Drug combination therapy is sometimes used in clinical situations. CYP has been intensely studied numerous times; thus, its pharmacokinetic interactions have been predicted to some extent. Basically, a drug interaction is defined as competitive inhibition of an enzyme by two drugs. We are concerned that fluvoxamine may have a drug interaction with paroxetine. Fluvoxamine inhibits CYP1A2 and CYP2C19 activity, and paroxetine inhibits CYP2D6 activity. However, recently, new drug targets have been identified, such as P-glycoprotein, a drug transporter. Fluvoxamine and paroxetine inhibit not only CYP but also P-glycoprotein. Additionally, there is an increased risk of upper gastrointestinal tract bleeding with the combination of a SSRI and NSAIDs. There are also individual differences in the pharmacokinetics of drugs due to genetic factors and individual differences in drug receptors, which have not yet been investigated for fluvoxamine or paroxetine. Obtaining clinical diagnoses of drug interactions is necessary in all patients.
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