Gram-negative bacterial resistance is increasingly prevalent in the United States, complicating the treatment of common infections like urinary tract infections (UTIs). This rise in resistance necessitates intravenous antibiotics, especially in complicated UTIs (cUTIs), where extended-spectrum β-lactamase (ESBL)-producing Enterobacterales account for a significant proportion of cases.
Tebipenem Pivoxil Hydrobromide (Tebipenem HBr)
Tebipenem pivoxil, marketed in Japan as Orapenem, is used for pediatric infections like otitis media, sinusitis, and pneumonia caused by penicillin-resistant Streptococcus pneumoniae and Haemophilus influenzae. Reformulated as tebipenem HBr to enhance stability and oral absorption (estimated bioavailability of 60%), it is rapidly converted to its active form, tebipenem. Tebipenem is primarily eliminated renally.
A Phase III clinical trial (NCT03788967) evaluated tebipenem HBr for cUTIs, comparing it to intravenous ertapenem. The study included patients with cUTIs and acute pyelonephritis, with a significant proportion exhibiting bacteremia and systemic inflammatory response syndrome. While tebipenem HBr demonstrated noninferiority to ertapenem for the primary endpoint (clinical cure and microbiologic response), concerns arose regarding its efficacy against ESBL-producing pathogens. The clinical response for ESBL-producing pathogens trended lower, with 83.9% response compared with 93.3% for ertapenem (difference, –9.50; 95% CI, –21.62 to 2.10).
In January 2022, the FDA granted priority review for tebipenem HBr's new drug application (NDA). However, the FDA's subsequent analysis, differing from the original statistical analysis plan, concluded that the prespecified noninferiority margin of -12.5% was not met, leading to the rejection of its approval. Spero Therapeutics, the manufacturer, has since shifted focus to other therapeutics, casting uncertainty on tebipenem HBr's future.
Sulopenem and Sulopenem Etzadroxil/Probenecid
Sulopenem, another carbapenem, is under development for cUTIs, available in both intravenous and oral formulations (sulopenem etzadroxil with probenecid). Sulopenem etzadroxil, an esterified prodrug, has an oral bioavailability of 20-34%, which can be increased with food or probenecid. Probenecid increases the AUC by 62%.
Clinical trials have assessed sulopenem etzadroxil/probenecid for both uncomplicated and complicated UTIs. In uncomplicated UTIs, sulopenem etzadroxil/probenecid showed superiority to ciprofloxacin in the micro-MITT R population (patients with ciprofloxacin-resistant uropathogens), with overall success rates of 62.2% vs. 36.0% (difference, 26.2%; 95% CI, 15.1-37.4). However, it was not noninferior to ciprofloxacin in the micro-MITT S population (patients with ciprofloxacin-susceptible uropathogens).
An intravenous-to-oral strategy using sulopenem formulations for cUTIs also failed to meet noninferiority criteria compared to ertapenem followed by ciprofloxacin (67.8% vs 73.0%; difference, –6.1%; 95% CI, –12.0 to –0.1). Iterum Therapeutics, the manufacturer, faced FDA denial of its NDA based on the uncomplicated UTI trial results, requiring additional evidence. The company is currently designing a new clinical trial to address the FDA's concerns.
Implications and Concerns
The introduction of effective oral carbapenems could transform the management of complicated UTIs caused by multidrug-resistant organisms, potentially reducing healthcare costs by minimizing the need for intravenous therapy. However, concerns exist regarding the potential for misuse and the acceleration of antimicrobial resistance. While oral carbapenems could expand treatment options for infections currently requiring parenteral administration, their availability remains uncertain due to regulatory challenges.
