Urinary metabolic markers reflect on hepatic, not intestinal, CYP3A activity in healthy subjects

Intestinal cytochrome P450 3A (CYP3A) plays an important role in oral drug metabolism, but only endogenous metabolic markers for measuring hepatic CYP3A activity were identified. Our study evaluated whether hepatic CYP3A markers reflected intestinal CYP3A activity. An open-label, three-period, six-treatment, one-sequence clinical trial was performed in 16 healthy Korean males. In the control phase, all subjects received a single dose of intravenous (IV) and oral midazolam (1 mg and 5 mg, respectively). Clarithromycin (500 mg) was administered twice daily for 4 days to inhibit hepatic and intestinal CYP3A, and 500 mL of grapefruit juice was given to inhibit intestinal CYP3A. Clarithromycin significantly inhibited total CYP3A activity, and the clearance of IV and apparent clearance of oral midazolam decreased by 0.15- and 0.32-fold, respectively. Grapefruit juice only reduced the apparent clearance of oral midazolam by 0.84-fold, which indicates a slight inhibition of intestinal CYP3A activity. Urinary markers, including 6β-OH-cortisol/cortisol and 6β-OH-cortisone/cortisone, were significantly decreased 0.5-fold after clarithromycin administration but not after grapefruit juice. The fold changes in 6β-OH-cortisol/cortisol and 6β-OH-cortisone/cortisone did not correlate to changes in intestinal availability but did correlate to hepatic availability. In conclusion, endogenous metabolic markers are only useful to measure hepatic, but not intestinal, CYP3A activity.

Assessment of potential interaction between simvastatin and clarithromycin in healthy adult male subjects

Cardiac patients with weak immune system are susceptible to bacterial infections. Their prescriptions frequently contain simvastatin and clarithromycin together. The objective of present project was to assess the potential interaction between simvastatin and clarithromycin by evaluating the clarithromycin effects on the pharmacokinetics of simvastatin in healthy adult male subjects. The study design comprised of two phases, used at interval of one week. In first phase simvastatin 20 mg alone was administered to each volunteer. In second phase, co-administration of simvastatin 20 mg with clarithromycin 250 mg was made under similar specified conditions. Blood samples were collected at specified time intervals. Simvastatin plasma concentrations were analyzed through High Performance Liquid Chromatography with UV detector at 238 nm wavelength. Using one compartment open model, MW/PHARM version 3.02 software program was used by F. Rombut for pharmacokinetic parameters calculation. Clarithromycin co-treatment resulted in 2.3 fold increase in maximum plasma concentration Cmax (from 2.47±0.34 ng.mL^-1 to 5.66±1.18 ng.mL^-1; p<0.05) and 3.9 fold increase in area under time versus concentration curve from 0 to 10 hours AUC_0-10 (from 15.10±3.73 ng.hr.mL^-1 to 58.49±15.73 ng.hr.mL^-1; p<0.05) of simvastatin. These results suggest that co-prescription of simvastatin and clarithromycin should be avoided to minimize the adverse events resulting from high simvastatin concentration, without sacrificing therapeutic worth of simvastatin.

Simultaneous determination of triple therapy for Helicobacter pylori in human plasma by reversed phase chromatography with online wavelength switching

The infection of gastric mucosa by Helicobacter pylori (HP) is an essential cofactor in the aetiology of gastroduodenal ulcer and gastric carcinoma. Because of the bacterial resistance, combination therapy containing omeprazole (OME), tinidazole (TNZ) and clarithromycin (CLA) is commonly used for eradication of HP. However, the simultaneous determination of the triple therapy in human plasma was not reported. A simple, reproducible, and selective HPLC method was developed for the simultaneous determination of the triple therapy mixture used for management of HP infections in human plasma. An HPLC procedure based on a liquid-liquid extraction, enrichment of the analytes and subsequent reversed-phase chromatography with UV detection was used. To enable sensitive and selective detection, the method involved the use of online wavelength switching detection, with two different detection wavelengths; 280nm for detection of OME and TNZ and 210nm for detection of CLA. Separations were performed on C18 analytical column with acetonitrile-10mM phosphate buffer of pH=3.0 at flow rate of 1.0mLmin(-1). The linear ranges in human plasma were 0.05-10μgmL(-1) with correlation coefficients >0.9990. The detection limits in human plasma were 0.02-0.07μgmL(-1). Validation parameters were assessed in compliance with US-FDA guidelines. The method proved to be valuable for the therapeutic drug monitoring after oral administration of triple therapy tablets.

Clarithromycin: Immunomodulatory therapy of experimental sepsis and acute pyelonephritis by Escherichia coli

The potency of clarithromycin as immunomodulator was assessed in an experimental model of sepsis based on acute pyelonephritis by susceptible Escherichia coli. 55 rabbits were utilized; 5 for preliminary pharmacokinetic study and 50 for treatment. The latter were divided into 5 groups of treatment, A: controls; B: clarithromycin pretreatment; C: amikacin pretreatment; D: clarithromycin treatment on presentation of pulmonary oedema; and E; amikacin treatment on presentation of pulmonary oedema. Survival was recorded; tumour necrosis factor-alpha (TNFalpha), and malondialdehyde (MDA) were estimated in serum; activities of caspase-3 in monocyte cytosolic extracts were studied; and bacterial counts made in various organs. Median survival of animals of groups A, B, C, D and E was 1.0, 21.0, 12.5, 2.0 and 5.0 d, respectively. TNFalpha and MDA and monocyte caspase-3 activity of group A increased over time; no increases were detected in groups B and C. Concentrations of MDA and activities of monocytic caspase-3 were decreased after administration of clarithromycin in group D, an effect not occurring in group E. Bacterial load was decreased in renal tissue of group D compared to group A. It is concluded that intravenous clarithromycin might constitute a promising immunomodulator in sepsis even in the advent of pulmonary oedema.

Long-term and per rectum disposition of Clarithromycin in the desert tortoise (Gopherus agassizii)

The macrolide antibiotic clarithromycin (CLARI) has a wide spectrum of activity and efficacy for Mycoplasma species. In addition, CLARI accumulates during re-dosing of Mojave desert tortoises (Gopherus agassizii). Here, we characterized plasma concentrations after a single dose, after 3.5 months of dosing, and after per rectum administration; all doses were 15 mg/kg. After a single dose, the median maximal plasma concentration (Cmax) was 1.69 mg/ml and occurred at a median of 6 h after administration, the estimated elimination half-life was 6.9 h, and the median accumulation index was 10%. Plasma concentrations after long-term dosing showed consistent intraturtle concentrations of at least 2 microg/ml, with 1 turtle showing increasing accumulation of CLARI at all 3 time points and the remaining 5 turtles showing increases by 3.5 mo. Compared with expected Cmax values, the median long-term values were approximately 3 times higher than expected in 4 of 6 turtles and approximately 2/3 of that expected in the remaining 2 turtles. Per rectum dosing caused antibiotic retention below target values. Together, these results support accumulation of CLARI after repeated oral dosing and indicate that stable concentrations are reached long-term. Either cystoenteric recycling of CLARI or large intestinal absorption of bypass CLARI may explain the observed cumulative increases. In addition, twice-weekly CLARI maintains target concentrations over time, and per rectum dosing will require higher doses or increased dose frequency to be successful. Based on this work, pharmacokinetic studies in exotic species should include multidose studies to verify initial kinetic estimates from single-dose trends.

[Clinical analysis of drug interaction between rifampicin and clarithromycin which are used for treating pulmonary Mycobacterium avium complex infection]

PURPOSE

We reviewed the interaction between rifampicin (RFP) and clarithromycin (CAM) during treatment of pulmonary Mycobacterium avium complex infection.

SUBJECTS AND METHODS

The subjects were patients with pulmonary non-tuberculous acid-fast bacillus infection during the period from September 2004 to January 2006 who consented to this study. Drug blood concentrations were compared with the minimum inhibitory concentrations for M. avium isolated from sputum and blood levels of CAM were assessed when the time of administration was changed for RFP.

RESULTS

The blood concentration of CAM showed a marked decrease in all cases (n = 6) when administered together with RFP, but there was no significant difference in the blood concentration of 14-R-hydroxy-clarithromycin (M-5), the active metabolite of CAM. However, the total blood concentration of CAM and M-5 showed a significant fall, similar to the blood concentration of CAM alone. When the blood concentration and bacterial MIC were compared for RFP, the blood concentration exceeded five MIC(s) in six samples as did the CAM+M-5 level in four out of six samples. There was no significant difference in the blood concentration of CAM (n = 5) when the time of RFP administration was altered. CONCLUSION; Because the total blood concentration of CAM+M-5 fell markedly by co-administration of RFP, this might have an influence on the antibacterial effect of CAM. In addition, examination of the administration of RFP and CAM at different times showed that the blood concentration of CAM did not increase and the influence of induction of hepatic drug-metabolizing enzymes by RFP could not be avoided.

[Measurement of rifampicin and clarithromycin in serum by high-performance liquid chromatography with electrochemical detection]

Rifampicin (RFP) induces hepatic drug-metabolizing enzymes, making drug interactions a very important clinical problem. Clarithromycin (CAM) metabolism is reportedly enhanced by induction of hepatic drug-metabolizing enzymes (CYP3A4) by RFP, so that the blood lend of CAM decreases when RFP is administered concurrently. We connected an electrochemical detector to a high-performance liquid chromatograph (HPLC) for simple, rapid, easy measurement of blood concentrations of RFP and CAM. Using samples of patient serum, normal serum, and reference standards, we compared HPLC by an external laboratory and the results of LC/MS/MS analysis with those of this new assay. A strong correlation was seen between our HPLC results and those of the external laboratory in RFP levels (r=0.975, p<0.01). A strong correlation was also seen between results we obtained for CAM with the electrochemical detector in this assay and values measured by LC/MS/MS analysis (r=0.995, p<0.01). Our method enabled simple, rapid measurement of RFP and CAM by connecting the HPLC and electrochemical detector in tandem. This system was used to modulate dosage during combined therapy with RFP and CAM. The therapeutic effect for nontuberculous mycobacteriosis is expected to improve, and our HPLC is expected to be useful for simple, rapid, easy measurement of blood concentrations.

Determination of clarithromycin in human serum by high-performance liquid chromatography after pre-column derivatization with 9-fluorenylmethyl chloroformate: Application to a bioequivalence study

A sensitive liquid chromatographic method for the analysis of clarithromycin, a macrolide antibiotic, in human serum using pre-column derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl) is described. The method involved liquid-liquid extraction of the drug and an internal standard (amantadine) followed by pre-column derivatization of the analytes with FMOC-Cl. A mixture of 0.05 M phosphate buffer containing triethylamine (2 mL L(-1); pH 3.8) and methanol (17:83, v/v) was used as mobile phase and chromatographic separation was achieved on a Shimpack CLC-ODS column. The eluate was monitored by a fluorescence detector with respective excitation and emission wavelengths of 265 and 315 nm. The analytical method was linear over the concentration range of 0.025-10 microg mL(-1) of clarithromycin in human serum with a limit of quantification of 0.025 microg mL(-1). The assay is sensitive enough to measure drug levels obtained in human single dose studies. In the present method, sensitivity and run time of analysis have been improved, and successfully applied in a bioequivalence study of three different clarithromycin preparations in 12 healthy volunteers.

Pulmonary disposition of erythromycin, azithromycin, and clarithromycin in foals

The objectives of the present study were to determine and compare the pulmonary disposition of azithromycin, clarithromycin, and erythromycin in foals. A single dose (10 mg/kg) of azithromycin, clarithromycin, or erythromycin was administered intragastrically to six healthy 1- to 3-month-old foals using an orthogonal design. Activity of the drugs was measured in serum, pulmonary epithelial lining fluid (PELF), and bronchoalveolar lavage (BAL) cells by use of a microbiologic assay. Peak drug activity in PELF was significantly higher in foals treated with clarithromycin (48.96+/-13.26 microg/mL) than in foals treated with azithromycin (10.00+/-7.46 microg/mL). Quantifiable erythromycin activity in PELF was only found in two of six foals. Peak drug activity in BAL cells was not significantly different between azithromycin (49.92+/-26.94 microg/mL) and clarithromycin (74.20+/-45.80 microg/mL) but activity for both drugs was significantly higher than that of erythromycin (1.02+/-1.11 microg/mL). Terminal half-life of azithromycin in serum (25.7+/-15.4 h), PELF (34.8+/-30.9 h), and BAL cells (54.4+/-17.5 h) was significantly longer than that of both clarithromycin and erythromycin. Peak azithromycin and clarithromycin activity was significantly higher in BAL cells, followed by PELF, and serum. In contrast, peak erythromycin activity in BAL cells was not significantly different from that of serum.

Determination of clarithromycin in human plasma by liquid chromatography–electrospray ionization tandem mass spectrometry

A rapid and sensitive method has been developed for the determination of clarithromycin in human plasma with liquid chromatography-tandem mass spectrometry. Clarithromycin and the internal standard, telmisartan were precipitated from the matrix (50 microl) with 200 microl acetonitrile and separated by HPLC using formic acid:10 mM ammonium acetate:methanol (1:99:400, v/v/v) as the mobile phase. The assay based on detection by electrospray positive ionization mass spectrometry in the multiple-reaction monitoring mode was finished within 2.4 min. Linearity was over the concentration range 10-5000 ng/ml with a limit of detection of 0.50 ng/ml. Intra- and inter-day precision measured as relative standard deviation were <3.73% and <9.93%, respectively. The method was applied in a bioequivalence study of two tablet formulations of clarithromycin.

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.

[Preparation and evaluation of clarithromycin emulsion for injection]

AIM

To prepare clarithromycin emulsion and investigate its pharmacokinetics in rats. And to do irritation test of the emulsion.

METHODS

High pressure homogenization method was used to prepare clarithromycin emulsion, and the Nicomp380 machine was used to test the mean particle size and zeta-potential of clarithromycin emulsion. Irritation of emulsion was also evaluated compared with the positive control of clarithromycin solution using rat paw lick test and rabbit ear vein irritation test. Microbiological assay method was used for determining the drug concentration in plasma. Pharmacokinetics of two dosage forms in rats was also studied.

RESULTS

The mean particle size and zeta potential of clarithromycin emulsion were 156 nm and -31.8 mV, respectively. The emulsion was stable during the storage time at 4 degrees C for 6 month. The pain caused by emulsion reduced significantly compared with that of clarithromycin solution based on the results of rat paw lick test and rabbit ear vein test. The drug concentration-time curves of clarithromycin emulsion and clarithromycin solution were similar and could be described by two compartment model. AUC(0-1) of clarithromycin emulsion and clarithromycin solution were (66.76 +/- 16.34) and (59.00 +/- 11.20) microg x h x mL(-1), respectively.

CONCLUSION

Stable emulsion could be prepared using high pressure homogenization method, and irritation caused by i.v. injection could be reduced significantly by using clarithromycin emulsion.

Identification of the time-point which gives a plasma rabeprazole concentration that adequately reflects the area under the concentration-time curve

OBJECTIVE

The purpose of this study is to evaluate whether a simple formula using limited blood samples can predict the area under the plasma rabeprazole concentration-time curve (AUC) in co-administration with CYP inhibitors.

METHODS

A randomized double-blind placebo-controlled crossover study design in three phases was conducted at intervals of 2 weeks. Twenty-one healthy Japanese volunteers, including three CYP2C19 genotype groups, took a single oral 20-mg dose of rabeprazole after three 6-day pretreatments, i.e., clarithromycin 800 mg/day, fluvoxamine 50 mg/day, and placebo. Prediction formulas of the AUC were derived from pharmacokinetics data of 21 subjects in three phases using multiple linear regression analysis. Ten blood samples were collected over 24 h to calculate AUC. Plasma concentrations of rabeprazole was measured by an HPLC-assay (l.l.q.=1 ng/ml).

RESULTS

The AUC was based on all the data sets (n=63). The linear regression using two points (C3 and C6) could predict AUC(0-infinity) precisely, irrespective of CYP2C19 genotypes and CYP inhibitors (AUC(0-infinity)=1.39xC3+7.17xC6+344.14, r (2)=0.825, p<0.001).

CONCLUSION

The present study demonstrated that the AUC of rabeprazole can be estimated by the simple formula using two-point concentrations. This formula can be more accurate for the prediction of AUC estimation than that reflected by CYP2C19 genotypes without any determination, even if there are significant differences for the CYP2C19 genotypes. Therefore, this prediction formula might be useful to evaluate whether CYP2C19 genotypes really reflects the curative effect of rabeprazole.

Studies on drug interactions between esomeprazole, amoxicillin and clarithromycin in healthy subjects

OBJECTIVE

A combination of esomeprazole, amoxicillin and clarithromycin may be used for Helicobacter pylori eradication. We explored the potential for interactions between these drugs.

METHODS

In 2 randomized, 4-way crossover studies, healthy CYP2C19 extensive metabolizers (EMs) received esomeprazole 40 mg once daily (n = 20) or 20 mg twice daily (b.i.d.) (n = 20), clarithromycin 500 mg b.i.d., amoxicillin 1 g b.i.d. or the combination of the 3 drugs for 7 days. In a third randomized, 2-way, crossover study, 6 healthy CYP2C 19 poor metabolizers (PMs) received esomeprazole 40 mg once daily with and without clarithromycin 500 mg b.i.d. for 1 week.

RESULTS

Triple therapy with esomeprazole 40 mg increased the area under the plasma concentration-time curve during the dosing interval (AUCtau) from 13.31 micromol x h/l (11.12-15.93) for esomeprazole alone to 22.69 micromol x h/l (18.94-27.17) for triple treatment. Respective AUCtau values with esomeprazole 20 mg b.i.d. were 4.97 micromol.h/l (3.97-6.21) and 11.29 micromol x h/l (9.03-14.12). Clarithromycin and amoxicillin plasma levels were largely unchanged by combination therapy. In PMs, the esomeprazole AUC also approximately doubled when administered in combination with clarithromycin. All treatments were well tolerated.

CONCLUSION

Clarithromycin decreases the metabolism rate of esomeprazole, leading to approximately doubled AUC values, both in EMs and PMs.

Clarithromycin is an effective immunomodulator in experimental pyelonephritis caused by pan-resistant Klebsiella pneumoniae

OBJECTIVES

To apply clarithromycin as an immunomodulatory treatment in experimental infection caused by pan-resistant Klebsiella pneumoniae.

METHODS

Acute pyelonephritis was induced in 80 rabbits after inoculation of the test isolate in the renal pelvis. Rabbits were divided into eight groups, with 10 animals in each group. In groups A-D, therapy was administered simultaneously with bacterial challenge as follows: A, controls; B, intravenous clarithromycin; C, amikacin; and D, both agents. In groups E-H, therapy was administered 24 h after bacterial challenge as follows: E, controls; F, intravenous clarithromycin; G, amikacin; and H, both agents. Blood was sampled for estimation of tumour necrosis factor-alpha (TNF-alpha) and malondialdehyde (MDA); monocytes were isolated for determination of intracellular activity of caspase-3 and ex vivo TNF-alpha secretion. Four days after bacterial challenge, animals were sacrificed for quantitative cultures and biopsies of organs.

RESULTS

Serum TNF-alpha at 48 h was lower in groups B, C and D compared with group A. Activity of caspase-3 of monocytes was lower at 48 h in group D compared with group A. Bacterial loads of liver and spleen were decreased in group D compared with those of group A. The numbers of inflammatory cells of spleen of group B were lower compared with those of group A; those of kidney and mesenteric lymph nodes of group D were lower than those of group A. Serum MDA of group H was lower than that of group E and serum TNF-alpha of group F was lower compared with that of group E. TNF-alpha of monocyte supernatants and activity of caspase-3 of monocytes of group F were lower than those of group E. Bacterial tissue loads did not differ among groups E, F, G and H. The numbers of inflammatory cells of liver of groups F and H were lower compared with those of group E; those of kidney of groups F, G and H were lower compared with those of group E.

CONCLUSIONS

Clarithromycin administered intravenously in experimental infection caused by pan-resistant K. pneumoniae attenuated systemic inflammatory response and local tissue damage. This effect is probably attributed to immunomodulatory intervention on blood monocytes.

Liquid chromatographic-electrospray tandem mass spectrometric determination of clarithromycin in human plasma

A rapid, sensitive and specific LC-MS-MS method has been developed for the determination of clarithromycin (CLA) in human plasma using roxithromycin (ROX) as the internal standard. Samples were prepared via liquid-liquid extraction with methyl tert-butyl ether (MTBE) and chromatographed on a Supelco RP(18) (4.6 x 50 mm, 3 microm particle size) column with a mobile phase consisting of acetonitrile:methanol:60 mM (pH 3.5) ammonium acetate buffer (32.5:32.5:35) at a constant flow rate of 0.8 mL/min. The run time was 3 min with retention times of approximately 1.65 and 1.70 min for CLA and ROX, respectively. Detection was performed on a PE Sciex API 365 mass spectrometer equipped with a turboionspray ionization source in multiple reaction monitoring (MRM) mode. The MRM pairs were m/z 748.5 --> m/z 158.2 for CLA and m/z 837.7 --> m/z 679.3 for ROX, respectively, with dwell times of 200 ms for each transition. The validated calibration curve range was 5.00-5000 ng/mL, based on 0.100 mL plasma sample volume with signal-to-noise ratio (S/N) greater than 60 for CLA at the lower limit of quantification level (5.00 ng/mL). The correlation coefficients (r(2)) of the calibration curves were better than or equal to 0.996. The inter-day (n = 18) precision and accuracy of the quality control (QC) samples were less than 3.58% RSD (relative standard deviation) and -10.8% bias, respectively. The intra-day (n = 6) precision and accuracy of the quality control samples were less than 5.0 and 12.6%, respectively. There was no significant deviation from the nominal values after a 10-fold dilution of high concentration QC samples using blank matrix. The QC samples were stable when left on the bench for 24 h or after three freeze-thaw cycles. The processed samples were also stable in HPLC autosampler at 10C for over 72 h. No matrix ionization suppression was observed when extracted blank matrix or reconstitution solvent was injected onto the system with post-column infusion of clarithromycin and roxithromycin. No carryover was observed when an extracted blank plasma sample was injected immediately after a 5000 ng/mL ULOQ (the upper limit of quantification) standard. The mean recovery was 81.5 and 78.3%, respectively, for clarithromycin and internal standard.

Comparison of clarithromycin and ciprofloxacin therapy for Bacillus anthracis Sterne infection in mice with or without 60Co gamma-photon irradiation

Biological agents and ionizing radiation lead to more severe clinical outcomes than either insult alone. This study investigated the survival of non-irradiated and (60)Co-gamma-irradiated mice given therapy for inhalation anthrax with ciprofloxacin (CIP) or a clinically relevant mixture of clarithromycin (CLR) and its major human microbiologically important metabolite 14-hydroxy clarithromycin (14-OH CLR). All B6D2F1/J 10-week-old female mice were inoculated intratracheally with 3 x 10(8) c.f.u. of Bacillus anthracis Sterne spores 4 days after the non-lethal 7 Gy dose of (60)Co gamma radiation. Twenty-one days of treatment with CLR/14-OH CLR, 150 mg kg(-1) twice daily, or CIP, 16.5 mg kg(-1) twice daily, began 24 h after inoculation. Pharmacokinetics indicate that the area under the curve (AUC) for 14-OH CLR on the concentration-versus-time graph was slightly higher in gamma-irradiated than non-irradiated animals. Neither drug was able to increase survival in gamma-irradiated animals. CIP and CLR/14-OH CLR therapies in non-irradiated animals increased survival from 49 % (17/35 mice) in buffer-treated animals to 94 % (33/35) and 100 %, respectively (P < 0.001). B. anthracis Sterne only was isolated from 25-50 % of treated mice with or without irradiation. Mixed infections with B. anthracis Sterne were present in 50-71 % of gamma-irradiated mice but only in 5-10 % of mice without irradiation.

Comparative bioavailability of clarithromycin formulations in healthy Brazilian volunteers

OBJECTIVE

To compare the bioavailability of clarithromycin 500 mg tablets (Merck S.A Industrias Quimicas, Sao Paulo, SP, Brazil, used as test formulation) and Klaricid (Abbott Laboratórios do Brasil Ltda, Sao Paulo, SP, Brazil, used as reference formulation) in 24 healthy volunteers.

MATERIAL AND METHODS

The study was conducted using an open, randomized, two-period crossover design with one-week interval between doses. Blood samples were collected at pre-dose, 0.33, 0.66, 1, 1.33, 1.66, 2, 2.5, 3, 4, 6, 8, 10, 12, 16, 20 and 24 hours after the administration. AUC was calculated by the trapezoidal rule extrapolation method. Cmax and tmax were compiled from the plasmatic concentration-time data. Analysis of variance was carried out using logarithmically transformed AUC(0-inf), AUC(0-24 h), Cmax and untransformed tmax.

RESULTS

Intraindividual coefficient of variation (CV%) values were 14.25% and 12.62%, respectively for Cmax and AUC(0-24 h). The geometric mean values (+/- SD) for AUC(0-24 h) (microg x h/ml), AUC(0-inf) (microg x h/ml), and Cmax (microg/ml) for test medication were 18.56 (+/- 6.87), 18.8 (+/- 5.70) and 2.45 (+/- 0.88); the obtained values for reference medication were 18.29 (+/- 5.39), 19.10 (+/- 7.21) and 2.5 (+/- 0.69). 90% Cl for clarithromycin geometric mean of AUC(0-24 h), AUC(0-inf) and Cmax ratios (test/reference) were: 93.6-105.9%, 93.8-106.2% and 89- 103.2%. CCONCLUSION The test medication was considered bioequivalent to the reference medication based on the rate and extent of absorption.

Pharmacokinetic interactions between omeprazole/pantoprazole and clarithromycin in health volunteers

The association omeprazole/clarithromycin is of current wide use in the treatment of Helicobacter pylori associated gastroduodenal ulcer. This combination may result in increased levels of omeprazole with potential interactions with commonly associated drugs. Kinetic/metabolic changes occurring after omeprazole/clarithromycin were compared to those occurring after pantoprazole/clarithromycin in healthy volunteers. Eight healthy volunteers, all males, age 25-34 years, all EM for CYP2C19, participated in a randomized, double blind crossover study in two periods of 7 days, separated by a 14-day washout. In each treatment period, subjects took either omeprazole 20mg b.i.d. together with clarithromycin 500 mg b.i.d., or pantoprazole 40 mg b.i.d. with the same dose of the antibiotic. The pharmacokinetic parameters of omeprazole and pantoprazole were compared to those after intake of both agents alone. Kinetics of unchanged clarithromycin was evaluated at the end of the two periods. The mean value of the area under the plasma concentration versus time curve (AUC) of unchanged omeprazole increased almost two-fold after concomitant administration of clarithromycin; the average 5-OH-omeprazole AUC was instead significantly reduced by 42%. Omeprazole clearance and volume of distribution were reduced significantly by 75 and 56%, respectively, after administration of the drug with clarithromicyn. No significant changes of the kinetic of pantoprazole and metabolites were observed. Kinetics of clarithromycin did not differ after the two associated treatments. The administration of clarithromycin with two different proton pump inhibitors indicates that the antibiotic can markedly increase omeprazole, not pantoprazole, levels. This observation may result in a better therapeutic response to omeprazole, but it may also potentially affect either the metabolism of CYP3A4 substrates or interfere with the absorption of drugs requiring an intact gastric digestion system.

Sensitive determination of clarithromycin in human plasma by high-performance liquid chromatography with spectrophotometric detection

A rapid, selective and sensitive high-performance liquid chromatographic method with spectrophotometric detection was developed for the determination of clarithromycin in human plasma. Liquid-liquid extraction of clarithromycin and norverapamil (as internal standard) from plasma samples was performed with n-hexane/1-butanol (98:2, v/v) in alkaline condition followed by back-extraction into diluted acetic acid. Chromatography was carried out using a CN column (250 mm x 4.6 mm, 5 microm) under isocratic elution with acetonitrile-50 mM aqueous sodium dihydrogen phosphate (32:68, v/v), pH 4.5. Detection was made at 205 nm and analyses were run at a flow-rate of 1.0 ml/min at 40 degrees C. The analysis time was less than 11 min. The method was specific and sensitive with a quantification limit of 31.25 ng/ml and a detection limit of 10 ng/ml in plasma. The mean absolute recovery of clarithromycin from plasma was 95.9%, while the intra- and inter-day coefficient of variation and percent error values of the assay method were all less than 9.5%. Linearity was assessed in the range of 31.25-2000 ng/ml in plasma with a correlation coefficient of greater than 0.999. The method was used to analyze several hundred human plasma samples for bioavailability studies.

A comparative clarithromycin bioavailability study: determination of clarithromycin and 14-(R)-hydroxyclarithromycin under fasting and fed conditions

OBJECTIVE

To report the first comprehensive analysis of clarithromycin (CLA) and 14-(R)-hydroxyclarithromcin (14R) bioequivalence metrics under both fasting and fed conditions when using a validated analytical method.

METHODS AND MATERIALS

In separate, single dose bioequivalence studies, fasting (n = 40) and fed (n = 18) non-smoking subjects entered a 2-treatment, 2-period, 2-sequence, crossover trial to assess the comparative bioavailability of a 500 mg generic clarithromycin tablet (IVAX Pharmaceuticals, NJ, USA) relative to the reference product (Biaxin Filmtab, Abbott Laboratories, IL, USA). The validated assay employed an HPLC coupled to a triple stage quadrupole mass spectrometer.

RESULTS

The analytics permitted plasma samples to be measured for both analytes with high precision and a lower limit ofquantitation (LLOQ) of 11 ng/ml. In both fasting and fed studies, and for both analytes, the IVAX product met the common mean geometric ratio and 90% confidence limits in order to be declared bioequivalent with Biaxin Filmtab. Furthermore, the intra-subject variabilities for the comparative AUC metrics in both studies and for both analytes were < or = 21% and < or = 26% for Cmax.

CONCLUSIONS

The fasting and fed results present definitive evidence that 500 mg IVAX clarithromycin and Biaxin Filmtab are bioequivalent under both fasting and fed conditions, whether based on CLA or 14R. Furthermore, at a 500 mg dose, clarithromycin is not a highly variable drug.

The Effect of Clarithromycin on Inflammatory Markers in Chronic Obstructive Pulmonary Disease: Preliminary Data

BACKGROUND:

Clarithromycin is an antimicrobial agent that can be used for treatment of chronic obstructive pulmonary disease (COPD) exacerbations with bronchodilator therapy. However, it has also been shown that clarithromycin has antiinflammatory effects by the inhibition of cytokine production.

OBJECTIVE:

To evaluate the antiinflammatory effect of clarithromycin on serum and sputum interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), and leukotriene B4 levels in patients with COPD.

METHODS:

Thirty men with mild to moderate COPD were enrolled in this prospective, single-center, double-blind, placebo-controlled study. None of the patients was receiving systemic or inhaled corticosteroids during the study. Subjects received either clarithromycin or placebo for 14 days. Before and after this treatment period, spirometric tests and arterial blood gas analysis were performed, blood was drawn for measurement of serum inflammatory markers, and sputum was induced.

RESULTS:

There were no statistically significant differences in baseline clinical or laboratory parameters between the groups. After the treatment, the induced sputum total cell counts, and IL-8 and TNF-α levels decreased significantly in the clarithromycin group compared with pretreatment levels (mean ± SD IL-8 1606 ± 367.3 vs 882 ± 143.6 pg/mL, p = 0.001; TNF-α 638.2 ± 287.5 vs 390 ± 235 pg/mL, p = 0.001). Similarly, decreases in serum inflammatory markers were found in the clarithromycin group while there was no significant change in the placebo group.

CONCLUSIONS:

This study demonstrated that the decrease in IL-8 and TNF-α levels might be related to the antiinflammatory effect of clarithromycin. Thus, we suggest that the use of clarithromycin in COPD exacerbations may either treat the infection or help control the inflammation. Future studies are needed to determine the clinical significance of these findings.

Differential efficacy of clarithromycin in lung versus thigh infection models

BACKGROUND

Differences in clarithromycin disposition and the resulting changes in bacterial density were studied using mouse lung and thigh infection models.

METHODS

Clarithromycin activity was evaluated against seven Streptococcus pneumoniae isolates with efflux-mediated resistance in both murine lung and thigh infection models. Intrapulmonary disposition of clarithromycin was also studied.

RESULTS

Consistent bacterial kill was observed in the lung model, whereas no drug effect was observed in the thigh model.

CONCLUSION

These differences in bacterial density were supported by high concentrations observed in epithelial lining fluid as compared to serum.

Concentration of clarithromycin and 14-R-hydroxy-clarithromycin in plasma of patients with Mycobacterium avium complex infection, before and after the addition of rifampicin

Clarithromycin (CAM) and rifampicin (RFP) have both been recognized to be effective antibiotic agents against Mycobacterium avium complex (MAC) infection. Rifamycin derivatives including RFP and rifabutin modulate the CAM metabolism by inducing the hepatic cytochrome p-450 3A4. To clarify the effect of RFP on the CAM metabolism, we measured the plasma concentration of CAM and 14-R-hydroxyclarithromycin (M-5), the major metabolite of CAM, in 9 patients suffering from MAC infection before and after the addition of RFP. After the addition of RFP, the mean plasma concentration of CAM significantly decreased, while that of M-5 did not. In addition, the amount of CAM + M-5 concentration also significantly decreased. As M-5 is less effective against MAC infection than CAM, more attention should thus be paid to the plasma CAM concentration in patients administered CAM and RFP concomitantly.

Average bioequivalence of generic clarithromycin tablets in healthy Thai male volunteers

The objective of this study was to assess bioequivalence of 500-mg clarithromycin tablets in 24 healthy volunteers. In a randomized, single dose, fasting state, two-period, crossover study design with a 1-week washout period, each subject received a 500-mg clarithromycin tablet. Plasma samples were collected over a 24-h period after administration and were analyzed by using a validated method using high performance liquid chromatography (HPLC) with electrochemical detection. The time to reach the maximal concentration (t(max),h), the peak concentration (C(max),ng/ml) and the area under the curve (AUC(0- infinity),ng h/ml) of the Reference and Test formulations were 2.1+/-0.7 vs 2.1+/-0.7, 2474+/-702 vs 2559+/-744 and 15803+/-6120 vs 17683+/-6650, respectively. Relative bioavailability was 1.12. The 90% confidence interval (90% CI) of C(max) and AUC(0- infinity) were 95.6-110.8% and 3.5-122.0%, respectively. Bioequivalence between the test and reference preparation can be concluded.

Effects of cysteine on the pharmacokinetics of intravenous clarithromycin in rats with protein-calorie malnutrition

Effects of cysteine on the pharmacokinetics of clarithromycin were investigated after intravenous administration of the drug at a dose of 20 mg/kg to control rats (4-week fed on 23% casein diet) and rats with PCM (protein-calorie malnutrition, 4-week fed on 5% casein diet) and PCMC (PCM treated with 250 mg/kg for oral cysteine twice daily during the fourth week). Clarithromycin has been reported to be metabolized via hepatic microsomal cytochrome P450 (CYP) 3A4 to 14-hydroxyclarithromycin (primary metabolite of clarithromycin) in human subjects. It has also been reported that in rats with PCM, CYP3A23 level decreased to 40-50% of control level, but decreased CYP3A23 level in rats with PCM completely returned to control level by oral cysteine supplementation (rats with PCMC). Human CYP3A4 and rat CYP3A23 proteins have 73% homology. In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity, AUC (567, 853 and 558 microg min/ml for control rats and rats with PCM and PCMC, respectively) and percentage of clarithromycin remaining after incubation with liver homogenate (69.6, 83.9 and 71.7%) were significantly greater than those in control rats and rats with PCMC. Moreover, in rats with PCM, the total body clearance, CL (35.3, 23.4 and 35.8 ml/min/kg), nonrenal clearance, CL(NR) (21.3, 15.2 and 24.1 ml/min/kg) and maximum velocity for the disappearance of clarithromycin after incubation with hepatic microsomal fraction, V(max) (351, 211 and 372 pmol/min/mg protein) were significantly slower than those in control rats and rats with PCMC. However, above mentioned each parameter was not significantly different between control rats and rats with PCMC. The above data suggested that metabolism of clarithromycin decreased significantly in rats with PCM as compared to control due to significantly decreased level of CYP3A23 in the rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters of clarithromycin (AUC, CL, CL(NR) and V(max)) were restored fully to control levels because CYP3A23 level was completely returned to control level in rats with PCMC.

Gastric juice, gastric tissue and blood antibiotic concentrations following omeprazole, amoxicillin and clarithromycin triple therapy

BACKGROUND

Amoxicillin and clarithromycin are key antibiotics in proton pump inhibitor-based Helicobacter pylori eradication therapies.

AIMS

To study gastric mucus and tissue concentrations and collect basic data about optimal antibacterial doses.

METHODS

Plasma, gastric mucosa and gastric juice antibiotic concentrations were measured following either low- or high-dose amoxicillin (750 or 1000 mg b.i.d.) and clarithromycin (400 or 500 mg b.i.d.) given in combination with omeprazole 20 mg bid to 12 male volunteers in an open crossover design. Gastric juice and mucosal biopsy collection was performed either 2 (n=6) or 6 hours (n=6) after dosing.

RESULTS

Amoxicillin concentrations 2 hours after high dosage were gastric juice > gastric body > antral mucosa > plasma. At 6 hours, plasma and gastric juice concentrations were still above the MIC for amoxicillin-susceptible bacteria but no antibiotic was detectable in mucosa samples. Clarithromycin concentrations after high dosage were gastric juice > mucosa > serum; all above the MIC for clarithromycin-susceptible bacteria at both 2 and 6 hours.

CONCLUSIONS

Both dosage regimens provided effective antibiotic concentrations in gastric juice at 2 hours. After dosing, both antibiotics demonstrated high gastric tissue concentrations via local diffusion while clarithromycin also provided sustained delivery (6 hours) via gastric mucosa penetration.

Average bioequivalence study of clarithromycin tablets in healthy male volunteers

OBJECTIVE

To evaluate the average bioequivalence of two formulations of 500 mg clarithromycin tablets in 24 healthy Thai male volunteers.

METHODS

In a randomized, single dose, fasting state, two-period, crossover study design with a 1-week washout period, each subject received a 500 mg clarithromycin tablet. Plasma samples were collected over a 24-h period after administration and were analysed by using a validated HPLC-ECD method. Pharmacokinetic parameters were determined by using non-compartmental analysis.

RESULTS

The time to reach the maximal concentration (tmax, h), the peak concentration (Cmax, ng/mL) and the area under the curve (AUC0- infinity, ng h/mL) of the Reference and Test formulations were 2.0 +/- 0.9 vs. 1.8 +/- 1.1, 3018 +/- 841 vs. 3014 +/- 752 and 23142 +/- 7348 vs. 22810 +/- 6027, respectively. The 90% confidence interval of Cmax and AUC0- infinity were 90.6-109.4 and 89.6-110.1%.

CONCLUSION

Bioequivalence between the Test and Reference formulation can be concluded.

Single- and multiple-dose pharmacokinetics of oral moxifloxacin and clarithromycin, and concentrations in serum, saliva and faeces

Moxifloxacin and clarithromycin are important antibacterial drugs in the treatment of community-acquired respiratory tract infections. In a double-blind, randomized, 2-period cross-over study the pharmacokinetics of moxifloxacin versus clarithromycin were determined after single and multiple doses in 12 healthy male volunteers. The concentrations of the antibiotics in serum, saliva and faeces were measured by validated high-performance liquid chromatographic methods. In serum, moxifloxacin exhibited a mean peak concentration of 3.1 +/- 0.6 mg/l after a time to peak concentration of 1.67 +/- 0.96 h on day 1, with a significant increase to 3.98 +/- 1.10 mg/l on day 7 (p < 0.05). The area under the curve-12 revealed a highly significant increase from 28.2 + 4.1 mg*h/l on day 1 to 39.5 +/- 6.6 mg*h/l on day 7 (p < 0.01). There were also significant differences in terminal half-life between day 1 and day 7 [10.6 h (range 9.0-12.8) vs 14.9 h (range 12.6-28.1); p < 0.01] and in mean residence time (15.1 +/- 1.9 vs 18.2 +/- 2.4 h; p < 0.01). The concentrations of moxifloxacin in saliva were well equilibrated with serum at a relatively constant saliva-serum ratio of about 0.8. Pharmacokinetic parameters of clarithromycin and its metabolite, 14-hydroxy-clarithromycin, were similar to previously published data. Accumulation was found. No serious adverse events were observed with either study drug.

Quantification of clarithromycin, its 14-hydroxy and decladinose metabolites in rat plasma, gastric juice and gastric tissue using high-performance liquid chromatography with electrochemical detection

A rapid, selective and sensitive HPLC assay has been developed for the simultaneous analysis of clarithromycin, its 14-hydroxy-clarithromycin metabolite, and its decladinose acid degradation product, in small volumes of rat gastric juice aspirate, plasma and gastric tissue. Sample were extracted with n-hexane/2-butanol (4:1) and the internal standard was roxithromycin. A Kromasil ODS 5 micrometer(75x4.6 mm I.D.) column was used with a mobile phase consisting of acetonitrile/aqueous phosphate buffer (pH 7, 0.086 M) (45:55 v/v). The column temperature was 30 degrees C and coulometric detection was used at 850 mV using a screen voltage of 600 mV. The analysis time was less than 8 min. The limits of quantitation for clarithromycin, 14-OH clarithromycin and decladinose clarithromycin were 0.15 microgram ml(-1) or lower in plasma (0.05 ml); 0.16 microgram ml(-1) or lower in gastric juice (0.2 ml); and 0.51 microgram g(-1) or lower for gastric tissue (0.25 g). The method was linear up to at least 20.3, 15.4 and 12.5 microgram ml(-1) for clarithromycin, 14-OH-clarithromycin and decladinose, respectively, in gastric juice aspirate and plasma and up to 40.6, 30.9 and 25.0 microgram g(-1) in gastric tissue. The assay was applied to the measurement of clarithromycin, 14-OH-clarithromycin and, for the first time, decladinose clarithromycin in pharmacokinetic studies of gastric transfer of clarithromycin in individual rats.

Pharmacodynamic modeling of clarithromycin against macrolide-resistant [PCR-positive mef(A) or erm(B)] Streptococcus pneumoniae simulating clinically achievable serum and epithelial lining fluid free-drug concentrations

The association between macrolide resistance mechanisms and clinical outcomes remains understudied. The present study, using an in vitro pharmacodynamic model, assessed clarithromycin (CLR) activity against mef(A)-positive and erm(B)-negative Streptococcus pneumoniae isolates by simulating free-drug concentrations in serum and both total (protein-bound and free) and free drug in epithelial lining fluid (ELF). Five mef(A)-positive and erm(B)-negative strains, one mef(A)-negative and erm(B)-positive strain, and a control [mef(A)-negative and erm(B)-negative] strain of S. pneumoniae were tested. CLR was modeled using a one-compartment model, simulating a dosage of 500 mg, per os, twice a day (in serum, free-drug C(p) maximum of 2 micro g/ml, t(1/2) of 6 h; in ELF, C(ELF(total)) maximum of 35 micro g/ml, t(1/2) of 6 h; C(ELF(free)) maximum of 14 micro g/ml, t(1/2) of 6 h). Starting inocula were 10(6) CFU/ml in Mueller-Hinton broth with 2% lysed horse blood. With sampling at 0, 4, 8, 12, 20, and 24 h, the extent of bacterial killing was assessed. Achieving CLR T/MIC values of > or =90% (AUC(0-24)/MIC ratio, > or =61) resulted in bacterial eradication, while T>MIC values of 40 to 56% (AUC(0-24)/MIC ratios of > or =30.5 to 38) resulted in a 1.2 to 2.0 log(10) CFU/ml decrease at 24 h compared to that for the initial inoculum. CLR T/MIC values of < or =8% (AUC(0-24)/MIC ratio, < or =17.3) resulted in a static effect or bacterial regrowth. The high drug concentrations in ELF that were obtained clinically with CLR may explain the lack of clinical failures with mef(A)-producing S. pneumoniae strains, with MICs up to 8 micro g/ml. However, mef(A) isolates for which MICs are > or =16 micro g/ml along with erm(B) may result in bacteriological failures.

In vivo pharmacodynamic evaluation of clarithromycin in comparison to erythromycin

The efficacy of various dosing regimens of clarithromycin and erythromycin against recently isolated Streptococcus pneumoniae strains was determined in vivo using two animal infection models (mouse peritonitis and thigh infection). For the thigh infection model, mice received a total dose of 4 mg/Kg of either clarithromycin or erythromycin, as a single total dose or divided into 2, 4 or 8 doses/24h. After 24h of therapy S. pneumoniae organisms were killed at 2.06 to 4.03 log10 CFU/thigh by clarithromycin and the one- or two-dose regimens were significantly more effective than the four- or eight-dose regimens. Organism killing following 24h of therapy with erythromycin ranged from 1.13 to 2.31 log10 CFU/thigh, with the one- or two-dose regimens significantly less effective than the four- or eight-dose regimens. In the mouse survival study, the same dose of either clarithromycin or erythromycin was given as a single total dose or divided into two or four doses with dosing intervals of 4 and 2-times the t1/2 respectively. The results obtained in this model show that there is a significant difference in survival when clarithromycin is administered less frequently (4% deaths for the one-dose regimen in comparison to 40% deaths with the four-dose regimen, P < 0.01, Chi-square test). With erythromycin there was a trend for increased survival with the multiple-dose regimen, with significantly higher survival when concentrations exceeding the MIC were maintained for a longer time period. These results indicate that the time during which serum concentrations exceeding the MIC value of the pathogen is an important parameter for efficacy for erythromycin. On the contrary, results with both animal models demonstrate that bacterial killing and survival are significantly higher among clarithromycin-treated mice when the antibiotic is administered less frequently and the highest Cmax/MIC ratio is achieved.

Pharmacokinetics of lansoprazole, amoxicillin and clarithromycin after simultaneous and single administration

In a randomized, double-blind, placebo-controlled, four-way crossover study, possible influences of the triple therapy with amoxicillin, clarithromycin and the proton pump inhibitor lansoprazole on the pharmacokinetics of each of the drugs and the active 14-OH-clarithromycin metabolite were assessed. Twelve Helicobacter pylori-negative healthy male volunteers (age 27 +/- 4.3 years; creatinine clearance 7.0 +/- 2.0 L/h) were given lansoprazole 30 mg, amoxicillin 1 g and clarithromycin 500 mg, alone and in triple combination. Drug elimination intervals were at least 9 days between the dosing periods. The study medication was administered twice daily for 4 days. On the fifth day of each period, drugs were only given once in the morning, and blood and urine samples were collected for 12 h. The concentrations of the three substances administered, and 14-OH-clarithromycin, were determined by validated HPLC methods. Alterations in the serum kinetics were found for lansoprazole and the active 14-OH-clarithromycin metabolite (all data expressed as mean +/- S.D.). For lansoprazole, the elimination half-life (t(1/2)) was significantly prolonged (1.46 versus 1.7 h, P < 0.05) and the area under the concentration-time curve from 0 to 8 h (AUC(0-8)) was significantly increased (3.65 versus 4.59 mg.h/L, P < 0.05) by combination of the drugs. For 14-OH-clarithromycin, the peak concentration (C(max)) was 0.95 versus 1.18 mg/L and the AUC from 0 to 12 h (AUC(0-12)) was 8.3 versus 10.5 mg.h/L (augmented significantly, P < 0.05). The amoxicillin concentrations were slightly elevated by concomitant administration of lansoprazole and clarithromycin but without statistical significance (11.1 versus 12.6 mg/L). For clarithromycin, the time to maximum concentration of drug in serum (T(max)) was increased (2.73 versus 3.31 h, P < 0.05), whereas AUC and C(max) remained unchanged. Simultaneous administration of lansoprazole, amoxicillin and clarithromycin increases the serum concentrations of lansoprazole and the active 14-OH-clarithromycin metabolite significantly. These effects were not so pronounced as to have any therapeutic influence, making dosage adjustment unnecessary.

A prospective study of the clarithromycin-digoxin interaction in elderly patients

The study was a prospective observational trial carried out to assess the clarithromycin-digoxin interaction in elderly patients chronically taking digoxin. Digoxin concentrations were determined before and after concomitant treatment with clarithromycin. A Bayesian approach was used to calculate digoxin pharmacokinetics. In the seven patients who were studied there was a significant increase in digoxin concentration after 4-7 days of clarithromycin treatment; digoxin clearance and elimination rate constant were 56-60% lower and elimination half-life was 82% longer. The pharmacokinetic clarithromycin-digoxin interaction in the elderly may be much more frequent than has been assumed up to now.

Disposition of oral clarithromycin in foals

Clarithromycin offers numerous advantages over erythromycin and thus, is an attractive alternative for the treatment of Rhodococcus equi infections in foals. The disposition of clarithromycin was investigated in 6 foals after intragastric administration at a dose of 10 mg/kg body weight. Detectable serum concentrations of clarithromycin were found in 3 of 6 foals at 10 minutes and in all foals by 20 minutes post-administration. Time to peak serum concentration (Tmax) was 1.5 hours and peak serum concentration (Cmax) was 0.92+/-0.17 microg/ml. Mean serum concentrations decreased to 0.03 microg/ml at 24 h. No adverse reactions were noted during or after IG administration in any of the foals. Based on the pharmacokinetic parameters, the MIC90 of R. equi isolates, and predicted steady state concentrations, an oral dose of 7.5 mg/kg given every 12 hours would appear appropriate for the treatment of R. equi infections in foals.

Influence of clarithromycin on early atherosclerotic lesions after Chlamydia pneumoniae infection in a rabbit model

Chlamydia pneumoniae may play a role in atherogenesis and vascular diseases, and antibiotics may prove useful in these conditions. Three groups of New Zealand White rabbits (24 per group) were infected via the nasopharynx with C. pneumoniae on three separate occasions (2 weeks apart). Group I was untreated and sacrificed at 12 weeks; group II received clarithromycin at 20 mg/kg/day for 8 days, beginning 5 days after each inoculation (early treatment); and group III received a similar dose of clarithromycin starting 2 weeks after the third inoculation and continued for 6 weeks thereafter (delayed treatment). To test for a possible anti-inflammatory effect of clarithromycin, two other groups of uninfected rabbits (12 animals in each) were fed 0.5% cholesterol-enriched chow, and one of these groups was treated with clarithromycin at 30 mg/kg/day for 6 weeks. Of 23 untreated infected rabbits, 8 developed early lesions of atherosclerosis, whereas 2 of the 24 early-treated group II had similar changes (P = 0.036 [75% efficacy]). However, in the delayed-treatment group, group III, 3 of 24 rabbits developed early lesions of atherosclerosis, thus demonstrating 62.5% reduction compared to the untreated controls (P = 0.07 [trend to statistical significance]). C. pneumoniae antigen was detected in 8 of 23 group I (untreated) rabbits versus 1 of 24 of the early-treated (group II) rabbits and 4 of 24 animals in the delayed group III (P = 0.009 and 0.138, respectively). All of the untreated, cholesterol-fed rabbits had moderate to advanced atherosclerosis (grade III or IV); clarithromycin had no effect on reducing the prevalence of but did reduce the extent of atherosclerosis in the cholesterol-fed rabbits by 17% compared to untreated controls. Thus, clarithromycin administration modified C. pneumoniae-induced atherosclerotic lesions and reduced the ability to detect organism in tissue. Early treatment was more effective than delayed treatment.

Serum bactericidal activity of extended-release clarithromycin against macrolide-resistant strains of Streptococcus pneumoniae

STUDY OBJECTIVE

To investigate the serum bactericidal activity (SBA) over time of extended-release clarithromycin against moderately resistant strains of Streptococcus pneumoniae.

DESIGN

Prospective, single-dose pharmacodynamic study.

SETTING

University-affiliated research center.

SUBJECTS

Eleven healthy male volunteers.

INTERVENTION

All volunteers received a single dose of extended-release clarithromycin as two 500-mg tablets, and blood samples were obtained at 0, 2, 6, 12, and 24 hours after administration of the dose.

MEASUREMENTS AND MAIN RESULTS

For each blood sample, a serum bactericidal titer (SBT) was determined against S. pneumoniae strains with minimum inhibitory concentrations (MICs) of 0.5, 1.0, 2.0, 4.0, and 8.0 microg/ml to clarithromycin. The median SBT was determined for each time period. The extended-release formulation of clarithromycin exhibited SBA for 24 hours against pneumococcal strains with MICs of 0.5, 1.0, and 2.0 microg/ml. No SBA was observed against isolates with MICs of 4.0 or 8.0 microg/ml.

CONCLUSION

The extended-release formulation of clarithromycin, taken once/day, will provide SBA for 24 hours against strains of S. pneumoniae with MICs of 2.0 microg/ml or less.

Sensitive liquid chromatography-tandem mass spectrometry method for the determination of clarithromycin in human plasma

A sensitive method for the determination of clarithromycin in plasma is described, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. Samples were prepared using liquid-liquid extraction and separated on a Supelco Discovery C18 column with a mobile phase consisting of acetonitrile, methanol and acetic acid. Detection was performed by a PE SCIEX API 2000 mass spectrometer in the multiple reaction monitoring (MRM) mode (LC-MS-MS) using TurbolonSpray ionization and monitoring the transition of the protonated molecular ion for clarithromycin at m/z 748.5 (M+1) to the predominant product ion of m/z 158.2. The mean recovery of clarithromycin was 87.3%, with a lower limit of quantification of 2.95 ng/ml when using 0.3-ml plasma. This high-throughput method was used to quantify 230 samples per day, and is sufficiently sensitive to be employed in pharmacokinetic studies.

Determination of clarithromycin in human plasma by HPLC with electrochemical detection: validation and application in pharmacokinetic study

A rapid, specific, precise and accurate HPLC method with electrochemical detection was developed and validated for the determination of clarithromycin in human plasma. After addition of the internal standard, the analytes were extracted from plasma under alkaline conditions with ethyl acetate:hexane 1:1. The inter-run precision of the method was less than 4.7%, the inter-run accuracy was better than 97.3% and the recovery of clarithromycin and roxithromycin (internal standard) were better than 82.5% and 86.2%, respectively. The method was found to be suitable for the quantitation of clarithromycin in bioequivalence and pharmacokinetic studies.

Crossover assessment of serum bactericidal activity of grepafloxacin, ofloxacin and clarithromycin against respiratory pathogens after oral administration to healthy volunteers

Serum bactericidal activity was studied in a crossover manner in 10 volunteers, after 2-day administration of grepafloxacin 600 mg qd, ofloxacin 400 mg bid and clarithromycin 500 mg bid. Bactericidal activity against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Klebsiella pneumoniae, was estimated using a standardized microdilution method. Grepafloxacin was highly active against Gram-negative organisms and adequate against pneumococci (mean, 1:13.3). Clarithromycin was very active against both penicillin-susceptible and penicillin-partially-resistant S. pneumoniae (1:102.5) but had poor activity against H. influenzae (1:3.1). Minor adverse effects were commonly associated with grepafloxacin.

Study on the electrochemical detection of the macrolide antibiotics clarithromycin and roxithromycin in reversed-phase high-performance liquid chromatography

The optimal conditions of the amperometric detection of the macrolide antibiotics clarithromycin and roxithromycin were found by cyclic voltammetric studies and HPLC-electrochemical detection responses obtained in different temperatures (25.5-60 degrees C) and different but almost isoelutropic binary, ternary and quaternary mixtures of aqueous buffer (pH 7), methanol, acetonitrile and isopropanol. These conditions were also proved to be applicable for the quantitative detection of clarithromycin in human plasma using roxithromycin as an internal standard and vice versa. It was demonstrated that increased attention has to be paid to eluent composition and column temperature to ensure sensitive and reproducible electrochemical responses as well as regularly shaped peaks for both macrolides tested.

Comparative serum bactericidal activity of clarithromycin and azithromycin against macrolide-sensitive and resistant strains of Streptococcus pneumoniae

The serum pharmacodynamics of clarithromycin and azithromycin were studied against isolates of S. pneumoniae, including efflux resistant (M. phenotype) strains, by analyzing their serum bactericidal activity (SBA) over time. Normal healthy subjects were given a single 500 mg oral dose of these macrolides and serum samples were collected over 12 hrs. Paired isolates with MICs ranging from 0.25 ug/ml to 8.0 ug/ml were analyzed. Prolonged (at least 6 hrs) SBA was observed with clarithromycin for strains with MICs < or = 2.0 ug/ml. No SBA was observed in strains with MICs >or = 4.0 ug/ml. Azithromycin exhibited SBA for at least 6 hrs for strains up to a MIC = 0.5 ug/ml. No SBA was observed for isolates with MICs > or = 1.0 ug/ml. In contrast to azithromycin, clarithromycin exhibited SBA for at least one-half of its normal dosing interval against S. pneumoniae strains well above its current susceptibility breakpoint concentration of 0.25 microg/ml. These findings may have relevance to the ongoing debate as to the appropriate susceptibility breakpoints for the newer macrolides.

Pharmacokinetics and comparative effects of telithromycin (HMR 3647) and clarithromycin on the oropharyngeal and intestinal microflora

The pharmacokinetics in plasma and saliva of a new ketolide, telithromycin (HMR 3647), and the effect on the normal oropharyngeal and intestinal microflora were studied in healthy volunteers and compared with those of clarithromycin. Ten subjects received 800 mg telithromycin perorally once daily and 10 other subjects received 500 mg clarithromycin bid for 10 days. Blood, saliva and faecal specimens were collected at defined intervals before, during and after administration for pharmacokinetic and microbiological analyses. In subjects receiving telithromycin, the mean C:(max), AUC and C:(24) (24 h) in saliva exceeded the values obtained from plasma, while saliva and serum pharmacokinetic parameters were in the same range for the clarithromycin group. The quantitative ecological disturbances in the normal microflora during administration of telithromycin were moderate and comparable to those associated with clarithromycin administration. No overgrowth of yeasts or Clostridium difficile occurred. Emergence of resistant strains was seen in both treatment groups. Administration of both telithromycin and clarithromycin was associated with significant increases in MICs for intestinal Bacteroides isolates, which persisted 2 weeks after discontinuation of treatment. In addition, a significant emergence of highly clarithromycin-resistant alpha-haemolytic streptococci, intestinal enterococci and Enterobacteriaceae was detected at day 10 in the clarithromycin group. In conclusion, administration of telithromycin resulted in high drug levels in saliva, which indicates a good therapeutic profile for throat infections. Telithromycin seems to have a more favourable ecological profile compared with clarithromycin in terms of resistance development in the normal microflora.

Clarithromycin bioequivalence study of two oral formulations in healthy human volunteers

OBJECTIVE

To assess the bioequivalence of two tablet formulations of clarithromycin (Clamicin 500 mg from Medley Indlistria Farmaceutica, Brazil, as the test formulation, and Biaxin 500 mg from Abbott Industries, USA, as the reference formulation).

METHODS

A single 500 mg oral dose of each formulation was administrated in 24 healthy volunteers of both sexes (12 males and 12 females). The study was conducted open, randomized, two-period crossover design with a 7-day interval between doses. The plasma concentrations of clarithromycin were quantified by reversed phase liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS) with positive ion electrospray ionization using multiple reaction monitoring (MRM) method. 14-hydroxyclarithromycin concentration was estimated semiquantitatively as equivalent of clarithromycin/ml. The precision of the method was evaluated using calibration curves and plasma quality control samples. The pharmacokinetic parameters calculated for both compounds included: AUC(0 - 48h), AUC(0 - infinity), Cmax, Cmax/AUC(0 - 48h), Tmax, T1/2 and Ke.

RESULTS

Standard curves of clarithromycin in plasma were linear in the range of 0.05 microg x ml(-1) to 10 microg x ml(-1) (r > 0.999). The limit of quantification was 5 ng/ml. Within- and between-run plasma quality control CV were 5.8% and 15.7%, respectively. Inaccuracy within- and between-runs were 14% and 17%, respectively. 90% CI for clarithromycin geometric mean AUC(0 - 48h), AUC(0 - infinity) and Cmax ratios (test/reference) were: 8.7% - 103.1%, 89.4% - 103.7% and 85.4% - 99.6%, respectively, and for hydroxyclarithomycin were 80.3% - 108.6%, 80.1% - 110.1% and 85.4% - 112.6%, respectively.

CONCLUSION

The method described for the quantification of charithomycin and its main metabolite is accurate and sensitive. Clamicin was considered bio-equivalent to Biaxin based on the rate and extent of absorption. Since these were no significant differences in the bioequivalence determined using the pharmacokinetic parameters of either clarithromycin or 14-hydroxyclarithromycin, we suggest that future bioequivalence trials of this drug may be performed by quantifying clarithromycin only.

Oral absorption of clarithromycin in acute illness and during convalescence in patients with community-acquired pneumonia

STUDY OBJECTIVE

To compare the extent of oral clarithromycin absorption in patients during an illness and in health.

DESIGN

Sequential two-phase prospective study including an acutely ill pneumonia phase (PP) and a subsequent convalescent phase (CP).

STUDY POPULATION

Patients >/= 18 years old with radiographically confirmed community-acquired pneumonia (CAP) who were admitted to the hospital.

METHODS

During both study phases, patients received one single 500-mg dose of oral clarithromycin. Serial blood samples were drawn over a 24-h period in order to characterize the plasma concentration-time curves. Area under the curve from zero to 24 h (AUC(0-24)), maximum plasma concentration (Cmax), and time to maximum concentration (Tmax) were determined for both clarithromycin and its metabolite, 14-hydroxyclarithromycin, and compared between the two phases.

RESULTS

Twelve patients completed both phases of the study. For clarithromycin, there was a significant increase AUC(0-24) (47.37 +/- 8.51 microg/h/mL vs 36.22 +/- 6.09 microg/h/mL) in favor of the PP. There were no significant differences detected with respect to Cmax (4.32 +/- 0.63 microg/mL vs 3.57 +/- 0.46 microg/mL), or Tmax (3.50 +/- 0.50 h vs 2.83 +/- 0.59 h) between PP and CP. For 14-hydroxyclarithromycin, the AUC(0-24) and Cmax were significantly higher (5.84 +/- 1.08 microg/h/mL vs 8.84 +/- 1.92 microg/h/mL; 0.42 +/- 0.08 microg/mL vs 0.76 +/- 0.23 microg/mL) in the CP as compared to the PP. Tmax remained unchanged.

CONCLUSION

The extent of absorption of oral clarithromycin was not diminished during an acute illness with CAP.

The steady-state disposition of indinavir is not altered by the concomitant administration of clarithromycin

STUDY OBJECTIVES

To evaluate the safety and potential pharmacokinetic interaction between indinavir and clarithromycin.

STUDY METHODS

In a randomized, three-period, crossover fashion, 12 healthy adults received the following for 1 week: 800 mg oral indinavir sulfate every 8 hours with placebo, 500 mg oral clarithromycin every 12 hours with placebo, and indinavir sulfate with clarithromycin. Plasma indinavir, clarithromycin, and 14-hydroxyclarithromycin concentrations were determined after the last dose in each treatment period.

RESULTS

Administration of indinavir sulfate with clarithromycin caused a statistically significant increase in four pharmacokinetic parameters: a 58% increase in plasma indinavir concentrations at 8 hours (P = .029), a 47% increase in values for clarithromycin area under the plasma concentration versus time curve from time zero to the last measured concentration [AUC(0-12h); P = .0002], and 49% and 48% decreases in 14-hydroxyclarithromycin AUC(0-12h) and maximum plasma concentration (Cmax) values, respectively (P = .0001 and P = .0001). These effects are not considered to be clinically significant in view of the insignificant effects on the values for indinavir area under the plasma concentration versus time curve from time zero to the last measured concentration [AUC(0-8h)] and Cmax, as well as the safety profile of clarithromycin.

CONCLUSIONS

The combination of indinavir sulfate and clarithromycin is generally well tolerated and can be coadministered without dose adjustment.

Potential interaction between itraconazole and clarithromycin

Three patients negative for human immunodeficiency virus infection were admitted for pulmonary Mycobacterium avium complex (MAC) and aspergillosis infections. They were treated with different drug combinations, but all regimens included clarithromycin for MAC and itraconazole for aspergillosis. All patients experienced an increase in clarithromycin concentrations and clarithromycin: 14-OH-clarithromycin ratio compared with expected range values. They had no clinical side effects. The time course suggested a possible interaction between clarithromycin and itraconazole, presumably through itraconazole's effects on cytochrome P450 3A4 activity. A bidirectional interaction cannot be ruled out. The data suggest that, when necessary, these two drugs can be administered together safely. Further investigation is necessary to determine the extent and clinical consequences of coadministration in humans.

Mononuclear and polymorphonuclear leukocyte dispositions of clarithromycin and azithromycin in AIDS patients requiring Mycobacterium avium complex prophylaxis

The intracellular dispositions of clarithromycin and azithromycin in AIDS patients requiring Mycobacterium avium complex (MAC) prophylaxis were studied. The dispositions of both drugs in mononuclear and polymorphonuclear leukocytes were markedly different. Our data support the proven efficacy of these agents for MAC prophylaxis since clarithromycin and azithromycin displayed sustained intracellular concentrations which exceeded their MICs for MAC throughout the dosing periods.

Human in vivo competitive inhibition of P450 substrates: increased plasma concentrations as a function of hepatic extraction ratio and percent inhibition

The purpose of this note is to posit and discuss the concept of "competitive inhibition potential" (CIP), which is an in vivo index of the ability of a competitive inhibitor to elevate plasma concentrations of drug substrates, when the competitive inhibitor is administered at its usual and customary dose.

Pharmacological considerations in the emergence of resistance

Resistance to macrolides in vitro is increasingly being reported. However, there has been no corresponding increase in clinical failures noted. Lack of clinical failures due to resistance is most likely the result of the high intracellular concentrations that these drugs achieve in phagocytes. In the case of clarithromycin, concentrations in both monocytes and granulocytes fluctuate between peaks of approximately 22-25 mg/l and troughs of approximately 5 mg/l during a standard dosing interval. In contrast, azithromycin attains concentrations of over 60 mg/l in granulocytes and at least 100 mg/l in monocytes. After 7 days, azithromycin concentrations of >32 mg/l are still observed. These data also imply that against pathogens with increasing minimum inhibitory concentrations (MICs), macrolides with relatively lower or less sustained intracellular concentrations will become ineffective clinically much sooner than compounds, such as azithromycin, that concentrate to a high degree and are retained in white blood cells for prolonged periods.