Cellulitis in the elderly can be a bit of a minefield, partly because of the potential for drug interaction and the need to accommodate for declining liver and renal function. There's also the rising incidence of methicillin-resistant Staphylococcus aureus (MRSA) to be considered.

That being said, most cellulitic conditions are due to acute infection by gram-positive organisms, such as Staphylococcus and Streptococcus. If pustules or abscesses are present, then cultures of these areas will be very helpful to identify the organism responsible. In their absence, however, it would be prudent to prescribe empiric antibiotics that have broad-spectrum activity against Staph and Strep. If there are constitutional symptoms, blood cultures may be useful as well.

Your local infection control or public health officer might be able to provide you with the statistics of MRSA in your community. It appears that the most effective and straight-forward approach to skin and soft-tissue infections with MRSA is incision and drainage, without using anti-MRSA medications. Sulfamethoxazole-trimethoprim (SMX-TMP), clindamycin and rifampin have some benefit in cases where the bacterium is suspected but there's no ability to incise and drain.