flucloxacillin + paracetamol

The combination of flucloxacillin and paracetamol is not a single formulated drug product but rather two separate medications that are sometimes used concurrently. This combination has been identified as having a rare but potentially serious drug interaction that can lead to high anion gap metabolic acidosis (HAGMA) due to pyroglutamic acidosis (PGA), also known as 5-oxoprolinaemia[1][3]. ## Drug Components **Flucloxacillin** is a beta-lactam antibiotic belonging to the penicillin group. It's commonly prescribed for treating infections caused by staphylococci and streptococci, most notably Staphylococcus aureus[1]. It's used to treat various infections including: - Skin and wound infections - Bone infections (osteomyelitis) - Ear infections - Chest infections - Heart infections (endocarditis) - Meningitis[6][8] **Paracetamol** (also known as acetaminophen) is one of the most commonly dispensed medications used for treating fever and pain[1]. ## Interaction Mechanism The interaction between flucloxacillin and paracetamol can lead to pyroglutamic acidosis through disruption of the γ-glutamyl cycle[1]. Both medications can cumulatively lead to an increase in 5-oxoproline (also known as pyroglutamic acid, pidolic acid, or pyroglutamate)[3]. This results in high anion gap metabolic acidosis, which if left unresolved can contribute significantly to mortality[4]. ## Risk Factors Patients at higher risk for developing this interaction include those with: - Severe renal impairment - Sepsis - Malnutrition - Advanced age (elderly patients) - Female sex - Multiple comorbidities - Polypharmacy - Maximum daily doses of paracetamol[3][4][9] ## Clinical Presentation and Management The interaction typically manifests as high anion gap metabolic acidosis. Symptoms may include nausea and worsening kidney function[4]. Management includes: 1. Discontinuation of both medications 2. Close monitoring of acid-base disorders 3. Testing for urinary 5-oxoproline 4. In severe cases, treatment with N-acetylcysteine to supplement glutathione 5. Sodium bicarbonate administration may be considered[3][4][7] ## Recommendations While the concomitant prescription of flucloxacillin and paracetamol is frequent, severe high anion gap metabolic acidosis is rare[7]. However, healthcare providers should: 1. Be aware of this potential interaction 2. Exercise caution when prescribing these medications together, especially in high-risk patients 3. Consider regular blood gas analysis to evaluate pH, bicarbonate, base excess, and anion gap in patients receiving long-term therapy with both medications 4. Carefully evaluate the need for paracetamol in patients receiving long-lasting flucloxacillin treatment[3][7] This interaction was first noted in 1989 and has been confirmed by the European Medicines Agency (EMA), which has recommended including warnings in the Summary of Product Characteristics (SmPC) for flucloxacillin[3][4].