First-Pass Effect
Definition
The phenomenon where an orally administered drug is significantly metabolized by the liver before reaching systemic circulation. This reduces the amount of active drug available to the body and is a major reason why oral doses are often higher than intravenous doses of the same drug.
Example
Nitroglycerin undergoes extensive first-pass metabolism, which is why it's given sublingually (under the tongue) rather than swallowed.
Related Terms
Mentioned in Guides
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