Fosfomycin for Injection (ZTI-01) Versus Piperacillin-tazobactam for the Treatment of Complicated Urinary Tract Infection Including Acute Pyelonephritis: ZEUS, A Phase 2/3 Randomized Trial

Background

ZTI-01 (fosfomycin for injection) is an epoxide antibiotic with a differentiated mechanism of action (MOA) inhibiting an early step in bacterial cell wall synthesis. ZTI-01 has broad in vitro spectrum of activity, including multidrug-resistant Gram-negative pathogens, and is being developed for treatment of complicated urinary tract infection (cUTI) and acute pyelonephritis (AP) in the United States.

Methods

Hospitalized adults with suspected or microbiologically confirmed cUTI/AP were randomized 1:1 to 6 g ZTI-01 q8h or 4.5 g intravenous (IV) piperacillin-tazobactam (PIP-TAZ) q8h for a fixed 7-day course (no oral switch); patients with concomitant bacteremia could receive up to 14 days.

Results

Of 465 randomized patients, 233 and 231 were treated with ZTI-01 and PIP-TAZ, respectively. In the microbiologic modified intent-to-treat (m-MITT) population, ZTI-01 met the primary objective of noninferiority compared with PIP-TAZ with overall success rates of 64.7% (119/184 patients) vs 54.5% (97/178 patients), respectively; treatment difference was 10.2% (95% confidence interval [CI]: −0.4, 20.8). Clinical cure rates at test of cure (TOC, day 19–21) were high and similar between treatments (90.8% [167/184] vs 91.6% [163/178], respectively). In post hoc analysis using unique pathogens typed by pulsed-field gel electrophoresis, overall success rates at TOC in m-MITT were 69.0% (127/184) for ZTI-01 versus 57.3% (102/178) for PIP-TAZ (difference 11.7% 95% CI: 1.3, 22.1). ZTI-01 was well tolerated. Most treatment-emergent adverse events, including hypokalemia and elevated serum aminotransferases, were mild and transient.

Conclusions

ZTI-01 was effective for treatment of cUTI including AP and offers a new IV therapeutic option with a differentiated MOA for patients with serious Gram-negative infections.

Clinical Trial Registration

NCT02753946

Parenteral Fosfomycin for the Treatment of Multidrug Resistant Bacterial Infections: The Rise of the Epoxide

Fosfomycin was initially discovered in 1969 but has recently gained renewed interest for the treatment of multidrug-resistant (MDR) bacterial infections, particularly in the United States. Its unique mechanism of action, bactericidal activity, broad spectrum of activity, and relatively safe and tolerable adverse effect profile make it a great addition to the dwindling antibiotic armamentarium. Fosfomycin contains a three-membered epoxide ring with a direct carbon to phosphorous bond that bypasses the intermediate oxygen bond commonly present in other organophosphorous compounds; this structure makes the agent unique from other antibiotics. Despite nearly 50 years of parenteral fosfomycin use in Europe, fosfomycin has retained stable activity against most pathogens. Furthermore, fosfomycin demonstrated in vitro synergy in combination with other cell wall-active antibiotics (e.g., β-lactams, daptomycin). These combinations may offer respite for severe infections due to MDR gram-positive and gram-negative bacteria. The intravenous (IV) formulation is currently under review in the United States, and apropos, this review collates more contemporary evidence (i.e., studies published between 2000 and early 2019) in anticipation of this development. The approval of IV fosfomycin provides another option for consideration in the management of MDR infections. Its unique structure will give rise to a promising epoxide epoch in the battle against MDR bacteria.

ZTI-01 (fosfomycin for injection) in the treatment of hospitalized patients with complicated urinary tract infections

Fosfomycin is a bactericidal antibiotic available since the 1970s whose intravenous formulation has been available in many countries outside the USA. Given the rise in drug-resistant bacteria, its introduction into the US market has become a necessity for addressing these organisms. This review provides an overview of the microbiology, clinical pharmacology and initial clinical experiences of the intravenous fosfomycin product (ZTI-01) that is undergoing clinical development in the USA for the treatment of complicated urinary tract infections and acute pyelonephritis.

Physical compatibility of fosfomycin for injection with select i.v. drugs during simulated Y-site administration

PURPOSE

The results of a study to determine the physical compatibility of ZTI-01 (fosfomycin for injection) in 0.9% sodium chloride or 5% dextrose during simulated Y-site administration with 37 i.v. antimicrobials and 58 nonantimicrobials are reported.

METHODS

Fosfomycin, an epoxide antibiotic with broad-spectrum activity against multidrug-resistant bacteria, is marketed in the United States only in an oral formulation with limited bioavailability, but an i.v. formulation is in development. Fosfomycin for injection and other evaluated drugs were reconstituted according to manufacturer recommendations and further diluted with 0.9% sodium chloride or 5% dextrose to the final desired concentrations. Y-site administration was simulated in glass culture tubes. Incompatibility was defined as changes in visual characteristics or a change in turbidity of >0.5 nephelometric turbidity units over the 120-minute observation period.

RESULTS

Of the 95 drugs tested, 16 were incompatible with fosfomycin in 0.9% sodium chloride, and 18 were incompatible with fosfomycin in 5% dextrose; incompatibility was observed with 10 of 37 antimicrobials, including the 3 commercially available amphotericin B products, anidulafungin, caspofungin, ceftaroline, ciprofloxacin, daptomycin, doxycycline, and isavuconazonium sulfate.

CONCLUSION

Fosfomycin for injection at a concentration of 30 mg/mL was physically compatible with 73 of 95 (77%) of the i.v. drugs tested at concentrations used clinically in both 0.9% sodium chloride injection and 5% dextrose injection. Twenty-two drugs were deemed incompatible in at least 1 of the 2 diluents.

Pharmacokinetics, Safety, and Tolerability of Single-Dose Intravenous (ZTI-01) and Oral Fosfomycin in Healthy Volunteers

The pharmacokinetics, safety, and tolerability of intravenous (i.v.) fosfomycin disodium (ZTI-01) and oral fosfomycin tromethamine were evaluated after a single dose in 28 healthy adult subjects. Subjects received a single 1-h i.v. infusion of 1 g and 8 g fosfomycin disodium and a single dose of 3 g oral fosfomycin tromethamine in a phase I, randomized, open-label, three-period crossover study. Serial blood and urine samples were collected before and up to 48 h after dosing. The mean pharmacokinetic parameters ± standard deviations of fosfomycin in plasma after 1 g and 8 g i.v., respectively, were the following: maximum clearance of drug in serum (C_max), 44.3 ± 7.6 and 370 ± 61.9 μg/ml; time to maximum concentration of drug in serum (T_max), 1.1 ± 0.05 and 1.08 ± 0.01 h; volume of distribution (V), 29.7 ± 5.7 and 31.5 ± 10.4 liters; clearance (CL), 8.7 ± 1.7 and 7.8 ± 1.4 liters/h; renal clearance (CL_R), 6.6 ± 1.9 and 6.3 ± 1.6 liters/h; area under the concentration-time curve from 0 to infinity (AUC_0-∞), 120 ± 28.5 and 1,060 ± 192 μg·h/ml; and half-life (t_1/2), 2.4 ± 0.4 and 2.8 ± 0.6 h. After oral administration, the parameters were the following: C_max, 26.8 ± 6.4 μg/ml; T_max, 2.25 ± 0.4 h; V/F, 204 ± 70.7 liters; CL/F, 17 ± 4.7 liters/h; CL_R, 6.5 ± 1.8 liters/h; AUC_0-∞, 191 ± 57.6 μg · h/ml; and t_1/2, 9.04 ± 4.5 h. The percent relative bioavailability of orally administered fosfomycin was 52.8% in relation to the 1-g i.v. dose. Approximately 74% and 80% of the 1-g and 8-g i.v. doses were excreted unchanged in the urine by 48 h compared to 37% after oral administration, with the majority of this excretion occurring by 12 h regardless of dosage form. No new safety concerns were identified during this study. The results of this study support further investigation of i.v. fosfomycin in the target patient population, including patients with complicated urinary tract infections and pyelonephritis.