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Norfloxacin: Cautions

Oral norfloxacin is generally well tolerated at dosages used in the treatment of urinary tract infections, and adverse effects of the drug are similar to those reported with other quinolone anti-infectives (e.g., ciprofloxacin, ofloxacin).

Adverse effects have been reported in about 3.5-10% of patients receiving norfloxacin and have been severe enough to require discontinuance in 1% or less of patients.

The most frequent adverse effects of the drug reported during clinical trials involved the GI tract or CNS; however, the adverse effect most frequently reported in postmarketing experience is rash.

Adverse effects have occurred in about 7% of patients receiving a single 800-mg oral dose of norfloxacin for the treatment of uncomplicated gonorrhea. Dizziness, nausea, and abdominal cramping are the adverse effects reported most frequently in patients receiving this single-dose regimen, and these effects have been reported in 2-3.5% of patients. In addition, diarrhea, vomiting, anorexia, constipation, dyspepsia, headache, tingling of the fingers, hyperhidrosis, decreased hemoglobin and hematocrit, decreased platelet count, and increased sum concentrations of AST (SGOT) were reported in 1% or less of patients receiving the single-dose regimen.

GI Effects

Nausea is one of the most frequent adverse effects of norfloxacin and has been reported in about 1-4% of patients receiving the drug. Other adverse GI effects, including abdominal pain, cramping, loose stools, diarrhea, vomiting, anorexia, dyspepsia, dysphagia, dysgeusia, stomatitis, dry mouth, bitter taste, heartburn, digestive disorders, constipation, flatulence, and pruritus ani, have been reported in 1% or less of patients.

Effects on Fecal Flora

Norfloxacin therapy exerts a selective effect on normal bowel flora. Total bacterial counts of normal gram-negative aerobic fecal flora are decreased, but total counts of normal anaerobic and gram-positive aerobic fecal flora are generally unaffected during or following therapy with usual dosage of the drug. Bacterial counts of normal fecal flora generally return to pretreatment levels within 1-2 weeks after norfloxacin is discontinued.

Although fluoroquinolones, including norfloxacin, are relatively inactive against Clostridium difficile in vitro, pseudomembranous colitis has been reported only rarely in patients receiving the drugs. In at least one patient, transient fecal colonization with C. difficile occurred 1 week after discontinuance of norfloxacin; however, there was no evidence of diarrhea or clostridia-produced toxin, and the strain was not present in feces 1 week later.

The reason for this relative lack of association between fluoroquinolone use and colitis has not been elucidated but may be related to achievement of fecal concentrations of the drugs that substantially exceed the MIC of C. difficile and/or the selective effect of the drugs on normal GI flora. Additional experience is necessary to determine the effect of fluoroquinolones on C. difficile-associated pseudomembranous colitis.

Nervous System Effects

Headache has been reported in up to 3% and dizziness in up to 2% of patients receiving norfloxacin. Other adverse nervous system effects occurring in up to 1% of patients include lightheadedness, asthenia, drowsiness, somnolence, depression, insomnia, anxiety, irritability, nervousness, euphoria, confusion or disorientation, dream abnormalities, hallucinations, personality changes, psychotic reactions, ataxia, paresthesia, and polyneuropathy including Guillain-Barre syndrome. Seizures myoclonus, and tremors have been reported rarely in patients receiving norfloxacin. Other severe adverse CNS effects, including increased intracranial pressure and toxic psychoses, have been reported with some other fluoroquinolones (e.g., ciprofloxacin).

Dermatologic and Sensitivity Reactions

Eosinophilia has been reported in up to 1.8%1, 2 and rash, fever, erythema, urticaria, and pruritus in up to 1% of patients receiving norfloxacin. Angioedema, toxic epidermal necrolysis, exfoliative dermatitis, vasculitis, erythema multiforme, and Stevens-Johnson syndrome also have been reported. Anaphylactoid reactions have occurred in patients receiving norfloxacin; the reaction reportedly consisted of swollen tongue, rash, dry mouth, extreme anxiety, and epiphora in one patient receiving the drug.

The manufacturer recommends that norfloxacin be discontinued at the first sign of rash or any other sign of hypersensitivity. In addition, serious and occasionally fatal hypersensitivity (anaphylactic) reactions have occurred, some with the initial dose, in patients receiving quinolone therapy.

Some such reactions were accompanied by cardiovascular collapse, loss of consciousness, paresthesia, pharyngeal or facial edema, dyspnea, urticaria, and/or pruritus; there was a history of hypersensitivity in only a few of these cases. If a severe hypersensitivity reaction occurs during norfloxacin therapy, the drug should be discontinued and the patient given appropriate therapy (e.g., epinephrine, corticosteroids, maintenance of an adequate airway, oxygen, maintenance of blood pressure) as indicated. Norfloxacin, like some other fluoroquinolones, also has been reported to cause photosensitivity reactions.

Genitourinary Effects

Increased serum creatinine and BUN1, 2, 9, 114 concentrations have occurred rarely in patients receiving norfloxacin. Interstitial nephritis and renal failure also have been reported. Although a causal relationship was not definitely established, acute renal failure was reported in a geriatric patient receiving the drug. Crystalluria, without evidence of renal toxicity, has been reported rarely in individuals who received higher than usual dosage of norfloxacin (i.e., 800-1600 mg as a single dose) and when urine pH was 6.5-7.8. Solubility of norfloxacin in urine depends on pH and temperature.

Although norfloxacin crystals in water are generally colorless needles, crystals of the drug in urine have been reported to be spherical with ragged edges and orange and green highlights. Needle-shaped crystals have also been found in the urine of some healthy adults who received placebo or a single 800- or 1600-mg dose of norfloxacin (1 or 2 times the recommended daily dose, respectively). Patients receiving the drug should avoid excessive dosage and maintain adequate fluid intake; in addition, alkaline urine should be avoided. In studies in dogs and rats, crystalluria occurred when norfloxacin was given in dosages of 50 and 200 mg/kg daily, respectively. In several dogs who received norfloxacin in dosages of 150-300 mg/kg daily for up to 6 months, crystalluria resulted in urinary obstruction and death. There is no evidence to date that norfloxacin crystalluria in humans is associated with renal toxicity.

Musculoskeletal Effects

Achilles, shoulder, and hand tendon ruptures that required surgical repair or resulted in prolonged disability have been reported in patients receiving fluoroquinolones, including norfloxacin. Norfloxacin should be discontinued in any patient who experiences pain, inflammation, or rupture of a tendon. Tendon rupture can occur during or following therapy with norfloxacin. Arthralgia, arthritis, myalgia, and joint swelling have occurred rarely in patients receiving norfloxacin.

Quinolones, including norfloxacin, may exacerbate myasthenia gravis and lead to life-threatening weakness of the respiratory muscles. In an immunosuppressed adult, acute ankle and hip pain followed by acute pain, tenderness, and swelling of the tendon sheath of the middle finger of both hands occurred after 4 weeks of norfloxacin therapy at the usual dosage; symptoms resolved after discontinuance of the drug. In another immunosuppressed adult, acute tendonitis of the Achilles tendons occurred after 13 days of norfloxacin at the usual dosage, but lessened when dosage of the drug was decreased slightly. In immature dogs, a single oral dose of norfloxacin 6 times the usual human dose caused lameness; histologic evaluation of the weight-bearing joints of these dogs revealed permanent lesions of the cartilage.

Most other fluoroquinolones (e.g., ciprofloxacin, gatifloxacin, moxifloxacin, levofloxacin, ofloxacin) also cause erosions of cartilage in weight-bearing joints and other signs of arthropathy in immature animals of various species. (See Cautions: Pediatric Precautions.) Morphologic changes observed in animals with quinolone-induced arthropathies include erosions in joint cartilage accompanied by noninflammatory, cell-free effusion of the joint space; the cartilage is incapable of regeneration and may serve as a site for the development of arthropathy deformans. In addition, breakdown products of cartilage may irritate the synovia. The relationship of these effects in animals and the rheumatologic symptoms associated with use of quinolones in humans is unknown.

Hepatobiliary Effects

Hepatitis, jaundice (including cholestatic jaundice), and increased serum concentrations of AST (SGOT), ALT (SGPT), and alkaline phosphatase have been reported in less than 2% of patients receiving norfloxacin. Increased serum LDH concentrations have been reported rarely.

Hematologic Effects

Decreased leukocyte or neutrophil counts have been reported in about 2% of patients receiving norfloxacin; thrombocytopenia also has been reported. In one patient, there was some evidence that leukopenia resulted from an immunologic rather than a toxic mechanism. Decreased hemoglobin concentration, decreased hematocrit, and hemolytic anemia have occurred rarely. Prolongation of prothrombin time occurred in at least one patient receiving norfloxacin.

Other Adverse Effects

Back pain, hyperhidrosis, and symptomatic hypoglycemia have been reported in patients receiving norfloxacin. Tinnitus and transient hearing loss also have been reported rarely in patients receiving the drug. Diplopia and weakness have been reported. Although other visual disturbances have been reported with some fluoroquinolones (e.g., ciprofloxacin), these adverse effects have not been reported with norfloxacin and there has been no evidence of ocular toxicity in animal studies using the drug.

Precautions and Contraindications

Norfloxacin is contraindicated in patients with a history of hypersensitivity to the drug or to other quinolones. Norfloxacin, like other quinolones, can cause serious, potentially fatal hypersensitivity reactions, occasionally following the initial dose. (See Cautions: Dermatologic and Sensitivity Reactions.) Patients receiving norfloxacin should be advised of this possibility and instructed to discontinue the drug and contact their physician at the first sign of rash or any other sign of hypersensitivity.

Crystalluria has been reported in some patients receiving high dosage of norfloxacin (principally at dosages higher than the recommended dosage) and in healthy adults who received placebo or a single 800- or 1600-mg dose of the drug. Although crystalluria is not expected to occur under usual conditions with the usual recommended dosage of the drug, patients should be instructed to drink sufficient quantities of fluids to ensure proper hydration and adequate urinary output during norfloxacin therapy. Measures also should be taken to avoid alkaline urine, and the usual recommended dosage of the drug should not be exceeded.

Norfloxacin should be used with caution in individuals with known or suspected CNS disorders, such as severe cerebral arteriosclerosis, seizure disorders, or other factors that predispose to seizures, since the effects of norfloxacin on brain function or on the electrical activity of the brain have not been fully evaluated. Patients should be cautioned to notify their clinician if they have a history of seizures. Seizures and myoclonus have been reported rarely in patients receiving norfloxacin.

Other severe CNS effects, including increased intracranial pressure, CNS stimulation (which may lead to tremors, restlessness, lightheadedness, confusion, and/or hallucinations), and toxic psychosis, have been reported rarely with some quinolones (e.g., ciprofloxacin), although these effects have not been definitely attributed to norfloxacin to date. If a severe adverse CNS reaction, including seizures, increased intracranial pressure, CNS stimulation, or toxic psychosis, occurs during norfloxacin therapy, the drug should be discontinued and appropriate therapeutic measures instituted.

Patients should be advised that norfloxacin may cause dizziness or lightheadedness, and their individual susceptibility to these adverse effects should be determined before operating a motor vehicle or machinery or engaging in activities requiring mental alertness and coordination.

Norfloxacin should be used with caution in patients with myasthenia gravis since quinolones, including norfloxacin, may exacerbate this condition and lead to life-threatening weakness of respiratory muscles. Patients receiving norfloxacin should be advised to discontinue the drug and inform their clinician if they experience pain, inflammation, or rupture of a tendon and to rest and refrain from exercise until a diagnosis of tendinitis or tendon rupture is excluded.

Doses and/or frequency of administration of norfloxacin should be decreased in patients with impaired renal function, since serum concentrations of the drug are higher and prolonged in these patients compared with patients with normal renal function. Patients receiving norfloxacin also should be advised to avoid excessive exposure to sunlight. Moderate to severe phototoxicity manifested as an exaggerated sunburn reaction has been reported during exposure to direct sunlight in patients receiving some fluoroquinolones (e.g., lomefloxacin, ofloxacin, sparfloxacin). Norfloxacin should be discontinued if phototoxicity occurs.

Pediatric Precautions

Because norfloxacin causes arthropathy in immature animals, the manufacturer states that the drug should not be used in children or adolescents younger than 18 years of age. Some clinicians state that the drug may be used cautiously in adolescents if skeletal growth is complete. The American Academy of Pediatrics (AAP) states that use of fluoroquinolones (e.g., ciprofloxacin, levofloxacin, lomefloxacin, norfloxacin, ofloxacin, sparfloxacin) in children younger than 18 years of age may be justified in special circumstances; however, the drugs should be used only after careful assessment of the risks and benefits for the individual patient and after these benefits and risks have been explained to the parents or caregivers.

The AAP states that fluoroquinolones may be useful when no other oral agent is available (to avoid use of a parenteral agent) or when the pediatric patient has an infection caused by multidrug-resistant gram-negative bacteria, such as certain strains of Pseudomonas, or Mycobacterium. Therefore, possible uses of fluoroquinolones in pediatric patients include the treatment of urinary tract infections caused by P. aeruginosa or other multidrug-resistant gram-negative bacteria, chronic suppurative otitis media or malignant otitis externa, chronic osteomyelitis, exacerbation of cystic fibrosis, mycobacterial infection, or other gram-negative bacterial infections in immunocompromised patients when prolonged oral therapy is desired.

A single oral dose of norfloxacin 6 times the usual human dose caused lameness in immature dogs; histologic evaluation of the weight-bearing joints of these dogs revealed permanent lesions of the cartilage. Most other ouinolones (e.g., ciprofloxacin, ofloxacin) also cause erosions of the cartilage in weight-bearing joints and other signs of arthropathy in immature animals of various species.

Mutagenicity and Carcinogenicity

Norfloxacin was not mutagenic in the dominant lethal test in mice and did not cause chromosomal aberrations in hamsters or rats receiving doses 30-60 times the usual human dose. In vitro studies using microbial (i.e., Ames test) or mammalian (i.e., Chinese hamster fibroblasts, V-79 mammalian cell assay) cell systems have not shown norfloxacin to be mutagenic. Although norfloxacin was weakly positive in the Rec-assay for DNA repair, other mutagenic assays, including more sensitive tests such as the V-79 mammalian cell assay, did not show evidence of mutagenicity. Results from the hepatocyte DNA repair assay have been equivocal. There was no evidence of carcinogenicity in rats receiving norfloxacin for 19 months, and there was no increase in neoplastic changes in rats receiving norfloxacin dosages 8-9 times the usual human dosage for up to 96 weeks.

Pregnancy, Fertitlity and Lactation

There are no adequate and controlled studies to date using norfloxacin in pregnant women. Since the drug, like most other fluoroquinolones, causes arthropathy in immature animals, norfloxacin should not be used in pregnant or nursing women. Norfloxacin has been embryocidal and caused slight maternotoxicity (vomiting and anorexia) in cynomolgus monkeys at dosages of 150 mg/kg or more daily.

Embryonic loss occurred in monkeys when norfloxacin was given in doses 10 times the maximum human dose and when peak plasma concentrations of the drug were 2-3 times higher than those attained in humans.

Preliminary evidence suggests that embryonic loss in monkeys may result from norfloxacin-induced suppression of placenta progesterone required for maintenance of fetal growth. In rabbits, norfloxacin dosages of 100 mg/kg daily caused embryotoxicity and maternotoxicity, but these effects reportedly resulted from the rabbit’s sensitivity to norfloxacin-induced changes in the microflora of the intestines and were not caused by a direct effect of the drug on the embryo. There was no evidence of teratogenicity in rats, rabbits, mice, or monkeys receiving norfloxacin doses 6-50 times the usual human dose. Reproduction studies in male and female mice using oral norfloxacin doses up to 30 times the usual human dose have not revealed evidence of impaired fertility.

Administration of high dosages (100 mg/kg daily) of norfloxacin and some other quinolones (e.g., pefloxacin, pipemidic acid; drugs not commercially available in the US) has been associated with impaired spermatogenesis and/or testicular damage (atrophy in rats and dogs) in chronic (for 3 months or longer) toxicity studies. It is not known whether norfloxacin is distributed into milk. Norfloxacin was not detected in the milk of lactating women who received a single 200-mg oral dose of the drug, but the possibility of distribution into milk following higher or multiple doses remains to be determined. Other quinolones are distributed into milk. Because of the potential for serious adverse effects of norfloxacin in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.