Assessment of adverse effects of drugs
Generally, the manifestations of adverse effects are not very different from those of diseases. Moreover, common adverse effects such as tiredness, drowsiness, headache, are observed in people not taking drugs. Particularly in the elderly, it is often difficult to differentiate the different manifestations of diseases from adverse effects induced by one of the many drugs taken. The improvement of the patient at the discontinuation of drugs constitutes a good argument for the existence of an adverse effect.
Thus, the assessment of the responsibility of a drug in the advent of an adverse effect in a patient, sometimes called imputability, must be based on a detailed analysis of the observation taking particularly into account chronological arguments.
The chronological arguments are: coincidence between the untoward effect and the intake of a drug, disappearance of the effect at the cessation of the drug, reappearance of the effect when the drug is restarted. But the restart of the suspected drug as diagnostic test is acceptable only if it does not make run a serious risk to the patient and can be useful for the future management of the patient. However, in case of addiction, the adverse effect can appear at the discontinuation of the drug and the manifestations are in general the opposite of those of the drug; for example a hypnotic discontinuation gives an increase of insomnia. Chronological considerations are not useful when there exit a long time, sometimes several years, between a drug treatment and the appearance of an adverse effect, for example an increase of the risk of ovarian cancer after ovarian stimulation for sterility or vaginal cancers in the daughters of women treated by diethylstilbestrol. In these latter cases only epidemiological studies are able to confirm the suspected relationships.
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