For general information on the cephalosporins including adverse effects, contraindications, overdosage, drug interactions, and monitoring parameters, refer to the monograph: Cephalosporins, General Information.
Chemistry - A semi-synthetic oral cephalosporin, cephalexin (as the monohydrate) occurs as a white to off-white, crystalline powder. It is slightly soluble in water and practically insoluble in alcohol.
Storage/Stability/Compatibility - Cephalexin tablets, capsules, and powder for oral suspension should be stored at room temperature (15-30°C) in tight containers. After reconstitution, the oral suspension is stable for 2 weeks.
Pharmacology/Spectrum of Activity - A first generation cephalosporin, cephalexin exhibits activity against the bacteria usually covered by this class. Refer to the monograph: Cephalosporins, General Information for more specific information.
Uses/Indications - There are no approved cephalexin products for veterinary use in the United States. It has been used clinically in dogs, cats, horses and birds, however.
Pharmacokinetics (specific) - After oral administration, cephalexin is rapidly and completely absorbed in humans. Cephalexin (base) must be converted to the HCl before absorption can occur and, therefore, absorption can be delayed. There is a form of cephalexin HCl commercially available for oral use which apparently is absorbed more rapidly, but the clinical significance of this is in question.
In a study done in dogs and cats (Silley et al. 1988), peak serum levels reached 18.6 micrograms/ml about 1.8 hours after a mean oral dose of 12.7 mg/kg in dogs, and 18.7 micrograms/ml, 2.6 hours after an oral dose of 22.9 mg/kg in cats. Elimination half-lives ranged from 1-2 hours in both species. Bioavailability was about 75% in both species after oral administration.
In the U.K., an oily suspension of the sodium salt (Ceporex® Injection— Glaxovet) is apparently available for IM or SQ injection in animals. In calves, the sodium salt had a 74% bioavailability after IM injection and a serum half-life of about 90 minutes.
Adverse Effects/Warnings - In addition to the adverse effects listed in the general statement on the cephalosporins, cephalexin has reportedly caused salivation, tachypnea and excitability in dogs, and emesis and fever in cats. Nephrotoxicity occurs rarely during therapy with cephalexin, but patients with renal dysfunction, receiving other nephrotoxic drugs or are geriatric may be more susceptible. Interstitial nephritis, a hypersensitivity reaction, has been reported with many of the cephalosporins including cephalexin. The incidence of these effects is not known.
For susceptible infections:
a) 25 mg/kg PO qid (Robinson 1987)
b) 22 - 33 mg/kg PO q6h (Brumbaugh 1987)
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Veterinary-Approved Products: None
Cephalexin ;(monohydrate) Capsules 250 mg, 500 mg and Tablets 250 mg, 500 mg and 1 gram; Keflex® (Dista); Biocef® (IEL); generic (Rx)
Cephalexin Oral Suspension 125 mg/5ml and 250 mg/5 ml in 100 and 200 ml
and UD 5ml; Keflex® (Dista);
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