The US Food and Drug Administration (FDA) is responsible not only for approving drugs for marketing, but also for monitoring their safety after marketing (Kennedy et al., 2001). Drug approvals are based on data obtained from clinical trials that are oftentimes limited in size and duration, and that have excluded patients with other therapies or comorbidities from study (Rogers, 1987). After marketing, new information relating to drug safety usually becomes available as product use becomes more widespread, and on occasion this may alter the benefit-risk profile of a drug (Friedman et al., 1999).
In the United States, pharmacovigilance is regarded as those aspects of drug safety monitoring and assessment that are related to or dependent upon voluntarily reported cases of adverse drug reactions (ADRs), or that relate to other activities, the primary purpose of which is the generation of a signal or hypothesis of a potential drug-adverse effect association. This perspective considers pharmacoepidemiology as being more closely related to population-based, systematic investigations that may range in complexity from purely descriptive to rigorous hypothesis-testing studies. There is admittedly a gray zone whereby the two approaches blend together.
There are many ways by which drug safety signals arise. The most common is through voluntary or spontaneous case reporting to regional or national pharmacovigilance centers, such as the FDA. Case reports and small case series from the medical literature also contribute. Other potential sources of safety concerns include pre-clinical animal testing, pre-marketing clinical trials, experience with other drugs in the same class and experience from other national centers around the world. The clinical pharmacology of the drug itself, its pharmacokinetics (absorption, distribution, metabolism and excretion) and phar-macodynamics, may raise other concerns related to organ-specific toxicity or drug-drug interactions.
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