Phenytoin and Clarithromycin Interaction
Drug interaction information between Phenytoin and Clarithromycin.
Phenytoin and Clarithromycin have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Phenytoin and Clarithromycin. 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
Clarithromycin can interfere with how your body processes phenytoin, which may lead to higher levels of the drug.
FDA Label Information
Other Drugs Metabolized by CYP450 Isoforms Other than CYP3A: Hexobarbital Phenytoin Valproate Use With Caution There have been postmarketing reports of interactions of clarithromycin with drugs not thought to be metabolized by CYP3A, including hexobarbital, phenytoin, and valproate.
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
Clarithromycin Also Interacts With
- Quetiapine major
- Pioglitazone major
- Fluconazole major
- Cyclosporine major
- Lurasidone major
Frequently Asked Questions
What SPL severity band is on file for Phenytoin + Clarithromycin?
Compiled FDA labeling labels this pair moderate. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Phenytoin has 147 labeled pairs on file vs Clarithromycin's 81. In the moderate band specifically: Phenytoin has 23 (also Apixaban, Aprepitant, Canagliflozin, Carbidopa/Levodopa); Clarithromycin has 35 (also Omeprazole, Methylprednisolone, Sildenafil, Valproate).
What mechanism field is on file for Phenytoin and Clarithromycin?
Clarithromycin can interfere with how your body processes phenytoin, which may lead to higher levels of the drug.
Clarithromycin carries more major-labeled pairs than Phenytoin
SPL source-record counts only. This page's band is moderate · classes on file: Phenytoin (Anticonvulsant (Hydantoin)); Clarithromycin (Macrolide Antibiotic).
Clarithromycin has 16 major-labeled pairs vs Phenytoin's 4. This page itself is in the moderate band, not the major band.
4 major · 23 moderate · 120 minor · 147 total
- Other moderate peers for Phenytoin
- Apixaban
- Aprepitant
- Canagliflozin
- Carbidopa/Levodopa
16 major · 35 moderate · 30 minor · 81 total
- Other moderate peers for Clarithromycin
- Omeprazole
- Methylprednisolone
- Sildenafil
- Valproate
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.