Pharmacokinetics of intravenously administered azithromycin in pediatric patients

Population Pharmacokinetics and Individualized Medication of Azithromycin for Injection in Children Under 6 Years Old

Pharmacokinetic data for injectable azithromycin in children remain limited. This study aims to develop and validate a population pharmacokinetic model of azithromycin for injection in children under 6 years old and optimize its dosage regimen in this population. We prospectively enrolled patients under 6 years old who received azithromycin for injection at Beijing Friendship Hospital, Capital Medical University. Demographic information, clinical characteristics, and venous blood samples were collected in accordance with the research protocol. Azithromycin concentrations were determined using a validated UPLC-MS/MS method. The population pharmacokinetic model was structured using Phoenix NLME. The adequacy and robustness of the model was evaluated using VPC and bootstrap. We optimized azithromycin's dosing regimen for injection through Monte Carlo simulations. We included 254 plasma concentration data from 148 patients to establish the model. The clearance and volume were 1.27 L/h/kg and 45.6 L/kg, respectively. The covariates included were weight and age. VPC plots and nonparametric bootstrap showed that the final PPK model was reliable and robust. Based on Monte Carlo simulation, we derived a simple and practical dosing scheme. The results provided reference for individualized dosing in this population. The individualized dosing scheme based on Monte Carlo simulation can optimize clinical decision-making and guide personalized therapy.

Azithromycin attenuates wheezing after pulmonary inflammation through inhibiting histone H3K27me3 hypermethylation mediated by EZH2

BACKGROUND

Histone methylation modification plays an irreplaceable role in the wheezing diseases. The aim of this study was to explore whether azithromycin (AZM) attenuates post-inflammatory wheezing through inhibiting hypermethylation of histone H3K27me3 mediated by EZH2.

RESULTS

A randomized controlled trial was conducted on 227 children who underwent fiber-optic bronchoscopy, and bronchoalveolar lavage fluid (BALF) was collected for analyses. The expressions of IL-6, IL-2, NF-κB P65, EZH2 and H3K27me3 in the BALF of wheezing cases were significantly increased when compared with levels in non-wheezing cases (P < 0.05), while IL-10 was decreased (P < 0.05). AZM attenuated the overexpression of NF-κB P65, EZH2 and H3K27me3 in wheezing cases (P < 0.05) and shortened the time of wheezing in wheezing cases (P < 0.05). An in vitro model of inflammation was established using rat alveolar macrophages induced by lipopolysaccharide (LPS). AZM, SN50 (a NK-κB inhibitor) and GSK126 (an EZH2 inhibitor) attenuated the overexpression of EZH2, NF-κB P65 and H3K27me3 induced by LPS in rat alveolar macrophages (P < 0.05). AZM, SN50 and GSK126 normalized the decreased expression of IL-10 induced by LPS in the same samples (P < 0.05). Co-immunoprecipitation results showed that H3K27me3 interacted with EZH2 and NF-κB P65, and immunofluorescence data showed that AZM and SN50 inhibited LPS-induced NF-κB P65 nuclear translocation in rat alveolar macrophages.

CONCLUSION

Histone H3K27me3 hypermethylation mediated by EZH2 may be involved in wheezing after pulmonary inflammation. AZM attenuated wheezing after pulmonary inflammation by inhibiting NF-κB P65-related hypermethylation of H3K27me3 mediated by EZH2.

Investigating the Critical Variables of Azithromycin Oral Absorption Using In Vitro Tests and PBPK Modeling

Azithromycin is an antibiotic listed in the essential list of medicines for adults and pediatrics. Conflicting evidence has been found regarding azithromycin classification according to the Biopharmaceutics classification system (BCS). The purpose of this study was to identify the critical variables that influence the oral absorption of azithromycin in adults and pediatrics. Azithromycin solubility and dissolution studies (oral suspension) were performed in buffers and biorelevant media simulating the fasted and fed gastrointestinal tract. A PBPK model was developed for azithromycin for healthy adult volunteers and pediatrics (Simcyp® v18.2) informed by in vitro solubility and dissolution studies to predict drug performance after administration of azithromycin as an oral suspension. The developed PBPK model predicted azithromycin plasma concentrations-time profiles after administration of an oral suspension to adults and pediatrics. Sensitivity analysis of solubility vs dose suggests that absorption is independent of solubility within the therapeutic dose range in both adults and pediatrics. The developed PBPK model for adults and pediatrics was consistent with the mechanism of permeation through the intestinal membrane (passive and active processes) being the rate-limiting step of azithromycin's absorption. The physiologically based approach proposed was shown to be useful to determine the factors controlling drug absorption in adults and pediatrics.

A comparison of efficacy and safety of complementary and alternative therapies for severe mycoplasma pneumonia in children: A protocol for systematic review and meta-analysis

BACKGROUND

In recent years, the incidence rate of children with severe Mycoplasma pneumoniae pneumonia (SMPP) is increasing, which poses a great threat to children's life and safety. There are some limitations in the existing drugs for the treatment of SMPP, and the supplementary and alternative therapy of SMPP plays an irreplaceable role in the treatment of this disease. This study will evaluate the efficacy and safety of various complementary and alternative therapies for SMPP by means of mesh meta-analysis. In order to provide the basis for clinical rational use.

METHODS

Two researchers will independently and comprehensively searched the Cochrane Central controlled trials registry, Cochrane Library, PubMed, web of science, EMBASE, CNKI, and Wanfang database to collect randomized controlled trials (RCT) studies on complementary and alternative therapies for SMPP. And the relevant references included in the systematic review/meta-analysis are screened. The retrieval time limit is from the establishment of the database to November 2020. We will use Revman 5.3 software for meta-analysis and use grade to grade the quality of evidence in the net meta-analysis (NMA).

RESULTS

The aim of this study was to compare the efficacy and safety of different complementary and alternative therapies in the treatment of SMPP, with a view to evaluating and ranking different interventions.

CONCLUSION

The supplement and replacement therapy of SMPP can improve the clinical efficacy, relieve the clinical symptoms, improve the quality of life of children, and reduce adverse reactions, which can provide strong support for the rational use of clinicians.

INPLASY REGISTRATION NUMBER

INPLASY2020110079.

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

Liquid Chromatography Mass Spectrometry Detection of Antibiotic Agents in Sputum from Persons with Cystic Fibrosis

Antibiotic therapy is expected to impact host microbial communities considerably, yet many studies focused on microbiome and health are often confounded by limited information about antibiotic exposure. Given that antibiotics have diverse pharmacokinetic and antimicrobial properties, investigating the type and concentration of these agents in specific host specimens would provide much needed insight into their impact on the microbes therein. Here, we developed liquid chromatography mass spectrometry (LC-MS) methods to detect 18 antibiotic agents in sputum from persons with cystic fibrosis. Antibiotic spike-in control samples were used to compare three liquid extraction methods on the Waters Acquity Quattro Premier XE. Extraction with dithiothreitol captured the most antibiotics and was used to detect antibiotics in sputum samples from 11 people with cystic fibrosis, with results being compared to the individuals' self-reported antibiotic use. For the sputum samples, two LC-MS assays were used; the Quattro Premier detected nanomolar or micromolar concentrations of 16 antibiotics, whereas the Xevo TQ-XS detected all 18 antibiotics, most at subnanomolar levels. In 45% of tested sputum samples (71/158), at least one antibiotic that was not reported by the subject was detected by both LC-MS methods, a discordance largely explained by the thrice weekly administration and long half-life of azithromycin. For ∼37% of samples, antibiotics reported as taken by the individual were not detected by either instrument. Our results provide an approach for detecting a variety of antibiotics at the site of infection, thereby providing a means to include antibiotic usage data into microbiome studies.

Population Pharmacokinetics and Dosing Optimization of Azithromycin in Children with Community-Acquired Pneumonia

Azithromycin is extensively used in children with community-acquired pneumonia (CAP). Currently, the intravenous azithromycin is used off-label in children partly due to lacking of pharmacokinetic data. Our objective was to evaluate the population pharmacokinetics (PPK) and optimize dose strategy in order to improve treatment in this distinctive population. This was a prospective, multicenter, open-labeled pharmacokinetic study. Blood samples were collected from hospitalized pediatric patients and concentrations were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). PPK analysis was conducted using NONMEM software. The pharmacokinetic data from 95 pediatric patients (age range, 2.1 to 11.7 years) were available for analysis. The PPK was best fitted by a two-compartment model with linear elimination. Covariate analysis verified that body weight and alanine aminotransferase (ALT) had significant effects on azithromycin pharmacokinetics, yielding a 24% decrease of clearance in patients with ALT of >40. Monte Carlo simulation showed that for children with normal liver function, a loading-dose strategy (a loading dose of 15 mg/kg of body weight followed by maintenance doses of 10 mg/kg) would achieve the ratio of the area under free drug plasma concentration-time curve over 24 h (fAUC) to MIC₉₀ (fAUC/MIC) target of 3 h in 53.2% of hypothetical patients, using a normative MIC susceptibility breakpoint of 2 mg/liter. For children with ALT of >40, the proposed dose needed to decrease by 15% to achieve comparable exposure. The corresponding risk of overdose for the recommended dosing regimen was less than 5.8%. In conclusion, the PPK of azithromycin was evaluated in children with CAP and an optimal dosing regimen was constructed based on developmental pharmacokinetic-pharmacodynamic modeling and simulation.

Comparative effectiveness of azithromycin for treating scrub typhus: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

Scrub typhus is a zoonotic disease that remains an important health threat in endemic areas. Appropriate anti-rickettsial treatment ensures a successful recovery. Doxycycline is a recommended drug, but it is contraindicated in pregnant women and young children. Azithromycin is a safer alternative drug, but its effectiveness remains largely unclear. Herein, we conducted a systematic review and meta-analysis to determine the effectiveness of azithromycin.

METHODS

Studies that investigated azithromycin in treating scrub typhus were systematically identified from electronic databases up to December 2016. Information regarding study population, disease severity, treatment protocols, and responses was extracted and analyzed.

RESULTS

In this review, 5 studies were included, which comprised a total of 427 patients. When comparing the treatment failure rate, we observed a favorable outcome in patients treated with azithromycin (risk ratio [RR] 0.83, 95% confidence interval [CI] 0.23-2.98). However, patients in the azithromycin group had longer time to defervescence (mean difference 4.38 hours, 95% CI -2.51 to 11.27) and higher rate of fever for more than 48 hours (RR 1.31, 95% CI 0.81-2.12). Moreover, patients treated with azithromycin had less adverse effects (RR 0.8, 95% CI 0.42-1.52).

CONCLUSIONS

Azithromycin is as effective as other anti-rickettsial drugs with higher treatment success rates, lower frequency of adverse effects, and longer time to defervescence (GRADE 2B). Therefore, it is reasonable to use azithromycin as the first-line treatment against scrub typhus. Further studies are warranted to elucidate the effectiveness of azithromycin in specific patient groups, at high dose and influence of drug resistance.

[The clinical effectiveness of azithromycin antimicrobial therapy used for the treatment of acute bacterial sinusitis in the patients presenting with concomitant pathology]

The objective of the present publication was to report the result of the evaluation of the clinical effectiveness of azithromycin (Sumamed) antimicrobial therapy used for the treatment of bacterial acute rhinsinusitis (ARS) in the patients presenting with concomitant pathology of the respiratory and cardiovascular systems. Dynamics of the reversal of the clinical symptoms of bacterial ARS in the patients of the study group is described. Neither adverse side effects nor complications in response to the treatment were documented. 98.6% of the patients recovered from the disease within 7 days after the onset of the treatment. It is concluded that antimicrobial therapy with the use of azithromycin (Sumamed) based at the outpatient settings provides a highly efficient tool for the treatment of the patients presenting with concomitant pathology of the respiratory and cardiovascular systems.

Considerations for a Pediatric Biopharmaceutics Classification System (BCS): application to five drugs

It has been advocated that biopharmaceutic risk assessment should be conducted early in pediatric product development and synchronized with the adult product development program. However, we are unaware of efforts to classify drugs into a Biopharmaceutics Classification System (BCS) framework for pediatric patients. The objective was to classify five drugs into a potential BCS. These five drugs were selected since both oral and intravenous pharmacokinetic data were available for each drug, and covered the four BCS classes in adults. Literature searches for each drug were conducted using Medline and applied to classify drugs with respect to solubility and permeability in pediatric subpopulations. Four pediatric subpopulations were considered: neonates, infants, children, and adolescents. Regarding solubility, dose numbers were calculated using a volume for each subpopulation based on body surface area (BSA) relative to 250 ml for a 1.73 m(2) adult. Dose numbers spanned a range of values, depending upon the pediatric dose formula and subpopulation. Regarding permeability, pharmacokinetic literature data required assumptions and decisions about data collection. Using a devised pediatric BCS framework, there was agreement in adult and pediatric BCS class for two drugs, azithromycin (class 3) and ciprofloxacin (class 4). There was discordance for the three drugs that have high adult permeability since all pediatric permeabilities were low: dolasetron (class 3 in pediatric), ketoprofen (class 4 in pediatric), and voriconazole (class 4 in pediatric). A main contribution of this work is the identification of critical factors required for a pediatric BCS.

Azithromycin: mechanisms of action and their relevance for clinical applications

Azithromycin is a macrolide antibiotic which inhibits bacterial protein synthesis, quorum-sensing and reduces the formation of biofilm. Accumulating effectively in cells, particularly phagocytes, it is delivered in high concentrations to sites of infection, as reflected in rapid plasma clearance and extensive tissue distribution. Azithromycin is indicated for respiratory, urogenital, dermal and other bacterial infections, and exerts immunomodulatory effects in chronic inflammatory disorders, including diffuse panbronchiolitis, post-transplant bronchiolitis and rosacea. Modulation of host responses facilitates its long-term therapeutic benefit in cystic fibrosis, non-cystic fibrosis bronchiectasis, exacerbations of chronic obstructive pulmonary disease (COPD) and non-eosinophilic asthma. Initial, stimulatory effects of azithromycin on immune and epithelial cells, involving interactions with phospholipids and Erk1/2, are followed by later modulation of transcription factors AP-1, NFκB, inflammatory cytokine and mucin release. Delayed inhibitory effects on cell function and high lysosomal accumulation accompany disruption of protein and intracellular lipid transport, regulation of surface receptor expression, of macrophage phenotype and autophagy. These later changes underlie many immunomodulatory effects of azithromycin, contributing to resolution of acute infections and reduction of exacerbations in chronic airway diseases. A sub-group of post-transplant bronchiolitis patients appears to be sensitive to azithromycin, as may be patients with severe sepsis. Other promising indications include chronic prostatitis and periodontitis, but weak activity in malaria is unlikely to prove crucial. Long-term administration of azithromycin must be balanced against the potential for increased bacterial resistance. Azithromycin has a very good record of safety, but recent reports indicate rare cases of cardiac torsades des pointes in patients at risk.

Pharmaceutical development and optimization of azithromycin suppository for paediatric use

Pharmaceutical development and manufacturing process optimization work was undertaken in order to propose a potential paediatric rectal formulation of azithromycin as an alternative to existing oral or injectable formulations. The target product profile was to be easy-to-use, cheap and stable in tropical conditions, with bioavailability comparable to oral forms, rapidly achieving and maintaining bactericidal concentrations. PEG solid solution suppositories were characterized in vitro using visual, HPLC, DSC, FTIR and XRD analyses. In vitro drug release and in vivo bioavailability were assessed; a study in rabbits compared the bioavailability of the optimized solid solution suppository to rectal solution and intra-venous product (as reference) and to the previous, non-optimized formulation (suspended azithromycin suppository). The bioavailability of azithromycin administered as solid solution suppositories relative to intra-venous was 43%, which compared well to the target of 38% (oral product in humans). The results of 3-month preliminary stability and feasibility studies were consistent with industrial production scale-up. This product has potential both as a classical antibiotic and as a product for use in severely ill children in rural areas. Industrial partners for further development are being sought.

Screening paediatric rectal forms of azithromycin as an alternative to oral or injectable treatment

The aim of this study was to identify a candidate formulation for further development of a home or near-home administrable paediatric rectal form of a broad-spectrum antibiotic - specially intended for (emergency) use in tropical rural settings, in particular for children who cannot take medications orally and far from health facilities where injectable treatments can be given. Azithromycin, a broad-spectrum macrolide used orally or intravenously for the treatment of respiratory tract, skin and soft tissue infections, was selected because of its pharmacokinetic and therapeutic properties. Azithromycin in vitro solubility and stability in physiologically relevant conditions were studied. Various pharmaceutical forms, i.e. rectal suspension, two different rectal gels, polyethylene glycol (PEG) suppository and hard gelatin capsule (HGC) were assessed for in vitro dissolution and in vivo bioavailability in the rabbit. Azithromycin PEG suppository appears to be a promising candidate.

Azithromycin maintenance therapy in patients with cystic fibrosis: a dose advice based on a review of pharmacokinetics, efficacy, and side effects

Azithromycin maintenance therapy results in improvement of respiratory function in patients with cystic fibrosis (CF). In azithromycin maintenance therapy, several dosing schemes are applied. In this review, we combine current knowledge about azithromycin pharmacokinetics with the dosing schedules used in clinical trials in order to come to a dosing advise which could be generally applicable. We used data from a recently updated Cochrane meta analysis (2011), the reports of clinical trials and pharmacokinetic studies. Based on these data, it was concluded that a dose level of 22-30 mg/kg/week is the lowest dose level with proven efficacy. Due to the extended half-life in patients with CF, the weekly dose of azithromycin can be divided in one to seven dosing moments, depending on patient preference and gastro-intestinal tolerance. No important side effects or interactions with other CF-related drugs have been documented so far.

Comparison of azithromycin pharmacokinetics following single oral doses of extended-release and immediate-release formulations in children with acute otitis media

An azithromycin extended-release (ER) oral suspension was developed to improve the gastrointestinal tolerability profile without substantially compromising systemic exposure. A single dose of 30 mg/kg azithromycin immediate-release (IR) oral suspension has been used in children to treat acute otitis media (AOM). This study was conducted to compare the pharmacokinetics of a 60-mg/kg azithromycin ER single dose with a 30-mg/kg azithromycin IR single dose in children with AOM aged 6 months to 6 years (n = 19 per treatment). Serum samples were collected at 1, 2, 3, 4, 8, 24, 48, and 72 h after dosing. The area under the curve from time zero to 72 h postdosing (AUC(0-72)) was calculated based on a noncompartmental method. One-way analysis of variance (ANOVA) was used to compare exposure parameters (e.g., AUC(0-72) and peak concentration) as well as concentrations at each time point. The adjusted geometric mean ratio of the ER/IR AUC(0-72) was 157.98% (90% confidence interval [CI], 98.87%, 252.44%), which met the predefined criterion of the lower boundary of the 90% CI of ≥ 80%. As expected, due to the slower-release profile of the ER formulation, the concentrations of the ER formulation during the first 3 h were lower than those of the IR formulation. After 3 h postdosing, the lower boundaries of the 90% CI for the ER/IR concentration ratios were greater than 100%. These results indicated that a 60-mg/kg single dose of ER azithromycin provides similar or greater systemic exposure in children than the 30-mg/kg single dose of IR azithromycin.

Pharmacokinetics, safety, and biologic effects of azithromycin in extremely preterm infants at risk for ureaplasma colonization and bronchopulmonary dysplasia

Ureaplasma spp. respiratory tract colonization is a significant risk factor for bronchopulmonary dysplasia (BPD), a chronic lung disorder in preterm infants. As an initial step preparatory to future clinical trials to evaluate the clinical efficacy of azithromycin to prevent BPD, the authors characterized the pharmacokinetics, safety, and biological effects of a single intravenous dose of azithromycin (10 mg/kg) in preterm neonates (n = 12) 24 to 28 weeks gestation at risk for Ureaplasma infection and BPD. A 2-compartment structural model with the clearance and volume of peripheral compartment (V2) allometrically scaled on body weight (WT) best described the pharmacokinetics of azithromycin in preterm neonates. The estimated parameters were clearance [0.18 L/h × WT(kg)(0.75)], intercompartmental clearance [1.0 L/h], volume of distribution of central compartment [0.93 L], and V2 [14.2 L × WT(kg)]. There were no serious adverse events attributed to azithromycin. A single dose of azithromycin did not suppress inflammatory cytokines or myeloperoxidase activity in tracheal aspirates. These results demonstrated the safety of azithromycin and developed a pharmacokinetic model that is useful for future simulation-based clinical trials for eradicating Ureaplasma and preventing BPD in preterm neonates.

Increased melibiose/rhamnose ratio in bile of rats with acute cholestasis

BACKGROUND AND AIM

Melibiose/rhamnose permeability test is used for noninvasive intestinal mucosa barrier testing. However, the possible escape route of the absorbed saccharides through either intact or impaired blood-biliary barriers has not so far been explored. The objective of the present study was therefore two-fold: First, to describe in detail the biliary pharmacokinetics of melibiose and rhamnose in rats; second, to evaluate the changes of both sugars' pharmacokinetics upon impairment of the blood-biliary barrier by acute extrahepatic cholestasis in rats.

METHODS

Bile duct obstructed (BDO), sham-operated and intact (unoperated) male Wistar rats were administered, 24 h after the appropriate intervention, with a single intravenous dose of melibiose and rhamnose, and a 4-h pharmacokinetic study was performed.

RESULTS

In intact animals, the biliary excretion of melibiose and rhamnose was only 0.06% and 0.4% of the administered dose, respectively, while the urinary excretion accounted for 70.6% and 61.7%, respectively. In BDO animals, the biliary excretion rate of both saccharides, especially that of melibiose, was increased with a consequent 4.4-fold rise of the biliary melibiose/rhamnose ratio, the accepted paracellular permeability indicator. Both, the renal clearance of melibiose and the urinary melibiose/rhamnose ratio remained uninfluenced by cholestasis.

CONCLUSION

The present study is the first to describe in detail pharmacokinetic parameters and the biliary excretion of melibiose and rhamnose in healthy and cholestatic rats. The altered melibiose/rhamnose biliary excretion ratio in BDO rats indicates that the test is able to detect the impairment of the blood-biliary barrier in acute extrahepatic cholestasis.

Amiodarone modulates pharmacokinetics of low-dose methotrexate in rats

Clinical studies of low-dose methotrexate (LDMTX) pharmacokinetics document increased plasma concentrations of MTX after co-administration of the drug with amiodarone or macrolide antibiotics. As drug-drug interactions may increase the toxicity of LDMTX, a rat model was used to follow renal and biliary elimination of MTX during its constant-rate i.v. infusion and concomitant single bolus i.v. injections of amiodarone or azithromycin. The mean steady-state plasma concentration of 1.7+/-0.1 micromol/l was reached and the total clearance achieved 17.7+/-1.0 ml/min/kg. Administration of amiodarone decreased the biliary clearance of MTX to 73% of the control values (p<0.05). Correspondingly, the total clearance decreased to 72% and plasma MTX concentrations were augmented to 2.5+/-0.4 micromol/l (p<0.05). Amiodarone-treated rats exhibited a 3.3-fold decrease in the renal clearance (p<0.05) of conjugated bilirubin, which was associated with its increased plasma concentration. In contrast, azithromycin did not alter any of the MTX pharmacokinetic parameters. In conclusion, this is the first report describing the impairment of MTX hepatic elimination during co-administration with amiodarone. This study also provides new insight into acute amiodarone-induced hyperbilirubinaemia, where increased bilirubin production and decreased renal clearance may contribute to this effect. Importantly, azithromycin seems to be a safe co-medication during LDMTX therapy.