• Belén Sádaba-Díaz de Rada, José Ramón Azanza-Perea, Emilio García-Quetglas, and Jesús Honorato-Pérez.
• Servicio de Farmacología Clínica, Clínica Universitaria de Navarra. España. bsadada@unav.es
• Enferm. Infecc. Microbiol. Clin. 2006 Nov 1; 24 (9): 546-50.

IntroductionA short antibiotic regimen is recommended for the treatment of uncomplicated lower urinary tract infection. Nevertheless, the treatment to follow in other situations is not so clearly defined. When the person affected by lower urinary tract infection is not a young woman, it is recommended to treat at least 7 days, and quinolones or cotrimoxazole are the antibiotics most often used. However, because of the frequency of drug resistance in this type if infection, it is advisable to apply antibiotics with lower rates of resistance, such as fosfomycin trometamol, for longer treatment periods than the often-used single dose.MethodsUsing the data on urinary elimination of fosfomycin after a single dose obtained in a prior study in healthy volunteers, we simulated the urinary concentrations of this antibiotic following administration of two doses. In addition, we calculated the interval of administration required to achieve urinary concentrations greater than 16 mg/L, the critical concentration of sensitivity for Escherichia coli, one of the most commonly implicated microorganisms in these infections.ResultsFosfomycin concentrations in urine persisted above the defined cut-off for 161 hours after administration of two 3-g doses of fosfomycin trometamol, 72 hours apart. This implied an efficacy time of 66% in a period of 7 days.ConclusionFrom the pharmacokinetic viewpoint, the optimum dosage of fosfomycin trometamol to achieve appropriate urinary concentrations along 7 days is administration of two 3-g doses, 72 hours apart.

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