Perhaps a little history will help explain the wide variations.
Keflex used to cover E. Coli, Proteus (mirabilis, not vulgaris), and
klebsiella very well. It is FDA indicated for UTIs, and in the early 1990's
was a first line drug for UTIs, especially as ampicillin resistant E. Coli
first became prevalent. Local resistance patterns haven't made it my first
choice in a while but it really isn't bad.
Harriet Lane 12th ed gives a dose range of 25-50 mg/kg for Keflex. The off
label use of the 50-100 mg/kg range was primarily for otitis media, largely
because cephalexin wasn't very effective for that indication (poor
penetration into the middle ear.) Use of the high dose dates from the 1970's
and largely went out of favor in the early 1980's when Ceclor took over the
market. High dose Keflex is unnecessary for most soft tissue infections, at
least so far. At a conference this weekend I heard secondhand about some
problems with MSSA resistance showing up. As mentioned before, BID dosing is
typically adequate for strep throats and mild cellulits, and works for UTIs.
Recall that Amoxicillin's recommended dose is 20-40 mg/kg, with the high
dose 80-100 mg/kg coming into use with PRSP in the late 1990's. So it also
has a very wide range.
Who knows what dose of levofloxacin we'll be putting in the water supply in
Kevin Powell MD PhD FAAP
Saint Louis, MO
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