1. Gastrointestinal reactions are relatively common and can manifest as abdominal discomfort or pain, diarrhea, nausea or vomiting.

2. Central nervous system reactions may include dizziness, headache, drowsiness or insomnia.

3. Allergic reaction rash, skin itching, exudative erythema multiforme and angioedema may occasionally occur. A few patients have photosensitivity reactions.

4. Crystalluria may occur when this product is used in large doses or when the urine pH value is above 7. In order to avoid the occurrence of crystalluria, it is advisable to drink more water and keep the 24-hour urine output above 1200ml.

5. Epileptic seizures, mental abnormalities, restlessness, disturbance of consciousness, hallucinations, and tremors.

6. A few patients may experience increased serum aminotransferase, increased blood urea nitrogen, and decreased leukocytes in peripheral blood, which are mostly mild and transient.

Reference source? Baidu Encyclopedia-Norfloxacin