The effects of sucrose on stability of human brain natriuretic peptide [hBNP (1-32)] and human parathyroid hormone [hPTH (1-34)]

Although the effect of sucrose on the physical stability of proteins has been well documented, its impact on their chemical stability is largely unknown. The aim of this study was to investigate the potential effects of sucrose on the structural conformation of human brain natriuretic peptide [hBNP (1-32)] and the synthetic human parathyroid hormone [hPTH (1-34)], and link these effects to chemical degradation pathways of these peptides. The stability of hBNP (1-32) and hPTH (1-34) was studied at pH 5.5. Aggregation was monitored using size exclusion high-performance liquid chromatography (SE-HPLC), whereas oxidation and deamidation products were measured by reversed phase (RP) HPLC. Fourier transform infrared (FT-IR) spectroscopy was used to study the peptides' conformation. Sucrose retarded aggregation, deamidation, and oxidation of hBNP (1-32) and hPTH (1-34), with a maximum effect at relatively high concentrations (as much as 1 m). FT-IR spectroscopy indicated that sucrose maintained the native conformation of hBNP (1-32) and induced small conformation changes in the hPTH (1-34) structure. Sucrose enhanced the stability of hBNP (1-32) and hPTH (1-34) in liquid formulations. The stabilizing effect of sucrose was due to a large extent to retardation of oxidation and deamidation of hBNP (1-32) and hPTH (1-34).

Determination of grepafloxacin in plasma and urine by a simple and rapid high-performance liquid chromatographic method

A rapid, specific, sensitive and economical method has been developed and validated for the determination of grepafloxacin in human plasma and urine. The assay consisted of reversed-phase HPLC with UV detection. Plasma proteins were removed by a fast and efficient procedure that has eliminated the need for costly extraction and evaporation. For the urine samples, the only required sample preparation was dilution. Separation was achieved on a reversed-phase TSK gel column with an isocratic mobile system. The method had a quantification limit of 0.05 microg/ml in plasma and 0.5 microg/ml in urine. The coefficients of variation (C.V.) were less than 4% for within- and between-day analyses. The method was successfully applied to a pharmacokinetic study, and was proved to be simple, fast and reproducible.

The effect of staggered dosing of sucralfate on oral bioavailability of sparfloxacin

AIMS

To investigate the effect of sucralfate on sparfloxacin absorption when administered concurrently or at strategically spaced dosing times designed to avoid the potential interaction.

METHODS

The study was a four-way crossover design where eight healthy Japanese volunteers were randomized to one of four treatment sequences at entry. A 300 mg dose of sparfloxacin was administered alone for treatment A (control). Treatments B, C and D included sucralfate 1.5 g every 12 h for five doses. For treatment B, the fifth dose of sucralfate was administered concurrently with sparfloxacin 300 mg. For treatment C, 300 mg sparfloxacin was given 2 h prior to the fifth dose of sucralfate. Treatment D consisted of sparfloxacin 300 mg given 4 h prior to the fifth dose of sucralfate. Blood and urine samples were collected at predetermined time intervals for 72 h. Sparfloxacin concentrations in plasma and urine and the concentrations of sparfloxacin metabolite in urine were determined by high performance liquid chromatography assays.

RESULTS

Sucralfate administrated concurrently with sparfloxacin decreased the mean AUC(0,infinity) of sparfloxacin 2-fold (P<0.001) and the mean Cmax 2.1-fold (P<0.001) compared with sparfloxacin alone. When sucralfate was administrated 2 h after sparfloxacin, the mean AUC(0,infinity) was decreased 1.5-fold (P<0.01) and the mean Cmax 1.4-fold (P<0.01). Sucralfate did not alter the extent of absorption of sparfloxacin when it was given 4 h after the administration of sparfloxacin. The relative bioavailabilities for treatments B, C and D were 0.50 (95% CI: 0.35-0.65), 0.64 (95% CI: 0. 51-0.77), and 0.92 (95% CI: 0.81-1.03), respectively, relative to sparfloxacin alone. The mean percentage of the sparfloxacin dose recovered in urine was significantly lower after sparfloxacin was administered with sucralfate than after sparfloxacin was administered alone or 2 h before the sucralfate dose (P<0.001). Treatments B, C and D were demonstrated to be equivalent to treatment A in the rate of absorption. The tmax, CLr and t1/2 were not significantly affected by sucralfate. The metabolism of sparfloxacin was not altered in the presence of sucralfate.

CONCLUSIONS

Oral administration of sucralfate with sparfloxacin or 2 h after sparfloxacin, decreased the extent of sparfloxacin absorption. When both drugs are to be administered together, sucralfate should be administered 4 h after sparfloxacin, allowing thus sufficient time for sparfloxacin absorption prior to the sucralfate dose and thereby minimizing the chance of a significant interaction.

Determination of sparfloxacin in plasma and urine by a simple and rapid liquid chromatographic method

A simple, specific, sensitive, and rapid method has been developed and validated for the determination of sparfloxacin in human plasma and urine. The assay consisted of reversed-phase HPLC with ultraviolet detection. Plasma proteins were efficiently removed by precipitation with perchloric acid after the addition of grepafloxacin as an internal standard. For the urine samples, the only required sample preparation was dilution. Separation was achieved on a C18 reversed-phase column. The quantification limit was 0.025 mg/L in plasma and 0.5 mg/L in urine. The coefficients of variation (CV) were less than 10% for intra-day and inter-day analyses. The recovery of sparfloxacin added to plasma and urine ranged from 96.7% to 97.9%. The method has been successfully applied to pharmacokinetic studies.

Simultaneous determination of grepafloxacin, ciprofloxacin, and theophylline in human plasma and urine by HPLC

A specific and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed and validated for the simultaneous determination of grepafloxacin, ciprofloxacin, and theophylline in human plasma and urine. This assay allows these drugs to elute and be resolved in a single chromatogram at 280 nm, using a linear gradient. The procedure involves liquid-liquid extraction. Separation was achieved on a C18 reversed-phase column. The quantification limits were 0.05 mg/L in plasma and 0.5 mg/L in urine for grepafloxacin and ciprofloxacin and 0.5 mg/L in plasma and urine for theophylline. Standard curves were linear (correlation coefficients >0.999) over the ranges 0.05 to 5 mg/L for grepafloxacin and ciprofloxacin in plasma, from 0.5 to 20 mg/L for theophylline in plasma, and from 0.5 to 500 mg/L for the three drugs in urine. The coefficients of variation for the three drugs were less than 10% for within- and between-day analyses. The recoveries averaged 94.5% for theophylline, 93% for ciprofloxacin, 93.7% for grepafloxacin, and 95.1% for the internal standard (IS). The assay can be used for pharmacokinetic studies of these drugs, to investigate the interaction of grepafloxacin and ciprofloxacin with theophylline, or for routine simultaneous monitoring of theophylline, grepafloxacin, and ciprofloxacin.

Influences of urinary pH on ciprofloxacin pharmacokinetics in humans and antimicrobial activity in vitro versus those of sparfloxacin

The impact of acidification and alkalinization of urine on the pharmacokinetics of ciprofloxacin was investigated after single 200-mg oral doses were administered to nine healthy male volunteers. In addition, the effect of human urine on the MICs of ciprofloxacin and sparfloxacin against some common urinary tract pathogens such as Escherichia coli and Pseudomonas aeruginosa was investigated. Acidic and alkaline conditions were achieved by repeated oral doses of ammonium chloride or sodium bicarbonate, respectively. Plasma ciprofloxacin levels in all subjects were adequately described in terms of two-compartment model kinetics with first-order absorption. Acidification and alkalinization treatments had no effect on ciprofloxacin absorption, distribution, or elimination. The total amount of unchanged ciprofloxacin excreted over 24 h under acidic conditions was 88.4 +/- 14.5 mg (mean +/- standard deviation) (44.2% of the oral dose) and 82.4 +/- 16.5 mg (41.2% of the oral dose) under alkaline conditions, while the total amount of unchanged drug excreted over 24 h in volunteers receiving neither sodium bicarbonate nor ammonium chloride was 90.53 +/- 9.8 mg (45.2% of the oral dose). The mean renal clearance of ciprofloxacin was 16.78 +/- 2.67, 16.08 +/- 3.2, and 16.31 +/- 2.67 liters/h with acidification, alkalinization, and control, respectively. Renal clearance and concentrations of ciprofloxacin in urine were not correlated with urinary pH. The antibacterial activity of ciprofloxacin and sparfloxacin against E. coli NIHJ JC-2 and P. aeruginosa ATCC 27853 was affected by human urine and in particular by its pH. The activities of both quinolones against E. coli NIHJ JC-2 were lower at lower urinary pH and rather uniform, while in the case of P. aeruginosa ATCC 27853 ciprofloxacin was more active than sparfloxacin.

Sparfloxacin pharmacokinetics in healthy volunteers: the influence of acidification and alkalinization

OBJECTIVE

To investigate the effect of acidification and alkalinization on the pharmacokinetics of sparfloxacin in healthy subjects.

METHODS

A single 200-mg oral dose of sparfloxacin was given to nine healthy Japanese volunteers on three separate occasions under different conditions of urinary pH. Acidic and alkaline conditions were achieved by repeated oral doses of ammonium chloride and sodium bicarbonate, respectively. The concentrations of sparfloxacin and its metabolite in plasma and urine were determined by high-performance liquid chromatography assays.

RESULTS

The difference between treatments for Cmax, AUCinfinity, and CL x f(-1) were found to be significant. The relative bioavailability of sparfloxacin was 84.4% and 122.3% after ammonium chloride and sodium bicarbonate treatments, respectively. The amount of unchanged sparfloxacin in urine samples collected 0-48 h after sparfloxacin administration represented 10.1% of the dose in the control, 14.3% of the dose in urine acidification and 8.4% of the dose with alkalinization of urine. Renal clearance was found to depend on urinary pH. However, the plasma elimination and the metabolism of sparfloxacin were not significantly altered by acidification or alkalinization of the urine.

CONCLUSION

The urinary pH dependence of the renal clearance of sparfloxacin will be of minor clinical importance with regard to the low contribution of renal excretion to the overall elimination of sparfloxacin. On the other hand, the alteration in the environmental pH in the gastrointestinal tract, produced by the concomitant ingestion of ammonium chloride or sodium bicarbonate, influences the absorption and bioavailability of sparfloxacin. This effect is likely to be clinically significant.

Determination of ciprofloxacin in plasma and urine by HPLC with ultraviolet detection

A simple, sensitive isocratic method for the detection and quantification of ciprofloxacin in plasma and urine has been developed. The assay consisted of reversed-phase HPLC with ultraviolet detection. Plasma proteins were removed by a fast and efficient procedure. For the urine samples, the only required sample preparation was dilution. Separation was achieved on a C18 reversed-phase column. The quantification limit was 0.01 mg/L in plasma and 0.5 mg/L in urine. This method was sufficiently sensitive for pharmacokinetic studies.