CIPROFLOXACIN

Ciprofloxacin Hydrochloride Tablets USP, 250 mg and 500 mg are synthetic broad spectrum antimicrobial agents for oral administration. Ciprofloxacin hydrochloride, USP, a fluoroquinolone, is the monohydrochloride monohydrate salt of 1-cyclopropyl-6-fluoro-1, 4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid. It is a faintly yellowish to light yellow crystalline substance with a molecular weight of 385.8. Its empirical formula is C 17 H 18 FN 3 O 3 •HCl•H 2 O and its chemical structure is as follows: Ciprofloxacin is 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid. Its empirical formula is C 17 H 18 FN 3 O 3 and its molecular weight is 331.4. It is a faintly yellowish to light yellow crystalline substance and its chemical structure is as follows: Ciprofloxacin Tablets USP are film-coated tablets and are available in 250 mg and 500 mg (ciprofloxacin equivalent) strengths. Ciprofloxacin Tablets are white to slightly yellowish. The inactive ingredients are pregelatinized starch, microcrystalline cellulose, colloidal silicon dioxide, crospovidone, magnesium stearate, hypromellose, titanium dioxide, polyethylene glycol and purified water. Chemical Structure Chemical Structure

Ciprofloxacin Tablets USP, 250 mg and 500 mg is indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the conditions and patient populations listed below. Please see Error! Hyperlink reference not valid. for specific recommendations. Adult Patients: Urinary Tract Infections caused by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Proteus mirabilis, Providencia rettgeri, Morganella morganii, Citrobacter diversus, Citrobacter freundii, Pseudomonas aeruginosa, methicillin-susceptible Staphylococcus epidermidis, Staphylococcus saprophyticus, or Enterococcus faecalis. Acute Uncomplicated Cystitis in females caused by Escherichia coli or Staphylococcus saprophyticus. Chronic Bacterial Prostatitis caused by Escherichia coli or Proteus mirabilis. Lower Respiratory Tract Infections caused by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Proteus mirabilis, Pseudomonas aeruginosa, Haemophilus influenzae, Haemophilus parainfluenzae, or penicillin-susceptible Streptococcus pneumoniae. Also, Moraxella catarrhalis for the treatment of acute exacerbations of chronic bronchitis. NOTE: Although effective in clinical trials, ciprofloxacin is not a drug of first choice in the treatment of presumed or confirmed pneumonia secondary to Streptococcus pneumoniae. Acute Sinusitis caused by Haemophilus influenzae, penicillin-susceptible Streptococcus pneumoniae, or Moraxella catarrhalis. Skin and Skin Structure Infections caused by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Proteus mirabilis, Proteus vulgaris, Providencia stuartii, Morganella morganii, Citrobacter freundii, Pseudomonas aeruginosa, methicillin-susceptible Staphylococcus aureus, methicillin-susceptible Staphylococcus epidermidis, or Streptococcus pyogenes. Bone and Joint Infections caused by Enterobacter cloacae, Serratia marcescens, or Pseudomonas aeruginosa. Complicated Intra-Abdominal Infections (used in combination with metronidazole) caused by Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, or Bacteroides fragilis. Infectious Diarrhea caused by Escherichia coli (enterotoxigenic strains), Campylobacter jejuni, Shigella boydii † , Shigella dysenteriae, Shigella flexneri or Shigella sonnei † when antibacterial therapy is indicated. Typhoid Fever (Enteric Fever) caused by Salmonella typhi. NOTE: The efficacy of ciprofloxacin in the eradication of the chronic typhoid carrier state has not been demonstrated. Uncomplicated cervical and urethral gonorrhea due to Neisseria gonorrhoeae. Pediatric patients (1 to 17 years of age): Complicated Urinary Tract Infections and Pyelonephritis due to Escherichia coli. NOTE: Although effective in clinical trials, ciprofloxacin is not a drug of first choice in the pediatric population due to an increased incidence of adverse events compared to controls, including events related to joints and/or surrounding tissues. (See WARNINGS , PRECAUTIONS, Pediatric Use , ADVERSE REACTIONS and CLINICAL STUDIES .) Ciprofloxacin, like other fluoroquinolones, is associated with arthropathy and histopathological changes in weight-bearing joints of juvenile animals. (See ANIMAL PHARMACOLOGY .) Adult and Pediatric Patients: Inhalational anthrax (post-exposure): To reduce the incidence or progression of disease following exposure to aerosolized Bacillus anthracis. Ciprofloxacin serum concentrations achieved in humans served as a surrogate endpoint reasonably likely to predict clinical benefit and provided the initial basis for approval of this indication. 5 Supportive clinical information for ciprofloxacin for anthrax post-exposure prophylaxis was obtained during the anthrax bioterror attacks of October 2001. (See also, INHALATIONAL ANTHRAX – ADDITIONAL INFORMATION ). † Although treatment of infections due to this organism in this organ system demonstrated a clinically significant outcome, efficacy was studied in fewer than 10 patients. If anaerobic organisms are suspected of contributing to the infection, appropriate therapy should be administered. Appropriate culture and susceptibility tests should be performed before treatment in order to isolate and identify organisms causing infection and to determine their susceptibility to ciprofloxacin. Therapy with Ciprofloxacin Tablets USP, 250 mg and 500 mg and may be initiated before results of these tests are known; once results become available appropriate therapy should be continued. As with other drugs, some strains of Pseudomonas aeruginosa may develop resistance fairly rapidly during treatment with ciprofloxacin. Culture and susceptibility testing performed periodically during therapy will provide information not only on the therapeutic effect of the antimicrobial agent but also on the possible emergence of bacterial resistance. To reduce the development of drug-resistant bacteria and maintain the effectiveness of Ciprofloxacin Tablets USP, 250 mg and 500 mg and other antibacterial drugs, Ciprofloxacin Tablets USP, 250 mg and 500 mg should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

- ADULTS Ciprofloxacin Tablets USP 250 mg and 500 mg should be administered orally to adults as described in the Dosage Guidelines table. The determination of dosage for any particular patient must take into consideration the severity and nature of the infection, the susceptibility of the causative organism, the integrity of the patient’s host-defense mechanisms, and the status of renal function and hepatic function. The duration of treatment depends upon the severity of infection. The usual duration is 7 to 14 days; however, for severe and complicated infections more prolonged therapy may be required. Ciprofloxacin should be administered at least 2 hours before or 6 hours after magnesium/aluminum antacids, or sucralfate, Videx® (didanosine) chewable/buffered tablets or pediatric powder for oral solution, other highly buffered drugs, or other products containing calcium, iron or zinc. ADULT DOSAGE GUIDELINES Infection Severity Dose Frequency Usual Durations † * used in conjunction with metronidazole † Generally ciprofloxacin should be continued for at least 2 days after the signs and symptoms of infection have disappeared, except for inhalational anthrax (post-exposure). ** Drug administration should begin as soon as possible after suspected or confirmed exposure. This indication is based on a surrogate endpoint, ciprofloxacin serum concentrations achieved in humans, reasonably likely to predict clinical benefit. 4 For a discussion of ciprofloxacin serum concentrations in various human populations, see INHALATIONAL ANTHRAX – ADDITIONAL INFORMATION . Urinary Tract Acute Uncomplicated 250 mg q 12 h 3 Days Mild/Moderate 250 mg q 12 h 7 to 14 Days Severe/Complicated 500 mg q 12 h 7 to 14 Days Chronic Bacterial Prostatits Mild/Moderate 500 mg q 12 h 28 Days Lower Respiratory Tract Mild/Moderate 500 mg q 12 h 7 to 14 days Severe/Complicated 750 mg q 12 h 7 to 14 days Acute Sinusitis Mild/Moderate 500 mg q 12 h 10 days Skin and Skin Structure Mild/Moderate 500 mg q 12 h 7 to 14 Days Severe/Complicated 750 mg q 12 h 7 to 14 Days Bone and Joint Mild/Moderate 500 mg q 12 h ≥4 to 6 weeks Severe/Complicated 750 mg q 12 h ≥4 to 6 weeks Intra-Abdominal * Complicated 500 mg q 12 h 7 to 14 Days Infectious Diarrhea Mild/Moderate/Severe 500 mg q 12 h 5 to 7 Days Typhoid Fever Mild/Moderate 500 mg q 12 h 10 Days Urethral and Cervical Gonococcal Infections Uncomplicated 250 mg single dose single dose Inhalational anthrax (post-exposure) ** 500 mg q 12 h 60 Days Conversion of I.V. to Oral Dosing in Adults: Patients whose therapy is started with CIPRO I.V. may be switched to Ciprofloxacin Tablets USP 250 mg and 500 mg when clinically indicated at the discretion of the physician (See CLINICAL PHARMACOLOGY and table below for the equivalent dosing regimens). Equivalent AUC Dosing Regimens Cipro Oral Dosage Equivalent Cipro I.V. Dosage 250 mg Tablet q 12 h 200 mg I.V. q 12 h 500 mg Tablet q 12 h 400 mg I.V. q 12 h 750 mg Tablet q 12 h 400 mg I.V. q 8 h Adults with Impaired Renal Function: Ciprofloxacin is eliminated primarily by renal excretion; however, the drug is also metabolized and partially cleared through the biliary system of the liver and through the intestine. These alternative pathways of drug elimination appear to compensate for the reduced renal excretion in patients with renal impairment. Nonetheless, some modification of dosage is recommended, particularly for patients with severe renal dysfunction. The following table provides dosage guidelines for use in patients with renal impairment: RECOMMENDED STARTING AND MAINTENANCE DOSES FOR PATIENTS WITH IMPAIRED RENAL FUNCTION Creatinine Clearance (mL/min) Dose > 50 See Usual Dosage. 30-50 250-500 mg q 12 h 5-29 250-500 mg q 18 h Patients on hemodialysis or Peritoneal dialysis 250-500 mg q 24 h (after dialysis) When only the serum creatinine concentration is known, the following formula may be used to estimate creatinine clearance. Weight (kg) x (140 - age) Men: Creatinine clearance (mL/min) = 72 x serum creatinine (mg/dL) Women: 0.85 x the value calculated for men. The serum creatinine should represent a steady state of renal function. In patients with severe infections and severe renal impairment, a unit dose of 750 mg may be administered at the intervals noted above. Patients should be carefully monitored. DOSAGE AND ADMINISTRATION - PEDIATRICS Ciprofloxacin Tablets USP 250 mg and 500 mg should be administered orally as described in the Dosage Guidelines table. An increased incidence of adverse events compared to controls, including events related to joints and/or surrounding tissues, has been observed. (See ADVERSE REACTIONS and CLINICAL STUDIES .) Dosing and initial route of therapy (i.e., I.V. or oral) for complicated urinary tract infection or pyelonephritis should be determined by the severity of the infection. In the clinical trial, pediatric patients with moderate to severe infection were initiated on 6 to 10 mg/kg I.V. every 8 hours and allowed to switch to oral therapy (10 to 20 mg/kg every 12 hours), at the discretion of the physician. PEDIATRIC DOSAGE GUIDELINES Infection Route of Administration Dose (mg/kg) Frequency Total Duration * The total duration of therapy for complicated urinary tract infection and pyelonephritis in the clinical trial was determined by the physician. The mean duration of treatment was 11 days (range 10 to 21 days). ** Drug administration should begin as soon as possible after suspected or confirmed exposure to Bacillus anthracis spores. This indication is based on a surrogate endpoint, ciprofloxacin serum concentrations achieved in humans, reasonably likely to predict clinical benefit. 5 For a discussion of ciprofloxacin serum concentrations in various human populations, see INHALATIONAL ANTHRAX – ADDITIONAL INFORMATION . Complicated Urinary Tract or Pyelonephritis Intravenous 6 to 10 mg/kg (maximum 400 mg per dose; not to be exceeded even in patients weighing > 51 kg) Every 8 hours 10-21 days* (patients from 1 to 17 years of age) Oral 10 mg/kg to 20 mg/kg (maximum 750 mg per dose; not to be exceeded even in patients weighing > 51 kg) Every 12 hours Inhalational Anthrax (Post-Exposure)** Intravenous 10 mg/kg (maximum 400 mg per dose) Every 12 hours 60 days Oral 15 mg/kg (maximum 500 mg per dose) Every 12 hours Pediatric patients with moderate to severe renal insufficiency were excluded from the clinical trial of complicated urinary tract infection and pyelonephritis. No information is available on dosing adjustments necessary for pediatric patients with moderate to severe renal insufficiency (i.e., creatinine clearance of < 50 mL/min/1.73m 2 ).

Ciprofloxacin is contraindicated in persons with a history of hypersensitivity to ciprofloxacin, any member of the quinolone class of antimicrobial agents, or any of the product components. Concomitant administration with tizanidine is contraindicated. (See PRECAUTIONS: Drug Interactions . )

Adverse Reactions in Adult Patients: During clinical investigations with oral and parenteral ciprofloxacin, 49,038 patients received courses of the drug. Most of the adverse events reported were described as only mild or moderate in severity, abated soon after the drug was discontinued, and required no treatment. Ciprofloxacin was discontinued because of an adverse event in 1% of orally treated patients. The most frequently reported drug related events, from clinical trials of all formulations, all dosages, all drug-therapy durations, and for all indications of ciprofloxacin therapy were nausea (2.5%), diarrhea (1.6%), liver function tests abnormal (1.3%), vomiting (1%), and rash (1%). Additional medically important events that occurred in less than 1% of ciprofloxacin patients are listed below. BODY AS A WHOLE: headache, abdominal pain/discomfort, foot pain, pain, pain in extremities, injection site reaction (ciprofloxacin intravenous) CARDIOVASCULAR: palpitation, atrial flutter, ventricular ectopy, syncope, hypertension, angina pectoris, myocardial infarction, cardiopulmonary arrest, cerebral thrombosis, phlebitis, tachycardia, migraine, hypotension CENTRAL NERVOUS SYSTEM: restlessness, dizziness, lightheadedness, insomnia, nightmares, hallucinations, manic reaction, irritability, tremor, ataxia, convulsive seizures, lethargy, drowsiness, weakness, malaise, anorexia, phobia, depersonalization, depression, paresthesia, abnormal gait, grand mal convulsion GASTROINTESTINAL: painful oral mucosa, oral candidiasis, dysphagia, intestinal perforation, gastrointestinal bleeding, cholestatic jaundice, hepatitis HEMIC/LYMPHATIC: lymphadenopathy, petechia METABOLIC/NUTRITIONAL: amylase increase, lipase increase MUSCULOSKELETAL: arthralgia or back pain, joint stiffness, achiness, neck or chest pain, flare up of gout RENAL/UROGENITAL: interstitial nephritis, nephritis, renal failure, polyuria, urinary retention, urethral bleeding, vaginitis, acidosis, breast pain RESPIRATORY: dyspnea, epistaxis, laryngeal or pulmonary edema, hiccough, hemoptysis, bronchospasm, pulmonary embolism SKIN/HYPERSENSITIVITY: allergic reaction, pruritus, urticaria, photosensitivity/phototoxicity reaction, flushing, fever, chills, angioedema, edema of the face, neck, lips, conjunctivae or hands, cutaneous candidiasis, hyperpigmentation, erythema nodosum, sweating SPECIAL SENSES: blurred vision, disturbed vision (change in color perception, overbrightness of lights), decreased visual acuity, diplopia, eye pain, tinnitus, hearing loss, bad taste, chromatopsia In several instances nausea, vomiting, tremor, irritability, or palpitation were judged by investigators to be related to elevated serum levels of theophylline possibly as a result of drug interaction with ciprofloxacin. In randomized, double-blind controlled clinical trials comparing ciprofloxacin tablets (500 mg BID) to cefuroxime axetil (250 mg-500 mg BID) and to clarithromycin (500 mg BID) in patients with respiratory tract infections, ciprofloxacin demonstrated a CNS adverse event profile comparable to the control drugs. Adverse Reactions in Pediatric Patients: Ciprofloxacin, administered I.V. and /or orally, was compared to a cephalosporin for treatment of complicated urinary tract infections (cUTI) or pyelonephritis in pediatric patients 1 to 17 years of age (mean age of 6 ± 4 years). The trial was conducted in the US, Canada, Argentina, Peru, Costa Rica, Mexico, South Africa, and Germany. The duration of therapy was 10 to 21 days (mean duration of treatment was 11 days with a range of 1 to 88 days). The primary objective of the study was to assess musculoskeletal and neurological safety within 6 weeks of therapy and through one year of follow-up in the 335 ciprofloxacin- and 349 comparator-treated patients enrolled. An Independent Pediatric Safety Committee (IPSC) reviewed all cases of musculoskeletal adverse events as well as all patients with an abnormal gait or abnormal joint exam (baseline or treatment-emergent). These events were evaluated in a comprehensive fashion and included such conditions as arthralgia, abnormal gait, abnormal joint exam, joint sprains, leg pain, back pain, arthrosis, bone pain, pain, myalgia, arm pain, and decreased range of motion in a joint. The affected joints included: knee, elbow, ankle, hip, wrist, and shoulder. Within 6 weeks of treatment initiation, the rates of these events were 9.3% (31/335) in the ciprofloxacin-treated group versus 6% (21/349) in comparator-treated patients. The majority of these events were mild or moderate in intensity. All musculoskeletal events occurring by 6 weeks resolved (clinical resolution of signs and symptoms), usually within 30 days of end of treatment. Radiological evaluations were not routinely used to confirm resolution of the events. The events occurred more frequently in ciprofloxacin-treated patients than control patients, regardless of whether they received I.V. or oral therapy. Ciprofloxacin-treated patients were more likely to report more than one event and on more than one occasion compared to control patients. These events occurred in all age groups and the rates were consistently higher in the ciprofloxacin group compared to the control group. At the end of 1 year, the rate of these events reported at any time during that period was 13.7% (46/335) in the ciprofloxacin-treated group versus 9.5% (33/349) comparator-treated patients. An adolescent female discontinued ciprofloxacin for wrist pain that developed during treatment. An MRI performed 4 weeks later showed a tear in the right ulnar fibrocartilage. A diagnosis of overuse syndrome secondary to sports activity was made, but a contribution from ciprofloxacin cannot be excluded. The patient recovered by 4 months without surgical intervention. Findings Involving Joint or Peri-articular Tissues as Assessed by the IPSC Ciprofloxacin Comparator *The study was designed to demonstrate that the arthropathy rate for the ciprofloxacin group did not exceed that of the control group by more than + 6%. At both the 6 week and 1 year evaluations, the 95% confidence interval indicated that it could not be concluded that ciprofloxacin group had findings comparable to the control group. All Patients (within 6 weeks) 31/335 (9.3%) 21/349 (6%) 95% Confidence Interval* (-0.8%, +7.2%) Age Group ≥ 12 months < 24 months 1/36 (2.8%) 0/41 ≥ 2 years < 6 years 5/124 (4%) 3/118 (2.5%) ≥ 6 years < 12 years 18/143 (12.6%) 12/153 (7.8%) ≥ 12 years to 17 years 7/32 (21.9%) 6/37 (16.2 %) All Patients (within 1 year) 46/335 (13.7%) 33/349 (9.5%) 95% Confidence Interval* (-0.6%, + 9.1%) The incidence rates of neurological events within 6 weeks of treatment initiation were 3% (9/335) in the ciprofloxacin group versus 2% (7/349) in the comparator group and included dizziness, nervousness, insomnia, and somnolence. In this trial, the overall incidence rates of adverse events regardless of relationship to study drug and within 6 weeks of treatment initiation were 41% (138/335) in the ciprofloxacin group versus 31% (109/349) in the comparator group. The most frequent events were gastrointestinal: 15% (50/335) of ciprofloxacin patients compared to 9% (31/349) of comparator patients. Serious adverse events were seen in 7.5% (25/335) of ciprofloxacin-treated patients compared to 5.7% (20/349) of control patients. Discontinuation of drug due to an adverse event was observed in 3% (10/335) of ciprofloxacin-treated patients versus 1.4% (5/349) of comparator patients. Other adverse events that occurred in at least 1% of ciprofloxacin patients were diarrhea 4.8%, vomiting 4.8%, abdominal pain 3.3%, accidental injury 3%, rhinitis 3%, dyspepsia 2.7%, nausea 2.7%, fever 2.1%, asthma 1.8% and rash 1.8%. In addition to the events reported in pediatric patients in clinical trials, it should be expected that events reported in adults during clinical trials or post-marketing experience may also occur in pediatric patients. Post-Marketing Adverse Event Reports: The following adverse events have been reported from worldwide marketing experience with quinolones, including ciprofloxacin. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Decisions to include these events in labeling are typically based on one or more of the following factors: (1) seriousness of the event, (2) frequency of the reporting, or (3) strength of causal connection to the drug. Agitation, agranulocytosis, albuminuria, anaphylactic reactions (including life-threatening anaphylactic shock), anosmia, candiduria, cholesterol elevation (serum), confusion, constipation, delirium, dyspepsia, dysphagia, erythema multiforme, exfoliative dermatitis, fixed eruption, flatulence, glucose elevation (blood), hemolytic anemia, hepatic failure (including fatal cases), hepatic necrosis, hyperesthesia, hypertonia, hypesthesia, hypotension (postural), jaundice, marrow depression (life threatening), methemoglobinemia, moniliasis (oral, gastrointestinal, vaginal), myalgia, myasthenia, myasthenia gravis (possible exacerbation), myoclonus, nystagmus, pancreatitis, pancytopenia (life threatening or fatal outcome), peripheral neuropathy, phenytoin alteration (serum), photosensitivity/phototoxicity reaction, potassium elevation (serum), prothrombin time prolongation or decrease, pseudomembranous colitis (The onset of pseudomembranous colitis symptoms may occur during or after antimicrobial treatment.), psychosis (toxic), renal calculi, serum sickness like reaction, Stevens-Johnson syndrome, taste loss, tendinitis, tendon rupture, torsade de pointes, toxic epidermal necrolysis (Lyell’s Syndrome), triglyceride elevation (serum), twitching, vaginal candidiasis, and vasculitis. (See PRECAUTIONS .) Adverse events were also reported by persons who received ciprofloxacin for anthrax post-exposure prophylaxis following the anthrax bioterror attacks of October 2001. (See also INHALATIONAL ANTHRAX – ADDITIONAL INFORMATION . ) Adverse Laboratory Changes: Changes in laboratory parameters listed as adverse events without regard to drug relationship are listed below: Hepatic – Elevations of ALT (SGPT) (1.9%), AST (SGOT) (1.7%), alkaline phosphatase (0.8%), LDH (0.4%), serum bilirubin (0.3%). Hematologic – Eosinophilia (0.6%), leukopenia (0.4%), decreased blood platelets (0.1%), elevated blood platelets (0.1%), pancytopenia (0.1%). Renal – Elevations of serum creatinine (1.1%), BUN (0.9%), CRYSTALLURIA, CYLINDRURIA, AND HEMATURIA HAVE BEEN REPORTED. Other changes occurring in less than 0.1% of courses were: elevation of serum gammaglutamyl transferase, elevation of serum amylase, reduction in blood glucose, elevated uric acid, decrease in hemoglobin, anemia, bleeding diathesis, increase in blood monocytes, leukocytosis.

Drug-drug Interactions: When Ciprofloxacin Tablets USP, 250 mg and 500 mg is given concomitantly with food, there is a delay in the absorption of the drug, resulting in peak concentrations that occur closer to 2 hours after dosing rather than 1 hour. The overall absorption of Ciprofloxacin Tablets USP, 250 mg and 500 mg however, is not substantially affected. Concurrent administration of antacids containing magnesium hydroxide or aluminum hydroxide may reduce the bioavailability of ciprofloxacin by as much as 90%. (See PRECAUTIONS .) The serum concentrations of ciprofloxacin and metronidazole were not altered when these two drugs were given concomitantly. Concomitant administration with tizanidine is contraindicated. (See CONTRAINDICATIONS. ) Concomitant administration of ciprofloxacin with theophylline decreases the clearance of theophylline resulting in elevated serum theophylline levels and increased risk of a patient developing CNS or other adverse reactions. Ciprofloxacin also decreases caffeine clearance and inhibits the formation of paraxanthine after caffeine administration. (See WARNINGS : PRECAUTIONS .) Drug Interactions: In a pharmacokinetic study, systemic exposure of tizanidine (4 mg single dose) was significantly increased (C max 7-fold, AUC 10-fold) when the drug was given concomitantly with ciprofloxacin (500 mg bid for 3 days). The hypotensive and sedative effects of tizanidine were also potentiated. Concomitant administration of tizanidine and ciprofloxacin is contraindicated. As with some other quinolones, concurrent administration of ciprofloxacin with theophylline may lead to elevated serum concentrations of theophylline and prolongation of its elimination half-life. This may result in increased risk of theophylline-related adverse reactions. (See WARNINGS .) If concomitant use cannot be avoided, serum levels of theophylline should be monitored and dosage adjustments made as appropriate. Some quinolones, including ciprofloxacin, have also been shown to interfere with the metabolism of caffeine. This may lead to reduced clearance of caffeine and a prolongation of its serum half-life. Concurrent administration of a quinolone, including ciprofloxacin, with multivalent cation-containing products such as magnesium/aluminum antacids, sucralfate, Videx® (didanosine) chewable/buffered tablets or pediatric powder, other highly buffered drugs, or products containing calcium, iron, or zinc may substantially decrease its absorption, resulting in serum and urine levels considerably lower than desired. (See Error! Hyperlink reference not valid. for concurrent administration of these agents with ciprofloxacin.) Histamine H 2 -receptor antagonists appear to have no significant effect on the bioavailability of ciprofloxacin. Altered serum levels of phenytoin (increased and decreased) have been reported in patients receiving concomitant ciprofloxacin. The concomitant administration of ciprofloxacin with the sulfonylurea glyburide has, on rare occasions, resulted in severe hypoglycemia. Some quinolones, including ciprofloxacin, have been associated with transient elevations in serum creatinine in patients receiving cyclosporine concomitantly. Quinolones, including ciprofloxacin, have been reported to enhance the effects of the oral anticoagulant warfarin or its derivatives. When these products are administered concomitantly, prothrombin time or other suitable coagulation tests should be closely monitored. Probenecid interferes with renal tubular secretion of ciprofloxacin and produces an increase in the level of ciprofloxacin in the serum. This should be considered if patients are receiving both drugs concomitantly. Renal tubular transport of methotrexate may be inhibited by concomitant administration of ciprofloxacin potentially leading to increased plasma levels of methotrexate. This might increase the risk of methotrexate associated toxic reactions. Therefore, patients under methotrexate therapy should be carefully monitored when concomitant ciprofloxacin therapy is indicated. Metoclopramide significantly accelerates the absorption of oral ciprofloxacin resulting in shorter time to reach maximum plasma concentrations. No significant effect was observed on the bioavailability of ciprofloxacin. Non-steroidal anti-inflammatory drugs (but not acetyl salicylic acid) in combination of very high doses of quinolones have been shown to provoke convulsions in pre-clinical studies.