Post-marketing surveillance using pharmacy-based cohorts: results of a pilot study

To assess the feasibility of recruiting subjects for follow-up studies of drug exposures using pharmacy records but without involving dispensing pharmacists.

Working with Eckerd Corporation, a large chain pharmacy, we attempted to enroll subjects taking either hyoscyamine (Levsin and others) or dicyclomine (Bentyl and others). Adults who filled prescriptions during the recruitment period were randomly assigned to one of four enrollment approaches that used a script and materials we provided: (1) an introductory phone call from an Eckerd pharmacy technician with an offer of a $5 payment; (2) an introductory phone call with no payment; (3) a questionnaire mailed from Eckerd with introductory letters enclosed and an offer of a $5 payment and (4) the same mailed packet but with no payment offered. Willing subjects responded directly to us; they received a follow-up questionnaire approximately 6 weeks following enrollment. This method also provided limited information about subjects who chose not to enroll, permitting us to assess the representativeness of the study population.

The enrollment rates for the four groups were 35, 22, 21 and 17% respectively. Rates of completion of the follow-up questionnaire were 86, 83, 83 and 79% respectively. Participants appeared to be representative of the target population. The differential cost per enrolled subject in each group was $39.25, $50.45, $41.95 and $48.26 respectively.

This method provides an efficient way to create cohorts of users of specific prescription medications, with enrollment and retention rates that compare favorably with other approaches, allows a limited evaluation of representativeness, and is logistically feasible.