Determination of polymyxin E1 in rat plasma by high-performance liquid chromatography

A precise and accurate HPLC assay for polymyxin E(1) in rat and dog plasma has been validated. Samples and standards are extracted from plasma with a 96-well C(8) extraction disk plate. Sample extracts are derivatized with dansyl chloride, and polymyxin E(1) derivative is quantitated on a C(8) column by HPLC with fluorescence detection. The assay is linear in the range of 0.050-5.00 micro g/ml for polymyxin E(1). The precision and accuracy of polymyxin E(1) plasma assay was well within the recommended limits set in the FDA Guidance for Bioanalytical Method Validation. Polymyxin E(1) stability in rat and dog plasma for 24 h at room temperature and through three freeze-thaw cycles was demonstrated.

Pharmacokinetics and bioavailability of aerosolized tobramycin in cystic fibrosis

STUDY OBJECTIVES

To describe the pharmacokinetics and bioavailability of inhaled tobramycin (TOBI; Chiron Corporation; Seattle, WA), 300-mg dose, delivered by a nebulizer (PARI LC Plus; Pari Respiratory; Richmond, VA) and a compressor (Pulmo-Aide, model 5650D; DeVilbiss Health Care; Somerset, PA) in cystic fibrosis (CF) patients during the pivotal phase III trials.

DESIGN

Data from two identical, 24-week, randomized, double-blind, placebo-controlled, parallel-group studies.

SETTING

US sites randomized 258 patients with CF to receive tobramycin, 300 mg twice daily, in three 28-day on/28-day off treatment cycles.

MEASUREMENT

Tobramycin sputum concentrations were assessed 10 min after the first and last doses were administered in the 20-week study. Serum tobramycin concentrations were assessed before and 1 h after the first and last doses had been administered. The population estimate of the apparent clearance was used to estimate the bioavailability fraction.

RESULTS

The mean peak sputum concentration was 1,237 microg/g. About 95% of patients achieved sputum concentrations > 25 times the minimum inhibitory concentration of the Pseudomonas aeruginosa isolates. One hour after the dose, the mean serum concentration was 0.95 microg/mL. Tobramycin did not accumulate in the sputum or serum over the course of the study. Pharmacokinetic data were best represented by a two-compartment model with biexponential decay and slope estimates comparable to those following parenteral administration. The estimated systemic bioavailability after aerosol administration was 11.7% of the nominal dose.

CONCLUSIONS

The administration of tobramycin, 300 mg bid, in a 28-day off/28-day on regimen produced low serum tobramycin concentrations, reducing the potential for systemic toxicity. High sputum concentrations ensure efficacious antibiotic levels at the site of the infection. Inhaled tobramycin significantly improved the therapeutic ratio over that of parenteral aminoglycosides.

Determination of terfenadine and terfenadine acid metabolite in plasma using solid-phase extraction and high-performance liquid chromatography with fluorescence detection

This work describes the methodology for the analysis of terfenadine and the acid metabolite of terfenadine in plasma using high-performance liquid chromatography. The use of solid-phase extraction allows the use of robotic or manual sample preparation for the efficient clean-up of terfenadine and terfenadine acid metabolite from plasma. Additional selectivity is obtained through the use of fluorescence detection. For terfenadine, the validated quantitation range of this method is 10.0-84.2 ng/ml with coefficients of variation of 5.7-30%. For terfenadine acid metabolite, the validated quantitation range of this method is 8.2-500 ng/ml with coefficients of variation of 4.1-24%.

Pharmacokinetics of subcutaneous and intramuscular butorphanol in dogs

Butorphanol tartrate was administered intramuscularly and subcutaneously to adult male and female dogs at a dose of 0.25 mg/kg. No significant absorption lag time and no significant difference bwtween peak intramuscular and subcutaneous serum concentrations were observed. The mean peak serum concentration was 29 ng/ml at mean times of 28 min after subcutaneous administration and 40 min after intramuscular administration. There were no significant differences in the pharmacokinetics of butorphanol in dogs with either route. The serum half-life was 1.62 hr, and the serum clearance was 3.45 liters/kg/hr. The apparent volume of distribution of butorphanol was 7.96 liters/kg. Although considerable inter- and intraanimal variation in Cmax and AUC was observed, there was no significant difference in the area under the serum concentration versus time curves, and the two administration routes were considered bioequivalent.