Absolute bioavailability of clarithromycin after oral administration in humans

Macrolide and Ketolide Antibiotics Inhibit the Cytotoxic Effect of Trastuzumab Emtansine in HER2-Positive Breast Cancer Cells: Implication of a Potential Drug-ADC Interaction in Cancer Chemotherapy

Macrolides are widely used for the long-term treatment of infections and chronic inflammatory diseases. The pharmacokinetic features of macrolides include extensive tissue distribution because of favorable membrane permeability and accumulation within lysosomes. Trastuzumab emtansine (T-DM1), a HER2-targeting antibody-drug conjugate (ADC), is catabolized in the lysosomes, where Lys-SMCC-DM1, a potent cytotoxic agent, is processed by proteinase degradation and subsequently released from the lysosomes to the cytoplasm through the lysosomal membrane transporter SLC46A3, resulting in an antitumor effect. We recently demonstrated that erythromycin and clarithromycin inhibit SLC46A3 and attenuate the cytotoxicity of T-DM1; however, the effect of other macrolides and ketolides has not been determined. In this study, we evaluated the effect of macrolide and ketolide antibiotics on T-DM1 cytotoxicity in a human breast cancer cell line, KPL-4. Macrolides used in the clinic, such as roxithromycin, azithromycin, and josamycin, as well as solithromycin, a ketolide under clinical development, significantly attenuated T-DM1 cytotoxicity in addition to erythromycin and clarithromycin. Of these, azithromycin was the most potent inhibitor of T-DM1 efficacy. These antibiotics significantly inhibited the transport function of SLC46A3 in a concentration-dependent manner. Moreover, these compounds extensively accumulated in the lysosomes at the levels estimated to be 0.41-13.6 mM when cells were incubated with them at a 2 μM concentration. The immunofluorescence staining of trastuzumab revealed that azithromycin and solithromycin inhibit the degradation of T-DM1 in the lysosomes. These results suggest that the attenuation of T-DM1 cytotoxicity by macrolide and ketolide antibiotics involves their lysosomal accumulation and results in their greater lysosomal concentrations to inhibit the SLC46A3 function and T-DM1 degradation. This suggests a potential drug-ADC interaction during cancer chemotherapy.

Physiologically based pharmacokinetic modeling to assess the drug-drug interactions of anaprazole with clarithromycin and amoxicillin in patients undergoing eradication therapy of H. pylori infection

OBJECTIVE

This study aimed to assess the pharmacokinetic (PK) interactions of anaprazole, clarithromycin, and amoxicillin using physiologically based pharmacokinetic (PBPK) models.

METHODS

The PBPK models for anaprazole, clarithromycin, and amoxicillin were constructed using the GastroPlus™ software (Version 9.7) based on the physicochemical data and PK parameters obtained from literature, then were optimized and validated in healthy subjects to predict the plasma concentration-time profiles of these three drugs and assess the predictive performance of each model. According to the analysis of the properties of each drug, the developed and validated models were applied to evaluate potential drug-drug interactions (DDIs) of anaprazole, clarithromycin, and amoxicillin.

RESULTS

The developed PBPK models properly described the pharmacokinetics of anaprazole, clarithromycin, and amoxicillin well, and all predicted PK parameters (Cmax,ss, AUC0-τ,ss) ratios were within 2.0-fold of the observed values. Furthermore, the application of these models to predict the anaprazole-clarithromycin and anaprazole-amoxicillin DDIs demonstrates their good performance, with the predicted DDI Cmax,ss ratios and DDI AUC0-τ,ss ratios within 1.25-fold of the observed values, and all predicted DDI Cmax,ss, and AUC0-τ,ss ratios within 2.0-fold. The simulated results show no need to adjust the dosage when co-administered with anaprazole in patients undergoing eradication therapy of H. pylori infection since the dose remained in the therapeutic range.

CONCLUSION

The whole-body PBPK models of anaprazole, clarithromycin, and amoxicillin were built and qualified, which can predict DDIs that are mediated by gastric pH change and inhibition of metabolic enzymes, providing a mechanistic understanding of the DDIs observed in the clinic of clarithromycin, amoxicillin with anaprazole.

Preparation and Characterization of pH-Independent Sustained-Release Tablets Containing Hot Melt Extruded Solid Dispersions of Clarithromycin : Tablets Containing Solid Dispersions of Clarithromycin

The limited solubility of clarithromycin (CAM), coupled with low bioavailability and rapid elimination, are major shortcomings, needed to be addressed to achieve optimum therapeutic goals. Therefore, sustained-release (SR) tablets containing solid dispersion (SD) granules of CAM were prepared in this study. Initially, SD granules of CAM were prepared by hot melt extrusion (HME) technique using Kollidon VA64 as a hydrophilic carrier. The saturation solubility of SD showed almost 4.5-fold increase as compared to pure CAM in pH 6.8 medium. In vitro drug dissolution data indicated a substantial increase in the dissolution of SD as compared to that of pure CAM. The thermal stability of drug, carrier, and SD at elevated HME temperatures was evident from the results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Powder X-ray diffraction (PXRD) data and scanning electron microscope (SEM) images revealed a decrease in the crystallinity and the uniform dispersion of drug, respectively. Moreover, Fourier transformed infrared spectroscopy (FT-IR) data confirmed the formation of hydrogen bond between the carbonyl group of drug and the hydroxyl group of carrier. SD loaded sustained-release (SD-SR) matrix tablets were prepared with hydrophobic polymers (Eudragit RS100 and Eudragit RL100). The pH-independent swelling and permeability of both polymers were responsible for the sustained drug release from SD-SR tablets. Pharmacokinetic (PK) studies suggested a 3.4-fold increase in the relative bioavailability of SD-SR tablets as compared to that of pure CAM.

Development of Genetically Encoded Biosensors for Reporting the Methyltransferase-Dependent Biosynthesis of Semisynthetic Macrolide Antibiotics

Clarithromycin is an improved semisynthetic analogue of the naturally occurring macrolide, erythromycin. The subtle modification of a methyl group on the C-6 hydroxyl group endows the molecule with improved acid stability and results in a clinically useful antibiotic. Here, we show that the effector specificity of the biosensor protein, MphR, can be evolved to selectively recognize clarithromycin and therefore report on the production of this molecule in vivo. In addition, a crystal structure of the evolved variant reveals the molecular basis for selectivity and provides a guide for the evolution of a new metabolic function using this biosensor.

Recent Advances in the Development of Macrolide Antibiotics as Antimicrobial Agents

The chemical modification of natural products has been a major method in the discovery and synthesis of new macrolide antibiotics (MA) to treat a variety of infectious diseases. However, a lot of MA obtained in the above methods are no longer effective, because the bacteria quickly develop their resistance to these new macrolides, which has become a great threat to successful treatment of infectious diseases, such as infections of the respiratory system and urinary system. In this paper, total synthetic methods for MA that include erythromycin A (ERY), azithromycin (AZM), the clinical candidate solithromycin (CEM-101), as well as 14-membered and 15-membered azaketolides have been systematically reviewed on the basis of the literature reported previously. The total synthetic methods we describe here helps to accelerate the discovery of newer MA to deal with the serious problem of bacterial resistance.

Harnessing the therapeutic potential of anticancer drugs through amorphous solid dispersions

The treatment of cancer is still a major challenge. But tremendous progress in anticancer drug discovery and development has occurred in the last few decades. However, this progress has resulted in few effective oncology products due to challenges associated with anticancer drug delivery. Oral administration is the most preferred route for anticancer drug delivery, but the majority of anticancer drugs currently in product pipelines and the majority of those that have been commercially approved have inherently poor water solubility, and this cannot be mitigated without compromising their potency and stability. The poor water solubility of anticancer drugs, in conjunction with other factors, leads to suboptimal pharmacokinetic performance. Thus, these drugs have limited efficacy and safety when administered orally. The amorphous solid dispersion (ASD) is a promising formulation technology that primarily enhances the aqueous solubility of poorly water-soluble drugs. In this review, we discuss the challenges associated with the oral administration of anticancer drugs and the use of ASD technology in alleviating these challenges. We emphasize the ability of ASDs to improve not only the pharmacokinetics of poorly water-soluble anticancer drugs, but also their efficacy and safety. The goal of this paper is to rationalize the application of ASD technology in the formulation of anticancer drugs, thereby creating superior oncology products that lead to improved therapeutic outcomes.

Comparing Various In Vitro Prediction Methods to Assess the Potential of a Drug to Inhibit P-glycoprotein (P-gp) Transporter In Vivo

The evaluation of potential of a new molecular entity (NME) to inhibit P-glycoprotein (P-gp) in vivo is an integral part of drug development and is recommended by regulatory agencies. In this study, we compared the performance of 5 prediction methods and their associated criteria (including those from the European Medicines Agency, the US Food and Drug Administration, and the Pharmaceuticals and Medical Devices Agency of Japan) for assessing the potential of an NME to inhibit P-gp in vivo based on in vitro assessment. We collected in vitro (eg, half-maximal inhibitory concentration [IC₅₀ ], fraction unbound to plasma protein) and in vivo (eg, dose, maximum concentration, change in maximum concentration or area under the plasma concentration-time curve of the substrate digoxin) data for 50 Food and Drug Administration-approved, orally administered drug products containing 53 NMEs, from the University of Washington Metabolism and Transport Drug Interaction Database, Drugs@FDA, and PubMed. All methods yielded similar accuracy with small differences in false-negative (FN) and false-positive (FP) predictions. In addition, use of ratio of the theoretical maximum gastrointestinal concentration to IC₅₀ is sufficient for a reasonable prediction for these orally administered drugs as potential P-gp inhibitors based on our dataset. The FN and FP rates varied depending on the cut-off value for the ratio of the theoretical maximum gastrointestinal concentration/IC₅₀ . Possible reasons underlying FP and FN results from different methods should be taken into consideration to predict in vivo P-gp inhibition.

Clarithromycin increases neuronal excitability in CA3 pyramidal neurons through a reduction in GABAergic signaling

Antibiotics are used in the treatment and prevention of bacterial infections, but effects on neuron excitability have been documented. A recent study demonstrated that clarithromycin alleviates daytime sleepiness in hypersomnia patients (Trotti LM, Saini P, Freeman AA, Bliwise DL, García PS, Jenkins A, Rye DB. J Psychopharmacol 28: 697-702, 2014). To explore the potential application of clarithromycin as a stimulant, we performed whole cell patch-clamp recordings in rat pyramidal cells from the CA3 region of hippocampus. In the presence of the antibiotic, rheobase current was reduced by 50%, F-I relationship (number of action potentials as a function of injected current) was shifted to the left, and the resting membrane potential was more depolarized. Clarithromycin-induced hyperexcitability was dose dependent; doses of 30 and 300 μM clarithromycin significantly increased the firing frequency and membrane potential compared with controls (P = 0.003, P < 0.0001). We hypothesized that clarithromycin enhanced excitability by reducing GABA_A receptor activation. Clarithromycin at 30 μM significantly reduced (P = 0.001) the amplitude of spontaneous miniature inhibitory GABAergic currents and at 300 μM had a minor effect on action potential width. Additionally, we tested the effect of clarithromycin in an ex vivo seizure model by evaluating its effect on spontaneous local field potentials. Bath application of 300 μM clarithromycin enhanced burst frequency twofold compared with controls (P = 0.0006). Taken together, these results suggest that blocking GABAergic signaling with clarithromycin increases cellular excitability and potentially serves as a stimulant, facilitating emergence from anesthesia or normalizing vigilance in hypersomnia and narcolepsy. However, the administration of clarithromycin should be carefully considered in patients with seizure disorders.

NEW & NOTEWORTHY

Clinical administration of the macrolide antibiotic clarithromycin has been associated with side effects such as mania, agitation, and delirium. Here, we investigated the adverse effects of this antibiotic on CA3 pyramidal cell excitability. Clarithromycin induces hyperexcitability in single neurons and is related to a reduction in GABAergic signaling. Our results support a potentially new application of clarithromycin as a stimulant to facilitate emergence from anesthesia or to normalize vigilance.

A new anti-microbial combination prolongs the latency period, reduces acute histologic chorioamnionitis as well as funisitis, and improves neonatal outcomes in preterm PROM

OBJECTIVE

Antibiotic administration is a standard practice in preterm premature rupture of membranes (PROM). Specific anti-microbial agents often include ampicillin and/or erythromycin. Anaerobes and genital mycoplasmas are frequently involved in preterm PROM, but are not adequately covered by antibiotics routinely used in clinical practice. Our objective was to compare outcomes of PROM treated with standard antibiotic administration versus a new combination more effective against these bacteria.

STUDY DESIGN

A retrospective study compared perinatal outcomes in 314 patients with PROM <34 weeks receiving anti-microbial regimen 1 (ampicillin and/or cephalosporins; n = 195, 1993-2003) versus regimen 2 (ceftriaxone, clarithromycin and metronidazole; n = 119, 2003-2012). Intra-amniotic infection/inflammation was assessed by positive amniotic fluid culture and/or an elevated amniotic fluid MMP-8 concentration (>23 ng/mL).

RESULTS

(1) Patients treated with regimen 2 had a longer median antibiotic-to-delivery interval than those with regimen 1 [median (interquartile range) 23 d (10-51 d) versus 12 d (5-52 d), p < 0.01]; (2) patients who received regimen 2 had lower rates of acute histologic chorioamnionitis (50.5% versus 66.7%, p < 0.05) and funisitis (13.9% versus 42.9%, p < 0.001) than those who had received regimen 1; (3) the rates of intra-ventricular hemorrhage (IVH) and cerebral palsy (CP) were significantly lower in patients allocated to regimen 2 than regimen 1 (IVH: 2.1% versus 19.0%, p < 0.001 and CP: 0% versus 5.7%, p < 0.05); and (4) subgroup analysis showed that regimen 2 improved perinatal outcomes in pregnancies with intra-amniotic infection/inflammation, but not in those without intra-amniotic infection/inflammation (after adjusting for gestational age and antenatal corticosteroid administration).

CONCLUSION

A new antibiotic combination consisting of ceftriaxone, clarithromycin, and metronidazole prolonged the latency period, reduced acute histologic chorioamnionitis/funisitis, and improved neonatal outcomes in patients with preterm PROM. These findings suggest that the combination of anti-microbial agents (ceftriaxone, clarithromycin, and metronidazole) may improve perinatal outcome in preterm PROM.

Repurposing Drugs in Oncology (ReDO)-clarithromycin as an anti-cancer agent

Clarithromycin (CAM) is a well-known macrolide antibiotic available as a generic drug. CAM is traditionally used for many types of bacterial infections, treatment of Lyme disease and eradication of gastric infection with Helicobacter pylori. Extensive preclinical and clinical data demonstrate a potential role for CAM to treat various tumours in combination with conventional treatment. The mechanisms of action underlying the anti-tumour activity of CAM are multiple and include prolonged reduction of pro-inflammatory cytokines, autophagy inhibition, and anti-angiogenesis. Here, we present an overview of the current preclinical (in vitro and in vivo) and clinical evidence supporting the role of CAM in cancer. Overall these findings justify further research with CAM in many tumour types, with multiple myeloma, lymphoma, chronic myeloid leukaemia (CML), and lung cancer having the highest level of evidence. Finally, a series of proposals are being made to further investigate the use of CAM in clinical trials which offer the greatest prospect of clinical benefit to patients.

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

The formulation, chemical and physical characterisation of clarithromycin-based macrolide solution pressurised metered dose inhaler

Objectives

The formulation of a clarithromycin (CLA) pressurised metered dose inhalers (pMDIs) solution formulation opens up exciting therapeutic opportunities for the treatment of inflammation in chronic obstructive lung diseases. In this study, we have formulated and tested a low dose macrolide formulation of CLA for treatment of inflammation and studied its physicochemical and aerosol properties.

Methods

The system was characterised for in-vitro aerosol performance using an Andersen cascade impactor. Short-term chemical and physical stability was assessed by dose content uniformity over a range of temperatures. Standard physicochemical characteristics were also investigated using scanning electron microscopy, thermo analysis and laser diffraction techniques.

Key findings

The formulation had a relatively high fine particle fraction (47%) and produced a particle size distribution suitable for inhalation drug delivery. Particles had an irregular morphology and were predominately amorphous. Furthermore, the short-term stability showed the formulation to be stable from 4 to 37°C.

Conclusions

This study demonstrated the feasibility of formulating a solution-based pMDI containing CLA for the treatment of lung inflammatory diseases.

Interplay of degradation, dissolution and stabilization of clarithromycin and its amorphous solid dispersions

Clarithromycin (CLA) is an aminomacrolide antibiotic whose physical properties are fascinating and challenging. It has very poor solubility at neutral intestinal pH, but much better solubility under acidic conditions due to amine protonation. The improved solubility in an acid environment is confounded by the poor chemical stability of clarithromycin that is quite labile toward acid-catalyzed degradation. This creates a complex system under gastrointestinal (GI) conditions: dissolution in the stomach, degradation, potential for precipitation in the small intestine, and interplay with the formulation components. We report herein a study of amorphous solid dispersion (ASD) of CLA with carboxyl-containing cellulose derivatives, which have recently been shown to be excellent ASD matrices for maximizing oral bioavailability. This approach was intended to improve CLA solubility in neutral media while minimizing release in an acid environment, and thereby increase its uptake from the small intestine. Amorphous polymer/CLA nanoparticles were also prepared by high-shear mixing in a multi-inlet vortex mixer (MIVM). Different extents of release were observed at low pH from the various formulations. Thus the solubility increase from nanosizing was deleterious to the concentration of intact CLA obtained upon reaching small intestine conditions; the high extent of release at gastric pH led to complete degradation of CLA. Using pH-switch experiments, it was possible to separate the effects of loss of CLA from solution by crystallization vs. that from chemical degradation. It was found that the hydrophobic cellulose derivative cellulose acetate adipate propionate (CAAdP) was effective at protecting CLA from dissolution in the stomach, and preventing CLA decomposition at low pH; 54% of CLA in CAADP ASD was released intact, vs. 0% and 6% from HPMCAS and CMCAB ASDs, respectively. We conclude that protection against degradation is central to enhancing overall release of intact CLA from ASD formulations; the formulations studied herein have great promise for simultaneous CLA solubility enhancement and protection from loss to chemical degradation, thereby reducing dose requirements and potentially decreasing colonic exposure to CLA (reduced colonic exposure is expected to minimize killing of beneficial colonic bacteria by CLA).

Characteristics and evaluation of an injectable clarithromycin lipid-based complex in vitro and in vivo

The purpose of this paper is to prepare a less-irritating and lipid-based clarithromycin complex (LCC) by the route of intravenous administration qualified with high drug-loading and fine particle size. The LCC was prepared by the injection of organic solvent phase (containing clarithromycin, sodium cholesterol sulfate and phospholipid at a molar ratio of 1:1:1.5) into the Tris buffer solution (0.05 M, pH 7.2) at 40 °C, and then was concentrated by ultrafiltration to remove the organic solvent. The technique of lyophilization was applied to obtain the LCC lyophilized products. Evaluation of the injectable LCC was performed by particle sizes analysis, transmission electron microscope, entrapment efficiency, stability and irritation tests. The LCC possessed a log-normal size distribution with an average size of 75.4 nm. The drug entrapment efficiency was above 97.0%, which was influenced by the amount of phospholipid, pH value of the media and ionic strength of aqueous suspension. The results of stability and irritation tests proved that LCC had more stability and less irritation. This unique LCC formulation may be applied to the human by the route of injection with less or no irritation. LCC could be an appropriate candidate for intravenous preparation and has a great potential for clinical and industrial-scale production.

Dissolution rate enhancement of clarithromycin using ternary ground mixtures: nanocrystal formation

Clarithromycin (CLA), a broad-spectrum macrolide, is a poorly soluble drug with dissolution rate limited absorption. The aim of this investigation was to prepare CLA nanoparticles from a ternary ground mixture in the presence of sodium lauryl sulfate (SLS) and polyvinyl pyrrolidone (PVP) as co-grinding water-soluble compounds, in order to improve the drug dissolution rate. Different weight ratios of CLA: SLS: PVP were ground in a dry process by planetary ball mill using different grinding ball size. Following the dissolution rate study, physical properties of the best dissolved co-ground formulation was studied. The accelerated stability studies were also conducted on the co-ground formulation. The results revealed that the dissolution rate of ternary ground mixtures was much higher than that of the intact drug (p < 0.001). Decreasing the grinding ball size and weight with the same rotation speed resulted in particles with decreased dissolution. On the other hand, increasing the PVP concentration in the formulations reduced the drug dissolution. Dissolution efficiencies (DE10 and DE30) for the best dissolved formulation, which consisted of the equal ratio of each co-ground component, were 8.7 and 5 folds higher than the untreated CLA, respectively. This formulation formed nanocrystals with enhanced solubility after dispersing in water. X-ray diffraction, differential scanning calorimetry and infrared spectrophotometry confirmed no chemical interaction and phase transition during the process. Accelerated stability studies confirmed that the co-ground mixture almost remained unchanged in terms of dissolution rate, drug assay and particle size after exposing in stability conditions for three months.

Development of a predictive in vitro dissolution for clarithromycin granular suspension based on in vitro-in vivo correlations

The objective of this study was to evaluate the in vitro behavior of different clarithromycin granular suspensions based on a developed in vitro-in vivo correlation model, using one reference and two test formulations. In vitro release rate data were obtained for each product using the USP apparatus II, operated at 50 rpm under different pH conditions. The dissolution efficiency was used to analyze the dissolution data. In vivo study was performed on six healthy male volunteers under fasting condition. Correlation was made between in vitro release and in vivo absorption. A linear model was developed using percent absorbed data versus percent dissolved data from the three products. Dissolution condition of 0.1N HCl for 1 h and then phosphate buffer at pH 6.8 was found to be the most discriminating dissolution method. Rate of absorption for the reference as estimated by Wagner-Nelson deconvolution was correlated with in vitro release with a correlation coefficient of 0.99. The in vivo results for the two test products were compared to the predicted values using the reference model with a correlation coefficient of 0.94. Furthermore, multiple level C correlations were obtained for some pharmacokinetic parameters with the corresponding in vitro kinetic parameters with correlation coefficients exceeding 0.90. Moreover, the interpretation of the in vitro and in vivo data with reference to formulations was discussed.

Interaction of macrolide antibiotics with intestinally expressed human and rat organic anion-transporting polypeptides

The macrolide antibiotics azithromycin and clarithromycin are large molecular weight compounds that exhibit moderate to excellent oral bioavailability in preclinical species and humans. Previous concomitant dosing studies in rats using rifamycin SV, a general organic anion-transporting polypeptide (OATP) inhibitor, suggested that the high oral absorption of azithromycin and clarithromycin may be caused by facilitative uptake by intestinal Oatps. In this study, we used OATP/Oatp-expressing cells to investigate the interaction of macrolides with rat Oatp1a5, human OATP1A2, and human/rat OATP2B1/Oatp2b1. These experiments showed that azithromycin and clarithromycin were potent inhibitors of rat Oatp1a5-mediated taurocholate uptake with apparent inhibitor constant (K(i)) values of 3.3 and 2.4 microM, respectively. The macrolides functioned as noncompetitive inhibitors but were not transport substrates for rat Oatp1a5, as assessed by direct uptake measurements of radiolabeled azithromycin and clarithromycin. cis-Inhibition and direct uptake studies further showed that azithromycin and clarithromycin were only very weak inhibitors and not substrates for human OATP1A2 and human/rat OATP2B1/Oatp2b1. In summary, these results indicate that the macrolides azithromycin and clarithromycin potently inhibit rat Oatp1a5 but do not significantly interact with OATP1A2 and OATP2B1/Oatp2b1. These intestinally expressed OATP/Oatp(s) are not responsible for the postulated facilitative uptake of azithromycin and clarithromycin, and alternative facilitative pathways must exist for their intestinal absorption.

Modeling the autoinhibition of clarithromycin metabolism during repeated oral administration

Clarithromycin decreases CYP3A4 activity and thus gradually inhibits its own metabolism as well as that of coadministered drugs. The aim of this study was to obtain an understanding of the time course of these changes. The plasma concentration-time profiles of clarithromycin and its active metabolite, 14(R)-hydroxy-clarithromycin, in 12 young healthy volunteers after oral administration of a clarithromycin suspension (500 mg twice a day [b.i.d.] for seven doses) were modeled by population pharmacokinetic analysis in the NONMEM program. The nonlinearity of clarithromycin metabolism was considered during model development, and the metabolite disposition kinetics were assumed to be linear. The absorption kinetics of clarithromycin were best described by a Weibull function model. The pharmacokinetics of clarithromycin and its 14(R)-hydroxyl metabolite were adequately described by a one-compartment model each for clarithromycin and its metabolite as well as an inhibition compartment that reflects the autoinhibition of clarithromycin metabolism. Up to 90% of the apparent total clarithromycin clearance (60 liters/h) was susceptible to reversible autoinhibition, depending on the concentration in the inhibition compartment. The proposed semimechanistic population pharmacokinetic model successfully described the autoinhibition of clarithromycin metabolism and may be used to adjust the doses of other drugs that are metabolized by CYP3A4 and that are coadministered with clarithromycin. Simulations showed that for the standard dose of 500 mg b.i.d., no further increase in the level of exposure occurs after approximately 48 h of treatment. For a 1,000-mg b.i.d. dose, the achievement of steady state is expected to take several days and to achieve a 3.6-fold higher level of clarithromycin exposure than the 500-mg b.i.d. dose. This evaluation provides a rationale for safer and more effective therapy with clarithromycin.

Prediction of oral clearance fromin vitrometabolic data using recombinant CYPs: Comparison among well-stirred, parallel-tube, distributed and dispersion models

Intrinsic clearances (CLint-HLM-total) for the metabolism of NE-100, metoprolol, clarithromycin (CAM), lornoxicam and tenoxicam were predicted from in vitro data with recombinant cytochorme P450s (CYPs) using relative activity factor (RAF) and then compared with CLint-HLM observed in human liver microsomes (HLM). The predicted CLint-HLM-total correlated well with the observed CLint-HLM in HLM. When oral clearances (CLoral) of low-clearance drugs such as metoprolol, CAM, lornoxicam and tenoxicam were predicted from the in vitro data using four physiological models (well-stirred, parallel tube, distributed and dispersion models), the predicted CLoral corresponded well with the observed CLoralin vivo and were similar among the four models. For a high-clearance drug, the predicted CLoral of NE-100 in extensive CYP2D6 metabolizers (EMs) was substantially different between individual models, although the predicted CLoral in a poor metabolizer of CYP2D6 (PMs) was similar. The CLoral ratio of NE-100 between the EMs and the PMs predicted from the dispersion model, which leads to a reliable prediction for the high-clearance drug, was 48.4, but the ratio decreased depending on the increase of the NE-100 plasma concentration. The results suggest that the CLoral decrease in the EMs is caused by saturation of NE-100 metabolism mediated by CYP2D6 and is based on increases in plasma NE-100 concentrations dependent on the dose of NE-100. The study suggests that the RAF and the in vitro-in vivo scaling approaches are useful for predicting CLoral from in vitro data with recombinant CYPs without using HLM and hepatocytes.

Interaction between midazolam and clarithromycin in the elderly

AIM

To assess the relative contribution of intestinal and hepatic CYP3A inhibition to the interaction between the prototypic CYP3A substrate midazolam and clarithromycin in the elderly.

METHODS

On day 1, 16 volunteers (eight male, eight female) aged 65-75 years weighing 59-112 kg received simultaneous doses of midazolam intravenously (i.v.) (0.05 mg kg(-1) over 30 min) and orally (p.o.) (3.5 mg of a stable isotope, (15)N(3)-midazolam). Starting on day 2, clarithromycin 500 mg was administered orally twice daily for 7 days. On day eight, i.v. and p.o. doses of midazolam were administered 2 h after the final clarithromycin dose. Serum and urine samples were assayed for midazolam, (15)N(3)-midazolam and metabolites by gas chromatography/mass spectometry.

RESULTS

Men and women exhibited similar i.v. (30.4 vs. 36.0 l h(-1)) and p.o. (119 vs. 124 l h(-1)) clearances of midazolam. Midazolam hepatic availability was significantly (P = 0.006) greater in men [0.79, 95% confidence interval (CI) 0.75, 0.84] than in women (0.66, 95% CI 0.59, 0.73), but midazolam intestinal availability (0.39 vs. 0.55) was not different. Following clarithromycin dosing, a significant decrease in systemic (33.2 l h(-1) to 11.5 l h(-1)) and oral (121 l h(-1) to 17.4 l h(-1)) midazolam clearance occurred. Oral, hepatic and intestinal availability was significantly increased after clarithromycin dosing from 0.34 to 0.72, 0.73 to 0.91 and 0.47 to 0.79, respectively. Clarithromycin administration led to an increase in the AUC of midazolam by 3.2-fold following i.v. dosing and 8.0-fold following p.o. dosing. Similar effects were observed for males and females.

CONCLUSIONS

Intestinal and hepatic CYP3A inhibition by clarithromycin significantly reduces the clearance of midazolam in the elderly.

Pharmacokinetics of single- and multiple-dose oral clarithromycin in soft tissues determined by microdialysis

The antimicrobial spectrum of clarithromycin renders this antibiotic a frequently used option in the treatment of skin and soft-tissue infections. In most cases, these infections are caused by extracellularly proliferating microorganisms. Thus, clarithromycin concentrations achieved in the interstitial space are considered particularly important for clinical efficacy. In the present study, clarithromycin concentrations in plasma and interstitial-space fluid of subcutaneous adipose tissue and skeletal muscle of six healthy male volunteers were assessed by means of the microdialysis technique after oral single-dose administration of 250 mg and multiple doses of 500 mg of clarithromycin twice a day (b.i.d.). The ratios of the area under the concentration-time curve of free clarithromycin from 0 to 24 h calculated for a single dose of 250 mg (fAUC(0-24)) in interstitial-space fluid to the fAUC(0-24) in plasma were 0.29 +/- 0.17 and 0.42 +/- 0.18 for subcutis and skeletal muscle, respectively. For 500 mg of clarithromycin at the steady state (3 to 5 days of intake twice daily), the fAUC(0-24(b.i.d.)) ratios at the steady state were 0.39 +/- 0.04 and 0.41 +/- 0.19 for subcutis and skeletal muscle, respectively. The half-life was around 2 h after a single dose but increased to approximately 4 h in plasma and tissues after repetitive clarithromycin administration. Based on subsequently performed pharmacokinetic-pharmacodynamic calculations, a dosing regimen of 500 mg b.i.d. may be ineffective in the treatment of soft-tissue infections caused by pathogens with a drug MIC higher than 0.125 mg/liter.

Optimizing the management of community-acquired respiratory tract infections in the age of antimicrobial resistance

Community-acquired respiratory tract infections (CARTIs) are the most common reason for prescribing antibiotics in the primary care setting. However, over the last decade, the management of CARTIs has become increasingly complicated by the steady increase in prevalence of drug-resistant pathogens responsible for these infections. As a result, significant attention has been directed at understanding the mechanisms of pathogen acquisition of resistance, drivers of resistance and methods for preventing the development of resistance. Data from recent surveillance studies suggest a slowing or decline in resistance rates to agents, such as beta-lactams, macrolides, tetracyclines and folic acid metabolism inhibitors. However, resistance to one antimicrobial family--the fluoroquinolones--while still low, appears to be on the increase. This is of significant concern given the rapid increase in resistance noted with older antibiotics in recent history. While the clinical implications of antibacterial resistance are poorly understood, the overall rates of antimicrobial resistance, as reported in recent surveillance studies, do not correspond to current rates of failure in patients with CARTIs. This disconnection between laboratory-determined resistance and clinical outcome has been termed the in vitro-in vivo paradox and several explanations have been offered to explain this phenomenon. Solving the problem of antimicrobial resistance will be multifactorial. Important factors in this effort include the education of healthcare providers, patients and the general healthcare community regarding the hazards of inappropriate antibiotic use, prevention of infections through vaccination, development of accurate, inexpensive and timely point-of-care diagnostic tests to aid in patient assessment, institution of objective treatment guidelines and use of more potent agents, especially those with a focused spectrum of activity, earlier in the treatment of CARTIs as opposed to reserving them as second-line treatment options. Ultimately, the single-most important factor will be the judicious use of antibiotics, as fewer antibiotic prescriptions lead to fewer antimicrobial-resistant bacteria.

Effect of macrolide antibiotics on uptake of digoxin into rat liver

The objective of this study was to examine the effect of macrolide antibiotics, clarithromycin, erythromycin, roxithromycin, josamycin and azithromycin, on the hepatic uptake of digoxin. The uptake of [(3)H]digoxin was studied in rats in vivo, using the tissue-sampling single-injection technique, and in isolated rat hepatocytes in vitro. The uptake of [(3)H]digoxin into rat hepatocytes was concentration-dependent with a Michaelis constant (K(m)) of 445 nM. All the macrolide antibiotics inhibited the uptake of [(3)H]digoxin into rat hepatocytes in a concentration-dependent manner. However, clarithromycin did not affect the in vivo hepatic uptake of digoxin in rats. The in vivo permeability-surface area product of digoxin for hepatic uptake (PS(inf)) was estimated to be 12.5 ml/min/g liver from the present in vitro data, which is far larger than the hepatic blood flow rate (1.4 ml/min/g liver). Macrolide antibiotics at clinically relevant concentrations inhibit digoxin uptake by rat hepatocytes in vitro, but not in vivo, probably because hepatic uptake of digoxin in rats is blood flow-limited. Clinically observed digoxin-macrolide interaction in humans could be due to macrolide inhibition of hepatic digoxin uptake, if the uptake is permeation-limited.

Pharmacokinetics of clarithromycin and concentrations in body fluids and bronchoalveolar cells of foals

OBJECTIVE

To determine pharmacokinetics of clarithromycin and concentrations in body fluids and bronchoalveolar (BAL) cells of foals.

ANIMALS

6 healthy 2-to 3-week-old foals.

PROCEDURES

In a crossover design, clarithromycin (7.5 mg/kg) was administered to each foal via IV and intragastric (IG) routes. After the initial IG administration, 5 additional doses were administered IG at 12-hour intervals. Concentrations of clarithromycin and its 14-hydroxy metabolite were measured in serum by use of high-performance liquid chromatography. A microbiologic assay was used to measure clarithromycin activity in serum, urine, peritoneal fluid, synovial fluid, CSF, pulmonary epithelial lining fluid (PELF), and BAL cells.

RESULTS

After IV administration, elimination half-life (5.4 hours) and mean +/- SD body clearance (1.27 +/- 0.25 L/h/kg) and apparent volume of distribution at steady state (10.4 +/- 2.1 L/kg) were determined for clarithromycin. The metabolite was detected in all 6 foals by 1 hour after clarithromycin administration. Oral bioavailability of clarithromycin was 57.3 +/- 12.0%. Maximum serum concentration of clarithromycin after multiple IG administrations was 0.88 +/- 0.19 microg/mL. After IG administration of multiple doses, clarithromycin concentrations in peritoneal fluid, CSF, and synovial fluid were similar to or lower than concentrations in serum, whereas concentrations in urine, PELF, and BAL cells were significantly higher than concentrations in serum.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of clarithromycin at 7.5 mg/kg every 12 hours maintains concentrations in serum, PELF, and BAL cells that are higher than the minimum inhibitory concentration (0.12 microg/mL) for Rhodococcus equiisolates for the entire 12-hour dosing interval.

Helicobacter pylori treatment: a practical approach

The treatment of Helicobacter pylori infection has become complicated by the lack of new treatment regimens and the emergence of drug resistant strains of H. pylori. Metronidazole and clarithromycin resistance are common in developed countries. Eradication rates have been falling in trials and in clinical practice around the world. A practical approach to the treatment of patients with H. pylori infection and those who fail initial eradication therapy is discussed.

Helicobacter pylori: factors affecting eradication and recurrence

Proton pump inhibitors play an important role in increasing the bioavailability of antibiotics in the gastric mucus by altering gastric volumes and increasing the stability of some antibiotics, e.g., clarithromycin. Increasing the doses of potent proton pump inhibitors has small effects on eradication rates but there may be differences between proton pump inhibitors that need further study.

Evaluation ofin-vitro dissolution andin-vivo absorption for two different film-coated pellets of clarithromycin

The aim of this study was to compare two formulations of film-coated pellets containing clarithromycin after single oral dose study in healthy male volunteers. Two formulations with different coating polymers were prepared: formulation-1 (F-1) was prepared by incorporating three kinds of pH-dependent gradient-release coated pellets into capsules and formulation-2 (F-2) was prepared by coated with an insoluble semiosmotic film. Release profiles of film-coated pellets were evaluated using paddle method under different conditions. Pharmacokinetic profiles of these formulations were obtained in three healthy male volunteers and compared to commercially available immediate release (IR) tablets. The relative bioavailability based on the AUC0-24h was found to be 96.2% and 58.7% for F-1 and F-2 compared with IR, and the Tmax was delayed.

Effect of CYP3A1(23) induction on clarithromycin pharmacokinetics in rats with diabetes mellitus

After intravenous and oral administration of clarithromycin at a dose of 20 mg/kg of body weight to rats with diabetes mellitus induced by alloxan (DMIA) and diabetes mellitus induced by streptozotocin (DMIS), the area under the curve values were significantly smaller than those of respective control rats. The in vitro intrinsic clearance values for the disappearance of clarithromycin were significantly faster in both rats with DMIA and rats with DMIS than in control rats. The above data suggested that metabolism of clarithromycin increased in both types of diabetic rat due to an increase in the expression and mRNA level of CYP3A1(23) in the rats.

Clarithromycin in 2003: sustained efficacy and safety in an era of rising antibiotic resistance

Data from surveillance studies show increasing prevalence of respiratory pathogens resistant to commonly used antibiotics. Thus, a Medline search was conducted to identify studies of clarithromycin, especially those addressing macrolide resistance. Changing trends of in vitro susceptibility have not affected clinical efficacy with clarithromycin. Over the last 12 years, clarithromycin study results have shown consistent rates of clinical cure and bacteriological eradication, which are similar to those observed with comparator agents. The incidence of clarithromycin treatment failure in patients infected with Streptococcus pneumoniae is substantially less than that predicted by macrolide resistance rates from surveillance programmes. In summary, despite widespread use since its introduction, clarithromycin remains active both in vitro and in vivo against clinically relevant respiratory tract pathogens.

Formulations of antibiotics for children in primary care: effects on compliance and efficacy

This review article is designed for pediatricians as well as primary care physicians in the outpatient setting as a clinical guide to antibiotic selection. It emphasizes variables related to compliance as well as efficacy. The aim is to give recommendations as to the choice of antibiotics, depending on factors such as taste, cost, efficacy, and compliance. Common bacterial pathogens causing infections in children are reviewed, along with their susceptibility patterns to antimicrobial agents. Emerging mechanisms of resistance, particularly the increasing resistance of pneumococci to beta-lactam antibiotics, are discussed because of their importance to antibiotic selection. Previously published studies that have examined the treatment of common outpatient infections in children, such as otitis media, streptococcal tonsillopharyngitis, and sinusitis, are summarized. Adverse reactions associated with antibiotics, second in importance only to efficacy, are reviewed. Finally, compliance issues, which include palatability, cost, duration of therapy, and administration frequency, are analyzed using recently published information related to each of these issues. The efficacy of the commonly used antibiotics for urinary tract infections, pneumonia, and streptococcal pharyngitis does not vary significantly; however, for otitis media and sinusitis, some studies have shown that treatment efficacy with the antibiotic does not vary significantly from that with placebo. Likewise, adverse reactions rarely provide a basis for antibiotic selection, since virtually all antibiotics are generally well tolerated. The final factor, compliance, is a major issue in determining both first- and second-line therapy of common outpatient infections in children. Although cost is not a factor in compliance in countries such as the UK where no copayment is required for pediatric drugs, it is of major importance in the US. This is followed by palatability, administration duration and finally administration frequency. As a group, cephalosporins are generally the best tasting but are relatively more expensive than macrolides. Antibiotics that can be given for 5 days, and just once or twice daily, are preferred by most parents and physicians. Since final assessment of antibiotic choice is likely to vary considerably among healthcare personnel, decisions must be made on an individual basis.

The evolution and role of macrolides in infectious diseases

Two of the most significant changes in the field of infectious disease management during the last few decades are the emergence of atypical and/or new pathogens that may have devastating consequences and the re-emergence of well-recognised organisms that have acquired antimicrobial resistance through a variety of mechanisms. Erythromycin, the prototype macrolide, was originally marketed approximately five decades ago as a useful alternative agent in the treatment of patients allergic to beta-lactam antibiotics. While clinically useful, its pharmacokinetic and adverse-event profile limited the use of erythromycin to these individuals. Enhancements of the macrolide structure circumvented many of the limitations of erythromycin and resulted in the development of azithromycin and clarithromycin. The clinical uses of clarithromycin and azithromycin are substantially wider than erythromycin due to the wide spectra of activity against the atypical and newer pathogens. In addition, these agents are well-tolerated and have a pharmacokinetic profile that allows once- or twice-daily administration. Studies also indicate that the more common of the two mechanisms of macrolide resistance in the US and Canada imparts only low-level resistance. The multitude of studies substantiating clinical as well as bacteriological success with these two agents indicates that, when used appropriately, they will stand the test of time and continue to be useful antimicrobial agents.

The macrolides

Erythromycin, which was introduced over 50 years ago, was the first macrolide to be used clinically. "New" macrolides, for the treatment of patients with various infectious diseases, were not clinically introduced until 40 years later. The pharmacokinetic and adverse events profile of erythromycin initially limited its use to an alternative agent for patients with allergy to beta-lactam agents. However, the emergence of atypical and/or new pathogens and the ongoing escalation of acquired antimicrobial resistance has impacted on the empirical and organism directed therapy of infectious diseases. Azithromycin and clarithromycin were developed by enhancing the basic macrolide structure. Some of the basic features associated with these new agents include a pharmacokinetic profiles that allow once or twice daily dosing with a much lower incidence of side effects and a substantially broader spectrum of activity which includes some Gram-negative bacilli, atypical pathogens and new, unconventional or uncommon pathogens. Clinical trial data has supported the use of "new" macrolides in a wide range of clinical indications, however, some specific indications are currently restricted to treatment with either azithromycin or clarithromycin. Macrolide resistance is a class effect and depending on the mechanism will confer either low or high level resistance. While resistance is problematic, it does not always result in clinical failure. The macrolides are a valuable class of antimicrobial agent and play an important role in the management of infectious diseases.

Human Bioequivalence Study of Clarithromycin from Two Tablet Formulations after Single Oral Administration

OBJECTIVE

The objective of this study was to compare the relative bioavailability and bioequivalence of a test (Claromycin®, GA Pharmaceuticals) and a reference (Klaricid®, Abbott) tablet containing 500mg clarithromycin in healthy volunteers under fasting conditions.

METHODS

This was a nonblinded, single-dose, randomised, two-period, crossover study in 16 healthy volunteers conducted under fasting conditions. Plasma samples were analysed for clarithromycin by a validated high performance liquid chromatography assay with electrochemical detection.

RESULTS

One volunteer did not receive the reference tablet. The parametric 90% confidence intervals of the geometric mean values of the test/reference ratios analysed for 16 participants were 84.2 to 111.6% (point estimate 97.3%) for the area under the plasma concentration-time curve for time zero to infinity (AUC0-∞), 82.2 to 117.6% (point estimate 98.3%) for time zero to time t (AUC0-t), and 74.4 to 142.9% (point estimate 103.1%) for peak plasma concentration (Cmax). No statistically significant differences were found between the formulations for the time to reach Cmax (tmax) and elimination half-life values. When the results were analysed for 15 participants, the 90% confidence intervals were 84.1 to 111.9% for AUC0-∞, 82.8 to 119.1% for AUC0-t, and 74.1 to 143.6% for (Cmax)

CONCLUSIONS

From the results of this study, it is concluded that the two tablet preparations of clarithromycin are bioequivalent in both the extent and the rate of absorption.

Pharmacokinetics of clarithromycin in the prostate: implications for the treatment of chronic abacterial prostatitis

PURPOSE

We studied the pharmacokinetics of orally administered clarithromycin in prostatic tissue to define its role in the treatment of chronic abacterial prostatitis caused by intracellular pathogens.

MATERIALS AND METHODS

A total of 45 men receiving 3 oral doses of 750 mg. clarithromycin at 12-hour intervals underwent suprapubic prostatectomy for benign prostate hyperplasia 4, 5, 6 and 7 hours after the last drug dose in 13, 12, 10 and 10 patients, respectively. Concentrations were determined in the prostate tissue and in plasma by an agar diffusion assay.

RESULTS

A mean peak level of clarithromycin of 3.22 and 3.08 microg./gm. of tissue was achieved 4 hours after the third drug dose at the center and periphery of the adenoma, respectively. Tissue levels remained statistically superior to plasma levels at all intervals.

CONCLUSIONS

The oral administration of clarithromycin achieved a prostate level much higher than the minimal inhibitory concentration of clarithromycin for the intracellular pathogens of chronic prostatitis. Thus, clarithromycin may be considered for treating chronic abacterial prostatitis.

Clinical pharmacokinetics of clarithromycin

Clarithromycin is a macrolide antibacterial that differs in chemical structure from erythromycin by the methylation of the hydroxyl group at position 6 on the lactone ring. The pharmacokinetic advantages that clarithromycin has over erythromycin include increased oral bioavailability (52 to 55%), increased plasma concentrations (mean maximum concentrations ranged from 1.01 to 1.52 mg/L and 2.41 to 2.85 mg/L after multiple 250 and 500 mg doses, respectively), and a longer elimination half-life (3.3 to 4.9 hours) to allow twice daily administration. In addition, clarithromycin has extensive diffusion into saliva, sputum, lung tissue, epithelial lining fluid, alveolar macrophages, neutrophils, tonsils, nasal mucosa and middle ear fluid. Clarithromycin is primarily metabolised by cytochrome P450 (CYP) 3A isozymes and has an active metabolite, 14-hydroxyclarithromycin. The reported mean values of total body clearance and renal clearance in adults have ranged from 29.2 to 58.1 L/h and 6.7 to 12.8 L/h, respectively. In patients with severe renal impairment, increased plasma concentrations and a prolonged elimination half-life for clarithromycin and its metabolite have been reported. A dosage adjustment for clarithromycin should be considered in patients with a creatinine clearance < 1.8 L/h. The recommended goal for dosage regimens of clarithromycin is to ensure that the time that unbound drug concentrations in the blood remains above the minimum inhibitory concentration is at least 40 to 60% of the dosage interval. However, the concentrations and in vitro activity of 14-hydroxyclarithromycin must be considered for pathogens such as Haemophilus influenzae. In addition, clarithromycin achieves significantly higher drug concentrations in the epithelial lining fluid and alveolar macrophages, the potential sites of extracellular and intracellular respiratory tract pathogens, respectively. Further studies are needed to determine the importance of these concentrations of clarithromycin at the site of infection. Clarithromycin can increase the steady-state concentrations of drugs that are primarily depend upon CYP3A metabolism (e.g., astemidole, cisapride, pimozide, midazolam and triazolam). This can be clinically important for drugs that have a narrow therapeutic index, such as carbamazepine, cyclosporin, digoxin, theophylline and warfarin. Potent inhibitors of CYP3A (e.g., omeprazole and ritonavir) may also alter the metabolism of clarithromycin and its metabolites. Rifampicin (rifampin) and rifabutin are potent enzyme inducers and several small studies have suggested that these agents may significantly decrease serum clarithromycin concentrations. Overall, the pharmacokinetic and pharmacodynamic studies suggest that fewer serious drug interactions occur with clarithromycin compared with older macrolides such as erythromycin and troleandomycin.

The macrolides: erythromycin, clarithromycin, and azithromycin

In addition to erythromycin, macrolides now available in the United States include azithromycin and clarithromycin. These two new macrolides are more chemically stable and better tolerated than erythromycin, and they have a broader antimicrobial spectrum than erythromycin against Mycobacterium avium complex (MAC), Haemophilus influenzae, nontuberculous mycobacteria, and Chlamydia trachomatis. All three macrolides have excellent activity against the atypical respiratory pathogens (C. pneumoniae and Mycoplasma species) and the Legionella species. Azithromycin and clarithromycin have pharmacokinetics that allow shorter dosing schedules because of prolonged tissue levels. Both azithromycin and clarithromycin are active agents for MAC prophylaxis in patients with late-stage acquired immunodeficiency syndrome (AIDS), although azithromycin may be the preferable agent because of fewer drug-drug interactions. Clarithromycin is the most active MAC antimicrobial agent and should be part of any drug regimen for treating active MAC disease in patients with or without AIDS. Although both azithromycin and clarithromycin are well tolerated by children, azithromycin has the advantage of shorter treatment regimens and improved tolerance, potentially improving compliance in the treatment of respiratory tract and skin or soft tissue infections. Intravenously administered azithromycin has been approved for treatment of adults with mild to moderate community-acquired pneumonia or pelvic inflammatory diseases. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens, particularly Streptococcus pneumoniae, group A streptococci, and H. influenzae. The emergence of macrolide resistance with these common pathogens may limit the clinical usefulness of this class of antimicrobial agents in the future.

Review and comparison of advanced-generation macrolides clarithromycin and dirithromycin

We reviewed English-language clinical studies, abstracts, and review articles identified from MEDLINE searches from January 1966-August 1998, and bibliographies of identified articles to compare advanced-generation macrolides dirithromycin and clarithromycin and their use for respiratory tract infections. Both agents have superior adverse effect profiles compared with erythromycin, the original macrolide. Both have broad antibacterial coverage, but clarithromycin usually has a lower MIC90 to susceptible organisms than dirithromycin; for most isolates this difference is not clinically significant. Clarithromycin has better in vitro coverage of Haemophilus influenzae, but this activity varies with formation of its bioactive metabolite, 14-hydroxyclarithromycin. Neither agent is ideal for H. influenzae eradication. The agents differ markedly in terms of pharmacokinetics, pharmacodynamics, metabolism, and cost, and thus with respect to drug interaction profiles and dosages. Dirithromycin's drug interaction profile is markedly better than clarithromycin's. Clarithromycin is dosed twice/day; dirithromycin's pharmacokinetics allow once/day dosing. Dirithromycin is less expensive with regard to both cost/day and cost/treatment regimen. Clarithromycin has been studied and approved for administration to children. In adults with respiratory tract infections who are receiving drugs that would interact with clarithromycin, and in those with renal dysfunction with or without coexisting hepatic dysfunction, dirithromycin appears to be superior in terms of safety and equivalent to clarithromycin in terms of efficacy.