George Louis Drusano

Background: Mycobacterium tuberculosis resistance to standard-of-care agents is increasing. It is imperative to identify new combinations that increase the rate and depth of bacterial kill, shorten therapy and also suppress resistance. There has been little prior effort to identify combination regimens that employ new or repurposed drugs in a rational way. Methods and Findings: Our group developed a pathway to combine agents to achieve this end. This pathway starts with standard baseline evaluations (e.g., MIC), leverages information from in vitro assessments (hollow fiber infection model), then analyzes 2-agent combinations in a 96 well quantitative culture checkerboard format (Greco URSA model with simulation). Finally, development of a high dimensional mathematical model allowed evaluation of 2- and 3-drug regimens in multiple metabolic states to draw inferences regarding combination therapies. We prospectively evaluated these regimens in animal models. We showed that a prospectively chosen regimen of pretomanid, moxifloxacin plus bedaquiline performed as predicted. In the BALB/c murine model, this regimen produced sterilization in a cohort that was held for 12 weeks after therapy cessation, as it did in the C3HeB/FeJ (“Kramnik”) murine model. Finally, this and other regimens were evaluated in a cynomolgus macaque model. The decrement of the ¹⁸ F-deoxyglucose signal in Positron emission tomography (PET)- computed tomography (CT) evaluations was best with this regimen. Other endpoints such as necropsy score and colony counts in lung and lymph nodes also demonstrated that this regimen behaved as predicted from our pathway/algorithm. Conclusions: We conclude that this provides a way forward for the future to identify the most promising regimens to shorten therapy for tuberculosis and suppress emergence of resistance.

We present a framework for maximum likelihood analysis on count observations that begin high and quickly drop to zero, for example, from hollow fiber drug comparison studies. This simulation study focuses on treating observed counts as Poisson or normally distributed for the purpose of estimating infection rebound after effective treatment. CFU profiles were simulated from inoculation to 96 h post‐treatment. The PK‐PD link was an Emax inhibitory model. Random parameters were pathogen growth and natural decay rates, drug concentration for half‐maximal effect, and drug pathogen kill rate. Other parameters, including PK, were fixed. Parameters were adjusted to attain 67% efficacy at 24 h. Random parameter values were optimized for profiles observed at 24, 48, 72, and 96 h assuming each of four probability assumptions: (1) all CFU measurements were Poisson distributed (truth); (2) CFU < 128 were Poisson, higher values were normally distributed; (3) all observations were normally distributed; and (4) observations were normally distributed but CFU < 10 were censored. CFU‐time profiles were re‐simulated using the optimized parameter densities. Rebound percentage (CFU ≥ 10 at 24 h post‐treatment) was best predicted using strategy 2, above. For limited periodically collected time series count data that quickly fall to 0, the true proportion reaching 0 (lack of rebound) was best modeled by assuming Poisson distribution at low counts. At higher counts (≥ 128), assuming normality is reasonable. Censoring observations leads to biased models.

LPC-233 (a.k.a. VB-233) is a potent antibiotic targeting the essential enzyme LpxC in Gram-negative bacteria. We present herein the pharmacokinetics and pharmacodynamics data of LPC-233 for treating murine infections caused by Burkholderia pseudomallei , a potential biodefense pathogen. A range of doses was evaluated in a post-aerosol exposure model of B. pseudomallei -infected mice. After the aerosol challenge with the B. pseudomallei strain K96243, treatment was initiated with 10, 30, or 90 mg/kg of LPC-233 orally every 12 h (q12h) or 90 mg/kg intraperitoneally q12h for 14 days. A vehicle-control arm and a positive-control arm consisting of one of the recommended standards of care, ceftazidime (150 mg/kg, q6h) injected subcutaneously, were included. LPC-233 significantly and dose-dependently rescued mice from B. pseudomallei infection in comparison with the vehicle ( P < 0.0001). At dose levels of 30 mg/kg or higher, the survival rate with LPC-233 was significantly higher than that from the ceftazidime arm ( P range: 0.001–0.05). LPC-233 reversed the murine body weight loss caused by the B. pseudomallei infection more rapidly than ceftazidime did, suggesting that it is a faster-acting antibiotic in this dosing regimen. Despite the outstanding survival advantage of LPC-233 over ceftazidime, no significant differences in tissue burdens (liver, lung, spleen, and blood) were observed among any of the treatment groups surviving to the termination of the experiment, suggesting that similar to commercial antibiotics, LPC-233 treatment for lethal B. pseudomallei infection may likely require both an acute phase of intensive treatment and an eradication phase of prolonged treatment.

Based on the fact that beta-lactam antibiotics demonstrate time-dependent killing, different dosing strategies have been implemented to increase the time that free (unbound) antibiotic concentrations remain above the minimal inhibitory concentration, including prolonged and continuous infusion. Multiple studies have been performed that compared continuous with traditional intermittent infusion to improve outcomes in patients with severe sepsis. These studies have yielded inconsistent results for patients, as measured by clinical response to treatment and mortality due to heterogeneity of included patients, pathogens, dosing strategies, and the absence of therapeutic drug monitoring. The Continuous Infusion versus Intermittent Administration of Meropenem in Critically Ill Patients and Beta-Lactam Infusion Group trials failed to show a difference in mortality between patients randomized to receive continuous or intermittent infusion of beta-lactam antibiotics deeper understanding of the pharmacokinetic and pharmacodynamic mechanisms that occur in critically ill patients should guide us in dose optimization and improvement in methodology for future clinical trials.

Bacillus anthracis , the causative agent of anthrax, is among the most likely bacterial pathogens to be used in a biological attack. Inhalation anthrax is a serious, life-threatening form of infection, and the mortality from acute inhaled anthrax can approach 100% if not treated early and aggressively. Food and Drug Administration-approved antibiotics indicated for post-exposure prophylaxis (PEP) or treatment of anthrax are limited. This study assessed the in vitro activity and in vivo efficacy of omadacycline and comparators against clinical isolates of B. anthracis, including a ciprofloxacin-resistant isolate. Minimum inhibitory concentrations (MICs) of omadacycline, ciprofloxacin, and doxycycline were determined against animal and human clinical isolates of B. anthracis , including the ciprofloxacin-resistant Ames strain BAC ^r 4-2. Mice were challenged with aerosolized BAC ^r 4-2 spores, and survival was monitored for 28 days post-challenge. Treatment was initiated 24 h after aerosol challenge and administered for 14 days. Omadacycline demonstrated in vitro activity against 53 B. anthracis isolates with an MIC range of ≤0.008–0.25 µg/mL, and an MIC ₅₀ /MIC ₉₀ of 0.015/0.03 µg/mL. Consistent with this, omadacycline demonstrated in vivo efficacy in a PEP mouse model of inhalation anthrax caused by the Ames BAC ^r 4-2 ciprofloxacin-resistant B. anthracis isolate. Omadacycline treatment significantly increased survival compared with the vehicle control group and the ciprofloxacin treatment group. As antibiotic resistance rates continue to rise worldwide, omadacycline may offer an alternative PEP or treatment option against inhalation anthrax, including anthrax caused by antibiotic-resistant B. anthracis .

Antimicrobial resistance in Neisseria gonorrhoeae is threatening the gonorrhoea treatment, and optimizations of the current ceftriaxone-treatment regimens are crucial. We evaluated the pharmacodynamics of ceftriaxone single-dose therapy (0.125–1 g) against ceftriaxone-susceptible and ceftriaxone-resistant gonococcal strains, based on EUCAST ceftriaxone-resistance breakpoint (MIC > 0.125 mg/L), in our hollow fibre infection model (HFIM) for gonorrhoea. Gonococcal strains examined were WHO F (ceftriaxone-susceptible, MIC < 0.002 mg/L), R (ceftriaxone-resistant, MIC = 0.5 mg/L), Z (ceftriaxone-resistant, MIC = 0.5 mg/L) and X (ceftriaxone-resistant, MIC = 2 mg/L). Dose-range HFIM 7 day experiments simulating ceftriaxone 0.125–1 g single-dose intramuscular regimens were conducted. Ceftriaxone 0.125–1 g single-dose treatments rapidly eradicated WHO F (wild-type ceftriaxone MIC). Ceftriaxone 0.5 and 1 g treatments, based on ceftriaxone human plasma pharmacokinetic parameters, eradicated most ceftriaxone-resistant gonococcal strains (WHO R and Z), but ceftriaxone 0.5 g failed to eradicate WHO X (high-level ceftriaxone resistance). When simulating oropharyngeal gonorrhoea, ceftriaxone 0.5 g failed to eradicate all the ceftriaxone-resistant strains, while ceftriaxone 1 g eradicated WHO R and Z (low-level ceftriaxone resistance) but failed to eradicate WHO X (high-level ceftriaxone resistance). No ceftriaxone-resistant mutants were selected using any ceftriaxone treatments. Ceftriaxone 1 g single-dose intramuscularly cure most of the anogenital and oropharyngeal gonorrhoea cases caused by the currently internationally spreading ceftriaxone-resistant gonococcal strains, which should be further confirmed clinically. A ceftriaxone 1 g dose (±azithromycin 2 g) should be recommended for first-line empiric gonorrhoea treatment. This will buy countries some time until novel antimicrobials are licensed. Using ceftriaxone 1 g gonorrhoea treatment, the EUCAST ceftriaxone-resistance breakpoint is too low.

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii . Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25–30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Despite their limitations, the pharmacokinetics (PK) and pharmacodynamics (PD) indices form the basis for our current understanding regarding antibiotic development, selection, and dose optimization. Application of PK-PD in medicine has been associated with better clinical outcome, suppression of resistance, and optimization of antibiotic consumption. Beta-lactam antibiotics remain the cornerstone for empirical and directed therapy in many patients. The percentage of time of the dosing interval that the free (unbound) drug concentration remains above the minimal inhibitory concentration (MIC) (%fT > MIC) has been considered the PK-PD index that best predicts the relationship between antibiotic exposure and killing for the beta-lactam antibiotics. Time dependence of beta-lactam antibiotics has its origin in the acylation process of the serine active site of penicillin-binding proteins, which subsequently results in bacteriostatic and bactericidal effects during the dosing interval. To enhance the likelihood of target attainment, higher doses, and prolonged infusion strategies, with/or without loading doses, have been applied to compensate for subtherapeutic levels of antibiotics related to PK-PD changes, especially in the early phase of severe sepsis. To minimize resistance and maximize clinical outcome, empirical therapy with a meropenem loading dose followed by high-dose-prolonged infusion should be considered in patients with high inoculum infections presenting as severe (Gram negative) sepsis. Subsequent de-escalation and dosing of beta-lactam antibiotics should be considered as an individualized dynamic process that requires dose adjustments throughout the time course of the disease process mediated by clinical parameters that indirectly assess PK-PD alterations.

Polymyxin B is a “last-line-of-defense” antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens.

In this study, we showed that early intervention with molnupiravir resulted in a greater antiviral effect, and we explained the mechanism behind this phenomenon. Our results predicted and explained the failure of molnupiravir in hospitalized patients and highlighted the utility of preclinical pharmacodynamic studies to design optimal antiviral regimens for the treatment of viral diseases.