Theophylline levels can be markedly increased in some patients by ciprofloxacin, and possibly pefloxacin. Norfloxacin and
ofloxacin normally cause a much smaller rise in
theophylline levels, although serious
toxicity has been seen in a few patients taking
norfloxacin. Convulsions have been reported with
theophylline and ciprofloxacin or
norfloxacin. With some of these cases it is difficult to know whether what happened was due to increased
theophylline levels, to patient pre-disposition, to potential additive effects on the seizure threshold, or to all three factors combined.
The dose should be modified based on the
theophylline level on day 2 of ciprofloxacin treatment. It may be prudent to follow similar precautions with
ofloxacin and
norfloxacin. Seizures resulting from concurrent use are relatively rare. Gatifloxacin,
levofloxacin,
lomefloxacin, moxifloxacin,
nalidixic acid and sparfloxacin appear not to significantly affect
theophylline levels.