Uptake of clarithromycin by rat lung cells

Delivering macrolide antibiotics to heal a broken heart - And other inflammatory conditions

Drug carriers to deliver macrolide antibiotics, such as azithromycin, show promise as antibacterial agents. Macrolide drug carriers have largely focused on improving the drug stability and pharmacokinetics, while reducing adverse reactions and improving antibacterial activity. Recently, macrolides have shown promise in treating inflammatory conditions by promoting a reparative effect and limiting detrimental pro-inflammatory responses, which shifts the immunologic setpoint from suppression to balance. While macrolide drug carriers have only recently been investigated for their ability to modulate immune responses, the previous strategies that deliver macrolides for antibacterial therapy provide a roadmap for repurposing the macrolide drug carriers for therapeutic interventions targeting inflammatory conditions. This review describes the antibacterial and immunomodulatory activity of macrolides, while assessing the past in vivo evaluation of drug carriers used to deliver macrolides with the intention of presenting a case for increased effort to translate macrolide drug carriers into the clinic.

Development and validation of a sensitive LC-MS/MS method for the quantitation of IMB-YH-4py5-2H, an antituberculosis candidate, and its application to the pharmacokinetic study

(E)-N,N-dimethyl-4-oxo-4-(4-(pyridin-4-yl)phenyl)but-2-enamide hydrochloride (IMB-YH-4py5-2H) is a novel Protein Kinase B (PknB) inhibitor with potent activity against Mycobacterium tuberculosis strains. In the present study, a sensitive and specific liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine IMB-YH-4py5-2H in rat plasma. Sample pretreatment was achieved by liquid-liquid extraction with ethyl acetate, and separation was performed on an XTerra MS C₁₈ column (2.1×50 mm, 3.5 μm) with gradient elution (methanol and 0.1% formic acid) at a flow rate of 0.3 mL/min. Detection was performed in multiple reaction monitoring (MRM) mode. Linear calibration curves were obtained over a concentration range of 1−100 ng/mL. The intra-day and inter-day precisions were lower than 8.46%, and the accuracies ranged from -8.71% to 12.36% at all quality control levels. The extraction recoveries were approximately 70%, and the matrix effects were negligible. All quality control samples were stable under different storage conditions. The validated method was successfully applied to a preclinical pharmacokinetic study in Sprague-Dawley rats. IMB-YH-4py5-2H demonstrated improved pharmacokinetic properties (higher exposure level) compared with its leading compound. IMB-YH-4py5-2H was also distributed throughout the lung pronouncedly, especially inside alveolar macrophages, indicating its effectiveness against lower respiratory infections.

Sustained distribution of aerosolized PEGylated liposomes in epithelial lining fluids on alveolar surfaces

The distribution characteristics of aerosolized PEGylated liposomes in alveolar epithelial lining fluid (ELF) were examined in rats, and the ensuing mechanisms were investigated in the in vitro uptake and protein adsorption experiments. Nonmodified or PEGylated liposomes (particle size 100 nm) were aerosolized into rat lungs. PEGylated liposomes were distributed more sustainably in ELFs than nonmodified liposomes. Furthermore, the uptake of PEGylated liposomes by alveolar macrophages (AMs) was less than that of nonmodified liposomes. In further in vitro uptake experiments, nonmodified and PEGylated liposomes were opsonized with rat ELF components and then added to NR8383 cells as cultured rat AMs. The uptake of opsonized PEGylated liposomes by NR8383 cells was lower than that of opsonized nonmodified liposomes. Moreover, the protein absorption levels in opsonized PEGylated liposomes were lower than those in opsonized nonmodified liposomes. These findings suggest that sustained distributions of aerosolized PEGylated liposomes in ELFs reflect evasion of liposomal opsonization with surfactant proteins and consequent reductions in uptake by AMs. These data indicate the potential of PEGylated liposomes as aerosol-based drug delivery system that target ELF for the treatment of respiratory diseases.

Intracellular pharmacokinetics of telithromycin, a ketolide antibiotic, in alveolar macrophages

OBJECTIVES

Telithromycin, a ketolide antibiotic, has an antibacterial range that covers intracellular parasitic pathogens that survive or multiply intracellularly in alveolar macrophages. The intracellular pharmacokinetics of TEL in alveolar macrophages was evaluated in vitro.

METHODS

Telithromycin (50 microm) was applied to NR8383 as cultured alveolar macrophages, followed by incubation at 37 degrees C or 4 degrees C. After incubation, the amount of telithromycin in cells was determined.

KEY FINDINGS

Telithromycin exhibited high accumulation in NR8383 and its intracellular accumulation was temperature dependent. Also, telithromycin distributed to the organelles and cytosol in NR8383 and, in particular, it accumulated in the acidic organelle compartments.

CONCLUSIONS

This study suggests that the high accumulation of telithromycin in NR8383 is due to its high influx via active transport systems and trapping in acidic organelles, such as lysosomes. Moreover, this study provides important information for optimizing the treatment of respiratory intracellular parasitic infections based on the intracellular pharmacokinetics of antibiotics and parasitic sites.

Efficient drug targeting to rat alveolar macrophages by pulmonary administration of ciprofloxacin incorporated into mannosylated liposomes for treatment of respiratory intracellular parasitic infections

The efficacy of pulmonary administration of ciprofloxacin (CPFX) incorporated into mannosylated liposomes (mannosylated CPFX-liposomes) for the treatment of respiratory intracellular parasitic infections was evaluated. In brief, mannosylated CPFX-liposomes with 4-aminophenyl-a-d-mannopyranoside (particle size: 1000 nm) were prepared, and the drug targeting to alveolar macrophages (AMs) following pulmonary administration was examined in rats. Furthermore, the antibacterial and mutant prevention effects of mannosylated CPFX-liposomes in AMs were evaluated by pharmacokinetic/pharmacodynamic (PK/PD) analysis. The targeting efficiency of CPFX to rat AMs following pulmonary administration of mannosylated CPFX-liposomes was significantly greater than that of CPFX incorporated into unmodified liposomes (unmodified CPFX-liposomes; particle size: 1000 nm). According to PK/PD analysis, the mannosylated CPFX-liposomes exhibited potent antibacterial effects against many bacteria although unmodified CPFX-liposomes were ineffective against several types of bacteria, and the probability of microbial mutation by mannosylated CPFX-liposomes was extremely low. The present study indicates that mannosylated CPFX-liposomes as pulmonary administration system could be useful for the treatment of respiratory intracellular parasitic infections.

Pharmacokinetic and Pharmacodynamic Efficacy of Intrapulmonary Administration of Ciprofloxacin for the Treatment of Respiratory Infections

The pharmacokinetic and pharmacodynamic efficacy of intrapulmonary administration of ciprofloxacin (CPFX) for the treatment of respiratory infections caused by pathogenic microorganisms resisting sterilization systems of alveolar macrophages (AMs) was evaluated by comparison with an oral administration. The time-courses of the concentration of CPFX in AMs and lung epithelial lining fluid (ELF) following intrapulmonary administration of CPFX solution to rats (200 microg/kg) were markedly higher than that following oral administration (10 mg/kg). The time-course of the concentrations of CPFX in plasma following intrapulmonary administration was markedly lower than that in AMs and ELF. These results indicate that intrapulmonary administration is more effective in delivering CPFX to AMs and ELF, compared with oral administration, in spite of a low dose and it avoids distribution of CPFX to the blood. In addition, the antibacterial effects of CPFX in AMs and ELF following intrapulmonary administration were evaluated by pharmacokinetics/pharmacodynamics analysis. The concentration of CPFX in AMs and ELF-time curve (AUC)/minimum inhibitory concentration of CPFX (MIC) ratio and the maximum concentration of CPFX in AMs and ELF (Cmax)/MIC ratio were markedly higher than the effective values. The present study indicates that intrapulmonary administration of CPFX is an effective technique for the treatment of respiratory infections.

Impact of transporter-mediated drug absorption, distribution, elimination and drug interactions in antimicrobial chemotherapy

A comprehensive list of drug transporters has recently become available as a result of extensive genome analysis. Membrane transporters play important roles in determining the pharmacokinetic aspects of intestinal absorption, tissue distribution, and the urinary and biliary excretions of a wide variety of therapeutic drugs. The identification and characterization of transporters responsible for the transfer of nutrients and xenobiotics, including drugs, is expected to provide a scientific basis for understanding drug disposition, as well as the molecular mechanisms of drug-drug/drug-food/drug-protein interactions and inter-individual/inter-species differences. This review focuses on the influence of transporters on the pharmacokinetics of beta-lactam antibiotics, new quinolones, and other antimicrobial agents, as well as focusing on the drug-drug interactions associated with transporter-mediated uptake from the small intestine and transporter-mediated elimination from the kidney and liver.

Influence of particle size on drug delivery to rat alveolar macrophages following pulmonary administration of ciprofloxacin incorporated into liposomes

In order to confirm the efficacy of ciprofloxacin (CPFX) incorporated into liposomes (CPFX-liposomes) for treatment of respiratory intracellular parasite infections, the influence of particle size on drug delivery to rat alveolar macrophages (AMs) following pulmonary administration of CPFX-liposomes was investigated. CPFX-liposomes were prepared with hydrogenated soybean phosphatidylcholine (HSPC), cholesterol (CH) and dicetylphosphate (DCP) in a lipid molar ratio of 7/2/1 by the hydration method and then adjusted to five different particle sizes (100, 200, 400, 1000 and 2000 nm). In the pharmacokinetic experiment, the delivery efficiency of CPFX to rat AMs following pulmonary administration of CPFX-liposomes increased with the increase in the particle size over the range 100-1000 nm and became constant at over 1000 nm. The concentrations of CPFX in rat AMs until 24 h after pulmonary administration of CPFX-liposomes with a particle size of 1000 nm were higher than the minimum inhibitory concentration of CPFX against various intracellular parasites. In a cytotoxic test, no release of lactate dehydrogenase (LDH) from rat lung tissues by pulmonary administration of CPFX-liposomes with a particle size of 1000 nm was observed. These findings indicate that efficient delivery of CPFX to AMs by CPFX-liposomes with a particle size of 1000 nm induces an excellent antibacterial effect without any cytotoxic effects on lung tissues. Therefore, CPFX-liposomes may be useful in the development of drug delivery systems for the treatment of respiratory infections caused by intracellular parasites, such as Mycobacterium tuberculosis, Chlamydia pneumoniae and Listeria monocytogenes.

Carrier-mediated uptake of grepafloxacin, a fluoroquinolone antibiotic, by the isolated rat lung cells

Grepafloxacin (GPFX) is a new quinolone antibiotic (NQ) which is highly distributed to the lung and other tissues. In the present study, to characterize the distribution mechanism of GPFX to the lung, the uptake of GPFX by isolated rat lung cells was examined in vitro. GPFX was rapidly taken up by the cells, and the uptake reached a steady-state within 5 min. The cell-to-medium concentration ratio at equilibrium was 56.8+/-1.9 microL/mg protein, which was much higher than the cellular volume. GPFX uptake consisted of a saturable component (Km: 264+/-181 microM, Vmax: 2.94+/-2.33 nmol/min/mg protein) and a nonsaturable component (Pdif: 7.04+/-2.17 microL/min/mg protein). The uptake of GPFX was reduced in the presence of ATP-depletors (FCCP and Rotenone) and by the replacement of sodium with choline in the medium, suggesting that GPFX uptake is at least partially mediated by an Na+- and energy-dependent process. GPFX uptake tended to be reduced in the presence of other NQs such as levofloxacin, lomefloxacin and sparfloxacin, but was only minimally affected by the substrates of several uptake mechanisms already identified in the liver and kidney such as taurocholate, p-aminohippurate, L-carnitine and tetraethylammonium. These results suggested that GPFX is taken up by the lung partially via carrier-mediated transport system(s), distinct from the identified transporters, and such active transport systems may at least partially account for the efficient distribution of GPFX to the lung.

Distribution characteristics of grepafloxacin, a fluoroquinolone antibiotic, in lung epithelial lining fluid and alveolar macrophage

The purpose of this study was to investigate the distribution of Grepafloxacin (GPFX), a new quinolone antimicrobial agent, in the lung epithelial lining fluid (ELF) and the alveolar macrophage (AM) in rats, which are potential infection sites in respiratory tract infections. We also aimed to clarify the mechanism governing the transferability of GPFX into the alveolus compartment from a kinetic point of view. The AUC ratios of ELF/plasma and AM/plasma after the oral administration of GPFX were 5.69 +/- 1.00 and 352 +/- 57, respectively, which were several-fold greater than those of ciprofloxacin (CPFX). Pharmacokinetic analyses of time profiles of GPFX concentrations in ELF and AM revealed that the influx clearance from plasma to ELF across the alveolar barrier is 5-fold greater than the efflux clearance from ELF. In addition, the permeability of GPFX across the cultured AM cell membrane was 7-fold and 11-fold greater than that of levofloxacin (LVFX) and CPFX, respectively. The extent of intracellular binding to AM cells (expressed as a constant (alpha)) was the greatest for GPFX, followed by CPFX and LVFX. There was a significant correlation between the alpha value and the partitioning to the immobilized artificial membrane (IAM) column, which consists of phospholipid residues covalently bound to silica. These results suggest that GPFX is highly distributed in ELF and AM, and that the high transferability of GPFX into ELF may be attributable to the existence of asymmetrical transport across the alveolar barrier. In addition, it was suggested that both rapid permeability across the AM cell membrane and avid binding to the membrane phospholipids may be responsible for the high accumulation of GPFX in AM.

Ketolides: an emerging treatment for macrolide-resistant respiratory infections, focusing on S. pneumoniae

Resistance to antibiotics in community acquired respiratory infections is increasing worldwide. Resistance to the macrolides can be class-specific, as in efflux or ribosomal mutations, or, in the case of erythromycin ribosomal methylase (erm)-mediated resistance, may generate cross-resistance to other related classes. The ketolides are a new subclass of macrolides specifically designed to combat macrolide-resistant respiratory pathogens. X-ray crystallography indicates that ketolides bind to a secondary region in domain II of the 23S rRNA subunit, resulting in an improved structure-activity relationship. Telithromycin and cethromycin (formerly ABT-773) are the two most clinically advanced ketolides, exhibiting greater activity towards both typical and atypical respiratory pathogens. As a subclass of macrolides, ketolides demonstrate potent activity against most macrolide-resistant streptococci, including ermB- and macrolide efflux (mef)A-positive Streptococcus pneumoniae. Their pharmacokinetics display a long half-life as well as extensive tissue distribution and uptake into respiratory tissues and fluids, allowing for once-daily dosing. Clinical trials focusing on respiratory infections indicate bacteriological and clinical cure rates similar to comparators, even in patients infected with macrolide-resistant strains.

Pharmacokinetic evaluation of high pulmonary disposition of clarithromycin after systemic administration

1. The distribution characteristics of clarithromycin to the lung were investigated in vivo and in isolated lung perfusion experiments. The in-vivo integration plot analysis showed that the pulmonary uptake and extracellular distribution in the lung were significantly higher for clarithromycin than for erythromycin. 2. In the rat lung single-pass perfusion study, the pulmonary extraction ratio (E(ss)) of clarithromycin at steady-state was significantly higher than that of erythromycin, and the E(ss) of clarithromycin tended to decrease as the inflow concentration increased, suggesting the involvement of carrier-mediated transport in the pulmonary disposition of clarithromycin. 3. The outflow patterns of clarithromycin or erythromycin at various inflow concentrations were simultaneously analysed based on a pharmacokinetic model, which consists of the non-specific binding site, the specific binding site and the subsequent uptake process. The parameters obtained suggested that clarithromycin would have the higher affinity and higher capacity for the specific binding site, and the higher equilibrium constant for the non-specific binding site than erythromycin. 4. The simulation study using those parameters demonstrated that clarithromycin could be bound to the specific binding site and subsequently taken up more extensively than erythromycin. 5. A multiple-indicator dilution study also indicated that clarithromycin was more readily associated and extracted with the lung than with erythromycin. In the inhibition study, it was suggested that the pulmonary uptake of clarithromycin could be ascribed not only to the non-specific binding depending on its lipophilic nature, but also in part to some specialized mechanisms such as organic cation transporters.

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.

Tissue selective drug delivery utilizing carrier-mediated transport systems

This paper describes some successful examples of a tissue selective drug delivery by utilizing specialized transporter(s) expressed in the targeted tissue cells. These are as follows: (1) oral delivery via H(+)/oligopeptide transporter, rat or human Pept1, in the intestine for beta-lactam antibiotics and a newly synthesized dipeptide, L-dopa-L-phenylalanine; (2) tumor cell specific delivery via the newly discovered H(+)/oligopeptide transporter(s) expressed in human fibrosarcoma cell line HT-1080 for model oligopeptides, glycylsarcosine and carnosine; (3) oral and hepatic delivery via an H(+)/monocarboxylate transporter in the intestine and an organic anion transporter in the liver for HMG-CoA reductase inhibitor, pravastatin; and (4) lung selective delivery via some type of transporter and avoidance of transfer into the brain via P-glycoprotein at the blood-brain barrier for a new quinolone antibacterial, HSR-903.

Requirements for intracellular accumulation and release of clarithromycin and azithromycin by human phagocytes

Determination of clarithromycin (CL) and azithromycin (AZ) uptake by human polymorphonuclear leukocytes (PMNs), monocytes and alveolar macrophages showed that AZ achieved higher levels than CL. The uptake kinetics of AZ were time-dependent over an 18 h period, while those of CL were similar to erythromycin (ER) kinetics, with a maximum level of incorporation being obtained after a 60 min incubation. The accumulation of both drugs was influenced by extracellular antibiotic-concentrations, PMN viability, extracellular calcium, physiological environmental temperature and pH. The uptake was not modified by inhibitors of cell metabolism or activators of cell membranes. After removal of extracellular antibiotic, the release of AZ from PMNs was very slow: nearly 50% of the drug remained cell-associated after 24 h incubation. The efflux of this derivative was significantly enhanced when drug-loaded PMNs were stimulated by phorbol-myristate acetate (PMA). The kinetics of CL release indicated that this macrolide behaved like ER. Nevertheless, about 10% of the initial cell-associated antibiotic showed a prolonged retention. On the whole, these data suggest that diffusion through cell membranes and trapping into acidic compartments of PMNs are important events in CL and AZ uptake.

Clarithromycin against Mycobacterium avium complex infections

The turning point in antimicrobial therapy of Mycobacterium avium infections came with the development of two new macrolides, clarithromycin and azithromycin. Controlled clinical trials, the first ever conducted with any agent among patients with M. avium infection, indicated the high efficiency of clarithromycin, in either acquired immune deficiency syndrome (AIDS) patients having a disseminated infection or non-AIDS patients with localized pulmonary disease. Monotherapy with clarithromycin resulted in elimination of bacteremia in almost all patients with disseminated infection, which is inevitably followed by a relapse of bacteremia in patients who survived long enough to reach this event. The strains susceptible to clarithromycin isolated before therapy contained 10(-8) or 10(-9) resistant mutants, and the relapses of bacteremia were caused by multiplication of these pre-existing mutants. Clarithromycin-resistance was associated with a mutation in the 23S rRNA gene. Cross-resistance between clarithromycin and azithromycin was confirmed with laboratory mutants and clinical isolates. At least two methods for determining the susceptibility of the M. avium isolates to clarithromycin are available: one is minimum inhibitory concentration (MIC) determination on Mueller-Hinton agar (pH 7.4) supplemented with 10% Oleic acid-albumin-dextrose catalase, the other is MIC determination in 7H12 broth, also at pH 7.4. The breakpoints for 'susceptible' for these methods are < or = 8.0 micrograms/ml and < or = 2.0 micrograms/ml, respectively. The breakpoints for 'resistant' are > 128 micrograms/ml for the agar method and > 32.0 micrograms/ml for the broth method. The predictability value of MIC determination was confirmed by comparing the test results with the patients' clinical and bacteriological response to therapy. The remaining major problem in the therapy of the M. avium infections is a selection of companion drugs to be used in combination with clarithromycin (or azithromycin) to prevent the emergence of the macrolide-resistance. A number of clinical trials are now in progress to find a solution to this problem.

Serum and cellular pharmacokinetics of clarithromycin 500 mg q.d. and 250 mg b.i.d. in volunteers

In an open-label, randomized, crossover study 12 healthy volunteers were given clarithromycin orally 250 mg twice daily (b.i.d.) and 500 mg once a day (q.d.). Blood and saliva samples were collected on study days 1 and 5 to determine the pharmacokinetics of clarithromycin and its 14-hydroxy metabolite in plasma and saliva, and to measure concentrations of clarithromycin in mononuclear cells (MNCs) and polymorphonuclear leucocytes (PMNs). The mean peak levels of clarithromycin on day 5 of therapy in serum (2.3 vs. 1.2 mg/l), saliva (1.1 vs. 0.3 mg/l) and blood cells 60 vs. 26 mg/l in MNCs and 29 vs. 14 mg/l in PMNs) were at least doubled, the trough levels were lower with 500 mg q.d. vs. 250 mg b.i.d. (0.09 vs. 0.28 mg/l in serum; 0.06 vs. 0.13 mg/l in saliva; < 1 vs. 6.8 mg/l in MNCs; 0.8 vs. 2.8 mg/l in PMNs). The mean relative peak serum concentrations of the 14-hydroxy metabolite were somewhat lower with the 500 mg dosage (0.78 vs. 0.46 mg/l). The peak concentrations of clarithromycin and its 14-hydroxy metabolite in saliva were 25-40% and 50-80% of the maximum serum concentrations with both dosage regimens. Clarithromycin exhibits good and rapid penetration into intracellular as well as into extravasal extracellular body compartments. Clarithromycin 500 mg q.d. compares favourably with 250 mg b.i.d., as far as peak serum levels and bioavailability are concerned, but trough levels are lower at the end of the 24-hour dosing interval.

Accumulation of clarithromycin in macrophages infected with Mycobacterium avium

Clarithromycin is known to accumulate in polymorphonuclear leukocytes, but no accumulation studies with macrophages have been reported. We exposed J774 macrophages, grown for 4-6 days, to clarithromycin 3.0 micrograms/ml for 2 hours. The cells were separated from the extracellular fluid, and the concentration of clarithromycin was determined in an agar diffusion bioassay. The accumulation of clarithromycin was 15.8-fold greater in the cells than it was in the extracellular fluid when the test was performed with noninfected cells, and 17.3-fold greater for cells infected with Mycobacterium avium. However, the ratio was substantially lower, only 3.7 for dead macrophages, suggesting that intracellular accumulation is probably an active process. These data may clarify the nature of the activity of clarithromycin against M. avium in macrophages.

Clarithromycin clinical pharmacokinetics

Clarithromycin is a semisynthetic macrolide antibiotic, structurally related to erythromycin. It has a more favourable pharmacokinetic profile than erythromycin, thus allowing twice-daily administration and possibly increasing compliance among outpatients. Clarithromycin is well absorbed from the gastrointestinal tract and its systemic bioavailability (about 55%) is reduced because of first-pass metabolism. It undergoes rapid biodegradation to produce the microbiologically active 14-hydroxy-(R)-metabolite. The maximum serum concentrations of clarithromycin and its 14-hydroxy metabolite, following single oral doses, are dose proportional and appear within 3 hours. With multiple doses, steady-state concentrations are attained after 5 doses and the maximal serum concentrations of clarithromycin and of the 14-hydroxy derivative appear within 2 hours after the last dose. Clarithromycin is well distributed throughout the body and achieves higher concentrations in tissues than in the blood. Also, the 14-hydroxy metabolite exhibits high tissue concentrations, with values about one-third of the parent compound concentrations. The presence of food appears to have no clinically significant effect on clarithromycin pharmacokinetics. The main metabolic pathways are oxidative N-demethylation and hydroxylation, which are saturable and result in nonlinear pharmacokinetics. The primary metabolite (14-hydroxy derivative) is mainly excreted in the urine with the parent compound. A reduction in urinary clearance in the elderly and in patients with renal impairment is associated with an increase in area under the plasma concentration-time curve, peak plasma concentrations and elimination half-life. Mild hepatic impairment does not significantly modify clarithromycin pharmacokinetics. In conclusion, clarithromycin, because of its antibacterial activity and pharmacokinetic properties, appears to be a useful alternative to other macrolides in the treatment of community acquired infections.

Clarithromycin. A review of its pharmacological properties and therapeutic use in Mycobacterium avium-intracellulare complex infection in patients with acquired immune deficiency syndrome

Results from noncomparative and placebo-controlled studies demonstrate the efficacy of clarithromycin in the treatment of disseminated Mycobacterium avium-intracellulare complex (MAC) infection in patients with acquired immune deficiency syndrome (AIDS). Whether given alone or in combination with other antimycobacterial treatments, doses of 500 to 2000mg (typically 1000mg) administered twice daily are effective in controlling bacteraemia in these patients. Clarithromycin has also been shown to improve clinical symptoms of infection and may improve quality of life in AIDS patients with MAC infection. Clarithromycin is generally well tolerated when used in the doses typically required for the treatment of MAC infection (1000 or 2000 mg/day). Gastrointestinal disturbances are the most commonly occurring adverse events and occur most frequently at dosages of 4000 mg/day. Thus, clarithromycin, as monotherapy or in combination with other antimycobacterial agents, is well tolerated and effectively eradicates MAC from the blood in the short term in patients with AIDS: however, short term monotherapy may lead to bacterial resistance, underscoring the importance of long term treatment with a combination of antimycobacterial agents. While the optimal combination regimen to prevent the development of resistance to antimycobacterial agents. While the optimal combination regimen to prevent the development of resistance to antimycobacterial agents by MAC remains to be determined, clarithromycin will almost certainly be a valuable agent in any such combination.

Clarithromycin: review of a new macrolide antibiotic with improved microbiologic spectrum and favorable pharmacokinetic and adverse effect profiles

OBJECTIVE

To compare the new macrolide antibiotic clarithromycin with erythromycin in terms of in vitro activity, pharmacokinetics, pharmacodynamics, clinical efficacy, and toxicity.

DATA IDENTIFICATION

An English-language literature search employing MEDLINE (1987-91), Index Medicus (1987-91), Program and Abstracts of the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy (1990), Program and Abstracts of the 31st Interscience Conference on Antimicrobial Agents and Chemotherapy (1991), and bibliographic reviews of related textbooks and review articles.

STUDY SELECTION

Eighty-five articles were selected. Clinical trials with clarithromycin have been limited, and emphasis was placed on trials reported in the Program and Abstracts of the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy and Program and Abstracts of the 31st Interscience Conference on Antimicrobial Agents and Chemotherapy.

DATA EXTRACTION

Articles were assessed for study quality and specific information addressing the stated purpose. In articles reporting the results of clinical trials, emphasis was placed on comparative efficacy and toxicity.

RESULTS OF DATA ANALYSIS

A review of 24 human trials suggests that clarithromycin is equally effective as erythromycin, penicillin VK, ampicillin, or amoxicillin for treatment of a variety of upper and lower respiratory tract or skin infections. Clarithromycin also appears to be better tolerated than these agents, with a lower incidence of gastrointestinal adverse effects. Limited clinical studies in patients with Mycobacterium leprae or Mycobacterium avium-intracellulare complex (MAI) suggest that clarithromycin may prove to be efficacious and well tolerated in the treatment of these infections.

CONCLUSIONS

Clarithromycin is as effective in vivo as erythromycin, with less gastrointestinal irritation. Additionally, clarithromycin appears to expand the traditional spectrum of macrolide antibiotics, with promising activity against M. leprae and MAI.

Clarithromycin. A review of its antimicrobial activity, pharmacokinetic properties and therapeutic potential

Clarithromycin is an acid-stable orally administered macrolide antimicrobial drug, structurally related to erythromycin. It has a broad spectrum of antimicrobial activity, similar to that of erythromycin and inhibits a range of Gram-positive and Gram-negative organisms, atypical pathogens and some anaerobes. Significantly, clarithromycin demonstrates greater in vitro activity than erythromycin against certain pathogens including Bacteroides melaninogenicus, Chlamydia pneumoniae, Chlamydia trachomatis, Mycobacterium chelonae subspecies--chelonae and--abscessus, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium avium complex, Legionella spp. and, when combined with its 14-hydroxy metabolite, against Haemophilus influenzae. However, bacterial strains resistant to erythromycin are also generally resistant to clarithromycin. The antimicrobial activity of clarithromycin appears to be enhanced by the formation in vivo of the microbiologically active 14-hydroxy metabolite. In combination, additive or synergistic activity against a variety of pathogens including Haemophilus influenzae, Moraxella catarrhalis, Legionella species (principally Legionella pneumophila) and various staphylococci and streptococci has been demonstrated. Clarithromycin has a superior pharmacokinetic profile to that of erythromycin, allowing the benefits of twice daily administration with the potential for increased compliance among outpatients where a more frequent regimen for erythromycin might otherwise be indicated. The clinical efficacy of clarithromycin has been confirmed in the treatment of infections of the lower and upper respiratory tracts (including those associated with atypical pathogens), skin/soft tissues, and in paediatrics. Clarithromycin was as effective as erythromycin and other appropriate drugs including beta-lactams (penicillins and cephalosporins) in some of the above infections. A most promising indication for clarithromycin appears to be in the treatment of immunocompromised patients infected with M. avium complex, M. chelonae sp. and Toxoplasma sp. Small initial trials in this setting reveal clarithromycin alone or in combination with other antimicrobials to be effective in the eradication or amelioration of these infections. Noncomparative studies have provided preliminary evidence for the effectiveness of clarithromycin in the treatment of infections of the urogenital tract, oromaxillofacial and ophthalmic areas. However, the promising in vitro and preliminary in vivo activity of clarithromycin against Mycobacterium leprae and Helicobacter pylori warrant further clinical trials to assess its efficacy in patients with these infections. Despite the improved pharmacokinetic profile and in vitro antimicrobial activity of clarithromycin over erythromycin, comparative studies of patients with community-acquired infections reveal the 2 drugs to be of equivalent efficacy. However, clarithromycin demonstrates greater tolerability, principally by inducing fewer gastrointestinal disturbances.(ABSTRACT TRUNCATED AT 400 WORDS)