What the FDA labels say about taking them together
Leflunomide and penicillin g
Leflunomide's FDA label of June 4, 2025 names penicillin g in its drug interactions section; the penicillin g labels PlainMeds reads (2) do not name leflunomide. The leflunomide label: “In patients taking ARAVA, exposure of drugs which are OAT3 substrates may be increased.”
Check it at the source: the leflunomide FDA label on DailyMed (effective June 4, 2025, sanofi-aventis U.S. LLC); the penicillin g FDA label on DailyMed (effective September 16, 2020, Sandoz Inc).
What does the leflunomide label say about penicillin g?
Leflunomide label, drug interactionsIn patients taking ARAVA, exposure of drugs which are OAT3 substrates (e.g., cefaclor, cimetidine, ciprofloxacin, penicillin G, ketoprofen, furosemide, methotrexate, zidovudine) may be increased.
Source: FDA drug label (Arava), sanofi-aventis U.S. LLC, effective June 4, 2025 (SPL set 320f63f2-fac3-4aee-aff8-85724e00ef52), via openFDA; the full label on DailyMed
What does the penicillin g label say about leflunomide?
Penicillin g's label (effective September 16, 2020) and its 1 other brand-application label do not name leflunomide in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Penicillin G Potassium), Sandoz Inc, effective September 16, 2020 (SPL set 91950983-4884-40d1-abd8-bcc953d61b7f), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Leflunomide | Penicillin g | |
|---|---|---|
| Labeled for | Rheumatoid arthritis | Bacterial infections |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.324 per tablet 10 mg tablet | n/a |
| Shortage now | A presentation being discontinued | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once