Ciprofloxacin

Summary

Synopsis

Ciprofloxacin belongs to the fluoroquinolone class of antimicrobial agents which primarily inhibit bacterial DNA gyrase. It is effective after oral or intravenous administration, demonstrating potent antibacterial activity against most Gram-negative, and many Gram-positive bacteria. Although most bacterial strains have remained susceptible to the drug, low rates of resistance have been observed in some strains of Pseudomonas aeruginosa and enterococci and higher rates in methicillin-resistant Staphylococcus aureus

Ciprofloxacin attains concentrations in most tissues and body fluids sufficient to inhibit the majority of susceptible pathogens. Its pharmacokinetic profile in the elderly (≥65 years) is broadly similar to that reported in younger persons, although plasma concentrations are higher, and renal clearance is decreased in elderly persons.

Ciprofloxacin is an effective treatment for those infections most common in elderly patients, including infections of the urinary tract, lower respiratory tract, skin and soft-tissues, and bone and joints, and is an effective agent for prophylaxis in transurethral surgery. Orally administered ciprofloxacin appeared to be at least as effective as alternative orally administered antimicrobial agents (trimethoprim, cotrimoxazole [trimethoprim/sulfamethoxazole), amoxicillin, amoxicillin/ clavulanic acid) and also as effective as various parenteral agents (ceftriaxone, cefamandole, ceftazidime, cefotaxime) in a small number of comparative clinical trials. However, further studies are needed to clarify the comparative efficacy of ciprofloxacin with that of other oral and parenteral agents in the elderly. Initial trials have also indicated therapeutic efficacy of oral ciprofloxacin in malignant external otitis and bacterial prostatitis.

Nevertheless, with its good tolerability profile and potent antimicrobial activity following oral administration, ciprofloxacin appears to offer a valuable alternative for treating various acute and chronic infections in elderly patients. Causative pathogens are frequently multiresistant in this patient group, and ciprofloxacin avoids or minimises the needfor parenteral therapy.

Pharmacodynamic Properties

Ciprofloxacin has demonstrated potent antibacterial activity against a wide range of bacterial species. Its primary mechanism of action involves inhibition of bacterial DNA gyrase, although other mechanisms, including interference with bacterial virulence factors, also appear to be involved. Considering the main causative pathogens found in elderly patients: ciprofloxacin has a mean concentration inhibitory to 90% of tested strains (MIC₉₀) of ≤ 1 mg/L (indicating susceptibility) against Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Haemophilus influenzae, Klebsiella pneumoniae, Moraxella (Branhamella) catarrhalis and Proteus mirabilis. Most strains of Providencia stuartii, Serratia marcescens and Pseudomonas aeruginosa are susceptible or moderately susceptible to the drug (mean MIC₉₀ ≥ 2 mg/L). Ciprofloxacin is inhibitory against most strains of methicillin-sensitive Staphylococcus aureus (MIC₉₀ 0.25 to 1.0 mg/L); however, methicillin-resistant strains are generally resistant to the drug (mean MIC₉₀ > 2.57 mg/L). Most strains of Streptococcus pneumoniae and Enterococcus faecalis are susceptible or moderately susceptible (mean MIC₉₀ ≤ 2 mg/L), whereas the majority of anaerobic bacteria are resistant to ciprofloxacin.

Bacterial strains resistant to nonquinolone antibacterial drugs generally remain susceptible to ciprofloxacin but cross-resistance between ciprofloxacin and other quinolones does occur. Although plasmid-mediated resistance to quinolones has not been found, chromosomal mutation affecting DNA gyrase and/or the cell membrane can confer resistance. Ciprofloxacin has retained a high level of activity against most bacterial species; however, rates of resistance to quinolones are increasing in P. aeruginosa, S. aureus, coagulase-negative staphylococci and enterococci, and are highest in methicillin-resistant S. aureus (10 to 83%), which has developed uniform resistance most fluoroquinolones.

Pharmacokinetic Properties

Peak serum ciprofloxacin concentrations (C_max) are reached in approximately 1 to 2 hours following oral administration and increase in proportion to the dose administered. In elderly individuals, C_max and the area under the serum concentration-time curve (AUC) were between 1.5 and 1.7 mg/L, and 6.4 and 7.4 mg/L · h, respectively, following a single 250mg oral dose, and ranged from 3.5 to 5 mg/L and from 8.2 to 13.3 mg/L·h, respectively, after intravenous administration of ciprofloxacin 200 or 250mg. C_max and AUC values were increased following oral administration of ciprofloxacin 500 or 750mg twice daily for 5 or 14 days. The absolute bioavailability of ciprofloxacin was between 72 and 79% in the elderly, and the apparent volume of distribution was estimated to be between 1.6 and 1.9 L/kg. The absolute bioavailability of ciprofloxacin was generally increased in elderly vs young individuals following oral administration

Therapeutic concentrations of ciprofloxacin have been reported in lung tissue, bronchial mucosa, sputum and pleural exudate, liver tissue, gallbladder tissue, pancreatic fluid, bile, gynaecological tissue, prostatic tissue and fluid, synovial tissue and fluid, bone, peritoneal or ascitic fluid and the anterior chamber and aqueous humour of the eye. The highest concentrations of the drug are found in bile, liver tissue, kidney tissue, gallbladder and prostatic fluid.

Ciprofloxacin is excreted by renal, as well as extrarenal routes. Small amounts of 4 metabolites, all of which have less antibacterial activity than ciprofloxacin, are present in urine and faeces. In elderly individuals, approximately 38% of a single oral 250mg ciprofloxacin dose and 52% of a single 250mg intravenous dose were recovered in urine over 24 hours. Total serum clearance rates ranged from 0.26 to 0.42 L/kg/h and renal clearance ranged from 0.13 to 0.2 L/kg/h, independent of dose. Total serum and renal clearance rates were lower in elderly than in younger people.

The elimination half-life of ciprofloxacin ranged from 3.3 to 6.8 hours in elderly vs 3 to 4 hours in younger persons.

Therapeutic Use

The clinical and bacteriological efficacy of ciprofloxacin has been investigated in the treatment of elderly patients with infections of the urinary tract (UTI), respiratory tract, skin and soft-tissues, and bone and joints, and also in patients with malignant external otitis

Bacteria were eradicated from 84 to 94% of patients with acute uncomplicated or complicated urinary tract infections following oral administration of ciprofloxacin 250, 500 or 750mg twice daily for 5 to 7 days, with complete resolution of signs and symptoms of infection in 88 to 90% of patients. In comparative studies, ciprofloxacin 100mg twice daily was at least as effective as cotrimoxazole 160/800mg or trimethoprim 200mg twice daily in eradicating pathogens from patients with acute uncomplicated UTI or bacteriuria.

Preoperative administration of a single oral dose of ciprofloxacin 500mg significantly reduced the incidence of postoperative UTI compared with placebo, and a 300mg intravenous dose was as effective as intravenous cefotaxime 1000mg in patients undergoing transurethral resection.

In patients with lower respiratory tract infections, clinical and bacteriological response rates ranged from 50 to 100% and from 66 to 93%, respectively, following treatment with ciprofloxacin 250 to 750mg orally or 200mg intravenously twice daily for 5 to 14 days. In comparative studies, the efficacy of oral ciprofloxacin 1000 mg/day was similar to that of oral amoxicillin 750 mg/day or amoxicillin/clavulanic acid 3000/750 mg/day. An oral dosage of 1500 mg/day was comparable to intramuscular cefamandole 4000 mg/day, or intramuscular ceftriaxone 1000 mg/day when given to patients who had received initial intravenous therapy during the acute phase of treatment. Ciprofloxacin should be used with caution in patients with pneumococcal pneumonia and is not recommended for use as first-line monotherapy against this infection, due to the moderate susceptibility of S. pneumoniae to the drug.

Oral ciprofloxacin 7S0mg twice daily for 5 to 10 days was at least as effective as intravenous cefotaxime 2000mg 3 times daily in patients with skin and soft-tissue infections. Bacteriological eradication was achieved at 88 vs 69% of sites and clinical response at 96 vs 94% of sites following ciprofloxacin and cefotaxime treatment, respectively. Clinical responses were observed in 76 to 89% of patients with chronic osteomyelitis 6 months to 1 year after treatment with ciprofloxacin 500 or 750mg twice daily for at least 60 days in small noncomparative clinical trials.

Ciprofloxacin 750mg twice daily was found to be effective in the treatment of malignant external otitis, inducing clinical responses and bacteriological eradication in 91 to 100% of patients. Clinical responses were achieved in 58 to 78% of patients with chronic bacterial prostatitis following ciprofloxacin 500mg twice daily in preliminary noncomparative studies. The efficacy of ciprofloxacin in the management of nosocomial gastrointestinal infections remains unclear.

Tolerability

The tolerability profile of ciprofloxacin in the elderly appears similar to that in younger patients. Adverse events are usually mild or moderate in intensity and rarely necessitate treatment withdrawal. Gastrointestinal symptoms (mainly nausea, vomiting and diarrhoea) are the most common events, occurring in about 5% of patients, followed by central nervous system events (headache, dizziness, anxiety and insomnia) in about 1.5% and skin reactions (in about 1.1%). Laboratory abnormalities include elevations in serum creatinine, liver enzymes and blood urea nitrogen levels, which are usually asymptomatic. Reports of serious or severe adverse events, including seizures, acute renal failure, interstitial nephritis, allergic reactions, palpitations and cardiac failure, have been rare

Concurrent administration of ciprofloxacin with theophylline inhibits theophylline metabolism, leading to increased plasma theophylline concentrations, and possibly theophylline toxicity.

Dosage and Administration

Ciprofloxacin is usually administered orally in a twice daily regimen for 7 to 14 days or until at least 2 days after signs and symptoms of infection have resolved

The recommended oral dosage is 250mg twice daily for mild to moderate, and 500mg twice daily for severe or complicated, urinary tract infections. Mild to moderate respiratory tract or skin and soft-tissue infections require a dosage of 500mg twice daily, while a dosage of 750mg twice daily is recommended for severe or complicated infections.

An intravenous dosage of 200 to 400mg twice daily is recommended for mild to moderate infections, and up to 400mg every 8 hours for severe life-threatening infections.

A 50% reduction in total daily dosage is recommended in patients with severe renal impairment (creatinine clearance ≤ 1.2 L/h).

As with other fluoroquinolones, the absorption of ciprofloxacin is significantly impaired by concurrent administration of antacids containing magnesium, aluminium, or calcium, sucralfate and preparations containing calcium, iron and zinc, which can result in subtherapeutic serum and urine concentrations of ciprofloxacin.