The pharmacokinetics and safety of duloxetine were evaluated in a single-blind, placebo-controlled, escalating multiple-dose study in 12 healthy male subjects. In the treatment group (n = 8), duloxetine was administered orally at a starting dose of 20 mg twice daily (bid) and escalated at weekly intervals to 30 mg bid, then to 40 mg bid. The observed plasma concentration-time data at all three dose levels were adequately described by a one-compartment model with a first-order absorption rate constant. The mean oral clearance, apparent volume of distribution, and half-life values were 114 L/h (range: 44 to 218 L/h), 1943 L (range: 803 to 3531 L), and 12.5 h (range: 9.2 to 19.1 h), respectively. Somnolence, nausea, and dry mouth were observed following the initial dose, but they resolved with continuing drug administration. Duloxetine was not associated with clinically significant changes in blood pressure (BP) or heart rate (HR) measured in the standing position. However, in recumbent position, small increases in systolic (< or = 9 mmHg) and diastolic (< or = 5 mmHg) BP and small decreases in HR (< or = 6 beats/min) were observed. Abrupt discontinuation of duloxetine was associated with a small increase in mean HR (< or = 12 beats/min). In 3 subjects, abrupt discontinuation was also associated with transient sleep disturbance. No clinically important changes in electrocardiograms, cardiac intervals, clinical laboratory tests, and neurological functions were observed. These results indicate that duloxetine exhibits linear pharmacokinetics with respect to dose and duration of treatment and that a multiple oral dose regimen starting at 20 mg bid and gradually escalating up to 40 mg bid was generally well tolerated.
Slower absorption from deltoid and femoral administrations resulted in an increased duration of action for both regular insulin and insulin lispro when compared to abdominal administration. However, notable increases in the onset of action were only apparent with regular insulin. The consistency with insulin lispro response from abdominal and extremity injection sites allows more potential sites for subcutaneous injection with an assured rapid response.
Administration of a new specific serotonin uptake inhibitor, fluoxetine, depressed the firing rate of raphe neurons. A highly significant increase in serum prolactin levels was observed after ip injection of 30 mg/kg of 5-hydroxytryptophan (5-HTP) in male or female rats pretreated with 10 mg/kg (ip) of fluoxetine. Neither 5-HTP nor fluoxetine given separately had any effect on serum prolactin levels. In animals pretreated with methysergide the combination of fluoxetine and 5-HTP did not increase significantly serum levels of prolactin. In addition, the serotonin agonist quipazine elevated significantly serum prolactin levels in male and female rats. The results of this study strengthen the idea that 5-HTP is acting via serotonin-containing neurons that influence anterior pituitary prolactin release, and that serotonin receptor activation leads to prolactin release.
This pharmacokinetic interaction is likely the result of an inhibition of CYP2D6 tricyclic metabolism by sertraline. When a tricyclic antidepressant, such as desipramine or imipramine, is coadministered with sertraline, lower dosages of the tricyclic agents may be necessary to prevent elevated tricyclic levels.
Dirithromycin is a new member of the macrolide class of antibiotics and has been developed for oral administration. Dirithromycin is a 14-membered lactone ring macrolide and is the C9-oxazine derivative of erythromycylamine. The human pharmacokinetics and clinical pharmacology of dirithromycin have been studied. Dirithromycin has unique pharmacokinetics which distinguish it from erythromycin. In man, following an oral 500 mg dose of dirithromycin, a mean peak plasma concentration (Cmax) of 0.48 mg/L (range 0.1-1.97) was observed at 4 h. The mean area under the plasma concentration versus time curve (AUC0-24h) measured 3.37 mg.h/L (range 0.39-17.16). No plasma accumulation was observed with multiple-dose administration. Dirithromycin may be taken without regard to meals, although food and H2-receptor antagonists may increase the systemic bioavailability in some patients. Based upon drug interaction studies performed with antipyrine and theophylline, dirithromycin has shown less potential to interact with other drugs metabolized by the cytochrome P450 system that does erythromycin. Plasma concentrations and AUCs were low due to rapid movement of the drug from the vascular space to the extravascular compartment, as reflected by tissue concentrations, which exceeded plasma concentrations 4 h after dosing. Dirithromycin achieves relatively high tissue concentrations (approximately 0.8-5.0 mg/kg) 4-24 h after dosing. The extensive tissue penetration is reflected in a large mean apparent volume of distribution of 800 L (range 504-1041). Dirithromycin is rapidly converted by non-enzymatic hydrolysis during absorption to erythromycylamine, which is microbiologically active. In a 14C-radiolabelled study, 60-90% of the administered dose was hydrolysed to erythromycylamine within 35 min of infusion. After 1.5 h, conversion to erythromycylamine in serum was virtually complete. Plasma protein binding was determined to be 15-30% by ultracentrifugation. Dirithromycin is characterized by a plasma elimination half-life of 44 h (range 16-65 h) that permits once-daily administration. Total body clearance was 226-1040 mL/min in the 14C-radiolabelled study. The primary route of elimination of dirithromycin/erythromycylamine was faecal/hepatic. Following intravenous administration, approximately 17-25% of the radioactivity appeared in the urine and 62-81% appeared in the stool, indicating predominantly hepatic excretion. With oral administration 1.2-2.9% of the radioactivity appeared in the urine and 81-97% in the stool. The major part of urinary excretion occurs within the first 48 h post-administration; however, urinary excretion of radioactivity lasted longer than 240 h. The absolute bioavailability calculated from dose-corrected urinary excretion data was 10% (6-14%).
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