Pharmacokinetics of famotidine in patients with cystic fibrosis.

Famotidine pharmacokinetics were studied in 13 patients with severe cystic fibrosis (CF) ranging from 10 to 47 years of age and 25 to 72 kg in weight. Patients were randomized to first receive famotidine either 20 mg intravenously or 40 mg orally. Twelve patients were crossed over to the alternate treatment. Repeated blood samples were obtained over 12 hours after intravenous and oral administration and urine was collected over 24 hours for quantitation of famotidine by means of high-performance liquid chromatography (HPLC). A compartment model-dependent approach was used to characterize the disposition of famotidine. From the intravenous data, the mean +/- standard deviation elimination half-life (t1/2) was 2.11 +/- 0.75 hours, the total clearance (Cl) was 0.79 +/- 0.41 L/kg/hr, the renal clearance was 0.57 +/- 0.26 L/kg/hr, the fraction eliminated unchanged in the urine was 83% +/- 16%, and the apparent volume of distribution (Vdss) was 1.33 +/- 0.53 L/kg. The bioavailability determined from comparison of intravenous and oral area under the curve data was 71% +/- 27%. Results of this study support an initial famotidine dose of 20 mg intravenously or 40 mg orally every 12 hours in patients with CF who are older than 9 years of age.

Influence of grapefruit juice on caffeine pharmacokinetics and pharmacodynamics.

The influence of grapefruit juice (GFJ) on caffeine's metabolism and the hemodynamic effects of this potential food interaction were studied in 10 normotensive volunteers. In this crossover study, caffeine (3.3 mg/kg) and water or caffeine and GFJ were given to participants. Nine serum caffeine concentrations were determined within 24 hours of each phase. In another phase of this study, caffeine was given with multiple GFJ doses to 6 of the 10 participants. Ambulatory blood pressure (BP) monitors were used for 12 hours to assess treatment hemodynamic effects. The mean area under the serum caffeine concentration-time curve (AUC0-infinity) values +/- SD for the caffeine with water group, caffeine with GFJ group, and caffeine with multiple GFJ group were 47.0 +/- 10.8, 48.7 +/- 15.2, and 49.6 +/- 7.0 micrograms/ml.hr, respectively (NS). There was no significant difference on the ambulatory systolic BP, diastolic BP, percentage of the time with a diastolic BP greater than 90 mm Hg, or heart rate area under the effect curves. We conclude that grapefruit juice had no effect on caffeine pharmacokinetics or hemodynamic effects.

Stability of amphotericin B in four concentrations of dextrose injection.

The stability of amphotericin B in 5%, 10%, 15%, and 20% dextrose injection was investigated. The dextrose solutions were prepared in triplicate from sterile water for injection and 70% dextrose injection and placed in empty 50-mL polyvinyl chloride bags. The pH of each solution was determined before amphotericin B was added to a concentration of approximately 100 micrograms/mL. The bags were stored at 15-25 degrees C and protected from light. Three 1-mL samples were taken from each bag at various times up to 24 hours. One sample was analyzed for precipitation and color and pH changes. Two samples were analyzed in duplicate by stability-indicating high-performance liquid chromatography. No visual changes were observed, and pH did not change substantially. The mean amphotericin B concentration was greater than 90% of the initial concentration at each sampling time. However, the drug concentration in 3 of the 27 samples from the admixtures with 10% dextrose injection and 5 of the 27 samples from the admixtures with 20% dextrose injection fell below 90% of the initial concentration. Amphotericin B 100 micrograms/mL was stable in 5%, 10%, 15%, and 20% dextrose injection when stored for up to 24 hours at 15-25 degrees C and protected from light.