This refers to the use of the prescription database for studies several years after the official monitoring period has been completed, aiming to establish rates of mortality, carcinogenesis and other selected morbidity. A pilot trial of record linkage using GP records, hospital discharge summaries and national registers of mortality, cancer and morbidity has been commenced with data collection undertaken for 200 patients from each of the metoprolol and captopril cohorts. The results from matching with national mortality, cancer and morbidity data have not yet been analysed. The combined results of record linkage with hospital and GP records resulted in useful data being received for 50% of patients whose treatment had commenced 10-16 years previously. This percentage should increase with the addition of the data from national registers.
Death rates are calculated and attempts are made to identify any significant differences in death rates between comparator drugs or changes in death rate over time and any differences from standardised population rates from national health statistics. Deaths are very poorly reported spontaneously. Most are obtained from the questionnaire on reasons for cessation of therapy.
If the data concerning death are incomplete, then a letter is sent to the doctor requesting the missing details. These may include the date and cause of death and confirmation that the patient was using the drug at or near the time of death. If the drug was not being used at the time of death, then the reason for cessation of therapy is requested. Copies of autopsy and/or coroners' reports are requested if these are available. It is sometimes helpful to ask if death was expected or unexpected. If death rates are particularly important, then record linkage is undertaken with the NZ Health Information Service, which maintains the national database of deaths, to identify any deaths that may have been missed by the routine follow-up procedures.
Death was the most common event recorded for omeprazole and the apparent high death rate was cause for concern. Over the monitoring period there were 407 deaths (18.5 per 1000 patients) compared with 140 (8.1 per 1000) for moclobemide being monitored at the same time. However, the omeprazole group was significantly older (mean 60 years) than the moclobemide cohort (mean 49 years) and when age-specific rates were examined there were no statistically significant differences. Death rates are particularly important in the study of drugs used in the treatment of asthma, as was revealed in the experience with fenoterol (Crane et al., 1989). At the time of writing they were being studied with particular care with the long acting beta agonists eformoterol and salmeterol (Castell-sague et al., 1999). Data are also being collected on the severity of disease with the objective of stratifying the results according to severity.
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