Drug-drug interaction of acetaminophen and roxithromycin with the cocktail of cytochrome P450 and hepatotoxicity in rats.

Acetaminophen (APAP) and roxithromycin (ROX) are often used in combination in clinical practice. To evaluate their drug-drug interactions (DDIs) and the hepatotoxicity of co-administration, rats were randomly separated into four groups: Control, APAP (50 mg/kg), ROX (5.5 mg/kg) and APAP-ROX (50 mg/kg and 5.5 mg/kg, respectively). The pharmacokinetic parameters between APAP and ROX were assayed by HPLC, and a cocktail method was used to evaluate the activities of cytochrome (CYP) 450. The liver microsome CYP2E1 protein was detected using Western blot. The levels of plasma parameters, mRNA levels of inflammatory factors (TNF-α, INF-γ, VCAM-1, CXCL-1 and STAT-3) and antioxidant factors (Nrf-2, GSTA, GCLC-1, HO-1 and NQO1) were determined using real-time PCR, along with the observation on histopathological changes in the liver tissue. APAP and ROX co-treatment significantly increased CYP2E1 activity, decreased CYP2D6 activity and prolonged APAP and ROX clearance. Co-treatment increased mRNA expressions of TNF-α, NQO1 and MDA while decreasing GPX and SOD levels. Histopathological evidence showed the changes of liver tissues in terms of structure, size and tight arrangement. This study confirmed that a combination of APAP and ROX inhibited APAP metabolism and that the peak concentration of ROX was delayed. The resulting high level of CYP2E1 may induce oxidative stress and cause liver damage.

Synthesis of 99m Tc-roxithromycin: A novel diagnostic agent to discriminate between septic and aseptic inflammation.

Roxithromycin is a second-generation macrolide antibiotic derived from erythromycin. In the current study, roxithromycin (ROX) was successfully labeled with technetium-99m for early diagnosis of bacterial infection and discrimination between septic and aseptic inflammation. The highest radiochemical purity of ≥95% was achieved by investigating different labeling parameters such as pH, ligand/reducing agent concentration, temperature, and amount of stabilizing agent. For this purpose, 0.3-0.5 mg ligand, 2-6 µg SnCl2 ·2H2 O as a reducing agent at basic pH (8-10 pH) and 2 mg mannitol used as a stabilizing agent, in the end, 370 MBq 99m Tc added into the reaction vials and incubated for a wide range of temperature (-4 to 65°C). The percent radiochemical purity of 99m Tc-roxithromycin was assessed with the help of the radio-thin-layer chromatography technique. The characterization studies were carried out using electrophoresis and Radio-HPLC techniques as well as saline stability and serum stability studies were also performed. Furthermore, biodistribution study was also performed in an inflamed animal model to discriminate between septic (heat-killed Staphylococcus aureus) and aseptic (turpentine oil) inflammatory lesions. The results were elaborated that 99m Tc-roxithromycin (99m Tc-ROX) was clearly bounded at the septic inflammation site (T/NT ratio of 7.08 ± 1.14) at 30 min postadministration, and maximum accumulation was seen in heart, lungs, liver, stomach, kidneys, and intestine. The results were suggested that 99m Tc-ROX might be used to discriminate between septic and aseptic inflammatory lesions at an early stage.

Stabilization Mechanism of Roxithromycin Tablets Under Gastric pH Conditions.

Macrolide antibiotics are widely used at clinical sites. Clarithromycin (CAM), a 14-membered macrolide antibiotic, was reported to gelate under acidic conditions. Gelation allows oral administration of acid-sensitive CAM without enteric coating by hindering the penetration of gastric fluid into CAM tablets. However, it is unknown whether this phenomenon occurs in other macrolide antibiotics. In this study, we examined the gelation ability of 3 widely used macrolide antibiotics, roxithromycin (RXM), erythromycin A, and azithromycin. The results indicated that not only CAM but also RXM gelated under acidic conditions. Erythromycin A and azithromycin did not gelate under the same conditions. Gelation of RXM delayed the disintegration of the tablet and release of RXM from the tablet. Disintegration and release were also delayed in commercial RXM tablets containing disintegrants. This study showed that 2 of the 4 macrolides gelated, which affects tablet disintegration and dissolution and suggests that this phenomenon might also occur in other macrolides.

Population-based meta-analysis of roxithromycin pharmacokinetics: dosing implications of saturable absorption and protein binding.

Objectives: The macrolide antibiotic roxithromycin has seen widespread clinical use for several decades; however, no population pharmacokinetic analysis has been published. Early studies indicated saturation of protein binding and absorption at doses within the approved range, which may impact pharmacodynamic target attainment since regimens of 150 mg twice daily and 300 mg once daily are used interchangeably in clinical practice. This study aimed to develop a population-based meta-analysis of roxithromycin pharmacokinetics, and utilize this model to inform optimal dosing regimens. Methods: Following an extensive search, roxithromycin pharmacokinetic data were collected or digitized from literature publications. Population pharmacokinetic modelling was undertaken with ADAPT. Dosing simulations were performed to investigate differences in exposure and pharmacodynamic target attainment between dosing regimens. Results: A two-compartment model with saturable absorption described the data ( n = 63); changes in free drug exposure were simulated using a saturable protein binding model. Simulations indicated that a 300 mg daily regimen achieves a 37% and 53% lower total or free AUC ( f AUC), respectively, compared with 150 mg twice daily. These pharmacokinetic differences translated to significantly lower target attainment ( f AUC/MIC ratio >20) with a 300 mg daily regimen at MICs of 0.5 and 1 mg/L (51% and 7%) compared with patients receiving 150 mg twice daily (82% and 54%). Conclusions: Roxithromycin displays saturable absorption and protein binding leading to lower exposure and lower target attainment at MICs ≥0.5 mg/L with widely used once-daily dosing regimens, indicating that twice-daily regimens may be preferable for pathogens less susceptible to roxithromycin.

Comparison of Pharmacokinetics and Tissue Distribution Kinetics of Roxithromycin and Expression of CYP 3A1 between Pregnant Mice and Foetuses.

The roxithromycin, macrolide antibiotics, is recommended for treating mycoplasma infection and has the potential to be administered to pregnant women who are susceptible to the infection. This study compared the pharmacokinetic properties and tissue distribution of roxithromycin among pregnant mice and their foetuses. We also determined the level of CYP3A1, a major enzyme for roxithromycin metabolism, in liver microsomes and investigated the placental transport properties of roxithromycin. Biosamples were collected from female mice at gestational day 17 after a single intragastric administration of roxithromycin. A sensitive and specific liquid chromatography-tandem mass spectroscopy method was developed to detect the drug concentration and to obtain kinetic data. The level of CYP3A1 was significantly lower in foetal liver compared with that in maternal liver according to Western blot data, suggesting a decreased metabolism and prolonged half-life of roxithromycin in the foetus. The tissue distributions of roxithromycin were similar between mother and foetus, indicating that the placental barrier did not block the transport of roxithromycin from mother to foetus. The current findings are consistent with the clinical efficacy of roxithromycin in both pregnant mothers and foetuses. Based on this study, it is feasible and reasonable to predict the transport properties of other lipophilic drugs during pregnancy.

Uptake, depuration, and bioconcentration of two pharmaceuticals, roxithromycin and propranolol, in Daphnia magna.

The objective of the present study was to investigate the uptake, depuration, and bioconcentration of two pharmaceuticals, roxithromycin (ROX) and propranolol (PRP), in Daphnia magna via aqueous exposure. Additionally, dietary and pH effects on the bioconcentration of two pharmaceuticals in daphnia were studied. During the 24-h uptake phase followed by the 24-h depuration phase, the uptake rate constants (k(u)) of ROX for daphnia were 9.21 and 2.77 L kg(-1) h(-1), corresponding to the exposure concentrations of 5 and 100 µg L(-1), respectively; For PRP at the nominal concentrations of 5 and 100 µg L(-1), k(u) were 2.29 and 0.99 L kg(-1) h(-1), respectively. The depuration rate constants (k(d)) of ROX in daphnia, at the exposure concentrations of 5 and 100 µg L(-1), were 0.0985 and 0.207 h(-1), respectively; while those of PRP were 0.0276 and 0.0539 h(-1) for the nominal concentrations of 5 and 100 µg L(-1), respectively. With the decreasing exposure concentrations, the bioconcentration factors (BCFs) in daphnia ranged from 13.4 to 93.5 L kg(-1) for ROX, and 18.4 to 83.0 L kg(-1) for PRP, revealing the considerable accumulation potential of these two pharmaceuticals. Moreover, after 6h exposure, the body burdens of ROX and PRP in dead daphnia were 4.98-6.14 and 7.42-12.9 times higher than those in living daphnia, respectively, implying that body surface sorption dominates the bioconcentration of the two pharmaceuticals in daphnia. In addition, the presence of algal food in the media could significantly elevate the kd values for both ROX and PRP, thereby restraining their bioconcentration in daphnia. A pH-dependent bioconcentration study revealed that the bioconcentration of the two pharmaceuticals in daphnia increased with increasing pH levels, which ranged from 7 to 9. Finally, a model was developed to estimate the relationships between pH and the BCFs of the two pharmaceuticals in zooplankton. The predicted values based on this model were highly consistent with wildlife monitoring data, implying that this model will be useful in identifying the bioaccumulation risks that pharmaceuticals pose to zooplankton.

Removal of pharmaceutically active compounds (PhACs) and toxicological response of Cyperus alternifolius exposed to PhACs in microcosm constructed wetlands.

This study investigated the effects of selected four pharmaceutically active compounds (PhACs) (carbamazepine, sulfamethoxazole, ofloxacin, and roxithromycin) on the photosynthesis and antioxidant enzymes of Cyperus alternifolius in constructed wetlands (CWs). Moreover, the removal and kinetics of PhACs in CWs were evaluated to explore the related removal mechanisms. Results showed that C. alternifolius can uptake and withstand certain PhACs. The PhAC tolerance of C. alternifolius might be attributed to their capacity to maintain relatively normal photosynthetic activity and elevated antioxidative defense. CWs offered comparable or even higher removal efficiencies for the selected PhACs compared with conventional WWTPs. The removal of the target PhACs was enhanced in the planted CWs versus the unplanted CWs mostly because of plant uptake and rhizosphere effects. In particular, carbamazepine, which is considered the most recalcitrant of the PhACs, was significantly reduced (p<0.05). The removal of target PhACs fitted into two distinct periods. The initial fast step (within the first 2 h) was essentially attributed to the adsorption onto the CW medium surface. The subsequent slow process (2-12 h) closely followed first-order kinetics probably because of the interaction between microorganisms and plants. The obtained results indicate that C. alternifolius can phytoremediate PhAC-contaminated waters in CWs.

Roxithromycin-loaded lipid nanoparticles for follicular targeting.

Particulate drug carriers e.g. nanoparticles (NPs) have been shown to penetrate and accumulate preferentially in skin hair follicles creating high local concentration of a drug. In order to develop such a follicle targeting system we obtained and characterized solid lipid nanoparticles (SLN) loaded with roxithromycin (ROX). The mean particle size (172±2 nm), polydisperisty index (0.237±0.007), zeta potential (-31.68±3.10 mV) and incorporation efficiency (82.1±3.0%) were measured. The long term stability of ROX-loaded SLN suspensions was proved up to 26 weeks. In vitro drug release study was performed using apparatus 4 dialysis adapters. Skin irritation test conducted using the EpiDerm™ tissue model demonstrated no irritation potential for ROX-loaded SLN. Ex vivo human skin penetration studies, employing rhodamine B hexyl ester perchlorate (RBHE) as a fluorescent dye to label the particles, revealed fluorescence deep in the skin, specifically around the hair follicles up to over 1mm depth. The comparison of fluorescence intensities after application of RBHE solution and RBHE-labelled ROX-loaded SLN was done. Then cyanoacrylate follicular biopsies were obtained in vivo and analyzed for ROX content, proving the possibility of penetration to human pilosebaceous units and delivering ROX by using SLN with the size below 200 nm.

Roxithromycin Pharmacokinetics in Hospitalized Geriatric Patients: Oral Administration of Whole Versus Crushed Tablets.

BACKGROUND: Drug administration as tablets to debilitated elderly patients in crushed form can modify the pharmacokinetic characteristics of the active components. Only scarce information is available on the pharmacokinetics when administered in such form. The aim of this study was to evaluate the pharmacokinetics of roxithromycin administered in crushed form and to compare it with the pharmacokinetics of a group of geriatric patients receiving it in the conventional tablet form. METHODS: Twenty patients from the acute ward of the Shmuel Harofeh Geriatric Medical Center in stable, clinical, and hemodynamic condition were studied. Patients in group 1 (n = 10) received medications orally in tablet form. Group 2 (n = 10) included age- and disease-matched patients from the same department, who received oral roxithromycin in crushed tablet form. The mean daily dose was the same in both groups: 300 mg (150 mg twice daily). The patients received the drug for 3 days before the initiation of the study. Blood samples for determination of the roxithromycin concentration were taken at the baseline, 1 hour before the drug administration, and at 1, 3, 4, 6, 8, and 10 hours after drug administration. Roxithromycin concentration was measured by a liquid chromatography-tandem mass spectrometry method. RESULTS: Pharmacokinetic parameters of roxithromycin were significantly different between the 2 groups: the Cmin and Cmax were significantly higher, the tmax significantly longer, AUC0-10 larger, and CL/F smaller in group 2. CONCLUSIONS: Roxithromycin pharmacokinetic parameters were significantly different between the 2 patient groups resulting in higher drug serum concentrations in the crushed tablets group. The impact of the increased drug exposure is unclear.

Study of pharmacokinetic interaction of paroxetine and roxithromycin on bencycloquidium bromide in healthy subjects.

PURPOSE: The aim of this study was to investigate the potential drug-drug interaction between Bencycloquidium bromide (BCQB) and paroxetine, and between BCQB and roxithromycin. METHODS: Two studies were conducted on healthy male Chinese volunteers. Study A was an open-label, two-period, one-sequence crossover study (n=21). Each participant received a single nasal spray dose of BCQB 180µg on day 1. After a 7-day wash-out period, subjects received 20mg of paroxetine from day 8 to 17, and were co-administered 20mg of paroxetine and BCQB 180µg on day 18. In study B, participants (n=12) were randomly assigned to two groups. In period I, group A received BCQB 180µg on day 1, followed by the same dose four times daily from day 4 to 10, then, on day 11 a single dose of 150mg roxithromycin with BCQB 180µg were co-administered. In parallel, group B received a single dose of roxithromycin 150mg on day 1, followed by 300mg of roxithromycin from day 4 to 10, then, on day 11 a single dose of BCQB 180µg with roxithromycin 300mg were co-administered. After a wash-out time of 7days the respective treatments of each group (A and B) were swapped in period II. Blood samples were collected for pharmacokinetic analysis. Statistical comparison of pharmacokinetic parameters was performed to identify a possible drug interaction between treatments. Tolerability was evaluated by recording adverse events. RESULTS: Study A: Geometric mean AUC0-36 for BCQB alone and co-administered with paroxetine were 474.3 and 631.3pgh/ml, respectively. The geometric mean ratio (GMR) of AUC0-36 was 1.33 (1.13-1.46), 90% C.Is, and was out the predefined bioequivalence interval (90% C.Is, 0.80-1.25). Geometric mean Cmax were 187.0 and 181.2pg/ml. Study B: The GMR of AUC0-36 was 0.98 (0.90-1.07), 90% C.Is for BCQB, and the GMR of AUC0-72 was 0.98 (0.87-1.11), 90% C.Is for roxithromycin. Both GMRs were within the predefined bioequivalence interval (90% C.Is, 0.80-1.25). Other pharmacokinetic parameters were within the predefined interval. No serious adverse events were reported and no significant clinical changes were observed in laboratory test results, vital signs and ECGs in any of the studies. All treatments were well tolerated. CONCLUSION: The co-administration of BCQB with paroxetine showed a moderate increase in BCQB exposure, but was not clinically relevant. Also, no drug interaction was found between BCQB and roxithromycin.

Decrease in gastrointestinal absorption of roxithromycin in bile duct cannulated rats due to depletion of bile salts.

The purpose of this study was to investigate the effect of bile salts on gastrointestinal absorption and the plasma second peak phenomenon of roxithromycin in rats. The pharmacokinetic parameters of roxithromycin were calculated after single oral administration at a dose of 20 mg/kg in sham-operated (control), bile duct cannulated (BDC) and bile salt co-administered bile duct cannulated (BSBDC) rats. In BDC rats, the total area under the plasma concentration-time curve from time zero to time infinity (AUC0-∞) and the peak plasma concentration (Cmax) were significantly smaller (0.572-fold) and lower (0.412-fold), respectively, than those in the control rats. These values were recovered by co-administration of bile salt (0.831- and 0.828-fold for AUC0-∞ and Cmax compared with the control, respectively). Thus, the decreased absorption of roxithromycin in BDC rats could be due to a depletion of bile. The solubility of roxithromycin was 3.09-fold increased at 30 mm of sodium taurocholate. The oral dosage regimen of roxithromycin could be changed in patients with bile deficiency or when the drug is administered to individuals on a high-fat diet, if the present rat data can be extrapolated to humans.

Investigating the barriers to bioavailability of macrolide antibiotics in the rat.

The aim of this study was to compare the roles of gastrointestinal absorption and hepatic extraction as barriers to oral bioavailability for macrolide antibiotics erythromycin, clarithromycin, roxithromycin and telithromycin. In this study, the in vitro metabolic stability in rat liver microsomes and hepatocytes, as well as the in vivo pharmacokinetics in rats were determined following intravenous, intraportal, oral and intraduodenal routes of administration. Pharmacokinetic parameters were calculated for each compound for each route of administration. In vitro metabolic stability studies point to low intrinsic clearance of the tested macrolides in both microsomes (<1 mL/min/g) and hepatocytes (<1 mL/min/g), indicating good stability. The oral bioavailability in rat was low to moderate (14, 36, 36 and 25% for erythromycin, clarithromycin, roxithromycin and telithromycin, respectively). Upon intraduodenal dosing, the bioavailability increased by 1.3-3-fold, the highest increase being with roxithromycin, suggesting some loss due to gastric instability. Following portal vein administration, no hepatic first pass effect was observed with roxithromycin, less than 10% with telithromycin, and ca. 20 and 25% for clarithromycin and erythromycin. Our data showed that the tested macrolides display good in vitro metabolic stability, as was confirmed in vivo where a low hepatic first pass effect was observed. The limited oral bioavailability is likely due to poor oral absorption and/or intestinal first pass metabolism.

Pharmacokinetics of tulathromycin and its metabolite in swine administered with an intravenous bolus injection and a single gavage.

Tulathromycin is a macrolide antimicrobial agent proposed for therapeutic use in treatment of porcine and bovine respiratory disease. In this study, the absolute bioavailability of tulathromycin solution was investigated in pigs. Eight pigs, with body weight of 20.5 ± 1.6 kg, were given a single dose of tulathromycin at 2.5 mg/kg oral (p.o.) and intravenous (i.v.) in a crossover design. The plasma concentrations of tulathromycin and its metabolite were determined by LC-MS/MS method, and the pharmacokinetic parameters of tulathromycin were calculated by noncompartmental analysis. After p.o. administration, the maximum plasma concentration (C(max) ) was 0.20 ± 0.05 µg/mL at 3.75 ± 0.71 h. The terminal half-life (t(1/2λz) ) in plasma was 78.7 ± 6.75 h, and plasma clearance (Cl/F) was 1.14 ± 0.28 L/h/kg. After i.v. injection, plasma clearance (Cl) was 0.580 ± 0.170 L/h/kg, the volume of distribution (Vz) was 64.3 ± 21.2 L/kg, and the t(1/2λz) was 76.5 ± 13.4 h. In conclusion, an analytical method for the quantification of tulathromycin and its metabolite in plasma in swine was developed and validated. Following p.o. administration to pigs at 2.5 mg/kg b.w., tulathromycin was rapidly absorbed and the systemic bioavailability was 51.1 ± 10.2.

An alternative liquid chromatography-mass spectrometric method for the determination of azithromycin in human plasma and its application to pharmacokinetic study of patients with malaria.

A simple, sensitive, selective and reproducible method based on high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/MS) was developed for the determination of a macrolide antibiotic azithromycin in human plasma. The internal standard (roxithromycin) was separated from azithromycin on a Hypersil Gold C18 column, with retention times of 10.71 and 13.67 minutes, respectively. The mobile phase consisted of a mixture of 20 mM ammonium acetate buffer (pH 5.2), acetonitrile and methanol (50:40:10, v/ v/v), running through the column at a flow rate of 0.3 ml/minute. Chromatographic analysis was carried out at 25 degrees C. Sample preparation was by liquid-liquid extraction with a mixture of 7:3 (v/v) diethylether:dichloromethane. The precision of the method based on within-day repeatability and reproducibility (day-to-day variation) was below 5% (% coefficient of variations: % CV). Good accuracy was observed for both intra-day and inter-day assays. The limit of quantification was acceptable at 0.5 ng using 200 microl plasma samples. The mean recoveries for azithromycin and the internal standard were greater than 85%. The method was applied successfully to the investigation of the pharmacokinetics of azithromycin when given in combination with fosmidomycin as oral doses of 750 mg twelve hourly for 3 days in 5 Thai male patients with acute uncomplicated falciparum malaria.

[Pharmacokinetics and relative bioavailability study of roxithromycin tablet in Chinese healthy volunteers by LC-MS/MS].

This is a study of assessing the comparative bioavailability of roxithromycin produced by two companies in 36 healthy volunteers. On the basis of informed consent, 36 healthy male volunteers received each medicine at the roxithromycin dose of 150mg in a cross-over study. There was a 1-week washout period among the doses. Plasma concentrations of roxithromycin were monitored by an LC-MS/MS for over a period of 72 hours after administration. In this study, roxithromycin was generally well tolerated. After an oral administration of roxithromycin capsule, the pharmacokinetic parameters of roxithromycin, such as AUC(0-72 h) (66 076 microg x L x h(-1) and 70 334 microg x L x h(-1) for test and reference capsule, respectively) and AUC(0-infinity) (68 153 microg x L x h(-1) and 72 362 microg x L x h(-1)) were significantly similar. For test and reference capsule, the values of C(max) were 6 631.5 microg x L(-1) and 7 033.9 microg x L(-1) respectively, of T1/2 were 15.39 +/- 4.61 h and 16.06 +/- 5.56 h, and of T(max) were 1.3 +/- 0.9 h and 1.4 +/- 0.7 h respectively. The relative bioavailability F was 94.9% +/- 22.4% of tested formulation. The values of 90% confidence interval around the ratios (test/reference) (obtained by analysis of variance, ANOVA) were 88.3%-101.2% for C(max), 86.2%-98.9% for AUC(0-72) h, being within the predefined acceptable range for the conclusion of bioequivalence. The results of statistical analysis suggest that the two formulations be bioequivalent.

Validation of a fully automated high throughput liquid chromatographic/tandem mass spectrometric method for roxithromycin quantification in human plasma. Application to a bioequivalence study.

A fully automated high-throughput liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed for the determination of roxithromycin in human plasma. The plasma samples were treated by liquid-liquid extraction (LLE) in 2.2 mL 96-deep-well plates. Roxithromycin and the internal standard clarithromycin were extracted from 100 microL of human plasma by LLE, using methyl t-butyl ether as the organic solvent. All liquid transfer steps were performed automatically using robotic liquid handling workstations. After vortexing, centrifugation and freezing, the supernatant organic solvent was evaporated and reconstituted. Sample analysis was performed by reversed-phase LC-MS/MS, with positive ion electrospray ionization, using multiple-reaction monitoring. The method had a very short chromatographic run time of 1.6 min. The calibration curve was linear for the range of concentrations 50.0-20.0x10(3) ng mL(-1). The proposed method was fully validated and it was proven to be selective, accurate, precise, reproducible and suitable for the determination of roxithromycin in human plasma. Therefore, it was applied to the rapid and reliable determination of roxithromycin in a bioequivalence study after per os administration of 300 mg tablet formulations of roxithromycin.

[Relative bioavailability of roxithromycin dispersive tablets in healthy volunteers].

The relative bioavailability of roxithromycin dispersive tablet in healthy volunteers was evaluated in this study. Its concentration in plasma was detected by high performance liquid chromatography (HPLC) after twenty healthy male volunteers were given each a single dose of 300 mg roxithromycin. The experiment data were obtained using DAS programme. The values of Cmax were 10.16+/-1.46 and 10.34+/-1.66 microg x ml(-1) at 2.33+/-0.61 and 2.28+/-0.62 h respectively; of t1/2 were 9.00+/-1.58 and 8.68+/-1.66 h respectively; of AUC0-->Tn were 143.32 +/-25. 80 and 138.93+/-22. 49 microg x h x ml(-1) respectively; of AUC0-->infinity were 158.63+/-26.86 and 153.77+/-24.75 microg x h x ml(-1) for test and reference drugs. Relative bioavailability of the tested roxithromycin was 103.63%+/-14.04%. The result showed that the two dispersive tablets are bioequivalent.

Simultaneous determination and pharmacokinetic study of roxithromycin and ambroxol hydrochloride in human plasma by LC-MS/MS.

BACKGROUND: Although roxithromycin and ambroxol HCl were often administered concomitantly for the treatment of respiratory infections, the pharmacokinetic interactions between them have not been reported. We investigated the interactions between these drugs in health male Chinese volunteers by LC-MS/MS in human plasma. METHODS: The pharmacokinetics were studied in 12 healthy male Chinese volunteers after an overnight fast by a single oral dose, 4-way crossover design with a period of 7-day washout. Each subjects was randomized to receive a single oral dose of 1 compound roxithromycin (150 mg) and ambroxol HCl (30 mg) dispersible tablet (test formulation, treatment A), one 150 mg roxithromycin dispersible tablet together with one 30 mg ambroxol HCl tablet (combined reference formulations, treatment B), one 150 mg roxithromycin dispersible tablet (reference formulation I, treatment C), or one 30 mg ambroxol HCl tablet (reference formulation II, treatment D) with 250 ml of water. Venous blood was collected at pre-dose (0 h) and 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 24, 48, 72 h after dosing. The plasma concentrations of roxithromycin and ambroxol HCl were simultaneously determined by using a validated internal standard LC-MS/MS method. RESULTS: No significant differences were observed for the major pharmacokinetic parameters such as C(max), T(max), t(1/2) and AUC of both roxithromycin and ambroxol HCl between different treatments. CONCLUSION: The pharmacokinetics of both roxithromycin and ambroxol HCl are not affected by their concomitant oral administration. Therefore, there are no obvious pharmacokinetic interactions between roxithromycin and ambroxol HCl after oral administration. Roxithromycin and ambroxol HCl dispersible tablets were bioequivalent with reference to the roxithromycin dispersible tablets and ambroxol HCl tablets in combination usage.

Determination of roxithromycin in human plasma by HPLC with fluorescence and UV absorbance detection: application to a pharmacokinetic study.

A selective HPLC method with fluorescence detection for the determination of roxithromycin (ROX) in human plasma was described. After solid-phase extraction (SPE), ROX and erythromycin (internal standard, I.S.) were derivatized by treatment with 9-fluorenylmethyl chloroformate (FMOC-Cl). Optimal resolution of fluorescence derivatives of ROX and I.S. was obtained during one analytical run using reversed phase, C(18) column. The mobile phase was composed of potassium dihydrogenphosphate solution, pH 7.5 and acetonitrile. Fluorescence of the compounds was measured at the maximum excitation, 255 nm and emission, 313 nm, of ROX derivatives. Validation parameters of the method were also established. After SPE, differences in recoveries of ROX and erythromycin from human plasma were observed. The linear range of the standard curve of ROX in plasma was 0.5-10.0 mg/l. The validated method was successfully applied for pharmacokinetic studies of ROX after administration of a single tablet of ROX.

Pharmacokinetic/pharmacodynamic modelling of roxithromycin for the inhibitory effect of tumour necrosis factor-alpha and interleukin-6 production in dogs.

The objective of the present study was to determine and characterize the relationship between the plasma concentration of roxithromycin, and its inhibitory effect on cytokine production, in order to predict its possible clinical relevance. Six healthy beagle dogs received a single intravenous dose of 20-mg roxithromycin per kg body weight. Blood samples were obtained at different time points. The plasma was analysed with respect to roxithromycin, tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). The concentration-effect relationship was explored by modelling the data using two compartmental model and an indirect response model with an E(max) concentration-effect relationship. The estimated pharmacokinetic parameters (geometric mean) were as follows: V(c) = 2.59 l; k(10) = 0.08/h; k(12) = 0.26/h; k(21) = 0.40/h. The pharmacodynamic parameters (geometric mean) for the inhibitory effect on cytokine production induced by heat-killed Staphylococcus aureus (HKSA) were for TNF-alpha (k(in) = 1.42 microg/h; k(out) = 1.10 microg/h; EC(50) > 5.69 mg/l) and for IL-6 (k(in) = 2.31 microg/h; k(out) = 2.04 microg/h; EC(50) = 21.07 mg/l) production, respectively. The inhibitory effect of roxithromycin on production can be adequately described by the indirect response model with an E(max) concentration-effect relationship.