Phosphonomycin Calcium salt

Here we present the results obtained in the treatment with fosfomycin of 58 patients of diverse obstetric-gynecological infections manifested by clinical symptomology and by the initial isolation of 70 strains of different germs, all of them sensitive to this antibiotic. The types of infections were urinary, abdominal wall, perennial septicemias, and endometritis; 45 of them motivated by or resulting from pregnancy, and the remaining 13 from gynecological causes. The most frequent treatment was 1 g/6h during 10 days, using sodium salt intramuscularly in 33 cases, and calcium salt taken orally in 26. The clinical results were good in 50 cases (86.2%) with improvement in 3 (5.1%) and persistency of the infection in 5. The bacteriological evolution was good on 34 occasions (58.6%), partial in 4 (6.8%), and poor in 6 (10.3%). In 14 cases no control could be made since the wound healed. The tolerance to the antibiotic was good and no manifestations of toxicity were observed.

The pharmacokinetic comparison of phosphonic acid derivatives is based upon a survey of available literature on the whole group of compounds and on our own studies on fosfomycin. All three clinically used compounds, fosfomycin, fosmidomycin, and alafosfalin, are available for both oral and parenteral administration. The highest bioavailability is observed for the trometamol derivative of fosfomycin (37-44%); the calcium salt of fosfomycin is 2-2.5 times less absorbed and fosmidomycin has a bioavailability of 20-30%. The peak serum concentration of fosfomycin when given as the trometamol salt is about 2 times higher than the one reached with fosfomycin calcium or fosmidomycin. Urine recovery of unchanged drug is comparable after intravenous doses of fosfomycin and fosmidomycin, 80-95%, whereas the figure is only 10-20% for alafosfalin because it is extensively metabolized. After oral administration, urine recovery is highest for fosfomycin trometamol, 35-60%, compared to approximately 25% (range 18-29%) for fosfomycin calcium, 26% for fosmidomycin, and 6-17% for alafosfalin.

Single-dose therapy of uncomplicated urinary tract infection (UTI) has been shown to be effective in many trials in adult women. The question which will be explored in this presentation is what properties constitute the ideal agent for the therapy of UTI. Important microbiological properties include spectrum of activity to include all common urinary pathogens, bactericidal action in urine and low prevalence of resistant bacteria. The vital feature of an antibacterial drug useful in the therapy of UTI is prolonged urinary concentrations. The agent must therefore be well absorbed and have slow renal excretion. Most beta-lactam drugs do not have these combined properties. Aminoglycosides are effective drugs but cannot be administered orally. Quinolones and the calcium salt of fosfomycin are useful but do not have an ideal pharmacokinetic profile. Cotrimoxazole, trimethoprim alone and the trometamol salt of fosfomycin all have good antibacterial activity combined with slow urinary excretion.

An efficient method for gas chromatographic analysis of fosfomycin in plasma was developed for preliminary investigations of the bioavailability in poultry of 3 commercial complexes of fosfomycin: a levorotatory Ca(-) salt, a racemic Ca(+/-) salt, and a tromethamine (THAM) salt. The method was used to determine whether the less expensive racemic mixture would provide equivalent levels of fosfomycin in blood as the pure Ca(-) form and the THAM salt. The THAM salt, a more expensive product to market, was thought to have the greatest bioavailability. The assay is selective, sensitive, and applicable to pharmacokinetic analysis.