[Fosfomycin trometamol: multiple-dose regimen for the treatment of lower urinary tract infections]

Fosfomycin as a potential therapy for the treatment of systemic infections: a population pharmacokinetic model to simulate multiple dosing regimens

Fosfomycin has emerged as a potential therapy for multidrug-resistant bacterial infections. In most European countries, the oral formulation is only approved as a 3 g single dose for treatment of uncomplicated cystitis. However, for the treatment of complicated systemic infections, this dose regimen is unlikely to reach efficacious serum and tissue concentrations. This study aims to investigate different fosfomycin-dosing regimens to evaluate its rationale for treatment of systemic infections. Serum concentration-time profiles of fosfomycin were simulated using a population pharmacokinetic model based on published pharmacokinetic parameter values, their uncertainty, inter-individual variability and covariates. The model was validated on published data and used to simulate a wide range of dosing regimens for oral and intravenous administration of fosfomycin. Finally, based on the minimum inhibitory concentration for E. coli, surrogate pharmacodynamic indices were calculated for each dosing regimen. This is the first population pharmacokinetic model to describe the oral pharmacokinetics of fosfomycin using data from different literature sources. The model and surrogate pharmacodynamic indices provide quantitative evidence that a dosing regimen of 6-12 g per day divided in 3 doses is required to obtain efficacious exposure and may serve as a first step in the treatment of systemic multi-drug-resistant bacterial infections.

Fosfomycin: Pharmacological, Clinical and Future Perspectives

Fosfomycin is a bactericidal, low-molecular weight, broad-spectrum antibiotic, with putative activity against several bacteria, including multidrug-resistant Gram-negative bacteria, by irreversibly inhibiting an early stage in cell wall synthesis. Evidence suggests that fosfomycin has a synergistic effect when used in combination with other antimicrobial agents that act via a different mechanism of action, thereby allowing for reduced dosages and lower toxicity. Fosfomycin does not bind to plasma proteins and is cleared via the kidneys. Due to its extensive tissue penetration, fosfomycin may be indicated for infections of the CNS, soft tissues, bone, lungs, and abscesses. The oral bioavailability of fosfomycin tromethamine is <50%; therefore, oral administration of fosfomycin tromethamine is approved only as a 3-gram one-time dose for treating urinary tract infections. However, based on published PK parameters, PK/PD simulations have been performed for several multiple-dose regimens, which might lead to the future use of fosfomycin for treating complicated infections with multidrug-resistant bacteria. Because essential pharmacological information and knowledge regarding mechanisms of resistance are currently limited and/or controversial, further studies are urgently needed, and fosfomycin monotherapy should be avoided.

[Randomized comparative study for the assessment of a new therapeutic schedule of fosfomycin trometamol in postmenopausal women with uncomplicated lower urinary tract infection]

OBJECTIVES

To compare two therapeutic regimes in terms of bacterial eradication of post-menopausal with uncomplicated acute cystitis who complete antibiotic treatment.

MATERIALS AND METHOD

A multicenter, randomized, prospective and controlled study between two short antibiotic regimes: fosfomycin trometamol (FMT) 3g, 2 doses separated by 72hours and ciprofloxacin 250mg every 12hours for 3 days. A total of 118 post-menopausal women were enrolled in the study. They underwent an initial urine culture to know the responsible microorganism and susceptibility to treatment. This was repeated 5-7 days and 4 weeks after the treatment to evaluate bacterial eradication. Clinical symptoms and treatment safety were also evaluated.

RESULTS

There were microbiological data at the onset of the treatment in 82 women (69.49%). Of these, 27 did not have positive culture at the first visit (30.51%), 76 (64.41%) fulfilled all the protocol requirements and adverse effects from the treatment were collected in 113 (95.76%) of the patients enrolled in the study. The germs isolated most frequently were Escherichia coli (E. coli) (76.83%), Klebsiella pneumoniae (K. pneumoniae) (7.32%), Proteus mirabilis (P. mirabilis) (4.89%) and Enterococo sp. (3.66%). In terms of efficacy, no differences were detected in the proportion of patients who achieved bacterial eradication between the two study arms: 62.16% of the patients who received FMT and 58.97% of those treated with ciprofloxacin (chi-square, p=0.78). The proportion of patients who achieved clinical cure was also similar (86.49% for FMT and 82.05% for ciprofloxacin; square, p=0.59). These results indicate similar efficacy of both antibiotics in the treatment of uncomplicated lower tract urinary infection in post-menopausal women. In regards to safety data, the proportion of global adverse effects associated to the treatments was 3.45% for FMT and 9.09% for ciprofloxacin. Treatment compliance was 100% for FMT and 83.64% for ciprofloxacin.

CONCLUSIONS

The FMT administered at a dose of 3g every 72hours (2 total doses) and ciprofloxacin at a dose of 250mg every 12hours during 3 days (6 total doses) have a comparable efficacy profile in lower tract urinary infection in post-menopausal women who adequately comply with the treatment, also having comparable safety. The FMT has a better antimicrobial susceptibility profile and better rate of treatment compliance.