Macrolide drug interactions: an update

Update on the pharmacological treatment of chronic obstructive pulmonary disease

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a common syndrome associated with smoking and environmental exposures coupled with genetic susceptibility. Recent major advancements in the treatment of COPD patients have become available.

AREAS COVERED

New data on the role of classic bronchodilators, including short-acting and long-acting beta2-agonists and anti-muscarinic antagonists, in the treatment of COPD patients are discussed. Data promoting a more targeted approach to inhaled and systemic corticosteroid use in COPD are reviewed. Phosphodiesterase (PDE) inhibitors, including the recently approved PDE 3/4 inhibitor inhaled ensifentrine, are noted. Selective use of antibiotics can play a role in complex COPD patients. COPD patients with evidence of asthma-COPD overlap syndrome and type-two lymphocytic inflammatory-mediated airway constriction appear to respond to biologics, particularly the anti-IL-4/IL-3 antagonist monoclonal antibody, dupilumab.

EXPERT OPINION

New therapeutic options have made the approach and treatment of the COPD patient much more complicated. These options tend to be very expensive. Attention to identifying the endotype and phenotype will help direct the pharmacotherapy.

Safety and Tolerability of Antimicrobial Agents in the Older Patient

Older patients are at high risk of infections, which often present atypically and are associated with high morbidity and mortality. Antimicrobial treatment in older individuals with infectious diseases represents a clinical challenge, causing an increasing burden on worldwide healthcare systems; immunosenescence and the coexistence of multiple comorbidities determine complex polypharmacy regimens with an increase in drug-drug interactions and spread of multidrug-resistance infections. Aging-induced pharmacokinetic and pharmacodynamic changes can additionally increase the risk of inappropriate drug dosing, with underexposure that is associated with antimicrobial resistance and overexposure that may lead to adverse effects and poor adherence because of low tolerability. These issues need to be considered when starting antimicrobial prescriptions. National and international efforts have been made towards the implementation of antimicrobial stewardship (AMS) interventions to help clinicians improve the appropriateness and safety of antimicrobial prescriptions in both acute and long-term care settings. AMS programs were shown to decrease consumption of antimicrobials and to improve safety in hospitalized patients and older nursing home residents. With the abundance of antimicrobial prescriptions and the recent emergence of multidrug resistant pathogens, an in-depth review of antimicrobial prescriptions in geriatric clinical practice is needed. This review will discuss the special considerations for older individuals needing antimicrobials, including risk factors that shape risk profiles in geriatric populations as well as an evidence-based description of antimicrobial-induced adverse events in this patient population. It will highlight agents of concern for this age group and discuss interventions to mitigate the effects of inappropriate antimicrobial prescribing.

Predicting Drug-Drug Interactions Based on Integrated Similarity and Semi-Supervised Learning

A drug-drug interaction (DDI) is defined as an association between two drugs where the pharmacological effects of a drug are influenced by another drug. Positive DDIs can usually improve the therapeutic effects of patients, but negative DDIs cause the major cause of adverse drug reactions and even result in the drug withdrawal from the market and the patient death. Therefore, identifying DDIs has become a key component of the drug development and disease treatment. In this study, we propose a novel method to predict DDIs based on the integrated similarity and semi-supervised learning (DDI-IS-SL). DDI-IS-SL integrates the drug chemical, biological and phenotype data to calculate the feature similarity of drugs with the cosine similarity method. The Gaussian Interaction Profile kernel similarity of drugs is also calculated based on known DDIs. A semi-supervised learning method (the Regularized Least Squares classifier) is used to calculate the interaction possibility scores of drug-drug pairs. In terms of the 5-fold cross validation, 10-fold cross validation and de novo drug validation, DDI-IS-SL can achieve the better prediction performance than other comparative methods. In addition, the average computation time of DDI-IS-SL is shorter than that of other comparative methods. Finally, case studies further demonstrate the performance of DDI-IS-SL in practical applications.

Azithromycin: A promising treatment option for Mycobacterium avium complex pulmonary disease in case of intolerance to clarithromycin

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Macrolides are invaluable for the treatment of MPD.

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Clarithromycin therapy for MPD can cause severe side effects.

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Azithromycin could be a good alternative to clarithromycin for the treatment of MPD.

Macrolide-based combination chemotherapy is recommended for the treatment of Mycobacterium avium complex (MAC) pulmonary disease (MPD). The susceptibility of the MAC to macrolide antibiotics (MAs) determines the efficacy of treatment and clinical course of MPD. However, MAs cause several adverse effects, resulting in the discontinuation of macrolide-based combination chemotherapy. We encountered two women aged 65 years and 66 years diagnosed with MPD based on bronchoscopic examinations. They were initially treated with clarithromycin-based combination chemotherapy. However, neither patient could continue with chemotherapy owing to adverse events such as rash and edema. We switched clarithromycin with azithromycin, and the patients were able to continue chemotherapy without adverse events. Both patients completed their treatment successfully. Azithromycin, which also belongs to the class of MAs, can be a promising therapeutic option for MPD in case of clarithromycin intolerance.

Clarithromycin Solid Lipid Nanoparticles for Topical Ocular Therapy: Optimization, Evaluation and In Vivo Studies

Solid lipid nanoparticles (SLNs) are being extensively exploited as topical ocular carrier systems to enhance the bioavailability of drugs. This study investigated the prospects of drug-loaded SLNs to increase the ocular permeation and improve the therapeutic potential of clarithromycin in topical ocular therapy. SLNs were formulated by high-speed stirring and the ultra-sonication method. Solubility studies were carried out to select stearic acid as lipid former, Tween 80 as surfactant, and Transcutol P as cosurfactant. Clarithromycin-loaded SLN were optimized by fractional factorial screening and 3² full factorial designs. Optimized SLNs (CL10) were evaluated for stability, morphology, permeation, irritation, and ocular pharmacokinetics in rabbits. Fractional factorial screening design signifies that the sonication time and amount of lipid affect the SLN formulation. A 3² full factorial design established that both factors had significant influences on particle size, percent entrapment efficiency, and percent drug loading of SLNs. The release profile of SLNs (CL9) showed ~80% drug release in 8 h and followed Weibull model kinetics. Optimized SLNs (CL10) showed significantly higher permeation (30.45 μg/cm²/h; p < 0.0001) as compared to control (solution). CL10 showed spherical shape and good stability and was found non-irritant for ocular administration. Pharmacokinetics data demonstrated significant improvement of clarithromycin bioavailability (p < 0.0001) from CL10, as evidenced by a 150% increase in C_max (~1066 ng/mL) and a 2.8-fold improvement in AUC (5736 ng h/mL) (p < 0.0001) as compared to control solution (C_max; 655 ng/mL and AUC; 2067 ng h/mL). In summary, the data observed here demonstrate the potential of developed SLNs to improve the ocular permeation and enhance the therapeutic potential of clarithromycin, and hence could be a viable drug delivery approach to treat endophthalmitis.

SIME: synthetic insight-based macrolide enumerator to generate the V1B library of 1 billion macrolides

We report on a new cheminformatics enumeration technology—SIME, synthetic insight-based macrolide enumerator—a new and improved software technology. SIME can enumerate fully assembled macrolides with synthetic feasibility by utilizing the constitutional and structural knowledge extracted from biosynthetic aspects of macrolides. Taken into account by the software are key information such as positions in macrolide structures at which chemical components can be inserted, and the types of structural motifs and sugars of interest that can be synthesized and incorporated at those positions. Additionally, we report on the chemical distribution analysis of the newly SIME-generated V1B (virtual 1 billion) library of macrolides. Those compounds were built based on the core of the Erythromycin structure, 13 structural motifs and a library of sugars derived from eighteen bioactive macrolides. This new enumeration technology can be coupled with cheminformatics approaches such as QSAR modeling and molecular docking to aid in drug discovery for rational designing of next generation macrolide therapeutics with desirable pharmacokinetic properties.

Outcomes Following Macrolide Use in Kidney Transplant Recipients

BACKGROUND

Calcineurin inhibitors (CNI; cyclosporine, tacrolimus) are critical for kidney transplant immunosuppression, but have multiple potential drug interactions, such as with macrolide antibiotics. Macrolide antibiotics (clarithromycin, erythromycin, and azithromycin) are often used to treat atypical infections. Clarithromycin and erythromycin inhibit CNI metabolism and increase the risk of CNI nephrotoxicity, while azithromycin does not.

OBJECTIVE

To determine the frequency of CNI-macrolide co-prescriptions, the proportion who receive post-prescription monitoring, and the risk of adverse drug events in kidney transplant recipients.

DESIGN

Retrospective cohort study.

SETTING

We used linked health care databases in Alberta, Canada.

PATIENTS

We included 293 adult kidney transplant recipients from 2008-2015 who were co-prescribed a CNI and macrolide.

MEASUREMENTS

The primary outcome was a composite of all-cause hospitalization, acute kidney injury (creatinine increase ≥0.3 mg/dL or 1.5 times baseline), or death within 30 days of the macrolide prescription.

METHODS

We identified CNI-macrolide co-prescriptions and compared outcomes in those who received clarithromycin/erythromycin versus azithromycin. We used a linear mixed-effects model to examine the mean change in serum creatinine and estimated glomerular filtration rate (eGFR).

RESULTS

Of the 293 recipients who were co-prescribed a CNI and a macrolide, 38% (n = 112) were prescribed clarithromycin/erythromycin while 62% (n = 181) were prescribed azithromycin. Compared with azithromycin users, clarithromycin/erythromycin users were less likely to have outpatient serum creatinine monitoring post-prescription (56% vs 69%, P = .03). There was no significant difference in the primary outcome between the 2 groups (17% vs 11%, P = .11); however, the risk of all-cause hospitalization was higher in the clarithromycin/erythromycin group (10% vs 3%, P = .02). The mean decrement in eGFR was significantly greater in the clarithromycin/erythromycin versus azithromycin group (-5.4 vs -1.9 mL/min/1.73 m2, P < .05).

LIMITATIONS

We did not have CNI levels to correlate with the timing of CNI-macrolide co-prescriptions. We also did not have information regarding the indications for macrolide prescriptions.

CONCLUSION

Clarithromycin and erythromycin were frequently co-prescribed in kidney transplant recipients on CNIs despite known drug interactions. Clarithromycin/erythromycin use was associated with a higher risk of hospitalization compared with azithromycin users. Safer prescribing practices in kidney transplant recipients are warranted.

A decade of outpatient antimicrobial use in older adults in Ontario: a descriptive study

BACKGROUND

Antimicrobials are frequently prescribed to community-dwelling older adults. Our aim was to examine the prevalence, quantity and indications of antimicrobial prescriptions to older residents of Ontario.

METHODS

We conducted a population-based analysis of outpatient antimicrobial prescriptions to residents of Ontario aged 65 years or more from 2006 to 2015. Antimicrobial prescriptions, infectious disease diagnoses and prescriber information were determined from linked health care databases. Our analyses were primarily focused on antibiotics, which account for most antimicrobial use.

RESULTS

We identified 2 879 779 unique Ontario residents aged 65 years or more over our study period. On average, 40.7% (range 40.1%-41.5%) of older adult outpatients in any given year received 1 or more antibiotic prescriptions. Antibiotic use remained stable over the study period, averaging 25.1 (range 24.1-25.6) defined daily doses per 1000 person-days per year. Selection of antibiotics evolved, with increasing use of penicillins and decreasing use of fluoroquinolones and macrolides. For 65.7% of prescriptions, no infectious disease diagnoses were identified within 7 days of the prescription. Among prescriptions with an associated diagnosis, upper respiratory tract infection was most common (18.9%), followed by urinary tract infection (6.2%), skin/soft-tissue infection (4.3%), lower respiratory tract infection (4.2%) and other infection (1.2%). Most antibiotics were prescribed by family physicians.

INTERPRETATION

Antibiotic use among older adult outpatients in Ontario remained stable between 2006 and 2015. Current methods of measuring use are not capable of accurately determining indication, and, thus, additional data sources to monitor the appropriateness of community antimicrobial use are needed.

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.

High Levels of Antibiotic Resistance Genes and Their Correlations with Bacterial Community and Mobile Genetic Elements in Pharmaceutical Wastewater Treatment Bioreactors

To understand the diversity and abundance of antibiotic resistance genes (ARGs) in pharmaceutical wastewater treatment bioreactors, the ARGs in sludge from two full-scale pharmaceutical wastewater treatment plants (PWWTPs) were investigated and compared with sludge samples from three sewage treatment plants (STPs) using metagenomic approach. The results showed that the ARG abundances in PWWTP sludge ranged from 54.7 to 585.0 ppm, which were higher than those in STP sludge (27.2 to 86.4 ppm). Moreover, the diversity of ARGs in PWWTP aerobic sludge (153 subtypes) was higher than that in STP aerobic sludge (118 subtypes). In addition, it was found that the profiles of ARGs in PWWTP aerobic sludge were similar to those in STP aerobic sludge but different from those in PWWTP anaerobic sludge, suggesting that dissolve oxygen (DO) could be one of the important factors affecting the profiles of ARGs. In PWWTP aerobic sludge, aminoglycoside, sulfonamide and multidrug resistance genes were frequently detected. While, tetracycline, macrolide-lincosamide-streptogramin and polypeptide resistance genes were abundantly present in PWWTP anaerobic sludge. Furthermore, we investigated the microbial community and the correlation between microbial community and ARGs in PWWTP sludge. And, significant correlations between ARG types and seven bacterial genera were found. In addition, the mobile genetic elements (MGEs) were also examined and correlations between the ARGs and MGEs in PWWTP sludge were observed. Collectively, our results suggested that the microbial community and MGEs, which could be affected by DO, might be the main factors shaping the profiles of ARGs in PWWTP sludge.

Analysis and prediction of drug-drug interaction by minimum redundancy maximum relevance and incremental feature selection

Drug-drug interaction (DDI) defines a situation in which one drug affects the activity of another when both are administered together. DDI is a common cause of adverse drug reactions and sometimes also leads to improved therapeutic effects. Therefore, it is of great interest to discover novel DDIs according to their molecular properties and mechanisms in a robust and rigorous way. This paper attempts to predict effective DDIs using the following properties: (1) chemical interaction between drugs; (2) protein interactions between the targets of drugs; and (3) target enrichment of KEGG pathways. The data consisted of 7323 pairs of DDIs collected from the DrugBank and 36,615 pairs of drugs constructed by randomly combining two drugs. Each drug pair was represented by 465 features derived from the aforementioned three categories of properties. The random forest algorithm was adopted to train the prediction model. Some feature selection techniques, including minimum redundancy maximum relevance and incremental feature selection, were used to extract key features as the optimal input for the prediction model. The extracted key features may help to gain insights into the mechanisms of DDIs and provide some guidelines for the relevant clinical medication developments, and the prediction model can give new clues for identification of novel DDIs.

Quantifying Attachment and Antibiotic Resistance of from Conventional and Organic Swine Manure

Broad-spectrum antibiotics are often administered to swine, contributing to the occurrence of antibiotic-resistant bacteria in their manure. During land application, the bacteria in swine manure preferentially attach to particles in the soil, affecting their transport in overland flow. However, a quantitative understanding of these attachment mechanisms is lacking, and their relationship to antibiotic resistance is unknown. The objective of this study is to examine the relationships between antibiotic resistance and attachment to very fine silica sand in collected from swine manure. A total of 556 isolates were collected from six farms, two organic and four conventional (antibiotics fed prophylactically). Antibiotic resistance was quantified using 13 antibiotics at three minimum inhibitory concentrations: resistant, intermediate, and susceptible. Of the 556 isolates used in the antibiotic resistance assays, 491 were subjected to an attachment assay. Results show that isolates from conventional systems were significantly more resistant to amoxicillin, ampicillin, chlortetracycline, erythromycin, kanamycin, neomycin, streptomycin, tetracycline, and tylosin ( < 0.001). Results also indicate that isolated from conventional systems attached to very fine silica sand at significantly higher levels than those from organic systems ( < 0.001). Statistical analysis showed that a significant relationship did not exist between antibiotic resistance levels and attachment in from conventional systems but did for organic systems ( < 0.001). Better quantification of these relationships is critical to understanding the behavior of in the environment and preventing exposure of human populations to antibiotic-resistant bacteria.

Akathisia with Erythromycin: Induced or precipitated?

Objective: A 28-year-old male diagnosed with schizophrenia, maintaining well on Olanzapine, developed akathisia soon after addition of Erythromycin for Pityriasis Rosea. This prompted us to evaluate the relationship of Erythromycin and akathisia. Method: We report the case and the literature focusing on akathisia as a possible adverse event of Erythromycin. Results: Akathisia resolved after Erythromycin was stopped following 5 days of treatment. Akathisia was possibly induced or precipitated with use of Erythromycin. Possible etiological reasons of this clinically significant association are discussed. Conclusion: Erythromycin, by itself, may induce akathisia or precipitate akathisia in individuals by interfering with metabolism of other culprit drugs.

Medical Management of Cyclosporine-Induced Gingival Overgrowth Using Oral Azithromycin in Six Dogs

Gingival overgrowth is an uncommon adverse effect of cyclosporine administration in veterinary species. In people, gingival overgrowth is a common complication of cyclosporine administration for immunosuppression, generally following transplant procedures. Azithromycin has been used successfully for managing gingival overgrowth in human transplant patients when cyclosporine administration cannot be reduced or discontinued. This case series describes six dogs being administered cyclosporine for various dermatologic diseases that developed gingival overgrowth. The dogs were prescribed systemic azithromycin, with or without concurrent dose reduction of cyclosporine. Oral administration of 6.6-10.8 mg/kg of azithromycin once daily for 4-14 weeks was effective for complete clinical resolution of gingival overgrowth. In most cases, gingival overgrowth did not recur even with continued cyclosporine administration long-term. Adverse events of long-term azithromycin administration did not occur in any of the dogs. This series highlights a potentially beneficial medical treatment option for gingival overgrowth even when cyclosporine dose reduction is not possible or elected, without the need for surgical resection of proliferative gingival tissue.

Risk of adverse events among older adults following co-prescription of clarithromycin and statins not metabolized by cytochrome P450 3A4

BACKGROUND

The cytochrome P450 3A4 (CYP3A4) inhibitor clarithromycin may also inhibit liver-specific organic anion-transporting polypeptides (OATP1B1 and OATP1B3). We studied whether concurrent use of clarithromycin and a statin not metabolized by CYP3A4 was associated with an increased frequency of serious adverse events.

METHODS

Using large health care databases, we studied a population-based cohort of older adults (mean age 74 years) who were taking a statin not metabolized by CYP3A4 (rosuvastatin [76% of prescriptions], pravastatin [21%] or fluvastatin [3%]) between 2002 and 2013 and were newly prescribed clarithromycin (n=51,523) or azithromycin (n=52,518), the latter an antibiotic that inhibits neither CYP3A4 nor OATP1B1 and OATP1B3. Outcomes were hospital admission with a diagnostic code for rhabdomyolysis, acute kidney injury or hyperkalemia, and all-cause mortality. All outcomes were assessed within 30 days after co-prescription.

RESULTS

Compared with the control group, patients co-prescribed clarithromycin and a statin not metabolized by CYP3A4 were at increased risk of hospital admission with acute kidney injury (adjusted relative risk [RR] 1.65, 95% confidence interval [CI] 1.31 to 2.09), admission with hyperkalemia (adjusted RR 2.17, 95% CI 1.22 to 3.86) and all-cause mortality (adjusted RR 1.43, 95% CI 1.15 to 1.76). The adjusted RR for admission with rhabdomyolysis was 2.27 (95% CI 0.86 to 5.96). The absolute increase in risk for each outcome was small and likely below 1%, even after we considered the insensitivity of some hospital database codes.

INTERPRETATION

Among older adults taking a statin not metabolized by CYP3A4, co-prescription of clarithromycin versus azithromycin was associated with a modest but statistically significant increase in the 30-day absolute risk of adverse outcomes.

The impact of drug interactions and polypharmacy on antimicrobial therapy in the elderly

Infectious diseases are more prevalent in older people than in younger adults, and represent a major healthcare issue in older populations. Indeed, infections in the elderly are often associated with higher morbidity and mortality, and may present atypically. Additionally, older patients are generally treated with polypharmacy regimens, which increase the likelihood of drug-drug interactions when the prescription of an antimicrobial agent is needed. A progressive impairment in the functional reserve of multiple organs may affect either pharmacokinetics or pharmacodynamics during aging. Changes in body composition occurring with advancing age, reduced liver mass and perfusion, and reduced renal excretion may affect either pharmacokinetics or pharmacodynamics. These issues need to be taken into account when prescribing antimicrobial agents to older complex patients taking multiple drugs. Interventions aimed at improving the appropriateness and safety of antimicrobial prescriptions have been proposed. Educational interventions targeting physicians may improve antimicrobial prescriptions. Antimicrobial stewardship programmes have been found to reduce the length of hospital stay and improve safety in hospitalized patients, and their use in long-term care facilities is worth testing. Computerized prescription and decision support systems, as well as interventions aimed at improving antimicrobial agents dosage in relation to kidney function, may also help to reduce the burden of interactions and inherent costs.

An in vitro study on the effects of nisin on the antibacterial activities of 18 antibiotics against Enterococcus faecalis

Enterococcus faecalis rank among the leading causes of nosocomial infections worldwide and possesses both intrinsic and acquired resistance to a variety of antibiotics. Development of new antibiotics is limited, and pathogens continually generate new antibiotic resistance. Many researchers aim to identify strategies to effectively kill this drug-resistant pathogen. Here, we evaluated the effect of the antimicrobial peptide nisin on the antibacterial activities of 18 antibiotics against E. faecalis. The MIC and MBC results showed that the antibacterial activities of 18 antibiotics against E. faecalis OG1RF, ATCC 29212, and strain E were significantly improved in the presence of 200 U/ml nisin. Statistically significant differences were observed between the results with and without 200 U/ml nisin at the same concentrations of penicillin or chloramphenicol (p<0.05). The checkerboard assay showed that the combination of nisin and penicillin or chloramphenicol had a synergetic effect against the three tested E. faecalis strains. The transmission electron microscope images showed that E. faecalis was not obviously destroyed by penicillin or chloramphenicol alone but was severely disrupted by either antibiotic in combination with nisin. Furthermore, assessing biofilms by a confocal laser scanning microscope showed that penicillin, ciprofloxacin, and chloramphenicol all showed stronger antibiofilm actions in combination with nisin than when these antibiotics were administered alone. Therefore, nisin can significantly improve the antibacterial and antibiofilm activities of many antibiotics, and certain antibiotics in combination with nisin have considerable potential for use as inhibitors of this drug-resistant pathogen.

Clinical hypotension with co-prescription of macrolide antibiotics and calcium-channel blockers in haemodialysis patients: a retrospective chart review

BACKGROUND

Macrolide antibiotics inhibit the cytochrome p450 enzyme system, which metabolizes calcium-channel blockers. This may result in a clinically significant interaction, causing hypotension in patients co-prescribed these two drugs. Since these drugs are frequently used in the haemodialysis population, we studied the effect of their co-prescription on actual blood pressure.

METHODS

A retrospective chart review of all haemodialysis patients was conducted to identify patients co-prescribed a macrolide and a dihydropyridine calcium-channel blocker. Blood pressure measurements before and during the macrolide co-prescription were abstracted and compared using a student's t test.

RESULTS

We identified 154 haemodialysis patients concurrently prescribed a macrolide antibiotic and a dihydropyridine calcium-channel blocker. There was no significant difference in episodes of intra-dialytic hypotension or actual blood pressure measurements in the period before macrolide co-prescription and the period during macrolide co-prescription.

CONCLUSION

In contrast to hospitalized patients receiving dihydropyridine calcium-channel blockers, concurrent administration of a macrolide antibiotic for infection did not result in hypotension in haemodialysis outpatients. Further research should be undertaken before a change in clinical practice against their co-prescription is considered.

Dissociative disorder induced by clarithromycin combined with rabeprazole in a patient with gastritis

Clarithromycin and rabeprazole are both valued for their safety profile. Very few cases of adverse side-effects related to these drugs, when given individually, have been reported; serious side-effects of clarithromycin in combination with rabeprazole have never been reported. The present case reports on a 51-year-old woman with gastritis who received clarithromycin combined with rabeprazole for Helicobacter pylori infection. After taking 500 mg clarithromycin and 10 mg rabeprazole orally she displayed acute psychotic symptoms of dissociative disorder, including: impairment of orientation and attention; the feeling of dreaming; disintegration of thinking; stereotyped speech; flattened emotion; amnesia. Routine blood investigations, computed tomography scans and electroencephalography showed no abnormalities. All symptoms disappeared without antipsychotic treatment ≈ 48 h after she had taken the two drugs. Combining clarithromycin with rabeprazole might increase the risk of neurotoxicity, particularly in susceptible individuals. This should be a concern in clinical practice.

Antimalarial interaction of quinine and quinidine with clarithromycin

Quinine (QN) and quinidine (QND) have been commonly used as effective and affordable antimalarials for over many years. Quinine primarily is used for severe malaria treatment. However, plasmodia resistance to these drugs and poor patient compliance limits their administration to the patients. The declining sensitivity of the parasite to the drugs can thus be dealt with by combining with a suitable partner drug. In the present study QN/QND was assessed in combination with clarithromycin (CLTR), an antibiotic of the macrolide family. In vitro interactions of these drugs with CLTR against Plasmodium falciparum (P. falciparum) have shown a synergistic response with mean sum fractional inhibitory concentrations (ΣFICs) of ≤1 (0.85 ± 0.11 for QN + CLTR and 0.64 ± 0.09 for QND + CLTR) for all the tested combination ratios. Analysis of this combination of QN/QND with CLTR in mouse model against Plasmodium yoelii nigeriensis multi-drug resistant (P. yoelii nigeriensis MDR) showed that a dose of 200 mg/kg/day for 4 days of QN or QND produces 100% curative effect with 200 mg/kg/day for 7 days and 150 mg/kg/day for 7 days CLTR respectively, while the same dose of individual drugs could produce only up to a maximum 20% cure. It is postulated that CLTR, a CYP3A4 inhibitor, might have caused reduced CYP3A4 activity leading to increased plasma level of the QN/QND to produce enhanced antimalarial activity. Further, parasite apicoplast disruption by CLTR synergies the antimalarial action of QN and QND.

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.

Clarithromycin, a cytochrome P450 inhibitor, can reverse mefloquine resistance in Plasmodium yoelii nigeriensis- infected Swiss mice

During the last 2 decades there have been numerous reports of the emergence of mefloquine resistance in Southeast Asia and nearly 50% resistance is reported in Thailand. A World Health Organization report (2001) considers mefloquine as an important component of ACT (artesunate+mefloquine) which is the first line of treatment for the control of uncomplicated/multi-drug resistant (MDR) Plasmodium falciparum malaria. In view of the emergence of resistance towards this drug, it is proposed to develop new drug combinations to prolong the protective life of this drug. Prior studies have suggested that mefloquine resistance can be overcome by a variety of agents such as ketoconazole, cyproheptadine, penfluridol, Icajine and NP30. The present investigation reports that clarithromycin (CLTR), a new macrolide, being a potent inhibitor of Cyt. P450 3A4, can exert significant resistance reversal action against mefloquine resistance of plasmodia. Experiments were carried out to find out the curative dose of CLTR against multi-drug resistant P. yoelii nigeriensis. Mefloquine (MFQ) and clarithromycin (CLTR) combinations have been used for the treatment of this MDR parasite. Different dose combinations of these two drugs were given to the infected mice on day 0 (prophylactic) and day 1 with established infection (therapeutic) to see the combined effect of these combinations against the MDR malaria infection. With a dose of 32 mg/kg MFQ and 225 mg/kg CLTR, 100% cure was observed, while in single drug groups, treated with MFQ or CLTR, the cure was zero and 40% respectively. Therapeutically, MFQ and CLTR combinations 32+300 mg/kg doses cleared the established parasitaemia on day 10. Single treatment with MFQ or CLTR showed considerable suppression of parasitaemia on day 14 but neither was curative. Follow-up of therapeutically treated mice showed enhanced anti-malarial action as reflected by their 100% clearance of parasitaemia. The present study reveals that CLTR is a useful antibiotic to be used as companion drug with mefloquine in order to overcome mefloquine resistance in plasmodia.

Factors affecting interindividual differences in clozapine response: a review and case report

OBJECTIVE

Clozapine is the most powerful new‐generation antipsychotic. Although this drug leads to great therapeutic benefits, two types of undesirable conditions frequently occur with its use: side effects and resistance to treatment. Therapeutic drug monitoring of clozapine would be very useful to avoid both these situations. The necessity of monitoring the therapy is the result of a wide interindividual variability in the metabolism of clozapine. In this review, we highlight all the conditions underlying this variability, analyzing them one by one.

METHODS

Relevant literature was identified through a search of MEDLINE and PubMed. In addition, the case of a treatment‐resistant patient with accelerated metabolism of clozapine is reported as representative of utility of therapeutic drug monitoring in terms of clozapine dose adjustment.

RESULTS

Genetic polymorphisms of cytochrome P450 enzymes and of neurotransmitter receptors; drug interactions; interactions of clozapine with other substances such as food and drink; smoking; and nonmodifiable variables such as age, ethnicity, and gender have been examined in relation to the existing scientific literature. The laboratory techniques that clinicians could use to identify these variables and adequate therapies are also reviewed.

Pharmacokinetic interactions between etravirine and non-antiretroviral drugs

Etravirine (formerly TMC125) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) with activity against wild-type and NNRTI-resistant strains of HIV-1. Etravirine has been approved in several countries for use as part of highly active antiretroviral therapy in treatment-experienced patients. In vivo, etravirine is a substrate for, and weak inducer of, the hepatic cytochrome P450 (CYP) isoenzyme 3A4 and a substrate and weak inhibitor of CYP2C9 and CYP2C19. Etravirine is also a weak inhibitor of P-glycoprotein. An extensive drug-drug interaction programme in HIV-negative subjects has been carried out to assess the potential for pharmacokinetic interactions between etravirine and a variety of non-antiretroviral drugs. Effects of atorvastatin, clarithromycin, methadone, omeprazole, oral contraceptives, paroxetine, ranitidine and sildenafil on the pharmacokinetic disposition of etravirine were of no clinical relevance. Likewise, etravirine had no clinically significant effect on the pharmacokinetics of fluconazole, methadone, oral contraceptives, paroxetine or voriconazole. No clinically relevant interactions are expected between etravirine and azithromycin or ribavirin, therefore, etravirine can be combined with these agents without dose adjustment. Fluconazole and voriconazole increased etravirine exposure 1.9- and 1.4-fold, respectively, in healthy subjects, however, no increase in the incidence of adverse effects was observed in patients receiving etravirine and fluconazole during clinical trials, therefore, etravirine can be combined with these antifungals although caution is advised. Digoxin plasma exposure was slightly increased when co-administered with etravirine. No dose adjustments of digoxin are needed when used in combination with etravirine, however, it is recommended that digoxin levels should be monitored. Caution should be exercised in combining rifabutin with etravirine in the presence of certain boosted HIV protease inhibitors due to the risk of decreased exposure to etravirine. Although adjustments to the dose of clarithromycin are unnecessary for the treatment of most infections, the use of an alternative macrolide (e.g. azithromycin) is recommended for the treatment of Mycobacterium avium complex infection since the overall activity of clarithromycin against this pathogen may be altered when co-administered with etravirine. Dosage adjustments based on clinical response are recommended for clopidogrel, HMG-CoA reductase inhibitors (e.g. atorvastatin) and for phosphodiesterase type-5 inhibitors (e.g. sildenafil) because changes in the exposure of these medications in the presence of co-administered etravirine may occur. When co-administered with etravirine, a dose reduction or alternative to diazepam is recommended. When combining etravirine with warfarin, the international normalized ratio (INR) should be monitored. Systemic dexamethasone should be co-administered with caution, or an alternative to dexamethasone be found as dexamethasone induces CYP3A4. Caution is also warranted when co-administering etravirine with some antiarrhythmics, calcineurin inhibitors (e.g. ciclosporin) and antidepressants (e.g. citalopram). Co-administration of etravirine with some antiepileptics (e.g. carbamazepine and phenytoin), rifampicin (rifampin), rifapentine or preparations containing St John's wort (Hypericum perforatum) is currently not recommended as these are potent inducers of CYP3A and/or CYP2C and may potentially decrease etravirine exposure. Antiepileptics that are less likely to interact based on their known pharmacological properties include gabapentin, lamotrigine, levetiracetam and pregabalin. Overall, pharmacokinetic and clinical data show etravirine to be well tolerated and generally safe when given in combination with non-antiretroviral agents, with minimal clinically significant drug interactions and no need for dosage adjustments of etravirine in any of the cases, or of the non-antiretroviral agent in the majority of cases studied.

The risk of hypotension following co-prescription of macrolide antibiotics and calcium-channel blockers

BACKGROUND

The macrolide antibiotics clarithromycin and erythromycin may potentiate calcium-channel blockers by inhibiting cytochrome P450 isoenzyme 3A4. However, this potential drug interaction is widely underappreciated and its clinical consequences have not been well characterized. We explored the risk of hypotension or shock requiring hospital admission following the simultaneous use of calcium-channel blockers and macrolide antibiotics.

METHODS

We conducted a population-based, nested, case-crossover study involving people aged 66 years and older who had been prescribed a calcium-channel blocker between Apr. 1, 1994, and Mar. 31, 2009. Of these patients, we included those who had been admitted to hospital for the treatment of hypotension or shock. For each antibiotic, we estimated the risk of hypotension or shock associated with the use of a calcium blocker using a pair-matched analytic approach to contrast each patient's exposure to each macrolide antibiotic (erythromycin, clarithromycin or azithromycin) in a seven-day risk interval immediately before admission to hospital and in a seven-day control interval one month earlier.

RESULTS

Of the 7100 patients admitted to hospital because of hypotension while receiving a calcium-channel blocker, 176 had been prescribed a macrolide antibiotic during either the risk or control intervals. Erythromycin (the strongest inhibitor of cytochrome P450 3A4) was most strongly associated with hypotension (odds ratio [OR] 5.8, 95% confidence interval [CI] 2.3-15.0), followed by clarithromycin (OR 3.7, 95% CI 2.3-6.1). Azithromycin, which does not inhibit cytochrome P450 3A4, was not associated with an increased risk of hypotension (OR 1.5, 95% CI 0.8-2.8). We found similar results in a stratified analysis of patients who received only dihydropyridine calcium-channel blockers.

INTERPRETATION

In older patients receiving a calcium-channel blocker, use of erythromycin or clarithromycin was associated with an increased risk of hypotension or shock requiring admission to hospital. Preferential use of azithromycin should be considered when a macrolide antibiotic is required for patients already receiving a calcium-channel blocker.

Common drug interactions leading to adverse drug events in the intensive care unit: management and pharmacokinetic considerations

Critically ill patients are predisposed to drug interactions because of the complexity of the drug regimens they receive in the intensive care setting. Drugs may affect the absorption, distribution, metabolism, and/or elimination of an object drug and consequently alter the intended pharmacologic response and potentially lead to an adverse event. Certain disease states that afflict critically ill patients may also amplify an intended pharmacologic response and potentially result in an unintended effect. A team approach is important to identify, prevent, and address drug interactions in the intensive care setting and optimize patient outcomes.

Rhabdomyolysis a result of azithromycin and statins: an unrecognized interaction

AIMS

In a systematic screening of the World Health Organization Adverse Drug Reaction database, VigiBase, in July 2008, a measure of association used to detect interactions (Omega) highlighted azithromycin with the individual statins atorvastatin, lovastatin and simvastatin and rhabdomyolysis. The aim was to examine all reports including rhabdomyolysis-azithromycin and statins in VigiBase to assess if the data were suggestive of an interaction.

METHODS

The individual case reports in VigiBase and the original files were reviewed. In order to investigate the reporting over time for rhabdomyolysis with azithromycin and statins to VigiBase, Omega values were generated retrospectively.

RESULTS

The reporting over time showed that rhabdomyolysis under concomitant use of azithromycin and statins was reported more often than expected from 2000 and onwards in Vigibase. After exclusion of possible duplicates and follow-up reports, 53 cases from five countries remained. Rhabdomyolysis occurred shortly after initiation of azithromycin in 23% of cases. In 11 patients an interaction had been suggested by the reporter. With the exception of one patient, the statin doses reported were within the recommended daily doses.

CONCLUSIONS

Case reports in VigiBase are suggestive that interactions between azithromycin and statins resulting in rhabdomyolysis may occur. This analysis showed the potential of the newly developed disproportionality measure, Omega, which can help to identify drug interactions in VigiBase in the future. The results also showed that reviewing spontaneous reports can add information to drug interactions not established previously.

Drug Interactions Between Antibiotics and Select Maintenance Medications: Seeing More Clearly Through the Narrow Therapeutic Window of Opportunity

OBJECTIVE

Infections often occur while treating patients with long-term medications for chronic illnesses. Treating these infections with systemic antibiotics often leads to pharmacokinetic and pharmacodynamic interactions between the antimicrobials and one or more of the maintenance medications. Previously optimized long-term regimens may become either subtherapeutic or super-therapeutic, with deleterious consequences. This article discusses some of the most significant and commonly encountered antibiotic drug interactions that may occur with medications with "narrow therapeutic windows" including warfarin, phenytoin, carbamazepine, theophylline, and the two calcineurin inhibitors. Given the logistics of many consultant pharmacists' practices, it may not always be possible for them to react prospectively when these combinations are prescribed at their facilities. Therefore, there are several things the pharmacist can do: provide regular and comprehensive inservice raining on this topic, be available as needed to answer patient-specific questions, and provide readily available charts and other educational materials that help identify and characterize these important interactions.

DATA SOURCES

A Medline search of the English literature was performed in October/November 2003, going back to 1980 for the commonly used antibiotics and drug interactions stated in this text. In some cases, cross referencing of articles reviewed also led to older publications. Textbooks dealing with drug interactions also were used as initial sources. However, whenever possible, any data quoted within the text were verified from the original research paper.

STUDY SELECTION

Pharmacokinetic studies, case reports, and general review articles published in the English medical literature were all selected for review. In cases where review articles were cited that summarize groups of data from previous original research papers, the authors made the best possible effort to verify the accuracy by referring to the original research papers.

DATA SYNTHESIS

Because of the breadth of the topic in terms of all the antibiotics discussed, the interacting medications that pertained to each antibiotic, and the lack of homogeneity among the various types of papers (most of which were case reports), most analyses include broad-based summaries based on the aggregate findings of the authors.

CONCLUSION

The addition of antibiotics to a stabilized medical regimen can result in either potentiation or antagonism of the clinical effects of narrow-therapeutic-window medications such as warfarin, phenytoin, theophylline, calcineurin inhibitors, carbamazepine, and numerous other agents. As usual in the clinical arena, awareness is the first step in appropriate management of these encounters.

Evaluation of potential interaction between vinorelbine and clarithromycin

BACKGROUND

Myelotoxicity, a major toxicity of vinorelbine. may be related to the degree of one's exposure to vinorelbine. In theory, clarithromycin has the potential to alter vinorelbine's pharmacokinetics by inhibiting CYP3A and/or P-glycoprotein; this may result in massive exposure to vinorelbine and severe toxicity. To date, macrolide-vinorelbine drug interactions have not been reported.

OBJECTIVE

To estimate the clinical risk of a interaction between vinorelbine and clarithromycin.

METHODS

In a retrospective cohort study, we searched computerized medical records of patients who had been administered vinorelbine in the University of Fukui Hospital. The study cohort was defined as all patients with non-small-cell lung cancer who received vinorelbine between May 30, 2003, and January 31, 2008. The treatment courses were classified according to whether or not clarithromycin was concomitantly administered with vinorelbine. Nadir neutrophil counts were recorded as the major outcomes. Vinorelbine-clarithromycin interaction was defined as a significant increase in the risk of severe neutropenia when the 2 drugs were administered concomitantly.

RESULTS

A total of 12 (63.2%) and 11 (27.5%) episodes of grade 3/4 neutropenia occurred among the patients who were and were not administered clarithromycin, respectively. The incidence of grade 4 neutropenia was higher in the group administered clarithromycin than in those who did not receive it (31.6% vs 2.5%; p = 0.0033). Vinorelbine dose, concomitant clarithromycin administration, and female sex were significantly correlated with severe neutropenia, with unadjusted odds ratios of 0.07 (95% CI 0.01 to 0.59), 4.52 (95% CI 1.41 to 14.45), and 4.55 (95% CI 1.39 to 14.29), respectively.

CONCLUSIONS

Compared with patients who are administered vinorelbine alone, patients who are administered clarithromycin during chemotherapy with vinorelbine are at a higher risk for severe neutropenia. Physicians should educate their patients about this interaction. If possible, clarithromycin administration should be avoided in patients who will undergo chemotherapy with vinorelbine in the near future. However, further prospective pharmacokinetic studies are required to confirm this interaction.

SFINX-a drug-drug interaction database designed for clinical decision support systems

OBJECTIVE

The aim was to develop a drug-drug interaction database (SFINX) to be integrated into decision support systems or to be used in website solutions for clinical evaluation of interactions.

METHODS

Key elements such as substance properties and names, drug formulations, text structures and references were defined before development of the database. Standard operating procedures for literature searches, text writing rules and a classification system for clinical relevance and documentation level were determined. ATC codes, CAS numbers and country-specific codes for substances were identified and quality assured to ensure safe integration of SFINX into other data systems. Much effort was put into giving short and practical advice regarding clinically relevant drug-drug interactions.

RESULTS

SFINX includes over 8,000 interaction pairs and is integrated into Swedish and Finnish computerised decision support systems. Over 31,000 physicians and pharmacists are receiving interaction alerts through SFINX. User feedback is collected for continuous improvement of the content.

CONCLUSION

SFINX is a potentially valuable tool delivering instant information on drug interactions during prescribing and dispensing.

Effect of erythromycin and azithromycin on sensation afferent nerve functions of gastrointestinal tract in rats

AIM: To investigate the effect of erythromycin and azithromycin on sensation afferent nerve functions of gastrointestinal tract in rats and its corresponding mechanism.

METHODS: Sixty-four rats were randomly divided into erythromycin group, azithromycin group, control group, low dose group (0.1 mg/kg), medium dose group (0.5 mg/kg) and high dose group (1 mg/kg). Spontaneous afferent nerve discharge and gastric distention-induced afferent nerve discharge of subdiaphragmatic vagus nerve were recorded half an hour before and after intravenous injection of different doses of erythromycin and azithromycinin.

RESULTS: Intravenous low erythromycin and azithromycin dose had no obvious exciting effect on spontaneous afferent nerve discharge and gastric distention- induced afferent nerve discharge of subdiaphragmatic vagus nerve after 20 min. Intravenous medium and high erythromycin and azithromycin dose had obvious exciting effect on spontaneous afferent nerve discharge (erythromycin: 8.34 ± 0.37, 8.54 ± 0.26 vs 7.78 ± 0.23, 7.84 ± 8.27; azithromycin: 8.57 ± 0.43, 8.28 ± 0.38 vs 7.74 ± 0.21, 7.86 ± 0.30) and gastric distention-induced afferent nerve discharge of subdiaphragmatic vagus nerve (erythromycin: 8.54 ± 0.34, 8.61 ± 0.20 vs 8.13 ± 0.36, 8.19 ± 0.21; azithromycin: 8.54 ± 0.30, 8.42 ± 0.21 vs 8.24 ± 0.22, 8.22 ± 0.19), which was statistically significant compared with the control and low dose groups.

CONCLUSION: Erythromycin and azithromycin have significant effects on sensation afferent nerve functions of gastrointestinal tract in rats.

Antibiotic drug interactions

Drug-drug interactions in the field of infectious diseases continue to expand as new drugs are approved, metabolic enzymes and transporters are identified, and recommendations for co-administration of drugs are revised. This article provides an overview of the principles and mechanisms of drug-drug interactions and describes pharmacokinetic-pharmacodynamic interactions commonly associated with antibacterial therapy, antiviral agents (non-retroviral), and drugs for tuberculosis.

Cytochrom-P450 mediierte Arzneimittelinteraktionen mit Antibiotika

This review focuses on drug interactions with commonly prescribed antibiotics. With each drug coadministered, the likelihood of an adverse interaction increases exponentially. Thus, poly-pharmacotherapy possesses important clinical challenges for clinicians and exposes patients to potentially life-threatening risks. In particular, following co-administration of drugs such as tricyclic antidepressants, anticoagulants and antiarrhythmics, which are characterized by narrow therapeutic windows, even small changes in plasma levels can cause serious adverse reactions and/or therapeutic failure. The hepatic and intestinal cytochrome, or CYP-450 enzyme system is responsible for the biotransformation of a multitude of drugs and is frequently involved in drug interactions. The present review therefore presents a comprehensive overview on potential drug interactions with antibiotics, which are mediated by the cytochrome-P450-enzymes.

Drug interactions during therapy with three major groups of antimicrobial agents

This review focuses on drug-drug interactions with three major groups of antimicrobial agents: macrolides (including azalides and ketolides), quinolones, which are widely used for the treatment of bacterial infections, and azoles, which are used for antifungal therapy. Macrolides and the ketolide telithromycin are potent inhibitors of CYP3A4 and thus interfere with the pharmacokinetics of many other drugs that are metabolised by this enzyme. In contrast, although closely related, azithromycin is not a cytochrome inhibitor. All quinolones form complexes with di- and trivalent cations and, therefore, the absorption of quinolones can be dramatically reduced when given concomitantly with mineral antacids, zinc or iron preparations. Ciprofloxacin exhibits an inhibitory potential for the cytochrome isoenzyme 1A2, resulting in an inhibition of theophylline metabolism. Other quinolones, such as levofloxacin or moxifloxacin, do not interfere with theophylline metabolism. The systemic azoles, such as ketoconazole, itraconazole, fluconazole and voriconazole, are inhibitors of CYP isoenzymes, such as CYP3A4, CYP2C9 and CYP2C19, to varying degrees. In addition, some are substrates of the MDR-1 gene product, P-glycoprotein. These features are the basis for most of the interactions occurring during azole therapy (e.g., in severely ill patients in the hospital who are treated with multiple drugs).

Life-threatening bradyarrhythmia after massive azithromycin overdose

9-month-old infant was inadvertently administered azithromycin 50 mg/kg, taken from floor stock, instead of the prescribed ceftriaxone. Shortly thereafter, she became unresponsive and pulseless. The initial heart rhythm observed when cardiopulmonary resuscitation was started was a widecomplex bradycardia, with a prolonged rate-corrected QT interval and complete heart block. The baby was resuscitated with epinephrine and atropine, but she suffered severe anoxic encephalopathy. Torsade de pointes and QT-interval prolongation have been reported after administration of macrolide antibiotics, including azithromycin, both intravenously and orally. This has occurred especially in the context of coadministered drugs that inhibit the cytochrome P450 (CYP) 3A4 isoenzyme, such as ketoconazole and astemizole. However, bradycardia with complete heart block has not, to our knowledge, been reported specifically with intravenous administration of azithromycin alone, either with therapeutic doses or overdose. Clinicians should be alerted about the potential of azithromycin to cause life-threatening bradycardia, and pharmacy systems should be implemented to ensure special care in the safe administration of this drug, especially when dispensed from a point-of-care source.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Fatal Interaction between Clarithromycin and Colchicine in Patients with Renal Insufficiency: A Retrospective Study

BACKGROUND

Clarithromycin is frequently used to treat community-acquired pneumonia in elderly persons. Like erythromycin, it may interact with other drugs by interfering with metabolism by cytochrome P450 enzymes and with the P-glycoprotein transporter system. Colchicine, used for treatment of acute gout and for prophylaxis, may cause bone marrow toxicity. It is metabolized by CYP3A4 and is transported by P-glycoprotein. Initial case reports suggested potentially fatal interactions between clarithromycin and colchicine.

METHODS

A retrospective study was conducted with 116 patients who were prescribed clarithromycin and colchicine during the same clinical admission. Case-control comparisons were made between patients who received concomitant therapy with the 2 drugs and patients who received sequential therapy. We assessed the clinical presentations and outcomes of the 2 patient groups and analyzed the risk factors associated with fatal outcomes.

RESULTS

Nine (10.2%) of the 88 patients who received the 2 drugs concomitantly died. Only 1 (3.6%) of the 28 patients who received the drugs sequentially died. Multivariate analysis of the 88 patients who received concomitant therapy showed that longer overlapped therapy (relative risk [RR], 2.16; 95% confidence interval [CI], 1.41-3.31; P< or =.01), the presence of baseline renal impairment (RR, 9.1; 95% CI, 1.75-47.06; P<.001), and the development of pancytopenia (RR, 23.4; 95% CI, 4.48-122.7; P<.001) were independently associated with death.

CONCLUSIONS

Clarithromycin increases the risk of fatal colchicine toxicity, especially for patients with renal insufficiency. Since there are other drugs for treatment of pneumonia and gout, these 2 drugs should not be coprescribed, because of the risk of fatality.

Antiinflammatory Therapies for Cystic Fibrosis: Past, Present, and Future

Inflammation is a major component of the vicious cycle characterizing cystic fibrosis pulmonary disease. If untreated, this inflammatory process irreversibly damages the airways, leading to bronchiectasis and ultimately respiratory failure. Antiinflammatory drugs for cystic fibrosis lung disease appear to have beneficial effects on disease parameters. These agents include oral corticosteroids and ibuprofen, as well as azithromycin, which, in addition to its antimicrobial effects, also possesses antiinflammatory properties. Inhaled corticosteroids, colchicine, methotrexate, montelukast, pentoxifylline, nutritional supplements, and protease replacement have not had a significant impact on the disease. Therapy with oral corticosteroids, ibuprofen, and fish oil is limited by adverse effects. Azithromycin appears to be safe and effective, and is thus the most promising antiinflammatory therapy available for patients with cystic fibrosis. Pharmacologic therapy with antiinflammatory agents should be started early in the disease course, before extensive irreversible lung damage has occurred.

Effect of multiple-dose erythromycin on everolimus pharmacokinetics

OBJECTIVE

We sought to quantify the influence of the CYP3A inhibitor erythromycin on the pharmacokinetics of everolimus, a CYP3A substrate.

METHODS

This was a two-period, single-sequence, crossover study in 16 healthy subjects. In period 1, subjects received the reference treatment of a single 2-mg dose of everolimus. In period 2, they received the test treatment of erythromycin 500 mg three times daily for a total of 9 days and a single 2-mg dose of everolimus coadministered on the fifth day of erythromycin therapy. The test/reference ratio and 90% confidence interval (CI) were derived for everolimus C (max) and AUC.

RESULTS

During erythromycin coadministration, everolimus C (max) increased 2.0-fold (90% CI, 1.8-2.3) from 20+/-5 ng/ml to 40+/-10 ng/ml. Everolimus AUC increased 4.4-fold (90% CI, 3.5-5.4) from 116+/-37 ng h/ml to 524+/-225 ng h/ml. Everolimus half-life was prolonged by 39% from 32+/-6 h to 44+/-6 h. Erythromycin predose concentrations were not changed after single-dose administration of everolimus.

CONCLUSION

Multiple-dose erythromycin increased single-dose everolimus blood levels by an average 4.4-fold (range, 2.0-12.6). During erythromycin treatment, a compensatory everolimus dose reduction should be made guided by everolimus therapeutic drug monitoring.

The Disease-Modifying Effects of Twice-Weekly Oral Azithromycin in Patients with Bronchiectasis

INTRODUCTION

Bronchiectasis is a chronic pulmonary process characterized by recurrent respiratory infections leading to destruction of airways secondary to inflammation. We investigated whether the addition of 6-months' twice-weekly azithromycin to the existing treatment regimen in patients with pulmonary bronchiectasis decreased the number of exacerbations and improved pulmonary function compared with a similar period of time without concurrent azithromycin.

METHODS

Thirty patients with high-resolution computed tomography scan-confirmed bronchiectasis were to be recruited. In random order, patients received usual medications for 6 months, and usual medications plus oral azithromycin 500mg twice weekly for 6 months. Patients receiving azithromycin first had a 1-month washout period prior to entering the second phase. Patients recorded weekly peak flow (PF) measurements. Pulmonary function tests (PFTs), 24-hour sputum volume, and needs for intervention with medication or ancillary support were collected at baseline and every 3 months. Exacerbation incidence and sputum volume measurements were compared from baseline to the end of each study phase.

RESULTS

Twelve patients were enrolled; 11 were included in the analysis. Owing to randomization, most patients received the azithromycin first, which was fairly well tolerated. PFTs did not change significantly during either study phase and PFs appeared to remain stable during azithromycin therapy and throughout the subsequent control phase. Azithromycin significantly decreased the incidence of exacerbations compared with usual medications (5 vs 16; p = 0.019). Mean 24-hour sputum volume significantly decreased (15% [p = 0.005]) during the active treatment phase, and remained decreased during the control phase (p = 0.028). Subjectively, patients reported increased energy and quality of life while receiving treatment with azithromycin.

CONCLUSIONS

The addition of twice-weekly azithromycin significantly decreased the incidence of exacerbation and 24-hour sputum volume and may have stabilized the PFTs and PFs in this 11-patient pilot study. The results of this study justify further investigation of adding azithromycin to the treatment regimens of patients with bronchiectasis for its disease-modifying effects.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.

Clinical relevance and management of drug-related QT interval prolongation

Much attention recently has focused on drugs that prolong the QT interval, potentially leading to fatal cardiac dysrhythmias (e.g., torsade de pointes). We provide a detailed review of the published evidence that supports or does not support an association between drugs and their risk of QT prolongation. The mechanism of drug-induced QT prolongation is reviewed briefly, followed by an extensive evaluation of drugs associated with QT prolongation, torsade de pointes, or both. Drugs associated with QT prolongation are identified as having definite, probable, or proposed associations. The role of the clinician in the prevention and management of QT prolongation, drug-drug interactions that may occur with agents known to affect the QT interval, and the impact of this adverse effect on the regulatory process are addressed.

Chronic metoclopramide therapy for diabetic gastroparesis

OBJECTIVE

To review the safety and efficacy of chronic metoclopramide for diabetic gastroparesis.

DATA SOURCES

Medical literature was accessed through MEDLINE (1965 to October 2002) and PubMed (1965 to October 2002). Key search terms included metoclopramide; diabetic gastroparesis; and dyskinesia, drug induced.

DATA SYNTHESIS

Metoclopramide is often used for diabetic gastroparesis, despite the risk of tardive dyskinesia. Published information is limited regarding long-term efficacy and toxicity of metoclopramide. The literature was assessed concerning these topics.

CONCLUSIONS

Limited data do not provide sufficient evidence to conclude whether metoclopramide is efficacious for chronic use. Routine monitoring may mitigate the risk associated with metoclopramide therapy.

Effect of the CYP3A4 inhibitor erythromycin on the pharmacokinetics of lignocaine and its pharmacologically active metabolites in subjects with normal and impaired liver function

AIMS

The objectives of this study were: (i) to evaluate the effect of a cytochrome P450 (CYP) 3A4 inhibitor, erythromycin, on the pharmacokinetics of intravenous lignocaine and its two pharmacologically active metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX); (ii) to assess whether the effects of the erythromycin inhibitory action on lignocaine clearance and the results of the MEGX liver function test depend on liver functional status; and (iii) to determine the effects of both moderate and severe liver dysfunction on the disposition kinetics of lignocaine.

METHODS

The study was carried out on 10 healthy volunteers, and 10 Child's class A and 10 class C cirrhotic patients, according to a double-blind, randomized, two-way crossover design. On day 1 of the investigation, all subjects received three oral doses of erythromycin (600 mg of the ethylsuccinate ester) or placebo, and two further doses on day 2. One hour after the fourth dose, subjects were given 1 mg kg-1 lignocaine intravenously. Timed plasma samples were then obtained until 12 h for determination of the concentrations of lignocaine, MEGX and GX.

RESULTS

Erythromycin caused statistically significant, although limited, modifications of lignocaine and MEGX pharmacokinetic parameters. In healthy volunteers, lignocaine clearance was decreased from 9.93 to 8.15 ml kg-1 min-1[mean percentage ratio (95% CI), 82 (65-98)] and the half-life was prolonged from 2.23 to 02.80 h [mean percentage ratio (95% CI), 130 (109-151)]; MEGX area under the concentration-time curve from 0 h to 12 h was increased from 665 to 886 ng ml-1 h [mean percentage ratio (95% CI), 129 (102-156)]. Quantitatively similar modifications were observed in the two cirrhotic groups. GX concentrations were lowered in all study groups, although not to statistically significant extents. Erythromycin coadministration caused no appreciable interference with the results of the MEGX test. Only in patients with Child's grade C liver cirrhosis were lignocaine kinetic parameters significantly altered with respect to healthy volunteers. Thus, clearance was approximately halved, steady-state volume of distribution was increased, and terminal half-life was more than doubled.

CONCLUSIONS

Although erythromycin only modestly decreases lignocaine clearance, it causes a concomitant elevation of the concentrations of its pharmacologically active metabolite MEGX. A pharmacodynamic study following lignocaine infusion to steady state appears necessary to assess the actual clinical relevance of these combined effects. The degree of liver dysfunction has no influence on the extent of the erythromycin-lignocaine interaction, whereas it markedly influences the extent of the changes in lignocaine pharmacokinetics. These findings indicate that no dose adjustment is needed in patients with moderate liver cirrhosis, whereas the lignocaine dose should be halved in patients with severe cirrhosis.

Blockade of human cardiac potassium channel human ether-a-go-go-related gene (HERG) by macrolide antibiotics

Several macrolides have been reported to cause QT prolongation and ventricular arrhythmias such as torsades de pointes. To clarify the underlying ionic mechanisms, we examined the effects of six macrolides on the human ether-a-go-go-related gene (HERG)-encoded potassium current stably expressed in human embryonic kidney-293 cells. All six drugs showed a concentration-dependent inhibition of the current with the following IC(50) values: clarithromycin, 32.9 microM; roxithromycin, 36.5 microM; erythromycin, 72.2 microM; josamycin, 102.4 microM; erythromycylamine, 273.9 microM; and oleandomycin, 339.6 microM. A metabolite of erythromycin, des-methyl erythromycin, was also found to inhibit HERG current with an IC(50) of 147.1 microM. These findings imply that the blockade of HERG may be a common feature of macrolides and may contribute to the QT prolongation observed clinically with some of these compounds. Mechanistic studies showed that inhibition of HERG current by clarithromycin did not require activation of the channel and was both voltage- and time-dependent. The blocking time course could be described by a first-order reaction between the drug and the channel. Both binding and unbinding processes appeared to speed up as the membrane was more depolarized, indicating that the drug-channel interaction may be affected by electrostatic responses.

Pharmacokinetic aspects of treating infections in the intensive care unit: focus on drug interactions

Pharmacokinetic interactions involving anti-infective drugs may be important in the intensive care unit (ICU). Although some interactions involve absorption or distribution, the most clinically relevant interactions during anti-infective treatment involve the elimination phase. Cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6 and 3A4 are the major isoforms responsible for oxidative metabolism of drugs. Macrolides (especially troleandomycin and erythromycin versus CYP3A4), fluoroquinolones (especially enoxacin, ciprofloxacin and norfloxacin versus CYP1A2) and azole antifungals (especially fluconazole versus CYP2C9 and CYP2C19, and ketoconazole and itraconazole versus CYP3A4) are all inhibitors of CYP-mediated metabolism and may therefore be responsible for toxicity of other coadministered drugs by decreasing their clearance. On the other hand, rifampicin is a nonspecific inducer of CYP-mediated metabolism (especially of CYP2C9, CYP2C19 and CYP3A4) and may therefore cause therapeutic failure of other coadministered drugs by increasing their clearance. Drugs frequently used in the ICU that are at risk of clinically relevant pharrmacokinetic interactions with anti-infective agents include some benzodiazepines (especially midazolam and triazolam), immunosuppressive agents (cyclosporin, tacrolimus), antiasthmatic agents (theophylline), opioid analgesics (alfentanil), anticonvulsants (phenytoin, carbamazepine), calcium antagonists (verapamil, nifedipine, felodipine) and anticoagulants (warfarin). Some lipophilic anti-infective agents inhibit (clarithromycin, itraconazole) or induce (rifampicin) the transmembrane transporter P-glycoprotein, which promotes excretion from renal tubular and intestinal cells. This results in a decrease or increase, respectively, in the clearance of P-glycoprotein substrates at the renal level and an increase or decrease, respectively, of their oral bioavailability at the intestinal level. Hydrophilic anti-infective agents are often eliminated unchanged by renal glomerular filtration and tubular secretion, and are therefore involved in competition for excretion. Beta-lactams are known to compete with other drugs for renal tubular secretion mediated by the organic anion transport system, but this is frequently not of major concern, given their wide therapeutic index. However, there is a risk of nephrotoxicity and neurotoxicity with some cephalosporins and carbapenems. Therapeutic failure with these hydrophilic compounds may be due to haemodynamically active coadministered drugs, such as dopamine, dobutamine and furosemide, which increase their renal clearance by means of enhanced cardiac output and/or renal blood flow. Therefore, coadministration of some drugs should be avoided, or at least careful therapeutic drug monitoring should be performed when available. Monitoring may be especially helpful when there is some coexisting pathophysiological condition affecting drug disposition, for example malabsorption or marked instability of the systemic circulation or of renal or hepatic function.