We followed 37,233 outpatients for 45 days after receiving a prescript
ion for ciprofloxacin to identify any newly diagnosed, important illne
sses that might have been caused by the drug. For 29 users the role of
ciprofloxacin in the etiology of the illness could not be confidently
ruled out (7.79/10,000 persons; 95% CI 5.42-11.18). In only seven was
a causal relation to ciprofloxacin considered likely: three skin reac
tions and one case each of thrombocytopenia, ''headache, nausea, and s
hakes,'' hallucinations, and palpitations. No fatal illnesses occurred
, and all patients recovered after discontinuing the drug. In addition
, few cases of photosensitivity were associated with the agent. We con
clude that important adverse reactions attributable to ciprofloxacin a
re uncommon.