Clarithromycin-nifedipine interaction as possible cause of vasodilatory shock

OBJECTIVE

To report a case of vasodilatory shock possibly resulting from a clarithromycin-nifedipine interaction.

CASE SUMMARY

A 77-year-old male with uncontrollable hypertension developed shock, heart block, and multiorgan failure 2 days after clarithromycin was added to his antihypertensive treatment (nifedipine, captopril, doxazosin). Invasive monitoring revealed hyperdynamic shock with decreased systemic vascular resistances.

DISCUSSION

Nifedipine is metabolized by isoenzyme CYP3A4. This metabolic pathway is inhibited by clarithromycin, thus potentially increasing the plasma nifedipine concentration, which may lead to excessive calcium-channel blocker effects. Clinical manifestations of excessive calcium-channel blockade comprise hypotension or vasodilatory shock and heart block, as in our case. An objective causality assessment revealed that this drug interaction was the possible cause of these adverse effects. Because of an initial diagnosis of septic shock, suspicion of this entity was delayed and specific diagnostic and treatment were not possible.

CONCLUSIONS

This life-threatening clinical picture, including shock and heart block, was possibly the result of a pharmacokinetic interaction between clarithromycin and nifedipine.

Antibacterial effect of Kampo herbal formulation Hochu-ekki-to (Bu-Zhong-Yi-Qi-Tang) on Helicobacter pylori infection in mice

Because Helicobacter pylori (H. pylori) infection is a major cause of gastroduodenal diseases in humans, the eradication of H. pylori using antibiotics is very effective for the treatment of gastroduodenal diseases. However, it has recently been reported that resistance to these antibiotics is developing. In the present study, the antibacterial effect of a Kampo (traditional Japanese medicine) herbal formulation, Hochu-ekki-to (RET; Formula repletionis animalis et supletionis medii), against H. pylori was examined in vitro and in vivo. HET inhibited the growth of antibiotic-resistant strains of H. pylori as well as antibiotic-sensitive strains at a dose of 2.5 mg/ml in vitro. When 1,000 mg/kg of HET was administered orally to C57BL/6 mice for 7 days before or after inoculation with H. pylori, H. pylori in the stomach was significantly reduced in the HET-pre-treatment group compared with the control group. Furthermore, HET in combination with antibiotics completely eradicated the bacteria in mice. The expression of interferon (IFN)-gamma was induced in the gastric mucosa of the mice pre-treated with HET. There were no significant differences between the colonization of H. pylori in the control and HET treatment groups in IFN-gamma gene-deficient mice. These results suggest that the antibacterial effect of HET may be partly due to IFN-gamma induction, and that HET may be clinically useful for treatment of H. pylori infection.

Localization of [14C]clarithromycin in rat gastric tissue when administered with lansoprazole and amoxicillin

After oral and intravenous administration of [14C]clarithromycin to rats, c. 60-70% of the radioactivity in the gastric tissue was found to be distributed in the mucosal layer. Co-administration of lansoprazole and amoxicillin had no apparent effect on this distribution pattern of [14C]clarithromycin. The amount of unchanged [14C]clarithromycin in gastric contents increased with co-administration of lansoprazole and amoxicillin. Microautoradiograms of the gastric mucosa showed that [14C]clarithromycin was highly distributed in the mucous layer and in surface epithelial cells following oral administration. Homogeneous distribution of radioactivity was evident in the fundic gland. With iv administration, [14C]clarithromycin seemed to be secreted by both secreting cells in the gland base and surface epithelial cells.

Comparative metabolic capabilities of CYP3A4, CYP3A5, and CYP3A7

The human cytochromes P450 (P450) CYP3A contribute to the biotransformation of 50% of oxidatively metabolized drugs. The predominant hepatic form is CYP3A4, but recent evidence indicates that CYP3A5 contributes more significantly to the total liver CYP3A than was originally thought. CYP3A7 is the major fetal form and is rarely expressed in adults. To compare the metabolic capabilities of CYP3A forms for 10 substrates, incubations were performed using a consistent molar ratio (1:7:9) of recombinant CYP3A, P450 reductase, and cytochrome b5. A wide range of substrate concentrations was examined to determine the best fit to kinetic models for metabolite formation. In general, K(m) or S(50) values for the substrates were 3 to 4 times lower for CYP3A4 than for CYP3A5 or CYP3A7. For a more direct comparison of these P450 forms, clearance to the metabolites was determined as a linear relationship of rate of metabolite formation for the lowest substrate concentrations examined. The clearance for 1'-hydroxy midazolam formation at low substrate concentrations was similar for CYP3A4 and CYP3A5. For CYP3A5 versus CYP3A4, clearance values at low substrate concentrations were 2 to 20 times lower for the other biotransformations. The clearance values for CYP3A7-catalyzed metabolite formation at low substrate concentrations were substantially lower than for CYP3A4 or CYP3A5, except for clarithromycin, 4-OH triazolam, and N-desmethyl diltiazem (CYP3A5 - CYP3A7). The CYP3A forms demonstrated regioselective differences in some of the biotransformations. These results demonstrate an equal or reduced metabolic capability for CYP3A5 compared with CYP3A4 and a significantly lower capability for CYP3A7.

Combination studies between polycationic peptides and clinically used antibiotics against Gram-positive and Gram-negative bacteria

The in vitro interaction between five polycationic peptides, buforin II, cecropin P1, indolicidin, magainin II, and ranalexin, and several clinically used antimicrobial agents was evaluated against several clinical isolates of Gram-positive and Gram-negative aerobic bacteria, using the microbroth dilution method. The combination studies showed synergy between ranalexin and polymyxin E, doxycycline and clarithromycin. In addition, magainin II was shown to be synergic with betalactam antibiotics.

Clarithromycin targeting to lung: characterization, size distribution and in vivo evaluation of the human serum albumin microspheres

Microspheres of clarithromycin have been prepared from human serum albumin using the emulsion polymerization technique. Albumin microspheres containing the active substance were injected into the tail vein of mice. Mice were sacrificed at intervals and microspheres collected from lungs and livers. The clarithromycin amount in microspheres was determined by reversed phase high performance liquid chromatographic (HPLC) method from the mice organs. Morphological and histopathological observations were also reported. The microsphere accumulation began at 10 min, and increased gradually until 6 h, then a decrease was observed. The microspheres were still present after 24 h. In the liver sample, no microsphere accumulation was observed at any time.

Antimicrobial activities and postantibiotic effects of clarithromycin, 14-hydroxy-clarithromycin, and azithromycin in epithelial cell lining fluid against clinical isolates of haemophilus influenzae and Streptococcus pneumoniae

The antimicrobial activity of concentrations of selected macrolides found in epithelial cell lining fluid was investigated. Clarithromycin demonstrated greater potency and a significantly longer postantibiotic effect (PAE) than azithromycin against Streptococcus pneumoniae. Azithromycin displayed greater potency, faster killing, and a longer PAE than clarithromycin against Haemophilus influenzae. Drug concentrations in epithelial cell lining fluid similar to those found in tissue did not improve the synergistic potential of 14-hydroxy-clarithromycin and indicate that a maximal PAE may exist despite increasing concentrations of drug.

Endothelial cell compatibility of clarithromycin for intravenous use

OBJECTIVES

Tolerance of intravenously applied clarithromycin has been tested on marginal ear veins of rabbits. Use of human umbilical venous endothelial cells (HUVEC) for testing antibiotic solutions for intravenous compatibility provides a valuable alternate model.

DESIGN AND METHODS

In order to evaluate the effect of clarithromycin on intracellular purines, reflecting cell viability, energy production, signal transduction and DNA/RNA synthesis, intracellular adenosine 5' triphosphate (ATP), adenosine 5' diphosphate (ADP), guanosine 5' triphosphate (GTP), and guanosine 5' diphosphate (GDP) levels were measured by means of high performance liquid chromatography (HPLC).

RESULTS

Incubation of cells with 2 mg/mL clarithromycin resulted in a rapid decrease of the intracellular ATP from 12.6 +/- 1.1 to 8.87 +/- 0.82 nmol/million cells or 1.5 +/- 0.6 nmol/million cells, after 20 or 60 min, respectively. In addition, ADP was extensively depleted. Purine nucleotide profiles were markedly different following exposure to 1 mg/mL clarithromycin. There was no significant decline of intracellular high energy phosphate levels after 20 min.

CONCLUSION

These results show that clarithromycin has a better endothelial compatibility if diluted to a final concentration of 1 mg/mL. These data are in line with our clinical observations that the occurrence of phlebitis could be minimized by diluting the manufacturers' preparation of clarithromycin to 1 mg/mL.

Oral cimetidine prolongs clarithromycin absorption

The present study was conducted to identify any potential interaction between oral cimetidine and clarithromycin. Twelve healthy subjects were administered single doses of clarithromycin alone and with oral cimetidine dosed to steady state. Cimetidine prolonged the absorption of clarithromycin, as evidenced by decreased peak concentrations of both clarithromycin and 14-OH-clarithromycin (14OHC) in serum (46 and 43%, respectively), a delay in the formation of 14OHC (increase of 68%), and increases in both of their half-lives (75 and 82%, respectively), despite no changes in total oral clearance or area under the concentration-time curve for either compound. No mechanism for this interaction has been identified.

Syncopal episodes associated with cisapride and concurrent drugs

OBJECTIVE

To report a case of QT prolongation and syncopal episodes resulting from concomitant use of cisapride and agents known to inhibit its metabolism.

CASE SUMMARY

A 53-year-old white woman was involved in two motor vehicle accidents on the same day after experiencing syncopal episodes. Cardiac and neurologic evaluations were negative; the syncopal episodes were attributed to QT prolongation associated with the concomitant use of cisapride and agents known to inhibit its metabolism.

DISCUSSION

This is the first case published in the English-language literature describing QT prolongation resulting from the concomitant use of cisapride and agents known to inhibit its metabolism. Clarithromycin inhibits CYP3A4, the isoenzyme responsible for the metabolism of cisapride. Concomitant administration of cisapride with agents known to inhibit CYP3A4 (i.e., azole antifungals, erythromycin, clarithromycin) may result in elevated cisapride concentrations. Elevated cisapride concentrations have been associated with QT prolongation, syncopal episodes, and cardiac dysrhythmias.

CONCLUSIONS

Acquired QT prolongation is a well-recognized adverse effect of several drugs. Recognition of newer drugs and drug combinations that place patients at risk for this potentially fatal adverse event is imperative for appropriate monitoring and prevention.

Factors affecting solubility and penetration of clarithromycin through gastric mucus

BACKGROUND

Factors influencing the pharmacokinetics of clarithromycin in gastric mucus are poorly defined.

AIM

To determine: (i) whether the clinical formulation of clarithromycin (Biaxin granules and powdered Biaxin tablets) affects the water solvency of the antibiotic or changes the barrier properties of pig gastric mucus (PGM), thereby influencing the penetration of clarithromycin through the gastric mucus layer; and (ii) whether topically active anti-ulcer agents affect clarithromycin penetration through gastric mucus.

METHODS

Solubility of clarithromycin in aqueous solution was studied at pH 7. PGM viscosities were determined using a falling ball microviscometer. Permeability of clarithromycin through PGM with and without added anti-ulcer drugs at pH 7 was monitored using a microfiltration device and an agar diffusion bioassay.

RESULTS

Clarithromycin showed the poorest solubility at pH 7, whereas both Biaxin formulations demonstrated identical solubility of their antibiotic ingredient. Clarithromycin and both Biaxin formulations markedly increased mucin viscosity over the pH range 2-7. PGM markedly retarded the penetration of clarithromycin: unformulated clarithromycin and Biaxin tablets penetrated more rapidly through mucus than Biaxin granules. Pre-treatment of PGM with aluminium-magnesium-containing antacids (Riopan and Talcid preparations) decreased the rate of clarithromycin penetration, whereas Carafate and Peptobismol had no significant effect on mucus penetration of clarithromycin.

CONCLUSIONS

The availability of clarithromycin in gastric mucus is significantly influenced by its clinical formulation, which affects its solubility as well as the viscous properties of mucus. Pulverized Biaxin tablets provide better local distribution of clarithromycin in mucus than Biaxin granules. Pre-treatment of mucus with anti-ulcer medications does not increase the penetration of clarithromycin through mucus.

Molecular basis of clarithromycin activity against Mycobacterium avium and Mycobacterium smegmatis

Clarithromycin, the 6-O-methyl derivative of erythromycin, is approved for treatment of Mycobacterium avium infections and for prophylaxis in patients at risk. Since clarithromycin is more active against mycobacteria than the parent compound, erythromycin, we evaluated the interaction of erythromycin and clarithromycin with cells and ribosomes isolated from M. avium and Mycobacterium smegmatis. The MIC of clarithromycin was 32 and 64 times lower than that of erythromycin for M. smegmatis and M. avium, respectively. The cellular uptake rate for clarithromycin was two- to five-fold faster than for erythromycin, and cell-associated clarithromycin reached a plateau two-fold higher than that of erythromycin after 3 h. Energy was not required for uptake. Fractionation of cell-associated clarithromycin yielded 12% in the walls, 21% bound to ribosomes, with the remainder being lost during work-up. In addition, three- to six-fold more clarithromycin was associated with the isolated cell integument compared with erythromycin. The Kd for clarithromycin binding to ribosomes was 2.9- and 3.5-fold tighter for M. smegmatis and M. avium, respectively, than for erythromycin, due mainly to a slower off-rate. The log partition coefficients of the non-ionized form (log Pu) for clarithromycin and erythromycin were 3.24 and 2.92, respectively. Thus clarithromycin is more hydrophobic than erythromycin. This would favour more rapid diffusion within and across hydrophobic regions of the cell integument, since once a solute saturates a membrane the net flux across the membrane must equal the net flux within the membrane as dictated by diffusion. We conclude that the lower MIC of clarithromycin for M. avium and M. smegmatis is due to a combination of increased cellular uptake, the major factor, possibly through a peripheral hydrophobic layer, and increased binding affinity to ribosomes.

In vitro activity of clarithromycin alone and in combination with ciprofloxacin or levofloxacin against Legionella spp.: enhanced effect by the addition of the metabolite 14-hydroxy clarithromycin

Clarithromycin is metabolized to an active metabolite, 14-hydroxy clarithromycin. These compounds have demonstrated excellent in vitro activity against Legionella species, with both agents having significantly lower MICs than erythromycin. Using a checkerboard assay, the activity of clarithromycin and its hydroxy metabolite, alone and in combination, was examined against 41 Legionella organisms. The activity of clarithromycin and 14-hydroxy clarithromycin, in a 2:1 ratio, plus ciprofloxacin or levofloxacin was also determined. Activity of the antibiotic combinations was determined by calculating the fractional inhibitory concentration index. An agar dilution method using buffered charcoal yeast extract media was used for susceptibility and synergy testing. An inoculum of 10(4) CFU/spot was used, with all plates incubated at 35 degrees C for 48 h. The MIC90 for clarithromycin or 14-hydroxy clarithromycin alone was 0.5, versus 0.25 microgram/mL for the combination. Additive effects were observed with clarithromycin and its hydroxy metabolite for 61% of the Legionella species, with fractional inhibitory concentration indices ranging from 0.63 to 1.25. The 14-hydroxy metabolite significantly increased the activity of both fluoroquinolone/clarithromycin combinations. Based on these data, in vitro susceptibility testing of agents such as clarithromycin should be reevaluated to account for the activity of active metabolites.

Lovastatin-induced rhabdomyolysis possibly associated with clarithromycin and azithromycin

OBJECTIVE

To describe two cases of rhabdomyolysis in patients taking lovastatin that were precipitated by the use of the newer macrolide antibiotics clarithromycin and azithromycin.

CASE SUMMARIES

In each case, the patients were treated over 5 years with lovastatin and developed rhabdomyolysis that coincided with the completion of a prescribed regimen of a newer macrolide antibiotic. Following intravenous hydration and administration of bicarbonate, the patients' condition resolved without permanent' sequelae.

DISCUSSION

Rhabdomyolysis is a clinical syndrome resulting from the destruction of skeletal muscle that may progress to renal failure Several drugs have been associated with rhabdomyolysis, including lovastatin, a hydroxymethylglutaryl-coenzyme A reductase inhibitor. Erythromycin is a macrolide antibiotic that may increase the risk of lovastatin-induced rhabdomyolysis. To our knowledge, these cases are the first published reports of lovastatin-induced rhabdomyolysis associated with azithromycin and clarithromycin.

CONCLUSIONS

The risk of drug-induced rhabdomyolysis due to the potential interaction between lovastatin and azithromycin or clarithromycin should be considered before the concomitant use of these agents.

Intrapulmonary steady-state concentrations of clarithromycin and azithromycin in healthy adult volunteers

The steady-state concentrations of clarithromycin and azithromycin in plasma were compared with concomitant concentrations in epithelial lining fluid (ELF) and alveolar macrophages (AM) obtained in intrapulmonary samples during bronchoscopy and bronchoalveolar lavage from 40 healthy, nonsmoking adult volunteers. Mean plasma clarithromycin, 14-(R)-hydroxyclarithromycin, and azithromycin concentrations were similar to those previously reported. Clarithromycin was extensively concentrated in ELF (range of mean +/- standard deviation concentrations, 34.4 +/- 29.3 microg/ml at 4 h to 4.6 +/- 3.7 microg/ml at 24 h) and AM (480 +/- 533 microg/ml at 4 h to 99 +/- 50 microg/ml at 24 h). The concentrations of azithromycin in ELF were 1.01 +/- 0.45 microg/ml at 4 h to 1.22 +/- 0.59 microg/ml at 24 h, and those in AM were 42.7 +/- 28.7 microg/ml at 4 h to 41.7 +/- 12.1 microg/ml at 24 h. The concentrations of 14-(R)-hydroxyclarithromycin in the AM ranged from 89.3 +/- 52.8 microg/ml at 4 h to 31.3 +/- 17.7 microg/ml at 24 h. During the period of 24 h after drug administration, azithromycin and clarithromycin achieved mean concentrations in ELF and AM higher than the concomitant concentrations in plasma.

Oxidative metabolism of clarithromycin in the presence of human liver microsomes. Major role for the cytochrome P4503A (CYP3A) subfamily

In vitro studies were conducted to identify the hepatic cytochrome P450 (CYP) protein(s) involved in the oxidative metabolism of [14C]clarithromycin (CLAR) in the presence of native human liver microsomes. The identity of the two major CLAR metabolites present in microsome incubates, 14-(R)-hydroxy-CLAR and N-desmethyl-CLAR, was confirmed by MS. Over the CLAR concentration range of 1.0-140 microM, the rate of CLAR 14-(R)-hydroxylation (KM = 48 +/- 17.7 microM; Vmax = 206 +/- 76 pmol/min/mg protein; Vmax/KM = 4.2 +/- 0.21 microliters/min/mg; mean +/- SD, N = 3 livers) and N-demethylation (KM = 59.1 +/- 24.0 microM; Vmax = 189 +/- 52.0 pmol/min/mg protein; Vmax/KM = 3.3 +/- 0.53 microliters/min/mg) conformed to monophasic (saturable) Michaelis-Menten kinetics and was highly correlated (r = 0.90-0.92; p < 0.001; N = 11) with CYP3A-selective erythromycin N-demethylase activity. Ketoconazole (< or = 2.0 microM) or troleadomycin, CYP3A-selective inhibitors, markedly decreased (> or = 99%) the formation of both metabolites, whereas inhibitors selective of other CYP forms were relatively ineffective (< or = 10% inhibition). In agreement with chemical inhibitor studies, CLAR metabolism was only detectable with human B-lymphoblastoid microsomes containing cDNA-expressed CYP3A4 (vs. CYP2C19, CYP2C9, CYP2D6, CYP1A2, CYP2E1, or CYP2A6). Furthermore, the apparent KM characterizing the 14-(R)-hydroxylation and N-demethylation of CLAR in the presence of insect cell microsomes containing cDNA-expressed CYP3A4 (KM = 18-63 microM) was similar to that obtained with native human liver microsomes. Based on the results of this study, it is concluded that the 14-(R)-hydroxylation and N-demethylation of CLAR is primarily mediated by one or more members of the human liver CYP3A subfamily.

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.

Penetration of clarithromycin into middle ear fluid of children with acute otitis media

OBJECTIVE

To determine the steady state plasma and middle ear fluid concentrations of clarithromycin and its metabolite, 14(R)-hydroxyclarithromycin in 32 pediatric patients with acute otitis media.

METHODS

After the sixth dose of a 7.5-mg/kg every-12-h regimen of clarithromycin suspension, tympanocentesis was performed at 2, 4, 8 or 12 hours postdose. Plasma and middle ear fluid samples were assayed for concentrations of clarithromycin and its 14-hydroxy metabolite.

RESULTS

Mean middle ear fluid concentrations ranged from 3.0 to 8.3 micrograms/g during the dosing interval for clarithromycin and from 1.5 to 3.8 micrograms/g for 14(R)-hydroxyclarithromycin. The mean middle ear fluid concentrations were consistently greater than corresponding mean plasma concentrations, which ranged from 0.7 to 3.4 micrograms/ml for clarithromycin and from 0.8 to 1.8 micrograms/ml for 14(R)-hydroxyclarithromycin. The ratios of middle ear fluid to plasma concentration appeared to increase during the dosing interval and were 8.8 and 3.8 for clarithromycin and 14(R)-hydroxyclarithromycin, respectively, 12 h after dosing.

CONCLUSIONS

Multiple oral doses of clarithromycin suspension produced sustained middle ear fluid concentrations of clarithromycin and 14(R)-hydroxyclarithromycin which exceed the minimum inhibitory concentrations of most otic pathogens.

Direct evidence for antipseudomonal activity of macrolides: exposure-dependent bactericidal activity and inhibition of protein synthesis by erythromycin, clarithromycin, and azithromycin

Several previous investigators have reported that long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infections, even though the clinically achievable concentrations of these medications are far below their MICs. In the present study, we examined how sub-MICs of macrolide antibiotics affect the viability of and protein synthesis in several strains of P. aeruginosa. We report that 48 h, but not 12 or 24 h, of growth on agar containing a clinically achievable concentration of azithromycin (0.5 microgram/ml, 1/128 the MIC) significantly reduces the viability of strain PAO-1. Similar effects were seen with erythromycin and clarithromycin at 2 micrograms/ml (1/128 and 1/64 the respective MICs), whereas josamycin, oleandomycin, ceftazidime, tobramycin, minocycline, and ofloxacin had no effect on viability, even following 48 h of incubation with concentrations representing relatively high fractions of their MICs. The bactericidal activity of azithromycin seen following 48 h of incubation was not limited to strain PAO-1 but was also seen against 13 of 14 clinical isolates, including both mucoid and nonmucoid strains. Although viability was not decreased prior to 48 h, we found that 4 micrograms of azithromycin per ml inhibits protein synthesis after as little as 12 h and that protein synthesis continues to decrease in a time-dependent manner. We likewise found that P. aeruginosa accumulates azithromycin intracellulary over the period from 12 to 36 h. These results suggested that sub-MICs of certain macrolides are bactericidal to P. aeruginosa when the bacteria are exposed to these antibiotics for longer periods. Exposure-dependent intracellular accumulation of the antibiotic and inhibition of protein synthesis may partially account for the antipseudomonal activity of macrolides over relatively prolonged incubation periods.

Effect of single oral dose of azithromycin, clarithromycin, and roxithromycin on polymorphonuclear leukocyte function assessed ex vivo by flow cytometry

Azithromycin was given as a single oral dose (20 mg/kg of body weight) to 12 volunteers in a crossover study with roxithromycin (8 to 12 mg/kg) and clarithromycin (8 to 12 mg/kg). Flow cytometry was used to study the phagocytic functions and the release of reactive oxygen products following phagocytosis by neutrophil granulocytes prior to administration of the three drugs, 16 h after azithromycin administration, and 3 h after clarithromycin and roxithromycin administration. Phagocytic capacity was assessed by measuring the uptake of fluorescein isothiocyanate-labeled bacteria. Reactive oxygen generation after phagocytosis of unlabeled bacteria was estimated by the amount of dihydrorhodamine 123 converted to rhodamine 123 intracellularly. Azithromycin resulted in decreased capacities of the cells to phagocytize Escherichia coli (median [range], 62% [27 to 91%] of the control values; P < 0.01) and generate reactive oxygen products (75% [34 to 26%] of the control values; P < 0.01). Clarithromycin resulted in reduced phagocytosis (82% [75 to 98%] of control values; P < 0.01) but did not alter reactive oxygen production (84% [63 to 113%] of the control values; P > 0.05). Roxithromycin treatment did not affect granulocyte phagocytosis (92% [62 to 118%] of the control values; P > 0.05) or reactive oxygen production (94% [66 to 128%] of the control value; P > 0.05). No relation between intra- and/or extracellular concentrations of azithromycin and/or roxithromycin and the polymorphonuclear phagocyte function and/or reactive oxygen production existed (P > 0.05 for all comparisons). These results demonstrate that the accumulation of macrolides in neutrophils can suppress the response of phagocytic cells to bacterial pathogens after a therapeutic dose.

Reaction of roxithromycin and clarithromycin with macrolide-inactivating enzymes from highly erythromycin-resistant Escherichia coli

The activities of two new 14-membered-ring macrolide antibiotics, roxithromycin (RXM) and clarithromycin (CAM), against highly erythromycin (EM)-resistant Escherichia coli strains were evaluated. Pretreatment of macrolide phosphotransferase (MPH) (2') I-producing strains with EM increased the MICs of EM and CAM without any noticeable change in the MIC of RXM. The MPH (2') II-producing strain was more susceptible to CAM, while the EM esterase-producing strains were more susceptible to RXM than EM. Pretreatment of these latter two strains with EM did not alter their susceptibility to either RXM or CAM. In addition, the compounds were assessed as substrates for inactivation by crude enzyme preparations. Of the 14-membered-ring macrolides, RXM was the least favored substrate for MPH (2') I or II. CAM and RXM were substrates for the EM esterase but were the least preferred of the 14-membered-ring macrolides.

[Protein binding of clarithromycin in patients with chronic renal failure]

Assessment was made on the serum protein binding of clarithromycin (CAM), a representative oral macrolide, using sera from healthy subjects (HS) and patients with chronic renal failure (CRF) applying equilibrium dialysis in vitro. The protein binding of CAM was 81.9 +/- 1.9%, 85.9 +/- 3.6%, 82.9 +/- 3.3% and 86.8 +/- 3.3% for sera from HS, from patients in conservative treatment (ND), from those receiving hemodialysis (HD) and from those with continuous ambulatory peritoneal dialysis (CAPD), respectively. There was no significant difference among these values. The protein binding of CAM was 82.9 +/- 3.3% and 68.8 +/- 3.5% for sera before and after HD, respectively. There was significant difference between these values. In the study of the protein binding in patients on HD at an albumin concentration of 0.5 mM, the protein binding of CAM for sera was found to be significantly decreased following HD as compared to that prior to HD. The addition of palmitic acid (PA), a common NEFA, to pooled sera from HS, the protein binding of CAM showed no change. These findings suggest that changes in the protein binding of CAM with HD have been possibly caused by an increase in a drug binding inhibiter other than NEFA (PA) or by an allosteric effect on the albumin binding capacity. At therapy using CAM, the possibility of enhanced pharmacological effects and increased adverse reactions of CAM due to decreased protein binding in patients on HD should be considered.

In vitro dissolution tests corresponding to the in vivo dissolution of clarithromycin tablets in the stomach and intestine

The correlation between in vivo and in vitro dissolution of clarithromycin (CAM) tablets was examined. In vivo dissolution rate constants in the stomach and the intestine were obtained from analysis of the urinary excretion data of CAM following oral administration to humans in the fasting or postprandial state using a pharmacokinetic model including gastrointestinal transit. In the present study, the flow-through cell method with moderate agitation was used, as the in vitro dissolution test related to the in vivo dissolution rate constants. Both the effects of pH of the dissolution medium and the volumetric solvent flow rate on the dissolution rate in the flow-through cell method were examined. The pH of the dissolution medium and the flow rate were related to the in vitro dissolution rate. Therefore, the conditions of the flow-through cell method in correlation with the in vivo dissolution rates in the stomach and intestine were determined by controlling the flow rate at pH 3.0 and 6.8 dissolution medium. The urinary excretion of CAM, simulated by substituting the in vitro dissolution rate constants into the equation, were consistent with the in vivo data. The in vitro tests corresponding to the in vivo dissolution in the stomach and intestine following a single oral administration in the fasting or postprandial state for a CAM tablet were established.

Acquired resistance in Mycobacterium avium complex strains isolated from AIDS patients and beige mice during treatment with clarithromycin

Clarithromycin has been reported to select clarithromycin resistant mutants of Mycobacterium avium complex (MAC) during treatment with clarithromycin in AIDS patients and beige mice. We selected resistant mutants in vitro at a frequency of 5 x 10(-9). Clarithromycin resistant strains of MAC isolated in AIDS patients and beige mice as well as derivatives selected in vitro had a unique pattern of acquired cross-resistance to macrolides and related antibiotics. In contrast, the pattern of resistance to non-macrolide antibiotics remained unchanged in clarithromycin resistant strains. A dramatic decrease in ribosome affinity for clarithromycin and erythromycin was found in clarithromycin resistant strains, but no mutation was found in the peptidyl domain of the 23S rRNA, indicating that another ribosomal modification is involved.