Famciclovir and Cimetidine Interaction
Drug interaction information between Famciclovir and Cimetidine.
Famciclovir and Cimetidine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Famciclovir and Cimetidine. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
How They Interact
Cimetidine does not interfere with the enzymes that turn famciclovir into its active form.
FDA Label Information
7.2 Potential for Other Drugs to Affect Penciclovir No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine. Clinical interaction studies of famciclovir with cimetidine and promethazine, in vitro inhibitors of aldehyde oxidase, did not show relevant effects on the formation of penciclovir.
Famciclovir Also Interacts With
- Allopurinol minor
- Digoxin minor
- Probenecid minor
- Theophylline minor
- Promethazine minor
Cimetidine Also Interacts With
- Levofloxacin major
- Posaconazole major
- Risperidone major
- Valproate major
- Empagliflozin moderate
Frequently Asked Questions
What SPL severity band is on file for Famciclovir + Cimetidine?
Compiled FDA labeling labels this pair minor. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Cimetidine has 77 labeled pairs on file vs Famciclovir's 7. In the minor band specifically: Famciclovir has 7 (also Allopurinol, Digoxin, Probenecid, Theophylline); Cimetidine has 63 (also Albendazole, Alogliptin, Alosetron, Alprazolam).
What mechanism field is on file for Famciclovir and Cimetidine?
Cimetidine does not interfere with the enzymes that turn famciclovir into its active form.
Cimetidine carries more major-labeled pairs than Famciclovir
SPL source-record counts only. This page's band is minor · classes on file: Famciclovir (Antiviral (Nucleoside Analog)); Cimetidine (H2 Receptor Antagonist).
Cimetidine has 4 major-labeled pairs vs Famciclovir's 0. This page itself is in the minor band, not the major band.
0 major · 0 moderate · 7 minor · 7 total
- Other minor peers for Famciclovir
- Allopurinol
- Digoxin
- Probenecid
- Theophylline
4 major · 10 moderate · 63 minor · 77 total
- Other minor peers for Cimetidine
- Albendazole
- Alogliptin
- Alosetron
- Alprazolam
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.