Chemical and biochemical characterization and in vivo safety evaluation of pharmaceuticals in drinking water.

The water constituents that are currently subject to legal control are only a small fraction of the vast number of chemical substances and microorganisms that may occur in both the environment and water resources. The main objective of the present study was to study the health impact resulting from exposure to a mixture of pharmaceuticals that have been detected in tap water at low doses. Analyses of atenolol, caffeine, erythromycin, carbamazepine, and their metabolites in blood, urine, feces, fat tissue, liver, and kidney after exposure to a mixture of these pharmaceuticals in treated drinking water were performed. The effects of this exposure were assessed in rats by measuring biochemical markers of organ injury or dysfunction. Simultaneously, the selected pharmaceuticals were also quantified in both physiological fluids and organ homogenates by liquid chromatography-tandem mass spectrometry (performed in multiple reaction monitoring mode and full scan mode). Following exposure of rats to a concentration of a pharmaceutical which was 10 times higher than the concentration known to be present in tap water, trace levels of some pharmaceuticals and their metabolites were detected in biological samples. This exposure did, however, not lead to significant organ injury or dysfunction. Thus, the authors report an experimental model that can be used to characterize the safety profile of pharmaceuticals in treated drinking water using a multiorgan toxicity approach. Environ Toxicol Chem 2016;35:2674-2682. © 2016 SETAC.

Determination of erythromycin A in rat plasma and urine by high-performance liquid chromatography with chemiluminescence detection using Tris(2,2'-bipyridine)ruthenium(II).

A simple and sensitive method was developed for the determination of erythromycin A (EA), decladinosyl erythromycin A (dClEA) and erythromycin B (EB) in rat plasma and urine by high-performance liquid chromatography with electrogenerated chemiluminescence detection using Tris(2,2'-bipyridine)ruthenium(II). The recovery rates of EA, dClEA and EB were 97, 94 and 85% from rat plasma and 89, 83 and 93% from rat urine, respectively. The calibration curves were linear over the concentration ranges 0.05-5 microg/mL for plasma and 0.5-50 microg/mL for urine. The precision and accuracy for all analytes in rat plasma were < or =9.0 and -6.3-7.2%, and those in urine were < or =9.4% and -6.1-7.6%, respectively. This method proved to be a powerful tool for determination of EA, dClEA and EB concentrations in samples from rats.

Effect of mibefradil on CYP3A4 in vivo.

Mibefradil, a calcium channel blocker, was removed from the market because of adverse drug interactions with coadministered CYP3A4 substrates. This study examined the effect of mibefradil on the activity of hepatic and intestinal CYP3A4 in vivo, employing the erythromycin breath test (EBT) and oral midazolam pharmacokinetics. This was a two-period, single-blind, placebo-controlled crossover study in which 8 male volunteers were randomized to the order of receiving placebo and a single 100-mg oral dose of mibefradil. Oral midazolam was coadministered with intravenous [14C N-methyl] erythromycin 1 hour after mibefradil/placebo administration. The EBT was performed 20 minutes following erythromycin administration. Blood and urine were collected during the 36 hours following probe drug administration for analysis of midazolam pharmacokinetics. Coadministration of mibefradil increased the Cmax of midazolam 3-fold, the AUC 8- to 9-fold, and the t1/2 4-fold. Mibefradil coadministration decreased the amount of exhaled 14CO2 in 6 of 8 subjects, with a mean decrease of 25%. It was concluded that a single oral dose of mibefradil significantly inhibits CYP3A4 in intestine and liver. These data support that adverse drug interactions involving mibefradil reflect inhibition of CYP3A4 in intestine and liver. Also, they suggest that the EBT, while a valid probe of in vivo hepatic CYP3A4 activity, is a single time point measurement and may be less sensitive than oral midazolam pharmacokinetics in detecting CYP3A4 inhibition.

Inhibitory effect of erythromycin on P-glycoprotein-mediated biliary excretion of doxorubicin in rats.

The macrolide antibiotic erythromycin has recently been shown to overcome the resistance to anticancer drugs that results from overexpression of P-glycoprotein. The present study, using erythromycin lactobionic acid as a model drug, investigated the inhibitory effects of erythromycin on the efflux of doxorubicin from P388/ADR cells expressing P-glycoprotein and on the biliary excretion mechanism of doxorubicin in rats, which is primarily mediated by P-glycoprotein. Erythromycin lactobionic acid was found to inhibit the efflux of doxorubicin (5 microM) from P388/ADR cells in a concentration-dependent manner. In rats receiving constant-rate infusion of doxorubicin (30 micrograms/min), both the biliary and renal clearance of this drug dramatically decreased and its plasma concentrations increased after an intravenous injection of erythromycin lactobionic acid (100 mg/kg as erythromycin). These results suggest that erythromycin competitively inhibits P-glycoprotein-mediated biliary and renal excretion of doxorubicin. The effect of erythromycin on the biliary secretion of doxorubicin was also analyzed quantitatively by the competitive inhibition model. The computer-estimated values of Vmax/Km, Km and Ki were 8.79 ml/minute, 0.82 microgram/ml and 0.41 microgram/ml, respectively. The findings of these experiments suggest that the inhibitory effect of erythromycin on the P-glycoprotein-mediated biliary excretion of doxorubicin is competitive and that combination chemotherapy of doxorubicin with erythromycin may induce toxicity as a result of increased plasma concentrations of doxorubicin.

Delivery of erythromycin to subcutaneous tissues in rats by means of a trans-phase delivery system.

Topical administration of antibiotics is associated with reduced risk of systemic side-effects and alteration of gut microflora, and results in higher concentrations of antibiotics at the site of application (and so a lower dose of the drug is required). In conditions such as acne vulgaris, infiltration of the antibiotics into the infected subcutaneous layers is highly desirable. A trans-phase delivery system (TPDS), a mixture of benzyl alcohol, acetone and isopropanol, has been shown to enhance the effective transport of the antibiotic erythromycin across the epidermal barrier and enhance accumulation in the dermis. Two formulations containing N-methyl[14C]erythromycin were compared, a TPDS solution and a propylene glycol solution. They were applied to the dorsal areas of 4-6 week old Fischer rats and tissues were removed for analysis of radioactivity after 2, 4, 8, 12 or 24 h and skin was biopsied and sectioned for autoradiography. The erythromycin dissolved in the TPDS solvent mixture penetrated the stratum corneum and a relatively high concentration was maintained in adjacent tissues for up to 24 h. Penetration was very effective and the erythromycin was detected in significant amounts in the underlying muscle, various organs and later in the urine. In contrast the propylene glycol carrier, probably because of its primarily hydrophilic character, caused the erythromycin to traverse tissue barriers rapidly and appear in the urine. Microautoradiographs qualitatively revealed progressive disappearance of radioactivity from the surface; this correlated with results obtained by direct isotope counting. The route of penetration, in addition to following the interkeratinocyte spaces, seemed to include the perimeter of the pilosebaceous glands and their appendages before diffusion into the capillaries. The propylene glycol solution seemed to traverse the epidermis and the papillary and reticular dermis more rapidly, which might explain its rapid appearance in the urine. These data suggest that the different solutions penetrate the skin by different mechanisms.

Influence of erythromycin pre- and co-treatment on single-dose pharmacokinetics of the HMG-CoA reductase inhibitor cerivastatin.

OBJECTIVE: Cerivastatin is a novel, synthetic, highly potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that effectively reduces serum cholesterol levels at very low doses. It is exclusively cleared from humans via cytochrome P450-mediated biotransformation (demethylation M1; hydroxylation M23) and subsequent biliary/renal excretion of the metabolites. The influence of concomitant administration of erythromycin, a potent CYP3A4 inhibitor, on cerivastatin bioavailability and pharmacokinetics was investigated. METHODS: Twelve healthy young male subjects received single oral doses of 300 microg cerivastatin alone or on the 4th day of a 4-day pre- and co-treatment with erythromycin 500 mg t.i.d. in a randomised, non-blind crossover study. Plasma and urine samples were analysed for cerivastatin and its major metabolites by validated specific high-performance liquid chromatography assays. RESULTS: Cerivastatin was safe and well tolerated. No clinically relevant treatment-emergent changes in laboratory parameters were observed. The pre- and co-treatment with erythromycin 500 mg t.i.d. had a modest influence on cerivastatin clearance, leading to a mean increase in the maximum plasma concentration (Cmax) of 13% and a slightly increased terminal half-life (approximately 10%), resulting in a mean elevation of the area under the curve (AUC) of 21%; time to peak (tmax) remained unchanged. While the mean AUC of the metabolite M1 following the combined dosing was decreased by 60% compared with mono-dosing, the mean AUC of M23 exhibited an increase of approximately 60%. The respective Cmax results paralleled these pronounced effects, whereas the influence on mean terminal half-lives was small (i.e. for M23, an approximate 20% increase) or not observable (i.e. for M1). CONCLUSIONS: Concomitant administration of erythromycin 500 mg t.i.d. affects, to a certain extent, the metabolism of cerivastatin, administered as a single oral dose of 300 microg, resulting in a slightly increased exposure of the parent drug and active metabolites which, however, does not need dose adjustment. In addition, the small increase in cerivastatin half-life does not predict an accumulation beyond steady state. The pharmacokinetic data for the major metabolites suggest that the M1 metabolic pathway is more sensitive to CYP3A4 inhibition than the parallel M23 pathway, supporting recent in vitro findings that further cytochrome P450 isozymes are differently involved in the metabolic pathways of cerivastatin.

Determination of erythromycin in urine and plasma using microbore liquid chromatography with tris(2,2'-bipyridyl)ruthenium(II) electrogenerated chemiluminescence detection.

Erythromycin is determined in both urine and plasma samples using microbore reversed-phase liquid chromatography with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)3(2+)] electrogenerated chemiluminescence (ECL) detection. Ru(bpy)3(2+) is included in the mobile phase thus eliminating band broadening caused by post-column reagent addition. Extra column band broadening is an important concern in microbore liquid chromatography due to the small peak volumes. Erythromycin was studied in both water and biological samples. The detection limit for erythromycin in standards is 0.01 microM or 50 fmol injected with a S/N of 3 and a linear working range that extends four orders of magnitude. Human urine and blood plasma were also studied. Urine samples were diluted and filtered before injection. Ultrafiltration was used to remove protein from blood plasma samples prior to injection. Erythromycin was selectively detected in the body fluid samples without any further sample preparation. The detection limits obtained for erythromycin in urine and plasma are 0.05 and 0.1 microM, respectively, for 5 microl injected on a 150x1 mm I.D. C18 column.

Highly sensitive high-performance liquid chromatographic determination method for a new erythromycin derivative, EM523, and its major metabolites in human plasma and urine using post-column tris(2,2'-bipyridine) ruthenium(III) chemiluminescence detection.

A method for the simultaneous determination of de(N-methyl)-N-ethyl-8,9 -anhydroerythromycin A 6,9-hemiacetal (EM523, I) and its three metabolites in human plasma and urine has been developed using high-performance liquid chromatography (HPLC) with chemiluminescence (CL) detection. Plasma and urine samples spiked with erythromycin as an internal standard were extracted with a mixture of dichloromethane and diethyl ether under alkaline conditions. The organic layer was evaporated under a stream of nitrogen gas. The reconstituted sample was injected into an HPLC apparatus and separated on an ODS column using a gradient elution method. The eluate was reacted on-line with a mixture of tris(2,2'-bipyridine) ruthenium(II) and peroxodisulfate, and the generated CL intensity was detected. Optimization of the CL reaction conditions resulted in a sensitive and stable CL intensity for the determination of I and its metabolites. The recovery of each compound from human plasma and urine, and the sensitivity, linearity, accuracy and precision of the method were satisfactory. The lower limits of quantitation for each compound using 0.2 ml of plasma and 0.1 ml of urine were 1 and 10 ng/ml, respectively. This method has been used for the determination of 1 in samples from clinical trials.

Comparative pharmacokinetics of dirithromycin and erythromycin in normal volunteers with special regard to accumulation in polymorphonuclear leukocytes and in saliva.

OBJECTIVE: In a randomized cross-over study, we assessed pharmacokinetics and intracellular concentrations in polymorphonuclear leukocytes (PMN) and saliva of erythromycin and erythromycylamine, the active metabolite of dirithromycin. METHODS: Ten healthy volunteers received 1 g erythromycin b.i.d. or 500 mg dirithromycin qd for 5 days (wash out period, 35 days). Concentrations of erythromycin and erythromycylamine were measured in serum, urine, saliva, and granulocytes by bioassay and high-performance liquid chromatography (HPLC) on days 1, 3, and 5 of each study period, respectively. RESULTS: While maximal serum concentrations (Cmax) and the area under the data (AUDtot) of erythromycin were significantly higher (Cmax 1.44 mg.l-1, AUDtot 5.66 mg.h.l-1) than those of erythromycylamine (Cmax 0.29 mg.l-1, AUDtot 1.96 mg.h.l-1), erythromycylamine had a significantly higher mean residence time (21 h) than erythromycin (5.5 h). Erythromycylamine accumulated significantly more in PMN than erythromycin; the accumulation factor of erythromycylamine was 100 with a maximal intracellular concentration of 13.4 mg.l-1, whereas the maximal accumulation factor of erythromycin was 4 with a maximal intracellular concentration of 6.1 mg.l-1. There were no significant differences in maximal saliva concentrations (erythromycin 0.35 mg.l-1, erythromycylamine 0.31 mg.l-1).

Compliance with antibiotic therapy: a comparison of deuterium oxide tracer, urine bioassay, bottle weights, and parental reports.

OBJECTIVE: To compare three traditional measures of compliance with antibiotic therapy (parent report diary, preregimen and postregimen bottle-weight difference, and urine bioassay for antibiotic activity), with a deuterium oxide tracer measure of compliance. METHODS: Clinical trial in which all four compliance measures were used for subjects participating in a comparison of the efficacy of azithromycin and penicillin in treating group A beta-hemolytic streptococcal infection. Subjects were 41 children, aged 3 to 15 years (average age, 7.9 years), in a suburban pediatric private practice, who had positive rapid streptococcal antigen test results. RESULTS: Of the 41 subjects, 20 children were randomly assigned to receive azithromycin and 21 to receive penicillin. Compliance was uniformly high by all four measures. Parent diaries indicated that all doses were administered. Urine bioassays were obtained for 40 subjects, and all showed antibiotic activity. Differences in bottle weights were obtained for 27 subjects and showed that 142% of the prescribed medication was missing from the bottles at the end of the regimen. The deuterium oxide measure was obtained for 40 subjects and showed that 107% of the prescribed azithromycin and 92% of the prescribed penicillin were ingested. The correlation coefficient between measured and expected deuterium enrichment was 0.89. There was no significant correlation between the bottle-weight measure and the deuterium oxide tracer. CONCLUSIONS: The bottle-weight measure overestimates compliance; the deuterium oxide tracer is feasible for use in an office setting and produces a high correlation between the expected urinary enrichment and the measured enrichment. Increased use of this quantitative and direct measure would improve the accuracy of compliance measurement in trials of pediatric liquid medications.

Comparison of the pharmacokinetics of three-day and five-day regimens of azithromycin in plasma and urine.

In an open crossover study, the pharmacokinetics of three-day and five-day regimens of azithromycin were compared. Fourteen healthy volunteers received oral doses of azithromycin once-daily, over three days (500 mg/day) and over five days (500 mg on day 1, followed by 250 mg/day on days 2-5). Plasma and urine concentrations were determined by HPLC. Azithromycin was found to be absorbed rapidly on the first and the last days of both regimens, with mean Tmax ranging between 2.5-3 h. On day 1, peak plasma concentrations were 0.37 mg/L and 0.31 mg/L, respectively, with three- and five-day regimens, and increased to 0.42 mg/L on the last day of the three-day regimen, but decreased to 0.18 mg/L at the end of the five-day regimen. Similarly, the AUC0-24 increased from 1.30 to 1.88 h.mg/L during the three-day regimen, and decreased from 1.24 to 0.80 h.mg/L on the five-day regimen. After absorption, azithromycin was distributed rapidly; the respective half-lives were 2.4 h and 2.2 h with the three-day and five-day regimens. Thereafter, a polyphasic decline of plasma concentrations was observed; the average half-lives between 8-48 h after administration were 27.9 h (three-day regimen) and 35.8 h (five-day regimen). In urine, 5.5% (three-day regimen) and 4.6% (five-day regimen) of the total dose was found as unchanged azithromycin over a 12-day period. The observed pharmacokinetics of azithromycin with both regimens conformed with the known pharmacokinetic behaviour of the drug. The treatment-related differences seen in the plasma concentrations were as expected from the different dosage schedules.

Sensitive high-performance liquid chromatographic determination of EM523, a new erythromycin derivative, in human plasma and urine with ultraviolet detection using column switching.

A sensitive high-performance liquid chromatographic (HPLC) method using column switching is described for the determination of EM523 (I), a new erythromycin derivative, in human plasma and urine. The analyte was extracted from alkalinized plasma or urine with a mixture of n-hexane and acetone. After the evaporation of the organic layer, the reconstituted residue was injected into the HPLC system and separated on the first column. After column switching, the heart-cut fraction contamination the analyte was further separated on the second column and monitored by ultraviolet absorbance at 210 nm. The detection limits were 1 ng/ml in plasma and 10 ng/ml in urine. The method was applied to the clinical trials of I.

Simultaneous determination of clarithromycin and 14(R)-hydroxyclarithromycin in plasma and urine using high-performance liquid chromatography with electrochemical detection.

A sensitive method for the simultaneous high-performance liquid chromatographic determination of clarithromycin and its active metabolite in plasma and urine is described. Alkalinized samples were coextracted with an internal standard and analyzed on a C8 column using electrochemical detection. Recoveries were greater than or equal to 85% and consistent. Standard curves for plasma were linear in the range 0-2 micrograms/ml for both compounds (r greater than 0.99), with limits of quantification of approximately 10.03 micrograms/ml (0.5-ml sample). Within-day and day-to-day precision were good, with coefficients of variation mostly within +/- 5%; accuracy for both compounds were routinely within 90-110% of theoretical values. Standard curves for urine were linear in the range 0-100 micrograms/ml with limits of quantification of 0.5 micrograms/ml (0.2-ml sample). Urine assays also had similar within-day and day-to-day precisions and accuracy.

Gynaecological tissue levels of azithromycin.

In an open study the concentrations of azithromycin in plasma, urine, peritoneal fluid and gynaecological tissue in 20 patients undergoing elective gynaecological surgery were compared. Patients were allocated to one of four groups and all patients received a single 500 mg oral dose of azithromycin prior to surgery. In Group I, the dose was administered 24 h before surgery. In Groups II, III and IV it was administered 48, 72 and 96 h, respectively, prior to surgery. A total of 19 patients completed the study; one patient had peri-operative complications and did not proceed to surgery. High concentrations of azithromycin were found in gynaecological tissue up to 96 h after administration. The mean maximum observed concentration 24 h after administration was 1.44 +/- 0.22 micrograms/g. Using all data, the depletion rate constant was 0.0104 h-1, equivalent to a half-life of approximately 67 h. The mean concentration of drug in peritoneal fluid was approximately 9% of the mean concentration in gynaecological tissue. Tissue and peritoneal fluid azithromycin concentrations were much higher than plasma levels at the time of surgery. Detectable plasma levels were only found in four patients from Groups I and II. Six percent of the total dose was excreted in the urine during the seven-day period after drug administration. The single dose of azithromycin was well tolerated by all the patients in this study and no treatment-related side effects or laboratory test abnormalities were seen. It is concluded that a single 500 mg oral dose of azithromycin produces high and sustained levels in gynaecological tissue up to 96 h after administration.

Erythromycin and phenoxymethylpenicillin (penicillin V) in the treatment of respiratory tract infections as related to microbiological findings and serum C-reactive protein.

Respiratory tract pathogens (beta-haemolytic streptococci groups A, C and G, Haemophilus influenzae, Branhamella catarrhalis or pneumococci), were isolated from nasopharyngeal and/or throat swabs in 73/138 (53%) patients greater than 10 years of age with a clinical diagnosis of acute sinusitis, acute tonsillitis, purulent nasopharyngitis or acute bronchitis. Serological evidence of a viral infection (influenza A and B, parainfluenza 1, 2 and 3, respiratory syncytial virus, adenovirus) or Mycoplasma pneumoniae infection was found in 10% of the patients. The serum content of C-reactive protein (S-CRP) was increased (greater than 12 mg/l) in 26/33 (79%) patients with streptococci and in 22/59 (37%) patients without respiratory tract bacteria. In patients with a serological evidence of a virus tonsillitis, the S-CRP was also high (32-64 mg/l). At follow-up 10-12 days after the first visit, the clinical effect of erythromycin and penicillin V was judged to be similar (90% clinical effect). Relapse or re-infection with group A streptococci were seen in 7 patients (4 on erythromycin, 3 on penicillin). In another 6 patients (3 on erythromycin, 3 on penicillin), antibiotic treatment was switched owing to persisting symptoms, probably due to H. Influenzae infection in 3 cases. The patients' own estimates of their symptoms suggested treatment with erythromycin to have a more rapid effect than treatment with penicillin.

Metabolism and disposition of clarithromycin in man.

The metabolic fate and pharmacokinetics of clarithromycin following a single 250- or 1200-mg oral dose of 14C-clarithromycin were studied in six healthy adult males. Peak plasma levels of clarithromycin averaged 0.6 microgram/ml after the low dose and 2.7 micrograms/ml after the high dose. The AUC of clarithromycin increased 13-fold, with the 4.8-fold increase in dose, while the plasma half-life increased from 4.4 hr to 11.3 hr. The major metabolite in plasma and urine was the microbiologically active 14-hydroxylated-R epimer of clarithromycin. After 5 days, a mean of 38% of the low dose (18% as clarithromycin) and 46% of the high dose (29% as clarithromycin) was recovered in the urine, with approximately one-third eliminated during the first 24 hr. The nature of the urinary and fecal metabolites revealed the involvement of three metabolic pathways, viz. 1) hydroxylation at the 14-position to form the R and S epimers, 2) N-demethylation, and 3) hydrolysis of the cladinose sugar. Secondary metabolism via these pathways was also evident. The overall recovery of metabolites, but not total radioactivity, decreased 42% after the high dose. The nonlinear pharmacokinetic behavior of clarithromycin and the decrease in metabolite production suggest that clarithromycin metabolism can be saturated at high doses.

Micro-method for the determination of roxithromycin in human plasma and urine by high-performance liquid chromatography using electrochemical detection.

A simple and sensitive high-performance liquid chromatographic micro-method for the determination of roxithromycin in human plasma and urine is described. A dichloromethane extract of the sample was chromatographed on a C18 reversed-phase column with acetonitrile-83 mM ammonium acetate-methanol (55:23:22, v/v) adjusted to pH 7.5 with acetic acid as the mobile phase. Roxithromycin and the internal standard, erythromycin, were detected by dual coulometric electrodes operated in the oxidative screen mode. The applied cell potential of the screen electrode was set at +0.7 V and the sample electrode at +0.9 V. The intra- and inter-assay coefficients of variation were less than or equal to 7.0%. The detection limit (signal-to-noise ratio = 3) was 0.1 microgram/ml for both plasma and urine. A study of drug stability during sample storage at 4, 20 and 37 degrees C showed no degradation of roxithromycin. The method is convenient for clinical monitoring and pharmacokinetic studies.

Thin-layer chromatographic study of the metabolites of erythromycins in the Wistar rat.

The metabolites of erythromycin A, anhydroerythromycin A, N-demethylerythromycin A and erythromycin B in the Wistar rat were studied by thin-layer chromatography. In some experiments germ-free rats, rats with a cannulated bile duct and a gastrectomized rat were used. The erythromycins examined were shown to undergo two principal changes, N-demethylation and acid-catalysed degradation. It was demonstrated that the stomach and the liver are not the sole sites of acid degradation and demethylation of erythromycins, respectively. Erythromycin A gives three principal metabolites, anhydroerythromycin A, anhydro-N-demethylerythromycin A and N-demethylerythromycin A, and erythromycin A enol ether and N-demethylerythromycin A enol ether are present to a minor extent. 5-O-Desosaminylerythronolide A was also identified, suggesting the presence of an erythromycin glycosidase.

Antibiotic concentration in suction skin blister fluid and saliva after repeated dosage of erythromycin acistrate and erythromycin base.

The drug concentration in plasma, suction skin blister fluid (SBF), urine and saliva after repeated dosage of either erythromycin acistrate (EA) or enterocoated pellets of erythromycin base (EB) was studied in young healthy volunteers with a cross-over design in two separate studies. In Study I, the total drug concentration (erythromycin + 2'-acetyl erythromycin) after EA (400 mg tid) was slightly higher than the erythromycin concentration after EB (500 mg tid). The concentration of erythromycin after EA was about half of that after EB. In SBF the total antibiotic concentration after EA and erythromycin concentration after EB were 49 and 46% of the corresponding plasma concentrations, respectively. The degree of hydrolysis of 2'-acetyl erythromycin was higher in SBF (44%) than in plasma (39%). An equal proportion (7.3-7.5%) of the dose was excreted in urine after administration of both drugs. The degree of hydrolysis of 2'-acetyl erythromycin in urine was 58%. In Study II, the plasma/saliva concentration ratio ranged from 0.11 to 0.17 after EA 400 mg tid, 0.12 to 0.20 after EA 500 mg tid and 0.17 to 0.22 after EB 500 mg tid. The degree of hydrolysis of 2'-acetyl erythromycin was considerably higher in saliva (61-78%) than in plasma (27-41%). In plasma, the percentage of hydrolysis of 2'-acetyl erythromycin was inversely correlated with the concentration of acid-alpha 1-glycoprotein. The penetration of 2'-acetyl erythromycin and erythromycin into the extravascular space as evaluated from SBF and saliva levels was equal, and adequate concentrations of erythromycin were obtained for the treatment of bacterial infections.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatography of erythromycin propionyl ester and erythromycin base in biological fluids.

The simultaneous determination of erythromycin propionate and erythromycin base in serum and urine by high-performance liquid chromatography using oleandomycin as internal standard is described. The separation was achieved on a reversed-phase C18 column employing acetonitrile-0.05 M phosphate buffer (65:35), adjusted to pH 7.0, as the mobile phase with coulometric detection. Hydrolysis of the ester during blood sample collection was minimised by immediate high-speed centrifugation of collected blood samples, followed by separation and immediate freezing of the serum fraction. A solid-phase extraction procedure, combined with a simple phase-separation step was used prior to chromatographic analysis. The method has the necessary precision, sensitivity and accuracy to allow the simultaneous determination of both components in serum and urine following a single 500-mg oral dose of erythromycin estolate.