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Discussion of a Post-Marketing Approval Study for 30-day Continuous Wear Contact Lenses. Gene Hilmantel, O.D., M.S. Bernard P. Lepri, O.D., M.S., M.Ed. James F. Saviola, O.D. Rosalie A. Bright, Ph.D.( OSB/DPS ).
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Discussion of a Post-Marketing Approval Study for 30-day Continuous Wear Contact Lenses
Gene Hilmantel, O.D., M.S. Bernard P. Lepri, O.D., M.S., M.Ed. James F. Saviola, O.D. Rosalie A. Bright, Ph.D.(OSB/DPS)
New contact lens materials with much higher oxygen transmission may have the potential for safer continuous wear for longer periods of time.
Although a serious problem, the incidence of ulcers is too low to reliably determine the risk in a reasonable PMA study.
The FDA’s position is that the best way to address this concern is to require a “Post-Marketing Approval Study” of the risk posed by 30-day “continuous wear.”
Relative Risk (Risk of EW ulcer/Risk of DW ulcer) (continuous wear) from Schein O, et al. The relative risk of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. New Eng J Med 1989;321:773-778
From the 1989 Schein data, it seems that a “relative risk” of about 12-15 (compared to Daily Wear) was considered unacceptable.
Poggio’s 1989 study* found that the incidence of ulcers was: • 4 per 10,000 in DW patients, • 20 per 10,000 in EW patients. *Poggio EC, et al. The incidence of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. New Eng J Med 1989;321:779-783
Assuming that 15x the risk of daily wear is unacceptable, this means that : • 15x(4/10,000) = 60/10,000 is too much risk. • 60/10,000 is about 2 - 4 times the risk of 7-day Extended Wear.
0.25 One year ulcer risk 0.0004 0.20 0.002 0.006 0.15 0.10 0.05 0.00 0 5 10 15 20 25 30 35 40 45 Lifetime ulcer risk Vs Number of Years Wearing Contacts Lifetime ulcer risk Number of Years Wearing Contacts
Question: Does the panel feel that using 60/10,000 ulcers/patient-year (about 3x the 7-day EW rate) as an upper limit is reasonable?
What Type of Study Should Be Recommended? Relative Risk Incidence Case-Control Study Follow Cohort
Advantages of a Case-Control Study: • Can assess relative risk of different actual wearing schedules. • Good for the study of rare diseases. • Relatively inexpensive. • Can assess relative risk of different hygiene practices. • “Real World” environment. Patients and practitioners NOT self or other selected.
Disadvantages of a Case-Control study: • Requires a waiting period (3 - 5 years?), until 30-day lenses have sufficient market share. • Only assesses relative risk, not actual incidence of ulcers. Ulcer rate for 7-day lenses may have decreased since 1989 (since 30-day wear was eliminated). • Generally produces large confidence intervals, or else need very large number of ulcers. E.g., in Schein(1989): RR of overnight EW to DW was 10.2, with a CI of 5.3 - 19.6.
Question: Will there be difficulty in getting enough EW ulcer cases? • Schein (1989) had 86 in study (52 were EW). • Half of all CL-related ulcers are DW. • Change in pattern of care for ulcers since 1980s.
Relationship between Sensitivity of test and required Sample Size. Cases ( EW Ulcers) Required for 80% Power to Detect Relative Risk* *Table is for testing H0: Relative Risk= 1. (30-Day/7-Day Wear) ONE-SIDED TEST, =.05.
Statistical POWER is a key measure of our confidence in product safety. • Power and sample size are strongly related. Cases (Ulcers) Required to Detect Relative Risk* *Table is for testing H0: Relative Risk= 1. (30-Day/7-Day Wear) ONE-SIDED TEST, =.05.
There is an interplay between Market Penetration and Sensitivity & Power of the test. Cases (Ulcers) Required for 90% Power to Detect Relative Risk* Table is for testing H0: Relative Risk= 1. ONE-SIDED TEST, =.05
Questions: • What statistical POWER would the panel recommend to ensure confidence in the result? • Should we wait for greater penetration of the market, in order to achieve greater sensitivity and power?
Following a cohort of 30-day wearers is an alternative way to assess risk. • Could be done by requiring a large number of practitioners to fill out a small follow-up questionnaire after 1 year of experience with the lens.
Advantages of a Cohort Study: • May yield results within ~ 2 years(?) of FDA approval. • Can assess incidence of ulcers. • May assess incidence of other complications. Disadvantages of a Cohort study: • Selected patients. • Selected practitioners. • Relatively controlled follow-up environment. • Cost?
Significant increases in ulcer rate are detectable with a large sample size. (Here, Testing the null hypothesis: ulcer rate 0.0020)* *For ONE-SIDED TEST; alpha=0.05
Question: What type of clinical setting does the panel recommend for implementation of a post-approval study? • private practitioners • commercial chains • HMOs • all of the above • sponsor’s discretion
Would the panel recommend: • a case-control study? • following a large cohort? • both?
Question: How would the panel define the endpoints that we are interested in for the study? • Endpoints used could be: • Patients with presumed infectious ulcers; • Patients with any type of ulcers; • Patients with central or para-central scars (not present at pre-fit); • Patients with reduction in acuity associated with scaring; • Other?
Questions? • Comments?