The New Zealand Intensive Medicines Monitoring Programme

The New Zealand Intensive Medicines Monitoring Programme which has been in operation for 20 years is described. The methodology is reviewed in detail and illustrated in the results. Some of the principles of early postmarketing surveillance and advantages and problems associated with the IMMP are discussed. The methodology is based on establishing cohorts of patients and the aggregation of adverse events from a combination of prescription follow-up (PFU) and intensified spontaneous reporting. In signal detection particular emphasis is placed on provisional 'causality' assessment and a study of the events thought not to be reactions (incidents) and in addition, their use in controlling for reporting bias particularly in respect of reaction rates and the identification of risk factors. With the small population base, cohorts are built up more slowly, but the longer duration of observation has advantages. Monitoring has been completed for 20 drugs with an average cohort size of 10,511 patients and a mean monitoring period of 55 months. The use of duplicate prescriptions with PFU achieved much higher reporting rates than IMMP spontaneous reporting. Information on deaths was best obtained from questionnaires on reasons for cessation of therapy which also provided data on efficacy.