Risk of Drug Interactions among Children Accessing: DISCUSSION part 2
This study had many limitations. For example, it would have been better to have a higher number of months of exposure. An observation period of 5 to 10 years might have generated stronger data. The drug interactions identified were all theoretical interactions; however, only those drug interactions that would ideally need to be avoided were taken into account. Each detected interaction was also documented clinically. A variety of factors might have led to underdetection of potential interactions. Certainly, some interactions might have been detected by the parents at the physician’s office. In fact, each parent received a list of medications contraindicated with cisapride from the pharmacy department at the time the medication was dispensed. However, when a medication with a potential interaction was prescribed, it was not possible to determine whether the community pharmacist detected the potential interaction and contacted the physician to request a modification of therapy. Another possible reason for a potential interaction being overlooked is that cisapride is no longer itemized in pharmacy computers since its withdrawal from the market. To correct this problem, Health Canada should develop a list of the unlicensed medications obtained through the SAP and make it available to clinical database providers. Also, pharmacists do not have access to the necessary clinical information needed to identify all potential drug interactions. For example, many clinical database providers do not carry or update information on SAP medications, a situation well described by McMullin. Finally, few pharmacists made notes in their patients’ files about the use of unlicensed medications, which further decreases the chance of detecting potential interactions.
From a clinical perspective, the proportion of patients exposed to a potential interaction with cisapride is worrisome. In a retrospective study involving both adults and children, the rate of exposure to a potential drug interaction with cisapride was 3%. In the current study, 12% of patients who took cisapride were exposed to a potential interaction. Given that such potential interactions could be prevented and given that the consequences may be fatal, it is clear that improvements are needed.The fact that most patients consult a limited number of health care professionals should in itself ensure adequate transmission of information. However, this was not confirmed by the current study. Although the examination of transmission of information was based on a telephone questionnaire, it is important to note that the rate of transmission was disappointing. Physicians had recorded information about the use of an unlicensed drug obtained through the SAP in the patient’s file in only 89% of cases. In the pharmacists’ files, the proportion fell to just 17%. It seems reasonable to expect that such important information would be known by all pharmacists and all physicians. Furthermore, knowledge about drugs and their interactions may be an issue. In a study examining knowledge of cisapride, only 22% of family doctors and 50% of pediatricians were aware of possible interactions with this drug.
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Finally, efforts are necessary to inform physicians about the use of unlicensed medications obtained through Health Canada’s SAP and its implications. Completion of the request forms is considered an administrative annoyance, and the task is commonly delegated to secretaries or other health care professionals such as hospital pharmacists. It would be desirable to modify the procedure to emphasize the clinical consequences of potential interactions and the responsibilities of the physician. A requirement to obtain written consent from the patients who receive SAP medications would help to ensure that they are aware of the risks and benefits. These measures could be useful in diminishing the risks associated with unlicensed medications.
In conclusion, 3 (8%) of the 39 patients taking unlicensed medications known to have drug interactions were exposed to a potential drug interaction during the study period. The interactions occurred in 4 (0.8%) of the 474 months of therapy with an unlicensed medication known to have one or more drug interactions. Measures should be taken to decrease the risk associated with the use of medications available through Health Canada’s SAP. A similar study over a longer period is needed to draw stronger conclusions.
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