From the Guidelines
Keflex (cephalexin) does not have better kidney penetration than Augmentin (amoxicillin-clavulanate). In fact, Augmentin generally achieves better urinary concentrations and is often preferred for complicated urinary tract infections. Both antibiotics are eliminated primarily through the kidneys, but Augmentin has a broader spectrum of activity against many urinary pathogens, including those that produce beta-lactamase enzymes. Keflex is a first-generation cephalosporin that achieves adequate urinary concentrations but may not cover some resistant organisms that Augmentin can treat. When treating kidney infections specifically, Augmentin's combination of amoxicillin with the beta-lactamase inhibitor clavulanate provides enhanced activity against many gram-negative bacteria commonly involved in pyelonephritis. However, the choice between these antibiotics should be based on the specific infection, local resistance patterns, patient factors, and ideally culture results rather than kidney penetration alone, as suggested by the clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months 1. Some key points to consider when choosing an antibiotic for urinary tract infections include:
- The usual choices for oral treatment of UTIs include a cephalosporin, amoxicillin plus clavulanic acid, or trimethoprim-sulfamethoxazole 1
- It is essential to know local patterns of susceptibility of coliforms to antimicrobial agents, particularly trimethoprim-sulfamethoxazole and cephalexin, because there is substantial geographic variability that needs to be taken into account during selection of an antimicrobial agent before sensitivity results are available 1
- Agents that are excreted in the urine but do not achieve therapeutic concentrations in the bloodstream, such as nitrofurantoin, should not be used to treat febrile infants with UTIs, because parenchymal and serum antimicrobial concentrations may be insufficient to treat pyelonephritis or urosepsis 1.
From the Research
Kidney Penetration of Keflex and Augmentin
- Keflex, also known as cephalexin, is a first-generation cephalosporin with excellent bioavailability and urinary penetration 2, 3.
- The urinary concentration of cephalexin routinely exceeds 1000 mg/L after even a small dose, making it effective in treating urinary tract infections 4.
- Augmentin, a combination of amoxicillin and clavulanate, is also used to treat urinary tract infections, but its kidney penetration is not as well-studied as cephalexin.
- However, it is known that amoxicillin is excreted primarily by the kidney and achieves high urinary concentrations 5.
Comparison of Keflex and Augmentin
- Cephalexin has been shown to be effective in treating uncomplicated urinary tract infections, with a high cure rate and low risk of resistance 2, 3.
- Augmentin is also effective in treating urinary tract infections, but its use is often limited by the risk of resistance and side effects 6, 5.
- In terms of kidney penetration, cephalexin appears to have better penetration than Augmentin, although direct comparisons are limited 4.
Clinical Use of Keflex and Augmentin
- Cephalexin is often used as a first-line treatment for uncomplicated urinary tract infections, particularly in patients with suspected or confirmed bacterial infections 2, 3.
- Augmentin is often used as a second-line treatment for urinary tract infections, particularly in patients with suspected or confirmed resistant bacterial infections 6, 5.
- The choice between cephalexin and Augmentin ultimately depends on the specific clinical scenario, including the severity of the infection, the suspected or confirmed pathogen, and the patient's medical history and allergies 6, 2, 3, 5, 4.