Famciclovir and Promethazine Interaction
Drug interaction information between Famciclovir and Promethazine.
Famciclovir and Promethazine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Famciclovir and Promethazine. 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
Promethazine does not significantly affect how famciclovir is processed or activated by the body.
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
- Cimetidine minor
Promethazine Also Interacts With
- Epinephrine minor
- Zaleplon minor
Frequently Asked Questions
What SPL severity band is on file for Famciclovir + Promethazine?
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?
Famciclovir has 7 labeled pairs on file vs Promethazine's 3. In the minor band specifically: Famciclovir has 7 (also Allopurinol, Digoxin, Probenecid, Theophylline); Promethazine has 3 (also Epinephrine, Zaleplon).
What mechanism field is on file for Famciclovir and Promethazine?
Promethazine does not significantly affect how famciclovir is processed or activated by the body.
Famciclovir's labeled portfolio outnumbers Promethazine
SPL source-record counts only. This page's band is minor · classes on file: Famciclovir (Antiviral (Nucleoside Analog)); Promethazine (Phenothiazine Antiemetic / Antihistamine).
0 major · 0 moderate · 7 minor · 7 total
- Other minor peers for Famciclovir
- Allopurinol
- Digoxin
- Probenecid
- Theophylline
0 major · 0 moderate · 3 minor · 3 total
- Other minor peers for Promethazine
- Epinephrine
- Zaleplon
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.