May cause life-threatening anaphylaxis/anaphylactoid reactions. Due to structural similarity with tetracyclines, use with caution in prior hypersensitivity and/or severe adverse reactions associated with tetracycline use. May be associated with antianabolic effects observed with tetracycline class (including increased BUN, azotemia, acidosis, and hyperphosphatemia). Abnormal liver function tests (total bilirubin, prothrombin time, transaminases) reported. Isolated cases of significant hepatic dysfunction and hepatic failure occurred. Adverse hepatic effects may occur after drug discontinuation. May be associated with pancreatitis, photosensitivity, and with pseudotumor cerebri due to structural similarities with tetracyclines. Prolonged use may result in fungal or bacterial superinfection, including C. difficile-associated diarrhea and pseudomembranous colitis. Use with caution in hepatic impairment. Not indicated for treatment of pneumonia. Demonstrated inferior efficacy, including lower cure rates and increased mortality, in subgroup of patients with ventilator-associated pneumonia. Use with caution if using as monotherapy for intestinal perforation. Permanent discoloration of teeth may occur if used during tooth development (fetal stage through children up to 8 years of age).