Here is a review of the literature for this class of antibiotics.
Gram-negative bacterial resistance in the United States continues to increase. As it has spread to the community setting, common infections such as urinary tract infections (UTIs) have become increasingly difficult to manage using oral medications and may necessitate the use of intravenous antibiotics. For complicated UTIs, 1 in 5 patients will have an infection caused by an extended-spectrum β-lactamase (ESBL)-producing Enterobacterales, which limits options when they also are resistant to fluoroquinolones and trimethoprim-sulfamethoxazole.1
Tebipenem and sulopenem are carbapenems with oral formulations that have been studied in phase 3 trials.2-5 Each typically has a broad spectrum of activity, including streptococci, methicillin-susceptible strains of staphylococci, Enterobacterales (including ESBL-producing strains), and many anaerobes. Notable exceptions to their useful activity include Enterococcus faecium, Clostridioides difficile, and many nonfermenting gram-negative bacilli such as Pseudomonas aeruginosa and Acinetobacter baumannii.6-8
TEBIPENEM PIVOXIL HYDROBROMIDE (TEBIPENEM HBR)
Tebipenem pivoxil is a formulation of tebipenem marketed in Japan as Orapenem for the management of otitis media, sinusitis, and pneumonia in pediatric patients with difficult to treat infections. Tebipenem pivoxil is used to manage infections caused by penicillin-resistant Streptococcus pneumoniae and Haemophilus influenzae.6,7 The drug has been reformulated as tebipenem HBr to improve stability and oral absorption. The oral bioavailability of tebipenem HBr is estimated to be 60%. It is rapidly converted to the active moiety, tebipenem, by carboxylesterases located in the intestinal epithelial cells.9 Tebipenem HBr is not metabolized by the liver or kidneys, but tebipenem undergoes renal elimination with 80% of the active metabolites excreted through the kidneys.10
The clinical efficacy and safety of tebipenem HBr for complicated urinary tract infections (cUTIs) were evaluated in a published double-blind, phase III, randomized clinical trial (NCT03788967) conducted at 101 sites in 15 different countries within central and eastern Europe, South Africa, and the United States. Patients were randomly assigned to either receive tebipenem HBr 600 mg by mouth every 8 hours or ertapenem (Invanz) 1 g intravenously every 24 hours for 7 to 10 days. The primary end point was a composite of clinical cure and microbiologic response, typical of trials for cUTIs. The median patient age was 58.1 years, and 50.8% of patients had a cUTI, with the remainder having acute pyelonephritis. Bacteremia was found in 11.5% of patients, and 19.7% of patients met criteria for systemic inflammatory response syndrome. Of the infecting pathogens, 90% were Enterobacterales, primarily Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Proteus mirabilis. ESBL production was detected in 23.4% of infecting pathogens, 39% of pathogens were fluoroquinolone nonsusceptible, and 43% of pathogens were resistant to trimethoprim-sulfamethoxazole. Tebipenem HBr was shown to be noninferior to intravenous ertapenem with respect to the primary end point (58.8% and 61.6%; weighted difference, –3.3%; 95% CI, –9.7 to 3.2). Tebipenem HBr was effective against common gram-negative pathogens, but 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).2
In January 2022, the FDA granted a priority review of a new drug application (NDA) for tebipenem HBr. The FDA then conducted an analysis of the microbiological intent-to-treat (micro-ITT) population separate from what was outlined in the original statistical analysis plan. From this analysis, the FDA concluded that the prespecified noninferiority margin of –12.5% was not met and halted the approval of the medication. Spero Therapeutics, the manufacturer of tebipenem HBr, released a statement shifting the company focus to other clinical therapeutics.11 These actions leave tebipenem HBr’s fate uncertain.
SULOPENEM AND SULOPENEM ETZADROXIL/PROBENECID
Sulopenem is another carbapenem being developed for cUTIs. It is available in both an intravenous formulation as sulopenem and oral formulation as sulopenem etzadroxil with probenecid.12 The pharmacokinetics and pharmacodynamics of sulopenem are similar to that of other intravenous carbapenems. Sulopenem etzadroxil is an esterified prodrug designed for oral administration. The oral bioavailability is estimated to be 20% to 34% under fasted conditions but can be increased when administered with food or probenecid. Food consumption increases the area under the curve (AUC) by 23.6%, and 500 mg of probenecid increases the AUC by 62%.12,13 The oral formulation is being paired with probenecid.
The clinical efficacy and safety of sulopenem etzadroxil/probenecid were first studied for the treatment of uncomplicated UTIs in adult women. Patients were randomly assigned to receive either sulopenem etzadroxil/probenecid (500 mg/500 mg) by mouth twice daily for 5 days with 3 days of placebo or ciprofloxacin 250 mg by mouth twice daily for 3 days with 5 days of placebo. The primary outcome was overall success, which was a composite outcome of clinical and microbiologic success. The data analysis in this trial included both a microbiologic modified ITT resistant (micro-MITT R) and microbiologic modified ITT susceptible (micro-MITT S) population. These populations included all randomly assigned patients who received at least 1 dose of study drug and had a baseline uropathogen that was either nonsusceptible or susceptible to ciprofloxacin, respectively. As expected, sulopenem etzadroxil/probenecid was superior to ciprofloxacin in the micro- MITT R population with an overall success rate of 62.2% with sulopenem etzadroxil/probenecid and 36.0% with ciprofloxacin (difference, 26.2%; 95% CI, 15.1-37.4). For the micro-MITT S population, sulopenem etzadroxil/probenecid was not noninferior to ciprofloxacin with overall success rates of 66.8% and 78.6%, respectively (difference, –11.8%; 95% CI, –18.0 to –5.6).3
Following the oral-only study, a study focusing on an intravenous to oral strategy of sulopenem formulations was conducted to assess the clinical efficacy and safety of intravenous sulopenem followed by oral sulopenem etzadroxil/probenecid for complicated UTIs. Patients were randomly assigned to receive either sulopenem 1000 mg intravenously for 5 days followed by sulopenem etzadroxil/probenecid (500 mg/500 mg) by mouth twice daily for 7 to 10 days of total treatment or ertapenem 1 g intravenously for 5 days followed by ciprofloxacin 500 mg by mouth twice daily (or amoxicillin-clavulanate if patient was ciprofloxacin resistant) for 7 to 10 total days of treatment. The primary outcome was the same as the previous trial. The intravenous and oral combination of sulopenem was not found to be noninferior to the combination of ertapenem and ciprofloxacin (67.8% vs 73.0%; difference, –6.1%; 95% CI, –12.0 to –0.1). This trial did not investigate complicated UTIs caused by multidrug resistant pathogens.4 In the previous 2 trials, the failure was hypothesized to be due to lower rates of asymptomatic bacteriuria, resulting in microbiologic failure in the patients treated with ciprofloxacin. The combination of intravenous and oral sulopenem also was investigated in complicated intra-abdominal infections and did not meet noninferiority criteria compared to the combination of ertapenem with step down to ciprofloxacin and metronidazole.5 Three clinical trials were completed and unfortunately all 3 missed their end points. The manufacturing company, Iterum Therapeutics, applied for an NDA based on results from the trial (NCT03354598) completed in uncomplicated UTIs that showed sulopenem etzadroxil/probenecid could be used for infections caused by fluoroquinolone-resistant pathogens. The FDA denied this request and required more supporting evidence to approve the medication. The manufacturing company, Iterum Therapeutics, is working with external vendors to design a clinical trial to provide additional evidence for the FDA.14
The approval of an effective oral carbapenem could change the way complicated UTIs caused by multidrug resistant organisms are managed. It could help reduce health care–related costs associated with the need for intravenous therapy by either preventing hospital admission or reducing hospital length of stay. However, the prospect of an oral carbapenem raises concern among health care professionals with regard to misuse further leading to antimicrobial resistance. Currently, tebipenem pivoxil, marketed in Japan as Orapenem for pediatric infections, is not recommended in first-line use but can be used after other antibiotics fail.16 The potential availability of oral carbapenems may worry infectious diseases clinicians, but they would increase options for oral therapy of infections currently treated parenterally. However, it seems these agents are not likely to be available as soon as once anticipated.