Solithromycin Pharmacokinetics in Plasma and Dried Blood Spots and Safety in Adolescents

Synthesis and antibacterial activity of novel 2‑fluoro ketolide antibiotics with 11,12‑quinoylalkyl side chains

A series of novel 2‑fluoro ketolide antibiotics with 11,12‑quinoylalkyl side chains derived from telithromycin and cethromycin were designed and synthesized. The corresponding targets 2a-o were tested for their in vitro activities against a series of macrolide-sensitive and macrolide-resistant pathogens. Some of them showed a similar antibacterial spectrum and comparable or slightly better activity to telithromycin. Among them, compounds 2g and 2k, displayed excellent activities against macrolide-sensitive and macrolide-resistant pathogens.

Solithromycin in Children and Adolescents With Community-acquired Bacterial Pneumonia

BACKGROUND

Solithromycin is a new macrolide-ketolide antibiotic with potential effectiveness in pediatric community-acquired bacterial pneumonia (CABP). Our objective was to evaluate its safety and effectiveness in children with CABP.

METHODS

This phase 2/3, randomized, open-label, active-control, multicenter study randomly assigned solithromycin (capsules, suspension or intravenous) or an appropriate comparator antibiotic in a 3:1 ratio (planned n = 400) to children 2 months to 17 years of age with CABP. Primary safety endpoints included treatment-emergent adverse events (AEs) and AE-related drug discontinuations. Secondary effectiveness endpoints included clinical improvement following treatment without additional antimicrobial therapy.

RESULTS

Unrelated to safety, the sponsor stopped the trial prior to completion. Before discontinuation, 97 participants were randomly assigned to solithromycin (n = 73) or comparator (n = 24). There were 24 participants (34%, 95% CI, 23%-47%) with a treatment-emergent AE in the solithromycin group and 7 (29%, 95% CI, 13%-51%) in the comparator group. Infusion site pain and elevated liver enzymes were the most common related AEs with solithromycin. Study drug was discontinued due to AEs in 3 subjects (4.3%) in the solithromycin group and 1 (4.2%) in the comparator group. Forty participants (65%, 95% CI, 51%-76%) in the solithromycin group achieved clinical improvement on the last day of treatment versus 17 (81%, 95% CI, 58%-95%) in the comparator group. The proportion achieving clinical cure was 60% (95% CI, 47%-72%) and 68% (95% CI, 43%-87%) for the solithromycin and comparator groups, respectively.

CONCLUSIONS

Intravenous and oral solithromycin were generally well-tolerated and associated with clinical improvement in the majority of participants treated for CABP.

Leveraging Physiologically Based Pharmacokinetic Modeling and Experimental Data to Guide Dosing Modification of CYP3A-Mediated Drug-Drug Interactions in the Pediatric Population

Solithromycin is a novel fluoroketolide antibiotic that is both a substrate and time-dependent inhibitor of CYP3A. Solithromycin has demonstrated efficacy in adults with community-acquired bacterial pneumonia and has also been investigated in pediatric patients. The objective of this study was to develop a framework for leveraging physiologically based pharmacokinetic (PBPK) modeling to predict CYP3A-mediated drug-drug interaction (DDI) potential in the pediatric population using solithromycin as a case study. To account for age, we performed in vitro metabolism and time-dependent inhibition studies for solithromycin for CYP3A4, CYP3A5, and CYP3A7. The PBPK model included CYP3A4 and CYP3A5 metabolism and time-dependent inhibition, glomerular filtration, P-glycoprotein transport, and enterohepatic recirculation. The average fold error of simulated and observed plasma concentrations of solithromycin in both adults (1966 plasma samples) and pediatric patients from 4 days to 17.9 years (684 plasma samples) were within 0.5- to 2.0-fold. The geometric mean ratios for the simulated area under the concentration versus time curve (AUC) extrapolated to infinity were within 0.75- to 1.25-fold of observed values in healthy adults receiving solithromycin with midazolam or ketoconazole. DDI potential was simulated in pediatric patients (1 month to 17 years of age) and adults. Solithromycin increased the simulated midazolam AUC 4- to 6-fold, and ketoconazole increased the simulated solithromycin AUC 1- to 2-fold in virtual subjects ranging from 1 month to 65 years of age. This study presents a systematic approach for incorporating CYP3A in vitro data into adult and pediatric PBPK models to predict pediatric CYP3A-mediated DDI potential. SIGNIFICANCE STATEMENT: Using solithromycin, this study presents a framework for investigating and incorporating CYP3A4, CYP3A5, and CYP3A7 in vitro data into adult and pediatric physiologically based pharmacokinetic models to predict CYP3A-mediated DDI potential in adult and pediatric subjects during drug development. In this study, minor age-related differences in inhibitor concentration resulted in differences in the magnitude of the DDI. Therefore, age-related differences in DDI potential for substrates metabolized primarily by CYP3A4 can be minimized by closely matching adult and pediatric inhibitor concentrations.

A Dried Blood Spot Analysis for Solithromycin in Adolescents, Children, and Infants: A Short Communication

BACKGROUND

Solithromycin is a fourth-generation macrolide antibiotic with potential efficacy in pediatric community-acquired bacterial pneumonia. Pharmacokinetic (PK) studies of solithromycin in pediatric subjects are limited, therefore application of minimally invasive drug sampling techniques, such as dried blood spots (DBS), may enhance the enrollment of children in PK studies. The objectives of this study were to compare solithromycin concentrations in DBS with those in liquid plasma samples (LPS) and to quantify the effects of modeling DBS concentrations on the results of a population PK model.

METHODS

Comparability analysis was performed on matched DBS and LPS solithromycin concentrations collected from two different phase 1 clinical trials of solithromycin treatment in children (clinicaltrials.gov #NCT01966055 and #NCT02268279). Comparability of solithromycin concentrations was evaluated based on DBS:LPS ratio, median percentage prediction error, and median absolute percentage prediction error. The effect of correcting DBS concentrations for both hematocrit and protein binding was investigated. In addition, a previously published population PK model (NONMEM) was leveraged to compare parameter estimates resulting from either DBS or LPS concentrations.

RESULTS

A total of 672 paired DBS-LPS concentrations were available from 95 subjects (age: 0-17 years of age). The median (range) LPS and DBS solithromycin concentrations were 0.3 (0.01-12) mcg/mL and 0.32 (0.01-14) mcg/mL, respectively. Median percentage prediction error and median absolute percentage prediction error of raw DBS to LPS solithromycin concentrations were 5.26% and 22.95%, respectively. In addition, the majority of population PK parameter estimates resulting from modeling DBS concentrations were within 15% of those obtained from modeling LPS concentrations.

CONCLUSIONS

Solithromycin concentrations in DBS were similar to those measured in LPS and did not require correction for hematocrit or protein binding.

Population Pharmacokinetics and Safety of Solithromycin following Intravenous and Oral Administration in Infants, Children, and Adolescents

Solithromycin is a novel fluoroketolide antibiotic which was under investigation for the treatment of community-acquired bacterial pneumonia (CABP). A phase 1 study was performed to characterize the pharmacokinetics (PK) and safety of solithromycin in children. Eighty-four subjects (median age, 6 years [age range, 4 days to 17 years]) were administered intravenous (i.v.) or oral (capsules or suspension) solithromycin (i.v., 6 to 8 mg/kg of body weight; capsules/suspension, 14 to 16 mg/kg on days 1 and 7 to 15 mg/kg on days 2 to 5). PK samples were collected after the first and multidose administration. Data from 83 subjects (662 samples) were combined with previously collected adolescent PK data (n = 13; median age, 16 years [age range, 12 to 17 years]) following capsule administration to perform a population PK analysis. A 2-compartment PK model characterized the data well, and postmenstrual age was the only significant covariate after accounting for body size differences. Dosing simulations suggested that 8 mg/kg i.v. daily and oral dosing of 20 mg/kg on day 1 (800-mg adult maximum) followed by 10 mg/kg on days 2 to 5 (400-mg adult maximum) would achieve a pediatric solithromycin exposure consistent with the exposures observed in adults. Seventy-six treatment-emergent adverse events (TEAEs) were reported in 40 subjects. Diarrhea (6 subjects) and infusion site pain or phlebitis (3 subjects) were the most frequently reported adverse events related to treatment. Two subjects experienced TEAEs of increased hepatic enzymes that were deemed not to be related to the study treatment. (The phase 1 pediatric studies discussed in this paper have been registered at ClinicalTrials.gov under identifiers NCT01966055 and NCT02268279.).

Clinical application of microsampling versus conventional sampling techniques in the quantitative bioanalysis of antibiotics: a systematic review

Conventional sampling techniques for clinical pharmacokinetic studies often require the removal of large blood volumes from patients. This can result in a physiological or emotional burden, particularly for neonates or pediatric patients. Antibiotic pharmacokinetic studies are typically performed on healthy adults or general ward patients. These may not account for alterations to a patient’s pathophysiology and can lead to suboptimal treatment. Microsampling offers an important opportunity for clinical pharmacokinetic studies in vulnerable patient populations, where smaller sample volumes can be collected. This systematic review provides a description of currently available microsampling techniques and an overview of studies reporting the quantitation and validation of antibiotics using microsampling. A comparison of microsampling to conventional sampling in clinical studies is included.

Comparative Analysis of Ampicillin Plasma and Dried Blood Spot Pharmacokinetics in Neonates

BACKGROUND

Dried blood spot (DBS) is a practical sampling strategy for pharmacokinetic studies in neonates. The utility of DBS to determine the population pharmacokinetics (pop-PK) of ampicillin, as well as accuracy versus plasma samples, was evaluated.

METHODS

An open-label, multicenter, opportunistic, prospective study was conducted in neonates. Ampicillin concentrations from plasma and DBS (CONCPlasma and CONCDBS) were measured by liquid chromatographic tandem mass spectrometry and analyzed using pop-PK and statistical (including transformation) approaches.

RESULTS

A total of 29 paired plasma and DBS samples from 18 neonates were analyzed. The median (range) gestational age and postnatal age were 37 (27-41) weeks and 8 (1-26) days, respectively. The geometric mean of CONCDBS to CONCPlasma ratio was 0.56. Correlation analysis demonstrated strong association between CONCPlasma and CONCDBS (r = 0.902, analysis of variance P < 0.001). Using linear regression transformation, the estimated CONCPlasma (eCONCPlasma) was derived using (CONCDBS - 3.223)/0.51. The median bias and geometric mean ratio improved to -11% and 0.88 (Wilcoxon signed-rank test, P < 0.001), respectively, when comparing eCONCPlasma to CONCPlasma. Furthermore, using pop-PK modeling, the median bias (interquartile range) for clearance and individual predicted concentrations improved to 8% (-11 to 50) and -8% (-34 to 11), respectively, when eCONCPlasma was used.

CONCLUSIONS

After transformation, DBS sampling accurately predicted ampicillin exposure in neonates.

Spotlight on solithromycin in the treatment of community-acquired bacterial pneumonia: design, development, and potential place in therapy

Community-acquired bacterial pneumonia (CABP) is a leading cause of death worldwide. However, antibacterial agents used to treat common pathogens in CABP are marked by adverse drug events and increasing antimicrobial resistance. Solithromycin is a new ketolide antibiotic, based on the macrolide antibiotic structure, being studied for use in CABP. It has efficacy in vitro against the common causative pathogens in CABP including Streptococcus pneumoniae, Haemophilus influenzae, and atypical pathogens. In Phase II and Phase III clinical trials, it has been demonstrated efficacious as a single agent for treatment of CABP with an apparently milder adverse event profile than alternative agents.

Solithromycin: A Novel Fluoroketolide for the Treatment of Community-Acquired Bacterial Pneumonia

Solithromycin is a novel fluoroketolide developed in both oral and intravenous formulations to address increasing macrolide resistance in pathogens causing community-acquired bacterial pneumonia (CABP). When compared with its macrolide and ketolide predecessors, solithromycin has several structural modifications which increase its ribosomal binding and reduce its propensity to known macrolide resistance mechanisms. Solithromycin, like telithromycin, affects 50S ribosomal subunit formation and function, as well as causing frame-shift errors during translation. However, unlike telithromycin, which binds to two sites on the ribosome, solithromycin has three distinct ribosomal binding sites. Its desosamine sugar interacts at the A2058/A2059 cleft in domain V (as all macrolides do), an extended alkyl-aryl side chain interacts with base pair A752-U2609 in domain II (similar to telithromycin), and a fluorine at C-2 of solithromycin provides additional binding to the ribosome. Studies describing solithromycin activity against Streptococcus pneumoniae have reported that it does not induce erm-mediated resistance because it lacks a cladinose moiety, and that it is less susceptible than other macrolides to mef-mediated efflux due to its increased ribosomal binding and greater intrinsic activity. Solithromycin has demonstrated potent in vitro activity against the most common CABP pathogens, including macrolide-, penicillin-, and fluoroquinolone-resistant isolates of S. pneumoniae, as well as Haemophilus influenzae and atypical bacterial pathogens. Solithromycin displays multi-compartment pharmacokinetics, a large volume of distribution (>500 L), approximately 67% bioavailability when given orally, and serum protein binding of 81%. Its major metabolic pathway appears to follow cytochrome P450 (CYP) 3A4, with metabolites of solithromycin undergoing biliary excretion. Its serum half-life is approximately 6-9 h, which is sufficient for once-daily administration. Pharmacodynamic activity is best described as fAUC_0-24/MIC (the ratio of the area under the free drug concentration-time curve from 0 to 24 h to the minimum inhibitory concentration of the isolate). Solithromycin has completed one phase II and two phase III clinical trials in patients with CABP. In the phase II trial, oral solithromycin was compared with oral levofloxacin and demonstrated similar clinical success rates in the intention-to-treat (ITT) population (84.6 vs 86.6%). Clinical success in the clinically evaluable patients group was 83.6% of patients receiving solithromycin compared with 93.1% for patients receiving levofloxacin. In SOLITAIRE-ORAL, a phase III trial which assessed patients receiving oral solithromycin or oral moxifloxacin for CABP, an equivalent (non-inferior) early clinical response in the ITT population was demonstrated for patients receiving either solithromycin (78.2%) or moxifloxacin (77.9%). In a separate phase III trial, SOLITAIRE-IV, patients receiving intravenous-to-oral solithromycin (79.3%) demonstrated non-inferiority as the primary outcome of early clinical response in the ITT population compared with patients receiving intravenous-to-oral moxifloxacin (79.7%). Overall, solithromycin has been well tolerated in clinical trials, with gastrointestinal adverse events being most common, occurring in approximately 10% of patients. Transaminase elevation occurred in 5-10% of patients and generally resolved following cessation of therapy. None of the rare serious adverse events that occurred with telithromycin (i.e., hepatotoxicity) have been noted with solithromycin, possibly due to the fact that solithromycin (unlike telithromycin) does not possess a pyridine moiety in its chemical structure, which has been implicated in inhibiting nicotinic acetylcholine receptors. Because solithromycin is a possible substrate and inhibitor of both CYP3A4 and P-glycoprotein (P-gp), it may display drug interactions similar to macrolides such as clarithromycin. Overall, the in vitro activity, clinical efficacy, tolerability, and safety profile of solithromycin demonstrated to date suggest that it continues to be a promising treatment for CABP.

Nature nurtures the design of new semi-synthetic macrolide antibiotics

Erythromycin and its analogs are used to treat respiratory tract and other infections. The broad use of these antibiotics during the last 5 decades has led to resistance that can range from 20% to over 70% in certain parts of the world. Efforts to find macrolides that were active against macrolide-resistant strains led to the development of erythromycin analogs with alkyl-aryl side chains that mimicked the sugar side chain of 16-membered macrolides, such as tylosin. Further modifications were made to improve the potency of these molecules by removal of the cladinose sugar to obtain a smaller molecule, a modification that was learned from an older macrolide, pikromycin. A keto group was introduced after removal of the cladinose sugar to make the new ketolide subclass. Only one ketolide, telithromycin, received marketing authorization but because of severe adverse events, it is no longer widely used. Failure to identify the structure-relationship responsible for this clinical toxicity led to discontinuation of many ketolides that were in development. One that did complete clinical development, cethromycin, did not meet clinical efficacy criteria and therefore did not receive marketing approval. Work on developing new macrolides was re-initiated after showing that inhibition of nicotinic acetylcholine receptors by the imidazolyl-pyridine moiety on the side chain of telithromycin was likely responsible for the severe adverse events. Solithromycin is a fourth-generation macrolide that has a fluorine at the 2-position, and an alkyl-aryl side chain that is different from telithromycin. Solithromycin interacts at three sites on the bacterial ribosome, has activity against strains resistant to older macrolides (including telithromycin), and is mostly bactericidal. Pharmaceutical scientists involved in the development of macrolide antibiotics have learned from the teachings of Professor Satoshi Omura and progress in this field was not possible without his endeavors.

The solithromycin journey-It is all in the chemistry

The macrolide class of antibiotics, including the early generation macrolides erythromycin, clarithromycin and azithromycin, have been used broadly for treatment of respiratory tract infections. An increase of treatment failures of early generation macrolides is due to the upturn in bacterial macrolide resistance to 48% in the US and over 80% in Asian countries and has led to the use of alternate therapies, such as fluoroquinolones. The safety of the fluoroquinolones is now in question and alternate antibiotics for the outpatient treatment of community acquired bacterial pneumonia are needed. Telithromycin, approved in 2003, is no longer used owing to serious adverse events, collectively called the 'Ketek effects'. Telithromycin has a side chain pyridine moiety that blocks nicotinic acetylcholine receptors. Blockade of these receptors is known experimentally to cause the side effects seen with telithromycin in patients use. Solithromycin is a new macrolide, the first fluoroketolide, which has been tested successfully in two Phase 3 trials and is undergoing regulatory review at the FDA. Solithromycin is differentiated from telithromycin chemically and biologically in that its side chain is chemically different and does not significantly block nicotinic acetylcholine receptors. Solithromycin was well tolerated and effective in clinical trials.

Efficacy of Solithromycin (CEM-101) for Experimental Otitis Media Caused by Nontypeable Haemophilus influenzae and Streptococcus pneumoniae

Solithromycin (CEM-101) is a "fourth-generation" macrolide, as it has three binding site and is acid stable. The three binding sites confer activity against bacteria resistant to the older macrolides and ketolides, including multidrug-resistant Streptococcus pneumoniae and nontypeable Haemophilus influenzae (NTHi). The objective of this study was to evaluate solithromycin pharmacokinetics (PK), middle ear fluid (MEF) concentrations, and microbiologic efficacy in a chinchilla model of experimental otitis media (EOM) due to strains of S. pneumoniae or NTHi. Plasma PK (maximum concentration of drug in serum [Cmax] and area under the concentration-time curve from 0 to 24 h [AUC0-24]) and middle ear fluid (MEF) concentrations were determined. Isolates with specified antimicrobial susceptibility patterns were inoculated directly into the middle ear (ME). Plasma and MEF were collected for PK and MEF cultures performed to determine efficacy. Solithromycin administered at 150 mg/kg of body weight/day resulted in Cmax and AUC0-24 values of 2.2 μg/ml and 27.4 μg · h/ml in plasma and 1.7 μg/ml and 28.2 μg · h/ml in extracellular MEF on day 1. By day 3, Cmax and AUC0-24 values had increased to 4.5 μg/ml and 54 μg · h/ml in plasma and 4.8 μg/ml and 98.6 μg · h/ml in extracellular MEF. For NTHi EOM, three isolates with MIC/minimal bactericidal concentration (MBC) ratios of 0.5/1 μg/ml (isolate BCH1), 2/2 μg/ml (isolate BMC1247C), and 4/4 μg/ml (isolate BMC1213C) were selected. The MEF of >85% of animals infected with BCH1 and BMC1247C was sterilized. For NTHi BMC1213, >85% of MEF cultures remained positive. For S. pneumoniae EOM, 3 isolates with MIC/MBC ratios of 0.06/0.125 μg/ml (S. pneumoniae 331), 0.125/1 μg/ml (S. pneumoniae CP-645 [MLSB phenotype]), and 0.5/2 μg/ml (CP-712 [mefA subclass mefA resistance]) were selected. Solithromycin sterilized MEF in 100% of animals infected with S. pneumoniae 331 and S. pneumoniae CP-645. ME infection persisted in 60% of animals infected with CP-712. In a model of EOM, solithromycin sterilized MEF in >85% of animals challenged with NTHi with an MIC of ≤2 μg/ml and 100% of ME infected with S. pneumoniae with an MIC of ≤0.125 μg/ml.