What the FDA labels say about taking them together
Allopurinol and ampicillin
Allopurinol's FDA label of May 21, 2026 names ampicillin in its drug interactions section, and ampicillin's label names allopurinol too. The allopurinol label: “… risk of skin rash, which may be severe: bendamustine, thiazide diuretics, ampicillin and amoxicillin.”
Check it at the source: the allopurinol FDA label on DailyMed (effective May 21, 2026, Rising Pharma Holdings, Inc.); the ampicillin FDA label on DailyMed (effective February 21, 2025, Sandoz Inc).
What does the allopurinol label say about ampicillin?
Allopurinol label, drug interactionsDRUG INTERACTIONS The following drugs may increase the risk of serious skin reactions: bendamustine, thiazide diuretics, ampicillin and amoxicillin.
Allopurinol label, warnings and precautionsConcomitant use of the following drugs may also increase the risk of skin rash, which may be severe: bendamustine, ampicillin and amoxicillin [ see Drug Interactions (7.1) ].
Aloprim label (Mylan Institutional LLC, February 18, 2022), drug interactionsKnown to Affect the Occurrence of Skin Rash and Hypersensitivity Concomitant use of the following drugs may increase the risk of skin rash, which may be severe: bendamustine, thiazide diuretics, ampicillin and amoxicillin.
Allopurinol label (Proficient Rx LP, February 1, 2023), drug interactionsAn increase in the frequency of skin rash has been reported among patients receiving ampicillin or amoxicillin concurrently with allopurinol compared to patients who are not receiving both drugs.
Source: FDA drug label (Aloprim, NDA020298), Mylan Institutional LLC, effective February 18, 2022 (SPL set 10cc918f-aa44-415b-932d-2404695ac449), via openFDA
Source: FDA drug label (Allopurinol), Rising Pharma Holdings, Inc., effective May 21, 2026 (SPL set 30ad5ba2-1cef-4933-b104-0597f6a2aaa2), via openFDA; the full label on DailyMed
What does the ampicillin label say about allopurinol?
Ampicillin label, drug interactionsDrug Interactions The concurrent administration of allopurinol and ampicillin increases substantially the incidence of skin rashes in patients receiving both drugs as compared to patients receiving ampicillin alone.
Source: FDA drug label (Ampicillin), Sandoz Inc, effective February 21, 2025 (SPL set 64a04e8c-8f78-46b3-8f45-56ef225a4f74), 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
| Allopurinol | Ampicillin | |
|---|---|---|
| Labeled for | Gout | Bacterial infections, Urinary tract infections |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.0315 per tablet 100 mg tablet | $0.441 per capsule 500 mg capsule |
| Shortage now | A presentation being discontinued | A presentation being discontinued |
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