Can You Take Augmentin and Keflex Together?
No, you should not take Augmentin (amoxicillin/clavulanate) and Keflex (cephalexin) together for the same infection, as this combination provides no additional therapeutic benefit and unnecessarily increases the risk of adverse effects and antibiotic resistance.
Rationale for Not Combining These Antibiotics
Both medications are beta-lactam antibiotics with overlapping spectrums of activity against common bacterial pathogens. Taking them simultaneously offers no synergistic effect and is not supported by any clinical guidelines or evidence 1, 2, 3.
Key Considerations:
Redundant Coverage: Both Augmentin and Keflex target gram-positive cocci (including Staphylococcus aureus and Streptococcus species) and many gram-negative organisms 1, 4. The clavulanate component in Augmentin extends coverage to beta-lactamase-producing organisms, but adding cephalexin provides no additional pathogens covered 5.
Increased Adverse Effects: Combining these agents doubles exposure to beta-lactam antibiotics, increasing the risk of gastrointestinal side effects (diarrhea, nausea), Clostridioides difficile infection, and allergic reactions 6, 5.
Cross-Allergenicity Warning: The FDA labels for both medications explicitly warn about cross-hypersensitivity between penicillins and cephalosporins, which may occur in up to 10% of patients with penicillin allergy 6. Taking both simultaneously compounds this risk.
When Each Antibiotic Should Be Used Alone
For mild-to-moderate skin and soft tissue infections: Either cephalexin (250-500 mg four times daily) OR amoxicillin/clavulanate (875/125 mg twice daily) is appropriate as monotherapy 1.
For respiratory tract infections: Amoxicillin/clavulanate is generally preferred over cephalexin due to better coverage of Haemophilus influenzae and Moraxella catarrhalis, particularly beta-lactamase-producing strains 7, 8, 9.
For urinary tract infections: Cephalexin may be used when first-line agents cannot be used, but amoxicillin/clavulanate is also acceptable 10.
For dental infections: Recent evidence shows cephalexin-clavulanate and amoxicillin-clavulanate have equivalent effectiveness, with clinical improvement in >96% of patients within 10 days 11.
Common Clinical Scenarios Where Confusion Arises
Switching vs. Combining
If a patient fails initial therapy with one agent, switching to the other (not adding it) may be appropriate if the organism is susceptible and the initial choice was suboptimal 1, 8. However, treatment failure more commonly indicates:
- Inadequate source control (abscess requiring drainage)
- Resistant organism requiring culture-guided therapy
- Non-bacterial etiology
Penicillin Allergy
For patients with non-severe penicillin allergy, cephalexin is an acceptable alternative to amoxicillin-based regimens 2, 3, 8. However, patients should receive ONE agent, not both 6.
Important Caveats
No pharmacokinetic interaction exists between these drugs 12, but this does not justify their combination—the issue is redundancy, not drug-drug interaction.
Guideline-recommended combinations for specific infections (e.g., ceftriaxone plus metronidazole for intra-abdominal infections) involve antibiotics with complementary spectrums 13, 14. Augmentin and Keflex do not have complementary activity.
First-generation cephalosporins like cephalexin are explicitly NOT recommended for Lyme disease, where they are ineffective, while amoxicillin is appropriate 2. This illustrates that even within beta-lactams, spectrum differences matter for specific pathogens.
Bottom Line
Select ONE appropriate antibiotic based on the infection type, local resistance patterns, and patient factors 1, 4, 14. If the chosen agent fails, reassess the diagnosis, obtain cultures if not already done, and consider switching to a different class or seeking infectious disease consultation 15. Combining Augmentin and Keflex serves no clinical purpose and violates antimicrobial stewardship principles 9.