Does finasteride interact with fluvoxamine?

Potential Drug Interaction Between Finasteride and Fluvoxamine

Fluvoxamine may interact with finasteride due to fluvoxamine's potent inhibition of multiple CYP450 enzymes, potentially increasing finasteride levels, though the clinical significance of this interaction is likely minimal for most patients. 1

Mechanism of Potential Interaction

• Fluvoxamine is a potent inhibitor of multiple cytochrome P450 enzymes, particularly CYP1A2, CYP2C19, CYP2C9, CYP3A4, and to a lesser extent CYP2D6 1
• Finasteride undergoes extensive hepatic metabolism to inactive metabolites with a terminal elimination half-life of 4.7-7.1 hours 2, 3
• Although specific CYP enzymes involved in finasteride metabolism aren't fully characterized in the available evidence, the inhibition of multiple CYP enzymes by fluvoxamine could theoretically affect finasteride clearance 4, 5

Clinical Significance

• No direct drug interactions between finasteride and fluvoxamine have been explicitly reported in the literature reviewed 2
• The 1996 clinical pharmacokinetics review of finasteride specifically states: "No drug interactions with finasteride have been reported" 2
• However, given fluvoxamine's broad inhibition of multiple CYP enzymes, caution is warranted as this could potentially:
  • Increase finasteride plasma concentrations
  • Prolong finasteride's half-life
  • Potentially increase risk of finasteride-related adverse effects 1

Monitoring Recommendations

• If co-administration is necessary, monitor for:
  • Sexual dysfunction (loss of libido, erectile dysfunction) which may be exacerbated 3
  • Changes in mood or sleep disturbances, as both medications have been associated with these effects 6
  • Consider starting fluvoxamine at a lower dose and titrating slowly when adding to established finasteride therapy 1

Alternative Options

• If concerned about potential interactions:
  • Consider alternative SSRIs with less impact on CYP450 enzymes, such as citalopram/escitalopram which have "the least effect on CYP450 isoenzymes compared with other SSRIs" 1
  • Sertraline may also be a better alternative as it "has less effect on metabolism of other medications" compared to fluvoxamine 1

Important Caveats

• The clinical significance of this potential interaction is likely minimal for most patients, as:
  • Finasteride has a relatively wide therapeutic window
  • Finasteride's metabolites are essentially inactive 2
  • No case reports of adverse outcomes from this specific drug combination were identified in the evidence provided 2, 3

Remember that individual patient factors including age, hepatic function, and concomitant medications may influence the significance of this potential interaction 2, 5.