Cephalexin, a first-generation bactericidal cephalosporin, is considered to be the first-choice antibiotic in the treatment of superficial pyoderma because it is both extremely effective and very safe (Frank and Kunkle,1993; Guaguere and others 1998).
It is very effective against Gram positive cocci, particularly Staphylococcus pseudointermedius, and is resistant to beta-lactamases (Mason and Keitzmann 1999).
When administered orally, cephalexin is well absorbed, with a 70 to 90 per cent bioavailability and optimal distribution in interstitial extracellular fluids (Papich1984; Mason and Keitzmann 1999).
It is still one of the most important tools available nowadays. The antistaphylococcal activity is no less potent than higher-tier antibiotics, and is appropriate for empirical treatment of uncomplicated canine pyoderma.
Because cephalexin is a time-dependent antibiotic, meaning that it requires concentrations constantly above the MIC to be effective, the suggested dose for cephalexin is between 15 to 30 mg/kg orally twice daily on a full stomach, and the duration of treatment should be three to eight weeks (Mason and Keitzmann, 1999; Scott and others 2001).
Because its absorption is not affected by the presence of food, and in some dogs it can cause vomiting if administered when the stomach is empty, it is usually advised that cephalexin is administered on a full stomach.
First-generation cephalosporins (e.g.cephalexin) are usually administered to dogs with superficial pyoderma without performing bacterial culture and susceptibility testing, the latter being reserved for cases with deep and/or recurrent pyoderma.
The duration of treatment will depend on the depth of the infection. Superficial pyodermas typically need two to three weeks of treatment. Deep pyodermas can be greatly improved after two weeks, but full resolution often takes four to six weeks or longer (Carlotti and Ovaert 1988; Angarano and MacDonald 1989; Guaguère and Marc 1989; Paradis and others 1990; Scott and others 1994; 2006, Carlotti and others 1995).
Treatment has to be continued until the infection is visually and palpably cured, and cytology is normal. It is conventional to continue treatment for another seven days in the case of superficial infections, and 14 days if there was deep infection (Scott and others 2001). Treated cases should be checked every two-four weeks. If there is any doubt that complete resolution has not occurred, treatment should be continued, checking cytology and/or culture to confirm that remission is progressing. It is important to note that the clinical signs associated with an underlying disease may still be present and must be differentiated from the clinical signs of the pyoderma.
Always remember to stress with the owner the importance of correct treatment and the necessity of finishing the full course of tablets. Provide written instructions and use precise terminology e.g ‘every 12 hours’ instead of ‘twice daily’. Always recommend that the owner comes back a few days before they run out of tablets and perform diagnostic tests to evaluate the need for continued therapy.