From the Guidelines
Keflex 500mg q6 and Keflex 1000mg BID are equivalent in terms of total daily dose, but the choice between them should be based on factors like the specific infection, patient preference, and adherence considerations, with no clear superiority of one over the other in terms of morbidity, mortality, or quality of life. When considering the treatment of group A streptococcal pharyngitis, the Infectious Diseases Society of America guidelines from 2012 1 recommend cephalexin at a dose of 20 mg/kg/dose twice daily (max = 500 mg/dose) for 10 days, which supports the use of the 500mg q12 regimen for this specific infection. However, this guideline does not directly compare the efficacy of different cephalexin dosing regimens in terms of patient outcomes such as morbidity, mortality, or quality of life. Key considerations in choosing between these regimens include:
- The specific infection being treated and its susceptibility to cephalexin
- Patient factors such as preference for fewer doses per day (which might improve adherence) versus more consistent antibiotic blood levels
- The potential for side effects and how they might be mitigated by the dosing schedule Given that both regimens provide the same total daily dose of 2000mg, the decision may lean towards the regimen that best promotes patient adherence and comfort, without compromising the antibiotic's efficacy. For most uncomplicated infections, either dosing regimen would be appropriate, with the choice depending on individual patient factors and the clinical context, as informed by guidelines and evidence such as that provided by 1.
From the FDA Drug Label
The usual adult dose is 250 mg every 6 hours For the following infections, a dosage of 500 mg may be administered every 12 hours: For more severe infections or those caused by less susceptible organisms, larger doses may be needed
The FDA drug label does not answer the question.
From the Research
Comparison of Keflex Dosages
- The provided studies do not directly compare the efficacy of Keflex 500mg q6h (every 6 hours) to Keflex 1000mg BID (twice a day) 2, 3, 4, 5, 6.
- However, a study on cephalexin, the active ingredient in Keflex, suggests that it can be conveniently administered as 500 mg twice or thrice daily, with good early bacteriological and clinical cures in uncomplicated lower urinary tract infections (uLUTIs) 4.
- Another study found that cephalexin levels in serum, synovial fluid, and joint tissues were high enough to have a possible therapeutic effect in bacterial arthritis sensitive to cephalexin after oral administration of 1 g every 6 hours 5.
- A review of antibiotic penetration into bone and joints found that cephalosporins, including cephalexin, showed good penetration into bone and joint tissues, reaching concentrations exceeding the minimum inhibitory concentrations (MIC) of common pathogens 6.
Pharmacokinetics and Efficacy
- The efficacy of cephalexin in treating various infections, including those caused by susceptible strains of Streptococcus, has been established in several studies 2, 4, 5, 6.
- However, the optimal dosage and frequency of administration may depend on the specific infection being treated and the patient's individual characteristics.
- The study on cephalexin levels in serum, synovial fluid, and joint tissues suggests that the drug can achieve therapeutic concentrations in these tissues after oral administration 5.
Clinical Implications
- While the provided studies do not directly compare the efficacy of Keflex 500mg q6h to Keflex 1000mg BID, they suggest that cephalexin can be an effective treatment option for various infections, including uLUTIs and bacterial arthritis.
- The choice of dosage and frequency of administration should be based on the specific clinical context and the patient's individual needs.
- Further studies are needed to determine the optimal dosage and frequency of administration for Keflex in different clinical scenarios 2, 3, 4, 5, 6.