Colistimethate sodium for the treatment of chronic pulmonary infection in cystic fibrosis: an evidence-based review of its place in therapy

Acute kidney injury in cystic fibrosis patients treated with intravenous colistimethate sodium or tobramycin

OBJECTIVES

Colistimethate sodium and tobramycin are important systemic antibiotics for treatment of cystic fibrosis (CF) pulmonary exacerbations but can induce acute kidney injury (AKI). We characterize the rate of AKI in CF patients treated with systemic colistimethate sodium compared with tobramycin.

METHODS

This single-centre, retrospective cohort study included hospitalized CF patients treated with IV colistimethate sodium or tobramycin. The primary outcome was AKI defined using the RIFLE criteria. Multivariate logistic regression using a mixed model was performed to identify variables that were independently associated with AKI.

RESULTS

Overall, 156 patients representing 507 care encounters were included. The OR of AKI was not increased with IV colistimethate sodium relative to IV tobramycin after adjusting for other potential predictor variables (aOR 1.00; 95% CI 0.16-6.03). The frequency of AKI was 9.5% across all encounters, 6.9% with IV colistimethate sodium and 9.9% with IV tobramycin, with RIFLE category R (risk) being the most common stage, accounting for 4.2% of encounters with IV colistimethate sodium and 9.2% with IV tobramycin. The concomitant use of another nephrotoxin (aOR 2.51; 95% CI 1.27-4.95) or the combination of vancomycin and piperacillin/tazobactam (aOR 5.95; 95% CI 2.05-17.3) were both associated with increased odds of AKI.

CONCLUSIONS

Systemic treatment with colistimethate sodium or tobramycin in the CF patient population is associated with a similar rate of nephrotoxicity. However, clinicians should be mindful of the increased risk for AKI in patients treated with either IV colistimethate sodium or IV tobramycin when used concurrently with other nephrotoxic agents, particularly the combination of vancomycin and piperacillin/tazobactam.

Secondary Prophylaxis With Inhaled Colistin to Prevent Recurrence of Pseudomonas aeruginosa and Extended-spectrum β-lactamase-producing Enterobacterales Pneumonia in ICU After Lung Transplantation: A Before-and-after Retrospective Cohort Analysis

BACKGROUND

Early pneumonia is an independent risk factor for 1-y mortality after lung transplantation (LTx). Pseudomonas aeruginosa is the most common isolate in early pneumonia and is also associated with an increased risk of chronic lung allograft dysfunction. The aim of our study was to evaluate the efficacy of secondary prophylaxis with inhaled colistin (IC) in preventing the recurrence of P aeruginosa or extended-spectrum β-lactamase-producing Enterobacterales (ESBL-PE) pneumonia in the postoperative period in the intensive care unit after LTx.

METHODS

We conducted a before-and-after retrospective cohort study by including all patients who underwent LTx between January 2015 and December 2020 in our center. Secondary prophylaxis with IC was instituted in January 2018 (observation period from January 2015 to December 2017, intervention period from January 2018 to December 2020).

RESULTS

A total of 271 lung transplants were included (125 in the observation period and 146 in the intervention period). The patients were predominately male (64.2%) with a median age of 57 y and received double LTx (67.9%) for chronic obstructive pulmonary disease/emphysema (36.2%) or interstitial lung disease (48.3%). The proportion of patients who experienced at least 1 recurrence of P aeruginosa or ESBL-PE pneumonia was significantly lower in the intervention period than in the observation period (0.7% versus 7.2%, P = 0.007).

CONCLUSIONS

Our study suggests a potential benefit of secondary prophylaxis with IC to prevent the recurrence of P aeruginosa or ESBL-PE pneumonia in the intensive care unit after LTx.

Alginate oligosaccharides enhance diffusion and activity of colistin in a mucin-rich environment

In a number of chronic respiratory diseases e.g. cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), the production of viscous mucin reduces pulmonary function and represents an effective barrier to diffusion of inhaled therapies e.g. antibiotics. Here, a 2-compartment Transwell model was developed to study impaired diffusion of the antibiotic colistin across an artificial sputum (AS) matrix/medium and to quantify its antimicrobial activity against Pseudomonas aeruginosa NH57388A biofilms (alone and in combination with mucolytic therapy). High-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) revealed that the presence of AS medium significantly reduced the rate of colistin diffusion (> 85% at 48 h; p < 0.05). Addition of alginate oligosaccharide (OligoG CF-5/20) significantly improved colistin diffusion by 3.7 times through mucin-rich AS medium (at 48 h; p < 0.05). Increased diffusion of colistin with OligoG CF-5/20 was shown (using confocal laser scanning microscopy and COMSTAT image analysis) to be associated with significantly increased bacterial killing (p < 0.05). These data support the use of this model to study drug and small molecule delivery across clinically-relevant diffusion barriers. The findings indicate the significant loss of colistin and reduced effectiveness that occurs with mucin binding, and support the use of mucolytics to improve antimicrobial efficacy and lower antibiotic exposure.

Developing ciprofloxacin dry powder for inhalation: A story of challenges and rational design in the treatment of cystic fibrosis lung infection

Cystic fibrosis (CF) is an inherited multisystem disease affecting the lung which leads to a progressive decline in lung function as a result of malfunctioning mucociliary clearance and subsequent chronic bacterial infections. Pseudomonas aeruginosa is the predominant cause of lung infection in CF patients and is associated with significant morbidity and mortality. Thus, antibiotic therapy remains the cornerstone of the treatment of CF. Pulmonary delivery of antibiotics for lung infections significantly reduces the required dose and the associated systemic side effects while improving therapeutic outcomes. Ciprofloxacin is one of the most widely used antibiotics against P. aeruginosa and the most effective fluoroquinolone. However, in spite of the substantial amount of research aimed at developing ciprofloxacin powder for inhalation, none of these formulations has been commercialized. Here, we present an integrated view of the diverse challenges associated with delivering ciprofloxacin dry particles to the lungs of CF patients and the rationales behind recent formulations of ciprofloxacin dry powder for inhalation. This review will discuss the challenges in developing ciprofloxacin powder for inhalation along with the physiological and pathophysiological challenges such as ciprofloxacin lung permeability, overproduction of viscous mucus and bacterial biofilms. The review will also discuss the current and emerging particle engineering approaches to overcoming these challenges. By doing so, we believe the review will help the reader to understand the current limitations in developing an inhalable ciprofloxacin powder and explore new opportunities of rational design strategies.

Does Cefiderocol Have a Potential Role in Cystic Fibrosis Pulmonary Exacerbation Management?

Cystic fibrosis (CF) is associated with frequent pulmonary exacerbations and the need for novel antibiotics against antimicrobial resistance. Cefiderocol is a newly approved therapeutic option active against a variety of multidrug resistant (MDR) bacteria such as gram-negative species commonly encountered by CF patients. This review describes the potential role of cefiderocol against Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and Burkholderia cepacia complex. Cefiderocol is a potential therapeutic option for MDR pathogens with minimum inhibitory concentrations (MICs) of ≤4 mg/L. Due to the lack of in vivo evidence in the CF population, cefiderocol may be utilized in patients in which alternative options are lacking due to MDR organisms or rapid pulmonary decline.

Magnetic Nanoparticle-Based Drug Delivery Approaches for Preventing and Treating Biofilms in Cystic Fibrosis

Biofilm-associated infections pose a huge burden on healthcare systems worldwide, with recurrent lung infections occurring due to the persistence of biofilm bacteria populations. In cystic fibrosis (CF), thick viscous mucus acts not only as a physical barrier, but also serves as a nidus for infection. Increased antibiotic resistance in the recent years indicates that current therapeutic strategies aimed at biofilm-associated infections are “failing”, emphasizing the need to develop new and improved drug delivery systems with higher efficacy and efficiency. Magnetic nanoparticles (MNPs) have unique and favourable properties encompassing biocompatibility, biodegradability, magnetic and heat-mediated characteristics, making them suitable drug carriers. Additionally, an external magnetic force can be applied to enhance drug delivery to target sites, acting as “nano-knives”, cutting through the bacterial biofilm layer and characteristically thick mucus in CF. In this review, we explore the multidisciplinary approach of using current and novel MNPs as vehicles of drug delivery. Although many of these offer exciting prospects for future biofilm therapeutics, there are also major challenges of this emerging field that need to be addressed.

Successes and Challenges: Inhaled Treatment Approaches Using Magnetic Nanoparticles in Cystic Fibrosis

Magnetic nanoparticles have been largely applied to increase the efficacy of antibiotics due to passive accumulation provided by enhancing permeability and retention, which is essential for the treatment of lung infections. Recurring lung infections such as in the life-shortening genetic disease cystic fibrosis (CF) are a major problem. The recent advent of the CF modulator drug ivacaftor, alone or in combination with lumacaftor or tezacaftor, has enabled systemic treatment of the majority of patients. Magnetic nanoparticles (MNPs) show unique properties such as biocompatibility and biodegradability as well as magnetic and heat-medicated characteristics. These properties make them suitable to be used as drug carriers and hyperthermia-based agents. Hyperthermia is a promising approach for the thermal activation therapy of several diseases, including pulmonary diseases. The benefits of delivering CF drugs via inhalation using MNPs as drug carriers afford application of sufficient therapeutic dosages directly to the primary target site, while avoiding potential suboptimal pharmacokinetics/pharmacodynamics and minimizing the risks of systemic toxicity. This review explores the multidisciplinary approach of using MNPs as vehicles of drug delivery. Additionally, we highlight advantages such as increased drug concentration at disease site, minimized drug loss and the possibility of specific cell targeting, while addressing major challenges for this emerging field.

Intracellular localization of polymyxins in human alveolar epithelial cells

Background

Current inhaled polymyxin therapy is empirical and often large doses are administered, which can lead to pulmonary adverse effects. There is a dearth of information on the mechanisms of polymyxin-induced lung toxicity and their intracellular localization in lung epithelial cells.

Objectives

To investigate the intracellular localization of polymyxins in human lung epithelial A549 cells.

Methods

A549 cells were treated with polymyxin B and intracellular organelles (early and late endosomes, endoplasmic reticulum, mitochondria, lysosomes and autophagosomes), ubiquitin protein and polymyxin B were visualized using immunostaining and confocal microscopy. Fluorescence intensities of the organelles and polymyxin B were quantified and correlated for co-localization using ImageJ and Imaris platforms.

Results

Polymyxin B co-localized with early endosomes, lysosomes and ubiquitin at 24 h. Significantly increased lysosomal activity and the autophagic protein LC3A were observed after 0.5 and 1.0 mM polymyxin B treatment at 24 h. Polymyxin B also significantly co-localized with mitochondria (Pearson's R = 0.45) and led to the alteration of mitochondrial morphology from filamentous to fragmented form (n = 3, P < 0.001). These results are in line with the polymyxin-induced activation of the mitochondrial apoptotic pathway observed in A549 cells.

Conclusions

Accumulation of polymyxins on mitochondria probably caused mitochondrial toxicity, resulting in increased oxidative stress and cell death. The formation of autophagosomes and lysosomes was likely a cellular response to the polymyxin-induced stress and played a defensive role by disassembling dysfunctional organelles and proteins. Our study provides new mechanistic information on polymyxin-induced lung toxicity, which is vital for optimizing inhaled polymyxins in the clinic.

Mode of nitric oxide delivery affects antibacterial action

Nitric oxide (NO) is a broad-spectrum antibacterial agent, making it an attractive alternative to traditional antibiotics for treating infections. To date, a direct comparison of the antibacterial activity of gaseous NO (gNO) versus water-soluble NO-releasing biopolymers has not been reported. In this study, the bactericidal action of NO-releasing chitosan oligosaccharides was compared to gNO treatment against cystic fibrosis-relevant Gram-positive and Gram-negative bacteria. A NO exposure chamber was constructed to enable the dosing of bacteria with gNO at concentrations up to 800 ppm under both aerobic and anaerobic conditions. Bacteria viability, solution properties (i.e., pH, NO concentration), and toxicity to mammalian cells were monitored to ensure a thorough understanding of bactericidal action and reproducibility for each delivery method. The NO-releasing chitosan oligosaccharides required significantly lower NO doses relative to gNO therapy to elicit antibacterial action against Pseudomonas aeruginosa and Staphylococcus aureus under both aerobic and anaerobic conditions. Reduced NO doses required for bacteria eradication using water-soluble NO-releasing chitosan were attributed to the release of NO in solution, removing the need to transfer from gas to liquid phase and the associated long diffusion distances of gNO treatment.

Nitric oxide diffusion through cystic fibrosis-relevant media and lung tissue

A simplified diffusion cell methodology was employed to measure the diffusion coefficient of nitric oxide (NO) through phosphate buffered saline (PBS) and artificial sputum medium (ASM)—an in vitro analog for airway mucus. Diffusion through the proteinaceous ASM yielded a significantly lower diffusion coefficient compared to PBS, which is attributed to both the physical obstruction by the mucin mesh and reactive nature of NO radicals towards the biological compounds in ASM. To further confirm that ASM was restricting NO from diffusing freely, a macromolecular propylamine-modified cyclodextrin donor (CD-PA) was employed to release the NO more slowly. The NO diffusion characteristics in ASM via the NO donor were also slower relative to PBS. As NO is likely to interact with lung cells after passing through the mucus barrier, the diffusion of both NO and the CD-PA macromolecular NO donor through differentiated lung tissue was investigated with and without an ASM layer. Comparison of NO diffusion through the three diffusion barriers indicated that the lung tissue significantly impeded NO penetration over the course of the experiment compared to PBS and ASM. In fact, the diffusion of CD-PA through the lung tissue was hindered until after the release of its NO payload, potentially due to the increased net charge of the NO donor structure. Of importance, the viability of the tissue was not influenced by the NO-releasing CD-PA at bactericidal concentrations.

Nitric oxide diffusion monitored through artificial sputum medium using an adaptable diffusion cell and released from donor through human lung tissue.

Emerging therapies against infections with Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa have been marked with the highest priority for surveillance and epidemiological research on the basis of parameters such as incidence, case fatality rates, chronicity of illness, available options for prevention and treatment, health-care utilization, and societal impact. P. aeruginosa is one of the six ESKAPE pathogens that are the major cause of nosocomial infections and are a global threat because of their capacity to become increasingly resistant to all available antibiotics. This review reports on current pre-clinical and clinical advances of anti-pseudomonal therapies in the fields of drug development, antimicrobial chemotherapy, vaccines, phage therapy, non-bactericidal pathoblockers, outer membrane sensitizers, and host defense reinforcement.

Using Small-Molecule Adjuvants to Repurpose Azithromycin for Use against Pseudomonas aeruginosa

A major contributor to fatalities in cystic fibrosis (CF) patients stems from infection with opportunistic bacterium Pseudomonas aeruginosa. As a result of the CF patient's vulnerability to bacterial infections, one of the main treatment focuses is antibiotic therapy. However, the highly adaptive nature of P. aeruginosa, in addition to the intrinsic resistance to many antibiotics exhibited by most Gram-negative bacteria, means that multi-drug-resistant (MDR) strains are increasingly prevalent. This makes the eradication of pseudomonal lung infections nearly impossible once the infection becomes chronic. New methods to treat pseudomonal infections are greatly needed in order to eradicate MDR bacteria found within the respiratory tract, and ultimately better the quality of life for CF patients. Herein, we describe a novel approach to combatting pseudomonal infections through the use of bis-2-aminoimidazole adjuvants that can potentiate the activity of a macrolide antibiotic commonly prescribed to CF patients as an anti-inflammatory agent. Our lead bis-2-AI exhibits a 1024-fold reduction in the minimum inhibitory concentration of azithromycin in vitro and displays activity in a Galleria mellonella model of infection.

Improved Physical Stability and Aerosolization of Inhalable Amorphous Ciprofloxacin Powder Formulations by Incorporating Synergistic Colistin

This study aimed to develop dry powder inhaler (DPI) combination formulations of ciprofloxacin and colistin for use in respiratory infections. Effects of colistin on physical stability and aerosolization of spray-dried ciprofloxacin were examined. The combination DPI formulations were produced by co-spray drying colistin and ciprofloxacin in mass ratios of 1:1, 1:3, and 1:9. Colistin and ciprofloxacin were also co-sprayed with l-leucine in the mass ratio of 1:1:1. The physical and aerosolization stability of the selected co-sprayed formulations stored at 20, 55, and 75% relative humidity (RH) were examined. Formulation characterizations were carried out using powder X-ray diffraction (PXRD) for crystallinity, scanning electron microscopy for morphology and particle size distribution, and dynamic vapor sorption for moisture sorption. Particle surface analysis was performed using X-ray photoelectron spectroscopy, energy dispersive X-ray spectrometry, and nano-time-of-flight secondary ion mass spectrometry. Potential intermolecular interactions were studied using Fourier-transform infrared spectroscopy (FTIR). Aerosol performance was evaluated using a multistage liquid impinger with a RS01 monodose inhaler device. PXRD diffractograms showed that the co-spray-dried colistin-ciprofloxacin formulation in the mass ratio (1:1) was amorphous at 55% RH for up to 60 days; whereas the co-spray-dried colistin-ciprofloxacin (1:3) and colistin-ciprofloxacin (1:9) crystallized after storage for 3 days at 55% RH. However, the extent of crystallization for the combination formulations was less as compared to the spray-dried ciprofloxacin alone formulation. Surface morphology of the co-spray-dried formulations at different concentrations did not change even after storage at 55% RH for 60 days, unlike the spray-dried ciprofloxacin alone powder which became rougher after 3 days of storage at 55% RH. Surface analysis data indicated surface enrichment of colistin in the co-spray-dried formulations. Increasing colistin concentration on the composite particles surfaces improved aerosol performance of ciprofloxacin. FTIR data demonstrated intermolecular interactions between colistin and ciprofloxacin, thereby delaying and/or preventing crystallization of ciprofloxacin when co-spray-dried. Co-spray drying ciprofloxacin with colistin in the mass ratio (1:1) completely prevented crystallization of ciprofloxacin at 55% RH for up to 60 days. However, the colistin-ciprofloxacin formulation (1:1) began to fuse when stored at 75% RH due to moisture absorption resulting in a compromised aerosol performance. In contrast, the colistin-ciprofloxacin-leucine (1:1:1) formulation demonstrated no particle fusion, enabling a stable aerosol performance at 75% RH for 7 days. This study demonstrated that incorporation of colistin in the spray-dried formulations can improve physical stability and aerosolization of amorphous ciprofloxacin at 55% RH. At 75% RH, further addition of l-leucine in the formulation prevented particle fusion and deterioration in aerosol performance, attributed to the enrichment of nonhygroscopic l-leucine on the particle surface.

Pharmacokinetics and pharmacodynamics of high doses of inhaled dry powder drugs

For many years, administration of drugs by inhalation has been the mainstay treatment for obstructive respiratory disorders such as asthma and chronic obstructive pulmonary disease. Antibiotics and other drugs have been administered for decades as aerosols to treat other pulmonary disease in a clinical setting, but it was until the early 1980's that colistin was formally marketed as a solution for nebulization in Europe (Colomycin, Pharmax, Bexley). The solubility of other drugs and the size of the dose required to achieve therapeutic concentrations at the site of action, made treatment times long and difficult to be performed at home. High dose dry powder delivery is a potentially effective way to deliver low potency drugs such as antibiotics. There are three major barriers to achieving the desired pharmacodynamic effect with these compounds: aerosol delivery, lung deposition and clearance. The powder formulation and device technology influence aerosol generation and may influence the size of the dose that can be achieved by inhalation in one puff. The site of deposition in the lungs is dictated by mechanisms of deposition which are influenced by the aerosol properties, particularly aerodynamic particle size distribution and the anatomy and physiology of the lungs. Finally, mechanisms of clearance dictate the local and systemic disposition of the drug, which in turn affects its pharmacokinetics and ultimately the pharmacodynamic effect and efficacy of treatment. Each of these factors will be considered and the implications for antimicrobial agent delivery as a high dose delivery example will be given.

Interaction of Bacterial Phenazines with Colistimethate in Bronchial Epithelial Cells

Multidrug-resistant bacterial infections are being increasingly treated in clinics with polymyxins, a class of antibiotics associated with adverse effects on the kidney, nervous system, or airways of a significant proportion of human and animal patients. Although many of the resistant pathogens display enhanced virulence, the hazard of cytotoxic interactions between polymyxin antibiotics and bacterial virulence factors (VFs) has not been assessed, to date. We report here the testing of paired combinations of four Pseudomonas aeruginosa VF phenazine toxins, pyocyanin (PYO), 1-hydroxyphenazine (1-HP), phenazine-1-carboxylic acid (PCA), and phenazine-1-carboxamide (PCN), and two commonly prescribed polymyxin drugs, colistin-colistimethate sodium (CMS) and polymyxin B, in three human airway cell lines, BEAS-2B, HBE-1, and CFT-1. Cytotoxicities of individual antibiotics, individual toxins, and their combinations were evaluated by the simultaneous measurement of mitochondrial metabolic, total transcriptional/translational, and Nrf2 stress response regulator activities in treated cells. Two phenazines, PYO and 1-HP, were cytotoxic at clinically relevant concentrations (100 to 150 μM) and prompted a significant increase in oxidative stress-induced transcriptional activity in surviving cells. The polymyxin antibiotics arrested cell proliferation at clinically achievable (<1 mM) concentrations as well, with CMS displaying surprisingly high cytotoxicity (50% effective dose [ED₅₀] = 180 μM) in BEAS-2B cells. The dose-response curves were probed by a median-effect analysis, which established a synergistically enhanced cytotoxicity of the PYO-CMS combination in all three airway cell lines; a particularly strong effect on BEAS-2B cells was observed, with a combination index (CI) of 0.27 at the ED₅₀. PCA, PCN, and 1-HP potentiated CMS cytotoxicity to a smaller extent. The cytotoxicity of CMS could be reduced with 10 mM N-acetyl-cysteine. Iron chelators, while ineffective against the polymyxins, could rescue all three bronchial epithelial cell lines treated with lethal PYO or CMS-PYO doses. These findings suggest that further evaluations of CMS safety are needed, along with a search for means to moderate potentially cytotoxic interactions.

lncRNAPCAT29 inhibits pulmonary fibrosis via the TGF‑β1‑regulated RASAL1/ERK1/2 signal pathway

Pulmonary fibrosis is a severe respiratory disease characterized by the aggregation of extracellular matrix components and inflammation‑associated injury. Studies have suggested that long non‑coding RNAs (lncRNA) may serve a role in the pathophysiological processes of pulmonary fibrosis. However, the potential molecular mechanisms involving the lncRNA, prostate cancer‑associated transcript 29 (lncRNAPCAT29) in the progression of pulmonary fibrosis are yet to be determined. In the present study, the role of lncRNAPCAT29 and the potential signaling mechanism in pulmonary fibrosis progression was investigated. Reverse transcription‑quantitative polymerase chain reaction and immunohistochemistry revealed that the expression levels of lncRNAPCAT29 were downregulated within interstitial lung cells from mice with silica‑induced pulmonary fibrosis. Transfection with lncRNAPCAT29 was associated with upregulated expression of microRNA (miRNA)‑221 and downregulated expression of transforming growth factor‑β1 (TGF‑β1); reduced inflammation and fibrotic progression was also associated with lncRNAPCAT29 transfection. TGF‑β1 expression levels were inhibited within pulmonary fibroblasts due to lncRNAPCAT29 expression; NEDD4 binding protein 2 and Plexin‑A4 expression levels were also suppressed. Analysis of the potential mechanism underlying silica‑induced pulmonary fibrosis revealed that the expression levels of RAS protein activator like 1 (RASAL1) and extracellular signal‑regulated kinases 1/2 (ERK1/2) were suppressed due to lncRNAPCAT29 expression. The results of the present study demonstrated that lncRNAPCAT29 induced miRNA‑221 upregulation and TGF‑β1 downregulation. These observations were associated with reduced inflammation and progression of silica‑induced pulmonary fibrosis via the TGF‑β1‑regulated RASAL1/ERK1/2 signaling pathway, which may serve as a potential target for the treatment of pulmonary fibrosis.

Colistin methanesulfonate infusion solutions are stable over time and suitable for home administration

The stability of colistin methanesulfonate (CMS) was determined in quadruplicate in elastomeric home infusion pumps containing 1, 2 or 3 MU CMS and in infusion bags with 2 MU CMS all in 100 mL normal saline. Infusions were stored at room temperature (20°C-24°C) with or without exposure to natural light or refrigerated (4°C-8°C) and protected from light up to 2 weeks. In the initial solution of 2 MU CMS in 100 mL saline sampled immediately after reconstitution and dilution, 1.5% of CMS was hydrolysed to colistin. When stored at room temperature and exposed to natural light, colistin concentration in elastomeric infusion pumps increased to 2.6% in 8 days and to 2.1% when stored at 4°C. CMS stability increases at lower temperatures and higher concentrations. Based on the current data, chemical stability of CMS infusion solution is sufficient for a shelf life of 7 days refrigerated plus 1 day at room temperature.

Accurate reporting of adherence to inhaled therapies in adults with cystic fibrosis: methods to calculate "normative adherence"

BACKGROUND

Preventative inhaled treatments in cystic fibrosis will only be effective in maintaining lung health if used appropriately. An accurate adherence index should therefore reflect treatment effectiveness, but the standard method of reporting adherence, that is, as a percentage of the agreed regimen between clinicians and people with cystic fibrosis, does not account for the appropriateness of the treatment regimen. We describe two different indices of inhaled therapy adherence for adults with cystic fibrosis which take into account effectiveness, that is, "simple" and "sophisticated" normative adherence.

METHODS TO CALCULATE NORMATIVE ADHERENCE

Denominator adjustment involves fixing a minimum appropriate value based on the recommended therapy given a person's characteristics. For simple normative adherence, the denominator is determined by the person's Pseudomonas status. For sophisticated normative adherence, the denominator is determined by the person's Pseudomonas status and history of pulmonary exacerbations over the previous year. Numerator adjustment involves capping the daily maximum inhaled therapy use at 100% so that medication overuse does not artificially inflate the adherence level.

THREE ILLUSTRATIVE CASES

Case A is an example of inhaled therapy under prescription based on Pseudomonas status resulting in lower simple normative adherence compared to unadjusted adherence. Case B is an example of inhaled therapy under-prescription based on previous exacerbation history resulting in lower sophisticated normative adherence compared to unadjusted adherence and simple normative adherence. Case C is an example of nebulizer overuse exaggerating the magnitude of unadjusted adherence.

CONCLUSION

Different methods of reporting adherence can result in different magnitudes of adherence. We have proposed two methods of standardizing the calculation of adherence which should better reflect treatment effectiveness. The value of these indices can be tested empirically in clinical trials in which there is careful definition of treatment regimens related to key patient characteristics, alongside accurate measurement of health outcomes.

Stability of colistimethate sodium in a disposable elastomeric infusion device

Infections of the respiratory tract with Pseudomonas aeruginosa in cystic fibrosis patients are frequently treated with colistimethate sodium (CMS). For the intravenous administration of CMS a disposable elastomeric pump is a convenient option. To date, there are no data available on the chemical stability of CMS solutions stored in elastomeric pumps. We evaluated the chemical stability of 0.8 mg/mL solutions of CMS by measuring the degradation over a period of 7 days. Test samples were prepared by diluting CMS with saline solution (0.9%). The preparations were transferred to 100-mL elastomeric pumps and stored at 4 °C. The chemical stability was measured by a high-performance liquid chromatography method with UV detection. There was no degradation of CMS (<0.5% of CMS present as colistin) for at least 3 day at 4 °C, and after 7 days all test samples remained chemically stable (<5% of CMS present as colistin). Since colistin formed in pharmacy-compounded CMS solutions prior to administration may cause toxicity, we advise that the solution should be used before the hydrolysis of CMS occurs. Therefore, we recommend that the 0.8 mg/mL solution of CMS can be stored for up to 3 days at 4 °C in an elastomeric pump.