Drug bioavailability is calculated during pharmacokinetic (PK) studies following IV and oral (or extravascular) doses. It is measured as the ratio of the dose-normalized area under the plasma time concentration curve (AUC) from the oral (or another extravascular route) administration to the AUC of an intravenous (IV) administration. In this setting, IV dosage is considered 100% available as it is administered directly into the systemic circulation. The importance of bioavailability studies lies in testing whether an active pharmaceutical ingredient can reach systemic circulation and its intended site of action while minimizing undesired off-target side effects. Typically, high bioavailability is desirable, but in some cases, low bioavailability is beneficial if the drug is administered directly to the site of action, or there are concerns about systemic toxicity.