Lipid droplets can promote drug accumulation and activation.

Genetic screens in cultured human cells represent a powerful unbiased strategy to identify cellular pathways that determine drug efficacy, providing critical information for clinical development. We used insertional mutagenesis-based screens in haploid cells to identify genes required for the sensitivity to lasonolide A (LasA), a macrolide derived from a marine sponge that kills certain types of cancer cells at low nanomolar concentrations. Our screens converged on a single gene, LDAH, encoding a member of the metabolite serine hydrolase family that is localized on the surface of lipid droplets. Mechanistic studies revealed that LasA accumulates in lipid droplets, where it is cleaved into a toxic metabolite by LDAH. We suggest that selective partitioning of hydrophobic drugs into the oil phase of lipid droplets can influence their activation and eventual toxicity to cells.

Pharmacokinetic/Pharmacodynamic Evaluation of Solithromycin against Streptococcus pneumoniae Using Data from a Neutropenic Murine Lung Infection Model.

Solithromycin (CEM-101) is a novel fluoroketolide antimicrobial agent with activity against typical and atypical pathogens associated with community-acquired bacterial pneumonia. Using a neutropenic murine lung infection model, the objectives of this study were to identify the pharmacokinetic/pharmacodynamic (PK/PD) index most closely associated with efficacy and the magnitude of such indices associated with solithromycin efficacy against Streptococcus pneumoniae Plasma and epithelial lining fluid (ELF) samples for pharmacokinetics (PK) were collected serially over 24 hours from healthy mice administered single doses of solithromycin (0.625 to 40 mg/kg). Neutropenic CD-1 mice infected with 108 CFUs of one of five S. pneumoniae isolates were administered solithromycin (0.156 to 160 mg/kg/day) via oral gavage. Doses were administered in a fractionated manner for mice infected with one isolate, while mice infected with the remaining four isolates received solithromycin as either a regimen every 6 hours or every 12 hours. A three-compartment model best described solithromycin PK in the plasma and ELF (r2 = 0.935 and 0.831, respectively). The ratio of total-drug ELF to free-drug plasma area under the concentration-time curve (AUC) from time 0 to 24 hours was 2.7. Free-drug plasma and total-drug ELF AUC to minimum inhibitory concentration ratios (AUC/MIC ratios) were most predictive of efficacy (r2 = 0.851 and 0.850, respectively). The magnitude of free-drug plasma/total-drug ELF AUC/MIC ratios associated with net bacterial stasis and a 1- and 2-log10 CFU reduction from baseline was 1.65/1.26, 6.31/15.1, and 12.8/59.8, respectively. These data provided dose selection support for solithromycin for clinical trials in patients with community-acquired bacterial pneumonia.

Solithromycin: A novel ketolide antibiotic.

PURPOSE: The pharmacology, pharmacokinetics, pharmacodynamics, antimicrobial activity, clinical safety, and current regulatory status of solithromycin are reviewed. SUMMARY: Solithromycin is a novel ketolide antibiotic developed for the treatment of community-acquired bacterial pneumonia (CABP). Its pharmacologic, pharmacokinetic, and pharmacodynamic properties provide activity against a broad range of intracellular organisms, including retained activity against pathogens displaying various mechanisms of macrolide resistance. Phase III clinical trials of solithromycin demonstrated noninferiority of both oral and i.v.-to-oral regimens of 5-7 days' duration compared with moxifloxacin for patients with moderately severe CABP. Nearly one third of patients receiving i.v. solithromycin experienced infusion-site reactions. Although no liver-related adverse events were reported in patients receiving oral solithromycin, more patients receiving i.v.-to-oral solithromycin experienced asymptomatic, transient transaminitis, with alanine transaminase levels of >3 to >5 times the upper limit, compared with those treated with moxifloxacin. These results led the Food and Drug Administration to conclude that the solithromycin new drug application was not approvable as filed, adding that the risk of hepatotoxicity had not yet been adequately characterized. The agency further recommended a comparative study of patients with CABP to include approximately 9,000 patients exposed to solithromycin in order to exclude drug-induced liver injury events occurring at a rate of 1 in 3,000 with 95% probability. CONCLUSION: Solithromycin is a novel ketolide antibiotic with activity against a broad spectrum of intracellular organisms, including those displaying macrolide resistance. While demonstrating noninferiority to a current first-line agent in the treatment of CABP, concerns for drug-induced liver injury and infusion-site reactions have placed its regulatory future in doubt.

Preclinical Study of Single-Dose Moxidectin, a New Oral Treatment for Scabies: Efficacy, Safety, and Pharmacokinetics Compared to Two-Dose Ivermectin in a Porcine Model.

BACKGROUND: Scabies is one of the commonest dermatological conditions globally; however it is a largely underexplored and truly neglected infectious disease. Foremost, improvement in the management of this public health burden is imperative. Current treatments with topical agents and/or oral ivermectin (IVM) are insufficient and drug resistance is emerging. Moxidectin (MOX), with more advantageous pharmacological profiles may be a promising alternative. METHODOLOGY/PRINCIPAL FINDINGS: Using a porcine scabies model, 12 pigs were randomly assigned to receive orally either MOX (0.3 mg/kg once), IVM (0.2 mg/kg twice) or no treatment. We evaluated treatment efficacies by assessing mite count, clinical lesions, pruritus and ELISA-determined anti-S. scabiei IgG antibodies reductions. Plasma and skin pharmacokinetic profiles were determined. At day 14 post-treatment, all four MOX-treated but only two IVM-treated pigs were mite-free. MOX efficacy was 100% and remained unchanged until study-end (D47), compared to 62% (range 26-100%) for IVM, with one IVM-treated pig remaining infected until D47. Clinical scabies lesions, pruritus and anti-S. scabiei IgG antibodies had completely disappeared in all MOX-treated but only 75% of IVM-treated pigs. MOX persisted ~9 times longer than IVM in plasma and skin, thereby covering the mite's entire life cycle and enabling long-lasting efficacy. CONCLUSIONS/SIGNIFICANCE: Our data demonstrate that oral single-dose MOX was more effective than two consecutive IVM-doses, supporting MOX as potential therapeutic approach for scabies.

Pharmacokinetic/pharmacodynamic-based treatment of disseminated Mycobacterium avium.

Disseminated Mycobacterium avium complex (MAC) is treated with a macrolide and ethambutol. However, the kill rates are extremely slow so that therapy takes many months to years to achieve and even then more than 40% of patients are not completely cured. Recent studies have demonstrated that assays that detect extracellular MAC have a limited predictive value. Antibiotics kill at a much slower and more disappointing rate against bacilli within macrophages. Use of pharmacodynamic/pharmacokinetic models has resulted in design of new doses and dosing schedules for disseminated MAC, as well as new susceptibility breakpoints for ethambutol and moxifloxacin.

Estimation of absolute oral bioavailability of moxidectin in dogs using a semi-simultaneous method: influence of lipid co-administration.

Moxidectin is a long-acting anthelmintic drug for which little is known about its kinetic behaviour in dogs and its oral absolute bioavailability has never been reported. We studied the pharmacokinetics of moxidectin in dogs, with a special emphasis on oral bioavailability and the influence of lipid co-administration, by using a semi-simultaneous method of administration. Ten Beagle dogs were dosed orally and then intravenously (i.v.) with 0.2 mg/kg moxidectin. The oral application was conducted with or without corn oil co-administration. Moxidectin concentration-time profiles in plasma were analysed using a compartmental modelling approach, designed to fit the oral and i.v. kinetic disposition curves simultaneously. In contrast to what happens in other species, our study indicates that the bioavailability of orally given moxidectin in dogs is nearly total (90.2 +/- 7.4%), and is not enhanced by lipid co-administration. The clearance, the volume of distribution, the mean residence time and the terminal half-life were similar to what was already described for other species. Finally our trial suggests that the body condition (degree of obesity) is likely to be a major determinant of moxidectin kinetics in dogs because of its modulation of the volume of distribution that indirectly controls the terminal half-life of the drug.

Contribution of lymphatic transport to the systemic exposure of orally administered moxidectin in conscious lymph duct-cannulated dogs.

Moxidectin, a macrocyclic lactone (ML), is a potent parasiticide widely used in veterinary medicine and currently under development for use in humans. The contribution of the lymphatic route to the intestinal absorption and transport of moxidectin to the systemic circulation was evaluated in lymph duct-cannulated dogs. Beagle dogs were operated for lymph duct cannulation and were orally dosed with 38g of corn oil and moxidectin (0.2mg/kg, n=3). The lymph and plasma were collected over 24h and moxidectin and triglyceride concentrations were measured. Similarly, control dogs (n=5) were dosed orally with moxidectin and oil and subsequently with moxidectin intravenously. Pharmacokinetic parameters were calculated for moxidectin in the plasma of the dogs. Moxidectin readily accumulated in the lymph and reached a plateau 8h post-administration, paralleling triglyceride appearance. The percentage of moxidectin recovered in lymph was 22+/-3% of the total administered dose with 92% being associated with triglyceride-rich particles. The systemic bioavailability of oral moxidectin coadministered with lipid was only 40% in the lymph duct-cannulated dogs compared with 71% in the controls. Our data clearly indicate that the lymphatic transport process contributes significantly to the post-prandial intestinal absorption of moxidectin and subsequently to its systemic bioavailability. The lymphatic transport of moxidectin offers potential strategies based on lipid formulations to improve the bioavailability of MLs when administered orally.

Application of pharmacokinetics and pharmacodynamics to antimicrobial therapy of community-acquired respiratory tract infections.

To achieve bacteriologic and clinical success, sufficient concentrations of antimicrobial at the site of infection must be maintained for an adequate period of time. These dynamics are determined by combining drug pharmacokinetic and pharmacodynamic (PK/PD) data with minimum inhibitory concentrations. Bacteriologically confirmed failures have been reported in otitis media and, with a lesser degree of evidence, in pneumococcal pneumonia with a variety of agents that include beta-lactams, macrolides and fluoroquinolones. These failures have been shown to be due to infection by resistant pathogens or suboptimal therapy. However, no clinical failure has been reported during therapy for bacteremic pneumococcal pneumonia with adequate doses of beta-lactams. The failures reported with macrolides or fluoroquinolones have been due to either preexisting resistance to these agents that cannot be overcome by increasing the dose of the antimicrobial or, more rarely, the emergence of resistance during therapy. In this review, we offer an overview of the most important attributes of the main antimicrobials that are currently used in the treatment of community-acquired respiratory tract infections from a PK/PD perspective.

Infection site concentrations: their therapeutic importance and the macrolide and macrolide-like class of antibiotics.

Much confusion exists over the pharmacodynamics of macrolides, azalides, and ketolides, as the concentration-time profile for these agents is low relative to the minimum inhibitory concentration (MIC) of the pathogens for which they are used. Studies of respiratory tract infection have highlighted the importance of drug concentrations at the site of infection and have demonstrated a role for white blood cells in the delivery of drug to the infection site. Population mathematical modeling and Monte Carlo simulation have shown that the ability of macrolides, azalides, and ketolides to concentrate at the infection site has a considerable effect on microbial activity. Studies of the pharmacodynamics of these agents in animal models have centered on the mouse thigh model; however, the suitability of this model for investigation of respiratory tract infections for macrolides and macrolide-like drugs is questionable. Comparison of the mouse thigh model with the mouse lung model shows immediate discrepancies, such as a need for higher area under the concentration-time curve (AUC):MIC ratios in the mouse thigh. There are obvious failings in the use of a thigh model, as it does not take into account the accumulation of white blood cells in the epithelial lining fluid and therefore ignores the impact of white blood cell delivery to the site of infection and release of significant amounts of drug during phagocytosis. Ultimately, whereas the mouse pneumonia model is useful in identifying pharmacodynamically linked variables and the magnitude of variable required for a successful microbiologic outcome, extrapolation to human dosing must involve the use of human epithelial lining fluid penetration data.

Enhancement of oral moxidectin bioavailability in rabbits by lipid co-administration.

Moxidectin is a member of the macrocyclic lactone family of drugs widely used for the control of internal and external parasites. Because moxidectin is highly lipophilic, we suspect that lymphatic transport influences the intestinal absorption of oral formulations of the drug. We studied the influence of lipid co-administration on the pharmacokinetics of an oral formulation of moxidectin in rabbits. Ten rabbits were orally administered 0.3 mg kg(-1) moxidectin with or without sunflower oil. Moxidectin and triglyceride were analyzed in plasma over 23 days. Sunflower oil co-administration significantly increased the area under the plasma concentration-time curve of moxidectin (98%, P<0.05) and prolonged its mean residence time from 1.52 days to 2.12 days (P<0.04). Simultaneously, an increase in plasma triglyceride was observed in response to oil administration. It is suggested that lipid administration increases the systemic availability of oral moxidectin by enhancing the extent of intestinal lymphatic transport of the drug. Lipid-based formulations should improve the bioavailability of moxidectin in rabbits.

[Bacterial resistance and pharmacodynamics as the basis for prescribing antibiotics in respiratory infections]. / Resistencias bacterianas y farmacodinámica como bases de la prescripción de antibióticos en infecciones respiratorias.

The choice of antibiotic therapy in respiratory tract infections is usually empirical. However, this choice is complicated by the increasing prevalence of resistant strains among the major bacterial pathogens involved in these infections, particularly Streptococcus pneumoniae. The aim of antimicrobial therapy in respiratory tract infections should be bacterial eradication, which is necessary to maximize clinical cure and minimize the development and spread of resistance. An increase in antimicrobial resistance reduces the probability of achieving eradication and increases the probability of clinical failure. Recent reports have demonstrated the clinical relevance of respiratory bacterial resistance to macrolides and some fluoroquinolones and betalactams. Unlike macrolide and fluoroquinolone resistance, penicillin resistance in Streptococcus pneumoniae can be overcome by increasing the dose, and hence increasing the time during which serum concentrations are above the MIC. Pharmacokinetic/pharmacodynamic (PK/PD) parameters can be used to establish breakpoints predictive of bacterial eradication. From the viewpoint of PK/PD, in Spain only high-doses of amoxicillin/clavulanic acid (875/125 mg tid and 2000/125 mg bid) and levofloxacin, among the oral antibiotics considered, achieve optimal coverage against S. pneumoniae and Haemophilus influenzae.

Optimizing outcomes with antimicrobial therapy through pharmacodynamic profiling.

In patients with infection, improving the probability of positive treatment outcomes depends on optimizing the interactions between the host, pathogen, and drug. In this setting, optimal regimens must be utilized which not only maximize effectiveness in a specific patient, but also minimize the development of microbial resistance. The probability of achieving a specifically targeted antimicrobial exposure can be assessed using Monte Carlo simulation, a technique which integrates an agent's in vitro potency distribution (i.e., minimum inhibitory concentrations [MICs]) with the pharmacokinetic profile. The targeted pharmacodynamic parameters assessed by this technique include the ratio of peak concentration (C(max)) to MIC (C(max) : MIC); the ratio of the area under the plasma concentration-time curve (AUC) to MIC (AUC : MIC), and the time the drug concentration exceeds the MIC (T > MIC). Some antimicrobials, e.g., the aminoglycosides, are most effective/bactericidal when they have a high C(max) : MIC ratio; others, e.g., the fluoroquinolones, are more effective when the AUC : MIC ratio is high. In both of these scenarios, organism eradication is concentration-dependent, and the therapeutic goal is to maximize drug exposure. Like the fluoroquinolones, the efficacy of telithromycin, a newly developed ketolide, is most related to the AUC : MIC ratio. Outcome for other agents, such as the beta-lactams, is best predicted by the T > MIC; in this case, organism eradication is time-dependent, and the therapeutic goal is to optimize the duration of antimicrobial exposure. This article discusses how the use of currently available antimicrobials can be optimized through an appreciation of pharmacodynamic profiling.