Flucloxacillin and Acetaminophen And Codeine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Flucloxacillin
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
You've been prescribed acetaminophen with codeine (a pain reliever) along with flucloxacillin (an antibiotic). When these two are taken together, there is a possible risk of a blood chemistry problem called high anion gap metabolic acidosis, which just means acid can build up in the body.
I want to be honest with you: this concern is theoretical, meaning it is based on how the drugs might behave rather than strong proof. It is more likely with higher doses or in people who are unwell. The good news is your care team can watch for it easily with routine checks, so keep taking both medicines as prescribed and let your doctor or pharmacist know if you feel unusually tired, short of breath, or confused.
Effect: Theoretical increased risk of high anion gap metabolic acidosis (HAGMA) with concomitant acetaminophen (paracetamol) and flucloxacillin.
- Mechanism: Unknown/uncertain; both agents are independently associated with 5-oxoprolinuria (pyroglutamic acidosis) via glutathione pathway disruption, plausibly additive. Neither is the affected agent in a classic CYP sense.
- Direction/magnitude: Additive acid-base risk; magnitude undefined.
- Onset: Unspecified. Evidence: Theoretical. Severity: Major.
- Monitoring: Watch acid-base status (serum bicarbonate, anion gap, ABG/VBG); consider urinary 5-oxoproline if HAGMA arises. If flucloxacillin continues after acetaminophen cessation, confirm HAGMA does not persist.
What happens
An increased risk of high anion gap metabolic acidosis (HAGMA)
Interaction Deep Dive
Exert caution when flucloxacillin is coadministered with acetaminophen due to the increased risk high anion gap metabolic acidosis (HAGMA). After coadministration of flucloxacillin and acetaminophen, a close monitoring is recommended in order to detect the appearance of acid-base disorders, namely HAGMA, including the search of urinary 5-oxoproline. If flucloxacillin is continued after cessation of paracetamol, it is advisable to ensure that there are no signals of HAGMA, as there is a possibility of flucloxacillin maintaining the clinical picture of HAGMA1.
Why it happens (mechanism)
Unknown
How to manage this interaction
Both medicines can usually be taken together, and this is mainly a caution rather than a hard stop. Here is how a care team typically handles it:
- Keep taking both exactly as prescribed unless your doctor tells you otherwise.
- Your team may monitor you more closely with blood tests that check your acid-base balance, especially if you are unwell, malnourished, or on higher doses.
- If a problem is suspected, they may check a urine test (5-oxoproline).
Tell your pharmacist or doctor if you notice fast breathing, unusual tiredness, confusion, or nausea, and let them know you are on both medicines.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Flucloxacillin and Acetaminophen And Codeine together?
Taking acetaminophen-codeine with flucloxacillin carries a theoretical risk of a blood acid imbalance (HAGMA); keep taking both as prescribed and let your care team monitor you, and report symptoms like fast breathing, tiredness, or confusion. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Flucloxacillin and Acetaminophen And Codeine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Flucloxacillin and Acetaminophen And Codeine interaction managed?
Both medicines can usually be taken together, and this is mainly a caution rather than a hard stop. Here is how a care team typically handles it: Keep taking both exactly as prescribed unless your doctor tells you otherwise. Your team may monitor you more closely with blood tests that check your acid-base balance, especially if you are unwell, malnourished, or on higher doses. If a problem is susp… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Flucloxacillin or Acetaminophen And Codeine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: FLUCILLIN oral capsules, flucloxacillin oral capsules. Pinewood Laboratories Ltd, Ballymacarbry, Tipperary, Ireland, 2023.
Keep reading about Acetaminophen And Codeine
Keep reading about Flucloxacillin
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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