Co-amoxiclav and Augmentin Are the Same Drug—No Interaction Exists
Co-amoxiclav and Augmentin are identical medications (both are amoxicillin/clavulanic acid combinations), so there is no drug interaction between them because they are the same compound. Taking both simultaneously would constitute therapeutic duplication and potential overdosing, not a drug interaction 1.
Understanding the Nomenclature
- Co-amoxiclav is the International Nonproprietary Name (INN) for the combination of amoxicillin and clavulanic acid
- Augmentin is the brand name for the same combination manufactured by GlaxoSmithKline
- Both contain amoxicillin (a beta-lactam antibiotic) plus clavulanic acid (a beta-lactamase inhibitor) 1, 2
Clinical Implications
Never prescribe or take both medications together. This would result in:
- Doubled antibiotic dosing leading to increased risk of adverse effects
- Excessive clavulanic acid exposure, which is particularly associated with gastrointestinal side effects including diarrhea and Clostridium difficile infection 2
- Unnecessary medication costs and complexity
Common Pitfalls to Avoid
- Regional naming confusion: Different countries use different names (co-amoxiclav in UK/Europe, Augmentin globally as brand name, amoxicillin-clavulanate in US)
- Medication reconciliation errors: Always verify generic and brand names when patients transfer between healthcare settings
- Patient confusion: Patients may not recognize that their "new" prescription is the same as their current medication if names differ
Actual Drug Interactions with Amoxicillin-Clavulanic Acid
While co-amoxiclav and Augmentin don't interact with each other (being identical), this combination does have clinically significant interactions with other drugs:
Warfarin
- Monitor INR closely when initiating amoxicillin-clavulanic acid in patients on warfarin 3, 1
- Although one randomized controlled trial showed no significant interaction 4, the FDA label warns of abnormal prothrombin time prolongation 1
- Practical approach: Check INR within 3-5 days of starting antibiotic therapy
Oral Contraceptives
- May reduce efficacy of oral contraceptives 1
- Advise backup contraception during antibiotic course and for 7 days after completion
Probenecid
- Decreases renal clearance of amoxicillin, leading to increased blood levels 1
- Co-administration not recommended 1
Allopurinol
- Concurrent use with ampicillin-class antibiotics substantially increases rash incidence 1
- Monitor closely for skin reactions if combination necessary
Bottom Line
If you've been prescribed both co-amoxiclav and Augmentin, or if you're considering taking both: Don't. Contact your prescriber immediately as this represents a prescribing error. Take only one of these medications as they are pharmaceutically identical.