Pharmacokinetics of disodium-fosfomycin in mongrel dogs

Pharmacokinetics/pharmacodynamics cut-off determination for fosfomycin using Monte Carlo simulation in healthy horses

Fosfomycin (FOM) is an approved veterinary medicinal product for large animals in Japan, but Clinical breakpoint (CBP) for antimicrobial susceptibility test (AST) is not defined for animals. This study aimed at conducting a pharmacokinetics/pharmacodynamics (PK/PD) analysis to determine the PK/PD cutoff for the CBP in horses. Drug concentrations following single intravenous administration (IV) of 20 mg/kg body weight (BW) FOM in nine horses were measured using liquid chromatography/mass spectrometry. The data were modelled using a nonlinear mixed-effects model, followed by Monte Carlo simulations. A 90% probability of target attainment for a PK/PD target of the ratio of Area Under the free plasma concentration-time curve divided by the minimal inhibitory concentration (MIC) >24 hr was set as PK/PD cut-off. The PK/PD cutoff for FOM 20 mg/kg BW q12 hr IV was estimated with the MIC value of ≤16.0 mg/L, and this regimen was considered effective against E. coli (MIC90; 16.0 mg/L) in healthy horses based on the MIC90 values of the wild population. Owing to the relevance of FOM to human health, veterinarians should use q 12 hr FOM 20 mg /kg against E. coli infections with an MIC <16 µg/mL, as suggested by our PK/PD cutoff after AST.

Plasma and Urine Pharmacokinetics of Oral Fosfomycin Tromethamine in Dogs

Fosfomycin is a broad-spectrum, bactericidal antibiotic with low toxicity. It has been used in human medicine and is a promising candidate for treating infections in veterinary medicine. Different Fosfomycin salts exhibit various degrees of bioavailability. Tromethamine salt is the most commonly used oral form due to its improved bioavailability. However, information regarding its use with dogs is limited. Therefore, this study aimed to investigate the pharmacokinetics of oral Fosfomycin tromethamine in canine plasma and urine using liquid chromatography tandem mass spectrometry (LC-MS/MS). Six healthy male beagles underwent a three-period three-treatment study: treatment 1 and 2 with single oral Fosfomycin tromethamine at 40 and 80 mg/kg (the total doses with tromethamine salt were 75 and 150 mg/kg, respectively), and treatment 3 with intravenously Fosfomycin disodium at 57 mg/kg (the total dose with disodium salt was 75 mg/kg). Dogs receiving oral Fosfomycin tromethamine at 75 and 150 mg/kg, maximal drug concentration (Cmax) in plasma produced results of 34.46 ± 12.52 and 66.40 ± 12.64 µg/mL, oral bioavailability (F) was approximately 38 and 45%, while urine Cmax was 4463.07 ± 2208.88 and 8784.93 ± 2303.46 µg/mL, respectively. No serious adverse effects were reported, except loose stool in some dogs. The tremendously high urine Fosfomycin concentrations indicate that oral Fosfomycin tromethamine is suitable as an alternative treatment for bacterial cystitis in dogs.

Fosfomycin Resistance in Bacteria Isolated from Companion Animals (Dogs and Cats)

Fosfomycin is an old antibacterial agent, which is currently used mainly in human medicine, in uncomplicated Urinary Tract Infections (UTIs). The purpose of this review is to investigate the presence and the characteristics of Fosfomycin resistance in bacteria isolated from canine or feline samples, estimate the possible causes of the dissemination of associated strains in pets, and underline the requirements of prospective relevant studies. Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines were used for the search of current literature in two databases. A total of 33 articles were finally included in the review. Relevant data were tracked down, assembled, and compared. Referring to the geographical distribution, Northeast Asia was the main area of origin of the studies. E. coli was the predominant species detected, followed by other Enterobacteriaceae, Staphylococci, and Pseudomonas spp. FosA and fosA3 were the more frequently encountered Antimicrobial Resistance Genes (ARGs) in the related Gram-negative isolates, while fosB was regularly encountered in Gram-positive ones. The majority of the strains were multidrug-resistant (MDR) and co-carried resistance genes against several classes of antibiotics and especially β-Lactams, such as bla_CTX-M and mecA. These results demonstrate the fact that the cause of the spreading of Fosfomycin-resistant bacteria among pets could be the extended use of other antibacterial agents, that promote the prevalence of MDR, epidemic strains among an animal population. Through the circulation of these strains into a community, a public health issue could arise. Further research is essential though, for the comprehensive consideration of the issue, as the current data are limited.

Urinary Pharmacokinetic and Pharmacodynamic Profiles of Fosfomycin against Extended-Spectrum β-Lactamase-Producing Escherichia coli with Canine Ex Vivo Modeling: A Pilot Study

Fosfomycin is a candidate drug for extended-spectrum β-lactamase (ESBL)-producing bacteria, but its efficacy is yet to be investigated in dogs. This study investigated the urinary pharmacokinetic/pharmacodynamic (PK/PD) profile of fosfomycin orally administered at 80 mg/kg to six healthy dogs to assess its efficacy for canine urinary tract infections (UTIs) caused by ESBL-producing bacteria. Four strains of ESBL-producing Escherichia coli (ESBL-EC) characterized by fosfomycin minimum inhibitory concentrations (MICs) of 0.5, 1, 2, and 32 µg/mL were used. Urine samples for the measurement of urinary drug concentrations and urinary bactericidal titers (UBTs) were obtained after drug administration. The urinary concentrations (µg/mL, mean ± SE) were 1348.2 ± 163.5, 1191.6 ± 260.2, and 661.1 ± 190.4 at 0-4, 4-8, and 8-12 h, respectively, after drug administration. The mean urinary area under the curve during the test period (AUC0-12) of fosfomycin was estimated to be 12,803.8 µg·h/mL. The UBTs for all tested strains fluctuated closely with urine concentration during the test period (r = 0.944-1.000), and the area under the UBT-versus-time curve correlated with the urinary AUC/MIC of each strain (r = 0.991). According to the optimal urinary PK/PD target value, fosfomycin at 80 mg/kg twice daily may be suitable for the treatment of canine UTIs caused by ESBL-EC presenting MIC ≤ 128 µg/mL.

Pharmacokinetics and Pharmacodynamics of Fosfomycin and Its Activity against Extended-Spectrum-β-Lactamase-, Plasmid-Mediated AmpC-, and Carbapenemase-Producing Escherichia coli in a Murine Urinary Tract Infection Model

Fosfomycin has become an attractive treatment alternative for urinary tract infections (UTIs) due to increasing multidrug resistance (MDR) in Escherichia coli. In this study, we evaluated the pharmacokinetic (PK) and pharmacodynamic (PD) indices of fosfomycin and its in vivo activity in an experimental murine model of ascending UTI. Subcutaneous administration of fosfomycin showed that the mean peak plasma concentrations of fosfomycin were 36, 280, and 750 mg/liter following administration of a single dose of 0.75, 7.5, and 30 mg/mouse, respectively, with an elimination half-life of 28 min, and urine peak concentrations of 1,100, 33,400, and 70,000 mg/liter expected to be sustained above 1 mg/liter (MIC of the test strain, NU14) for 5, 8, and 9.5 h, respectively. The optimal PK/PD indices for reducing urine colony counts (number of CFU per milliliter) were determined to be the area under the concentration-time curve/MIC from 0 to 72 h and the maximum concentration/MIC on the basis of the dose-dependent bloodstream PK and the results of an evaluation of six dosing regimens. With a dosing regimen of 15 mg/mouse twice (every 36 h), fosfomycin significantly reduced the number of CFU per milliliter of all susceptible strains in urine, including clinical MDR strains, except for one clinical strain (P = 0.062). Variable degrees of reduction were observed in the bladder and kidneys. No significant reductions in the number of CFU per milliliter were observed with the resistant strains. In conclusion, fosfomycin shows concentration-dependent in vivo activity, and the results suggest that fosfomycin is an effective alternative to carbapenems in treating MDR E. coli in uncomplicated UTIs. The data on the effectiveness of fosfomycin against the MDR isolates along with the results of PK/PD modeling should facilitate the further development of improved recommendations for its clinical use.

Fosfomycin residues in colostrum: Impact on morpho-physiology and microbiology of suckling piglets

Fosfomycin is a broad-spectrum bactericidal antibiotic widely used in pig farms for the treatment of a wide variety of bacterial infections. In this study, the elimination of disodium fosfomycin in colostrum/milk of the sow and the impact of this antibiotic on the microbiota and intestinal morpho-physiology of suckling piglets were analyzed. The average amount of fosfomycin eliminated in colostrum (after administration of 15 mg/kg IM) during the first 10 hr postpartum was 0.85 μg/ml, and the mean residual amount ingested by the piglets was 0.26 mg/kg. The elimination profile of fosfomycin concentrations in colostrum occurs at a time of profound changes in the morpho-physiology of the gastrointestinal tract of the piglet. However, the studied concentrations did not produce imbalances on the microbiota or on the morpho-physiology of the gastrointestinal tract of the piglet. Concentrations of fosfomycin were maintained in the mammary gland above the MIC for more than 8 hr for pathogenic bacteria of productive importance. This would indicate that fosfomycin may be considered safe for the specific treatment of bacterial infectious processes in sows during the peri- and postpartum period. This first study with disodium fosfomycin stimulates awareness in the proper use of antimicrobials at farrowing.

Fosfomycin susceptibility of canine methicillin-resistant Staphylococcus pseudintermedius isolates

The effectiveness of fosfomycin was examined across 31 methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains by agar dilution. Prevalence of the fosfomycin-resistance determinant gene, fosB, was assessed by PCR analysis. Results found that 84% of isolates were fosfomycin-susceptible. Interestingly, 87% of isolates possessed fosB, indicating no association between this putative staphylococci resistance gene and phenotypic resistance. Further evaluation of fosfomycin as a potential treatment of MRSP in dogs is warranted.

Penetration of fosfomycin into IPEC-J2 cells in the presence or absence of deoxynivalenol

Fosfomycin (FOS) is an antibiotic used in pig farms for treatment and prevention of infections caused by resistant bacteria during the post-weaning period. Antibiotics and non-toxic concentrations of mycotoxins, such as deoxynivalenol (DON) are frequently found in the diet of animals. These compounds can establish interactions in the intestinal tract, which could affect and/or modify the penetration of FOS to enterocytes. The aim of this study was to determine the penetration of FOS into IPECJ-2 cells, a cell line derived from the small intestine of piglets, in the presence and absence of DON. The results from this study showed that there was statistically significant difference in the intracellular concentration of FOS between cells incubated with 580 µg/ml FOS and cells incubated with 580 µg/ml FOS and 1 µg/ml DON. The Cmax of the intracellular antibiotic in the culture plates incubated with FOS in absence of DON was 45.81 µg/ml with a tmax of 4 h. When IPEC-2 cells were incubated with FOS and DON the Cmax was 20.06 µg/ml and the tmax was 30 min. It is concluded that the non-toxic concentration of DON on IPEC-J2 cells after short-term exposure, interferes with the pharmacokinetics of the antibiotic.

Correlation between in silico physicochemical characteristics of drugs and their mean residence time in human and dog

The correlation between 52 physicochemical parameters and mean residence time (MRT) for 27 drugs used in human and dog were investigated. The physicochemical parameter values calculated provided a basis for deriving a series of arithmetic expressions, which were used to build a mathematical model describing the relationship between them and the MRT values. From the entire set of analyzed parameters, a subset of 14 was identified that contributed to the derivation of an arithmetic expression: Log(PSA - WPSA + ACID) x [XlogP - (LogKp - EAxLn(Caco2 + AMINE + SAF))] + (AMIDE + IP - FG) - Ln(MW + PISA) the value of which is highly correlated with the MRT value in dogs (P < .001) and allowed prediction of the MRT predicted (MRT(pred)). In humans, no correlation was found that allowed the calculation of MRT(pred). These results indicate that predicting the pharmacokinetics of any specific drug for humans based on pharmacokinetic data obtained in the dog should be undertaken with knowledge of the inherent limitations.

Disodium-fosfomycin pharmacokinetics and bioavailability in post weaning piglets

Disodium-fosfomycin pharmacokinetics has been studied in different species after oral, intravenous, intramuscular and subcutaneous administration. At present there are neither documented clinical experiences of the use of fosfomycin in pigs nor any published studies in weaning piglets, although it is a period of high incidence of infectious diseases. The pharmacokinetics and the bioavailability of sodium fosfomycin were studied in post weaning piglets after intravenous and intramuscular administration of 15 mg/kg of body weight. Plasma concentrations were measured by a high-performance liquid ms/ms. After IV administration the area under the fosfomycin concentration:time curve in plasma was AUC(0-12) of 120.00 ± 23.12 μg h/ml and the volume of distribution (Vd) of 273.00 ± 40.70 ml/kg. The elimination was rapid with a plasma clearance of 131.50 ± 30.07 ml/kg/h and a T(1/2) of 1.54 ± 0.40 h. Peak serum concentration (Cmax), Tmax, AUC(0-12) and bioavailability for the IM administration were 43.00 ± 4.10 μg/ml, 0.75 ± 0.00 h, 99.00 ± 0.70 μg h/ml and 85.5 ± 9.90% respectively. Different authors have determined a minimum inhibitory concentration (MIC90) ranging from 0.25 μg/ml for Streptococcus sp. and 0.5 μg/ml for Escherichia coli. Considering the above, and according to the values of plasma concentration vs time profiles observed in this study, effective plasma concentrations of fosfomycin for sensitive bacteria can be obtained following IV and IM administration of 15 mg/kg in piglets.

Fosfomycin: an old, new friend?

Fosfomycin (FOM) is an antibiotic which has varying application indications across the globe. European, Japanese, South African and Brazilian usage practices are much broader, involving multiple formulations of FOM than the currently limited application of FOM in the United States, where uncomplicated urinary tract infection represents the only indication for FOM-tromethamine. Based on early difficulty in determining FOMs genuine in vitro activity, there was initial skepticism about its efficacy and application range. However, in the mid 1970s, correctly executed experiments coupled with an improved understanding of microbiological concepts opened the door for broader use of FOM. During the following 40 years FOM was evaluated in pre-clinical and clinical trials in a wide range of applications and in a multitude of settings. The gathering of pharmacokinetic and pharmacodynamic data was incorporated into large scale studies in which FOM efficacy was further explored and proven. Among European nations, intravenous FOM-disodium for patients presenting with soft tissue infections, sepsis or deep seated infectious processes has become well accepted over the last two decades. The recent emergence of bacterial strains, which impede and encumber pharmacotherapy, namely, MRSA, ESBL and MSSA, lends itself to the idea of reviving long-standing, sensibly used antimicrobial agents like FOM. This review provides a comprehensive conspectus on FOM's history, mode of action, tissue penetration characteristics, resistance, antibacterial activity, combination partners and clinical uses among other facets of interest.