time limits for review established under the Federal Food, Drug, and Cosmetic Act (the act). The time limits for PMA, 510(k), and IDE applications are 180, 90, and 30 days, respectively. FDA regulations allow for both the suspension and resetting of the FDA review clock under certain circumstances. How review time is calculated differs for 510(k)s and PMAs. If a PMA application is incomplete, depending on the extent of the deficiencies, FDA may place the application on hold and request further information. When the application is placed on hold, the FDA review clock is stopped until the agency receives the additional information. With minor deficiencies, the FDA review clock resumes running upon receipt of the information. With major deficiencies, FDA resets the FDA clock to zero upon receipt of the information. In this situation, all previously accrued FDA time is disregarded. (The resetting of the FDA clock can also be triggered by the applicant’s submission of unsolicited supplementary information.) The amount of time that accrues while the agency is waiting for the additional information constitutes non-FDA time. For 510(k)s, the FDA clock is reset upon receipt of a response to either major or minor deficiencies. For this report, we define FDA time as the total amount of time that the application is under FDA’s review process. That is, our measure of FDA time does not include the time that elapses during any suspension, but does include time that elapsed before the resetting of the FDA clock. The total amount of time that accrues while the agency is waiting for additional information constitutes non-FDA time. (The sum of FDA and non-FDA time is our first measure of duration—total elapsed time.) The act establishes three classes of medical devices, each with an increasing level of regulation to ensure safety and effectiveness. The least regulated, class I devices, are subject to compliance with general controls. Approximately 40 percent of the different types of medical devices fall into class I. At the other extreme is premarket approval for class III devices, which constitute about 12 percent of the different types of medical devices. Of the remainder, a little over 40 percent are class II devices, and about 3 percent are as yet unclassified. In May 1994, FDA implemented a three-tier system to manage its review workload. Classified medical devices are assigned to one of three tiers according to an assessment of the risk posed by the device and its complexity. Tier 3 devices are considered the riskiest and require intensive review of the science (including clinical data) and labeling. Review of the least risky devices, tier 1, entails a “focused labeling review” of the intended use. In addition to the three tiers is a group of class I devices that pose little or no risk and were exempted from the premarket notification (510(k)) requirements of the act. Under the class and tier systems, approximately 20 percent of the different types of medical devices are exempted from premarket notification. A little over half of all the different types of medical devices are classified as tier 2 devices. Tiers 1 and 3 constitute 14 and 12 percent of the different types of medical devices, respectively. From 1989 through 1991, the median time between the submission of a 510(k) application and FDA’s decision (total elapsed time) was relatively stable at about 80 to 90 days. The next 2 years showed a sharp increase that peaked at 230 days in 1993. Although the median review time showed a decline in 1994 (152 days), it remained higher than that of the initial 3 years. (See figure 1.) Similarly, the mean also indicated a peak in review time in 1993 and a subsequent decline. The mean review time increased from 124 days in 1989 to 269 days in 1993. In 1994, the mean dropped to 166 days; however, this mean will increase as the 13 percent of the applications that remained open are closed. (See table II.1.) Of all the applications submitted to FDA to market new devices during the period under review, a little over 90 percent were for 510(k)s. Between 1989 and 1994, the number of 510(k) applications remained relatively stable, ranging from a high of 7,023 in 1989 to a low of 5,774 in 1991. In 1994, 6,446 applications were submitted. Of the 40,950 510(k) applications submitted during the period under review, approximately 73 percent were determined to be substantially equivalent. (That is, the device is equivalent to a predicate device already on the market and thus is cleared for marketing.) Only 2 percent were found to be nonequivalent, and 6 percent remained open. Other decisions—including applications for which a 510(k) was not required and those that were withdrawn by the applicant—account for the rest. (See appendix I for details on other FDA decision categories.) For applications determined to be substantially equivalent, non-FDA time—the amount of time FDA placed the application on hold while waiting for additional information—comprised almost 20 percent of the total elapsed time. (See table II.7.) Figure 2 displays FDA and non-FDA time to determine equivalency for 510(k) applications. The trends in review time differed for original PMAs and PMA supplements. There was no clear trend in review times for original PMA applications using either medians or means since a large proportion of the applications had yet to be completed. The median time between the submission of an application and FDA’s decision (total elapsed time) fluctuated from a low of 414 days in 1989 to a high of 984 days in 1992. Less than 50 percent of the applications submitted in 1994 were completed; thus, the median review time was undetermined. (See figure 3.) Except for 1989, the means were lower than the medians because of the large number of open cases. The percent of applications that remained open increased from 4 percent in 1989 to 81 percent in 1994. The means, then, represent the time to a decision for applications that were less time-consuming. When the open cases are completed, lengthy review times will cause an increase in the means. (See table III.1.) For PMA supplements, the median time ranged from 126 days to 173 days in the first 3 years, then jumped to 288 days in 1992. In 1993 and 1994, the median declined to 242 and 193 days, respectively. (See figure 4.) This trend was reflected in the mean review time that peaked at 336 days in 1992. Although the mean dropped to 162 days in 1994, this is expected to increase because 21 percent of the applications had not been completed at the time of our study. (See table III.7.) Applications for original PMAs made up less than 1 percent of all applications submitted to FDA to market new devices in the period we reviewed. PMA supplements comprised about 8 percent of the applications. The number of applications submitted for PMA review declined each year. In 1989, applications for original PMAs numbered 84. By 1994, they were down to 43. Similarly, PMA supplements decreased from 804 in 1989 to 372 in 1994. (See tables III.1 and III.7.)