From the Guidelines
Cephalexin can be dosed twice daily (BID) instead of four times daily (QID) for certain infections, such as those caused by Staphylococci, oxacillin-susceptible, or β-hemolytic streptococci, as shown in Table 3 of the guidelines by the Infectious Diseases Society of America 1. When considering the dosing frequency of cephalexin, it's essential to take into account the type of infection being treated and its severity.
- For infections caused by Staphylococci, oxacillin-susceptible, the guidelines suggest cephalexin 500 mg PO tid or qid as the preferred treatment, but also list cefadroxil 500 mg PO bid as an alternative option 1.
- For β-hemolytic streptococci, cephalexin 500 mg PO tid or qid is listed as an alternative treatment, with penicillin V 500 mg PO bid to qid as the preferred option 1. The decision to use BID or QID dosing should be based on the individual patient's circumstances, including the severity of the infection, renal and hepatic function, and potential drug interactions or contraindications.
- Patient adherence is typically better with less frequent dosing, which may lead to better overall treatment outcomes.
- However, for more severe infections, the QID regimen may provide more consistent antibiotic levels in the bloodstream. It's crucial to consider the pharmacokinetics of cephalexin, which shows a half-life of about 1 hour, but clinical experience has shown that BID dosing works well for many common infections 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: streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age. For streptococcal pharyngitis in patients over 1 year of age and for skin and skin structure infections, the total daily dose may be divided and administered every 12 hours.
Cephalexin dosing can be administered every 12 hours for certain infections, such as:
- Streptococcal pharyngitis
- Skin and skin structure infections
- Uncomplicated cystitis in patients over 15 years of age A dosage of 500 mg every 12 hours can be used for these infections, which is equivalent to bid (twice a day) dosing. However, for other infections, the usual adult dose is 250 mg every 6 hours, which is equivalent to qid (four times a day) dosing. 2
From the Research
Cephalexin Dosage Frequency
- Cephalexin can be administered twice daily (bid) or four times daily (qid) with equal effectiveness in certain conditions, such as group A streptococcal pharyngitis 3 and uncomplicated urinary tract infections (uUTI) 4.
- The bid regimen may improve patient adherence due to the reduced frequency of dosing 4.
- Studies have shown that cephalexin bid and qid regimens have similar treatment failure rates, with 7.3% and 5.3% failure rates, respectively, in patients with GAS pharyngitis 3, and 12.7% and 17% failure rates, respectively, in patients with uUTI 4.
Efficacy of Cephalexin
- Cephalexin is effective in the treatment of skin and skin-structure infections, with a microbiologic eradication rate of 92% 5.
- Cephalexin remains an effective and highly useful antibiotic for the treatment of streptococcal and staphylococcal skin infections, with cure rates of 90% or higher 6.
- Cephalexin is comparable to other antibiotics, such as erythromycin, clindamycin, and dicloxacillin, in the treatment of streptococcal and staphylococcal infections 6.
Considerations for Antibiotic Treatment
- The need for antibiotic treatment should be carefully evaluated, considering the severity of symptoms and the presence of toxinic symptoms 7.
- The bacterial targets for antibiotics are mainly Staphylococcus aureus and Streptococcus pyogenes, and the choice of antibiotic should be based on the suspected or confirmed pathogen 7.