Findings confirm the safety of gadopentetate dimeglumine.
A postmarket surveillance program in outpatients receiving cimetidine was initiated seven months after its approval for marketing. During the first phase of the program, data were obtained over a three-month period for 9,907 patients who received the drug. The overall incidence of adverse effects reported was 4.4%, and the types of adverse effects did not differ from those reported in premarketing controlled studies. Physician response was excellent (85.1%), and the methods used were successful in providing data on a large number of patients who received the drug in routine clinical practice. The results confirmed the safety profile of cimetidine. A follow-up phase, initiated six months after the initial phase of the surveillance program, will provide longer-term data on these patients.
Outpatient Surveillance ProgramTo the Editor.\p=m-\Regarding the article by Gifford et al (1980;243:1532) on the postmarket surveillance (PMS) of cimetidine, if the goals of postmarket surveillance as outlined in the article can be realized, PMS programs can be of value to individual clinicians, the pharmaceutical industry, and federal agencies. Some questions arose that we think were not completely addressed in the article. These pertain to the method employed by Gifford and his group in the reporting of adverse effects. Perhaps the most important was the method of assigning causality in assessing the reports of deaths. We refer specifically to the statement that "deaths that occurred after stopping treatment were clearly unrelated to cimetidine." In assessing the possible drug relatedness of these deaths, one must consider whether the onset of the precipitating event leading to death was within the prescribing time frame. To consider only the end point of death could lead to misinterpretation, and we would suggest that these cases be reevaluated if this has not been considered.In the "Comment," Gifford et al state that results of this observation¬ al study do not differ from those of prémarketing clinical trials. We would like to suggest several reasons for this. We believe that the reported overall incidence of PMS adverse reactions of 4.4% (442/9,907) is an underestimate. The proper calcula¬ tion of incidence would be 577 events per 9,907 patients per population at risk or 5.82%. Furthermore, the ratio¬ nale for including in the calculation 881 cases that were later deleted is not clear. Assuming none of the adverse reactions occurred within this group, the rate would be 577/ 9,026, or 6.39%. These estimates are slightly higher and may be substan¬ tially different from earlier clinical trials.Finally, the authors did not specify the duration of follow-up but implied that there may have been different lengths of observation from patient to patient. If this were true it could invalidate a measure of event fre¬ quency such as incidence that in¬ volves a specific unit of time (eg, X cases per 1,000 per year). If the PMS observation time is not longer than that of the earlier clinical trials, it is unlikely that the types of reactions reported would differ.The process of detecting rare or unexpected reactions depends on both increasing the sample size and ex¬ tending the observation time, unless the drug is to be given for a limited time in all cases. For short-term therapy, the observation period should extend at least for the dura¬ tion of therapy. If both the clinical trials and the PMS study were of shorter duration than current thera¬ py, this could explain the similarity in reported reactions.We look forward to the reporting of the results on phase II of this study and encourage the sharing of any additional experience in postmarket drug surveillance. As stated by Gif¬ ford et al, additional experience will allow for a better assessment of the value of PMS programs. for their comments on our article and app...
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