VIENNA – An investigational antibiotic effective against several types of gram-negative antibiotic-resistant bacteria has proved its mettle against serious infections of the urinary tract, respiratory tract, and bloodstream.

Plazomicin (Achaogen, San Francisco) posted good results in two phase III studies, handily besting comparator drugs considered gold standard for treating complicated urinary tract infections and pyelonephritis, as well as bloodstream infections and hospital- and ventilator-associated bacterial pneumonia.

Both the EPIC (Evaluating Plazomicin In cUTI) and CARE (Combating Antibiotic Resistant Enterobacteriaceae) trials have provided enough positive data for the company to move forward with a new drug application later this year. The company also plans to seek European Medicines Agency approval in 2018.

Plazomicin is an aminoglycoside that has been modified with several side chains that block aminoglycoside-modifying enzymes, Daniel Cloutier, PhD, principal clinical scientist of Achaogen said at the European Society of Clinical Microbiology and Infectious Disease annual congress.

“Aminoglycoside enzymes tend to travel along with beta-lactamases and carbapenemases as well, so this drug retains potent bactericidal activity against extended spectrum beta-lactamase producing Enterobacteriaceae, carbapenem-resistant Enterobacteriaceae, and aminoglycoside-resistant Enterobacteriaceae,” said Dr. Cloutier, who presented the results of the EPIC trial. The drug is given once-daily as a 30-minute intravenous infusion.

EPIC enrolled 609 adult patients with complicated urinary tract infections or acute pyelonephritis; Dr. Cloutier presented a modified intent-to-treat analysis comprising 388 of these. They were randomized to plazomicin 15 mg/kg every 25 hours or to IV meropenem 1 gram every 24 hours. Treatment proceeded for 4-7 days, after which patients could step down to oral therapy (levofloxacin 500 m/day), for a total of 7-10 days of treatment. About 80% of patients had both IV and oral therapy. At 15-19 days from the first dose, patients had a test of cure; at 24-32 days from first dose, they returned for a safety follow-up.

Patients were a mean of 60 years old. About 60% had a complicated UTI; the rest had acute pyelonephritis. About 35% had a mean creatinine clearance of more than 30-60 mL/min; the rest had a mean clearance of more than 60-90 mL/min.

The primary efficacy endpoint was microbial eradication. Plazomicin performed significantly better than meropenem in this measure (87% vs.72%), a mean difference of about 15%. Patients with pyelonephritis responded marginally better than those with complicated UTI, both groups favoring plazomicin (mean treatment differences of 17.5% and 13.7%, respectively).

The results were similar when the investigators examined groups by whether they needed oral step-down treatment. In the IV-only groups, plazomicin bested meropenem in microbiological eradication by almost 19% (84% vs. 65%). In the IV plus oral therapy group, the mean difference was 14%, also in favor of plazomicin (88% vs. 74%).

Plazomicin was significantly more effective then meropenem in all of the resistant Enterobacteriaceae groups (ESBL-positive, and levofloxacin- and aminoglycoside-resistant). It was also significantly more effective against E. coli (17% treatment difference), Klebsiella pneumonia (9%), and Proteus mirabilis (25%). However, it was 20% less effective than meropenem against E. cloacae.

At late follow-up, 2% of the plazomicin group and 8% of the meropenem group had relapsed – a significant difference.

Plazomicin and meropenem had similar safety profiles. Diarrhea and hypertension were the most common adverse events (about 2% in each group). Headache occurred in 3% of the meropenem patients and 1% of the plazomicin patients. Nausea, vomiting, and anemia occurred in about 1% of each group.

More patients taking plazomicin experienced a serum creatinine clearance increase of at least 0.5 mg/dL during treatment (7% vs. 4%). All but two patients taking plazomicin experienced a full recovery by the last follow-up visit.

The CARE trial was much smaller, comprised of 39 patients who had either bloodstream infections, or hospital-acquired or ventilator-associated bacterial pneumonia caused by carbapenem-resistant Enterobacteriaceae. Lynn Connolly, MD, senior medical director and head of late development at Achaogen, presented the data. Recruitment for such a narrow diagnosis was difficult, and hampered patient accrual, she noted.

CARE’s primary endpoints were a combination of all-cause mortality and significant disease-related complications, and all-cause mortality only, both at 28 days.

Patients were randomized 1:1 to either plazomicin 15 mg/kg every 24 hours, or colistin in a 300-mg loading dose, followed by daily infusions of 5 mg/kg. Everyone, regardless of treatment group, could also receive meropenem or tigecycline if deemed necessary. Treatment lasted 7-14 days. There was a test of cure at 7 days from the last IV dose, a safety assessment at 28 days, and a long-term follow-up at 60 days.

The patients’ mean age was about 65 years. Most (about 80%) had a bloodstream infection; bacterial pneumonias were present in the remainder. Most infections (85%) were monomicrobial, with polymicrobial infections making up the balance. Tigecycline was the favored adjunctive therapy (60%), followed by meropenem.

At day 28, plazomicin was associated with significantly better overall outcomes than colistin. It reduced the combination mortality/significant disease complications endpoint by 26% (23% vs. 50% meropenem). This translated to a 53% relative reduction in the risk of death.

Plazomicin also reduced all-cause mortality only by 28% (12% vs. 40% meropenem). This translated to a relative risk reduction of 70.5%.

The study drug performed well in the subgroup of patients with bloodstream infections, reducing the occurrence of the composite endpoint by 39% (14% vs. 53%), and of the mortality-only endpoint by 33% (7% vs. 40%). This translated to a 63% increased chance of 60-day survival in the plazomicin group.

Almost all patients in each group experienced at least one adverse event; 28% were deemed related to plazomicin and 43% to colistin. Many of these events were related to renal function (33% plazomicin, 52% colistin). Serum creatinine increases of at least 0.5 mg/dL during IV treatment occurred in fewer taking plazomicin (1 vs. 6 taking colistin). Full renal recovery occurred in the patient taking plazomicin, but only in three taking colistin.

“These data suggest that plazomicin could offer an important new treatment option for patients with serious infections due to carbapenem-resistant Enterobacteriaceae,” Dr. Connolly said.

msullivan@frontlinemedcom.com

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Plazomicin beats gold standard antibiotics in complex, gram-negative bacterial infections