Postmarketing drug surveillance by record linkage in Tayside

The feasibility of conducting postmarketing drug surveillance by record linkage in Tayside was assessed. The key feature of the method is that all hospital discharge data are already computerised by the area health board and may be accessed through the unique community health number (CHNo) which has been allocated to all Tayside residents. The 12 861 prescriptions for cimetidine dispensed in Tayside over a nine month period were collected and the CHNo identified for 76%. These corresponded to 3802 individuals and their discharge data, together with those for an equal number of controls matched by age, sex, and general practitioner were retrieved from the computer. The expected excess of those diseases for which cimetidine is prescribed (peptic ulcer and oesophagitis) was observed. Other drug-disease associations were observed but may have been due to confounding and emphasise the inadequacy of community based controls. The major advantages of record linkage are, firstly, the low cost of the method, the present study costing just over pounds 12 000, and, secondly, the duration of patient follow up which may may be extended for as many years as required simply by rerunning the computer programs. To assemble large patient cohorts the study would have to be extended to other area health boards that are currently developing similar computer systems. Record linkage may provide a cost effective method for the follow up of patients to identify serious adverse drug reactions, particularly those that take several years to develop.