Epidemiological Studies of Populations Using Drugs

Epidemiological Studies of Populations Using Drugs. The Monograph on digoxin exemplifies the complications in drug nomenclature that may arise due to differences in professional practice and disciplines (e.g. manufacturer, medical professional). As explained therein, the term “digitalis” as used with reference to chemical specifications may refer to a plant extract, while the same word in a medical therapeutic context may refer to a particular category of agents (e.g. digoxin, digitoxin).

Complicate adoption of a particular term as the appropriate identification

Such incongruities not only contribute to potential misunderstanding of data; in an immediate sense, they may complicate adoption of a particular term as the appropriate identification of the subject of a Monograph and/or the subject of evaluation statements adopted within a particular Monograph. In some instances, studies may generate epidemiological data that refer to the use of particular classes of drug, rather than particular individual drugs. Interpretation of such data to infer effects attributable to particular drugs, such as pioglitazone, rosiglitazone and hydrochlorothiazide, and the small number of available epidemiological studies, may render this task difficult or almost impossible.

Associations reported in epidemiological studies

Historically, in IARC Monographs evaluations for which relevant epidemiological data were available, determination of causality on the basis of associations reported in epidemiological studies has always been recognized as both challenging and of critical importance. In general terms, this subject is addressed in the Preamble to the IARC Monographs, and the matters raised in that context are fundamental to all such epidemiological data.
In the specific case of epidemiological findings in relation to pharmaceutical drugs, it is self-evident that the exposed individuals are not a representative sample of the community, but rather are individuals identified by a diagnosis in consequence of which they have received the drug in question. At one extreme, increased risk of cancer in such individuals may be caused by the drug they have received.

Risk of cancer; or because the symptoms of an undiagnosed cancer

At the other extreme, an association between increased risk of cancer and use of a particular drug may be totally independent of causality and arise for several reasons: because patients with a particular disease are at greater risk of malignancy; because patients with a particular disease are more liable than the community in general to be exposed to an independent factor that causes or is correlated with increased risk of cancer; or because the symptoms of an undiagnosed cancer may also prompt the use of a drug, which can subsequently be suspected as its cause. An additional problem is that patients commonly receive more than one drug, and determination of the carcinogenicity of any single drug may be difficult.