Can Paxlovid (nirmatrelvir and ritonavir) cause interstitial cystitis?

Paxlovid and Interstitial Cystitis: Current Evidence

There is no established evidence that Paxlovid (nirmatrelvir and ritonavir) causes interstitial cystitis. Based on the available medical literature, Paxlovid has not been documented to cause interstitial cystitis as a side effect.

Known Urological Effects of Paxlovid Components

Ritonavir

• Ritonavir has occasionally been reported to cause acute renal failure, but this is rare and not specifically linked to interstitial cystitis 1
• The most common urological side effects associated with ritonavir are related to nephrotoxicity rather than bladder inflammation 1

Protease Inhibitors and Urological Effects

• Among protease inhibitors, indinavir (not nirmatrelvir) has been most commonly associated with urological symptoms including crystalluria, dysuria, and urgent urination 1
• Indinavir has been linked to interstitial nephritis, but this differs from interstitial cystitis which specifically affects the bladder 1

Documented Adverse Effects of Paxlovid

• The most common adverse effects of Paxlovid include:
  • Dysgeusia (altered taste)
  • Diarrhea
  • Treatment-related adverse events that are generally mild to moderate 2, 3
• Serious adverse events with Paxlovid are relatively uncommon compared to placebo 2
• The Cochrane review of nirmatrelvir/ritonavir does not mention interstitial cystitis or any bladder-specific adverse effects 2

Drug Interactions and Considerations

• Paxlovid (particularly the ritonavir component) is a potent inhibitor of CYP3A4, which can lead to significant drug interactions 4, 3
• Ritonavir can increase the concentration of drugs metabolized through the CYP3A4 pathway, potentially increasing risk of adverse effects from those medications 1, 4
• Patients with reduced kidney function require careful consideration when using Paxlovid, as dose adjustments may be necessary 1, 3

Clinical Implications

• For patients with existing interstitial cystitis, there is no specific contraindication to using Paxlovid based on current evidence 2, 3
• For patients experiencing new urinary symptoms while on Paxlovid:
  • Consider alternative causes including urinary tract infection
  • Evaluate for potential drug interactions that might be causing urological symptoms 4
  • Monitor for signs of nephrotoxicity, which is a rare but documented effect of ritonavir 1

Conclusion

While Paxlovid has various potential side effects and drug interactions, there is no established connection between Paxlovid and interstitial cystitis in the current medical literature. Patients experiencing bladder symptoms while on Paxlovid should be evaluated for other causes of their symptoms.