Cephalexin:

Cephalexin is labeled for the treatment of secondary superficial bacterial pyoderma in dogs caused by susceptible strains of Staphylococcus pseudintermedius. Cephalexin has also been used clinically in cats, horses, rabbits, ferrets, and birds, particularly for susceptible staphylococcal infections. Cephalexin is considered a first-tier drug for the treatment of bacterial skin infections.^1,2 Although a small study reported efficacy of cephalexin for uncomplicated cystitis,³ bacterial susceptibility patterns have suggested cephalexin is not an ideal empiric antibiotic for treating UTI in dogs and cats.^4-6

The World Health Organization has designated cephalexin as a Highly Important antimicrobial for human medicine.

Adverse effects with the cephalosporins are usually not serious and have a relatively low frequency of occurrence.

When given orally, cephalosporins may cause GI effects (eg, vomiting, diarrhea, anorexia). Administration of the drug with a small meal may help alleviate these effects. Because the cephalosporins may also alter gut flora, antibiotic-associated diarrhea or proliferation of resistant bacteria in the colon can occur.

Cephalexin has reportedly caused lethargy, pruritus, salivation, tachypnea, and excitability in dogs and emesis and fever in cats. Rarely, cephalexin has been implicated in causing serious skin reactions (eg, erythema multiforme, cutaneous vasculitis, toxic epidermal necrolysis) in small animals. Hypersensitivity reactions unrelated to dosage can occur with these agents and can manifest as rashes, fever, eosinophilia, lymphadenopathy, interstitial nephritis, or anaphylaxis. The incidence of these effects is not known.

Nephrotoxicity can occur rarely during therapy with cephalexin, but patients that have renal dysfunction, are receiving other nephrotoxic drugs, or are geriatric may be more susceptible.

High doses or very prolonged use has been associated with neurotoxicity, neutropenia, agranulocytosis, thrombocytopenia, hepatitis, positive Coombs test, interstitial nephritis, and tubular necrosis. Longer prothrombin times have also been noted. Except for tubular necrosis and neurotoxicity, these effects have an immunologic component.