Quantitative determination of olanzapine in rat brain tissue by high-performance liquid chromatography with electrochemical detection.

A sensitive assay was developed for the measurement of olanzapine in rat brain tissue using HPLC with electrochemical detection. The assay has a lower limit of quantitation of 0.5 ng/ml in tissue homogenate and utilizes a liquid-liquid extraction followed by reversed-phase HPLC for the quantitative analysis of olanzapine. The method provided a linear response for olanzapine over a concentration range of 0.5-100 ng/ml with a coefficient of determination (r2) greater than 0.9995. The extraction efficiencies of olanzapine and internal standard (LY170158) were greater than 82% in brain tissue. The intra-assay and inter-assay relative errors ranged from -5.38 to 17.60% and -3.25 to 10.53%, respectively. The intra-assay and inter-assay RSD values were in the range of 1.12 to 6.96% and 3.78 to 6.68%. Long-term stability studies showed that brain tissue homogenate samples spiked with olanzapine and internal standard are stable at -70 degrees C for at least 110 days. However, a room temperature stability study showed that olanazapine was not stable in brain homogenate if the sample was exposed at 25 degrees C longer than 2 h. This method has been used for the study of the disposition and pharmacokinetics of olanzapine in male Sprague-Dawley rats.

Synergistic effects of olanzapine and other antipsychotic agents in combination with fluoxetine on norepinephrine and dopamine release in rat prefrontal cortex.

To understand the mechanism of the clinical efficacy of olanzapine and fluoxetine combination therapy for treatment-resistant depression (TRD), we studied the effects of olanzapine and other antipsychotics in combination with the selective serotonin uptake inhibitors fluoxetine or sertraline on neurotransmitter release in rat prefrontal cortex (PFC) using microdialysis. The combination of olanzapine and fluoxetine produced robust, sustained increases of extracellular levels of dopamine ([DA](ex)) and norepinephrine ([NE](ex)) up to 361 +/- 28% and 272 +/- 16% of the baseline, respectively, which were significantly greater than either drug alone. This combination produced a slightly smaller increase of serotonin ([5-HT](ex)) than fluoxetine alone. The combination of clozapine or risperidone with fluoxetine produced less robust and persistent increases of [DA](ex) and [NE](ex). The combination of haloperidol or MDL 100907 with fluoxetine did not increase the monoamines more than fluoxetine alone. Olanzapine plus sertraline combination increased only [DA](ex). Therefore, the large, sustained increase of [DA](ex), [NE](ex), and [5-HT](ex) in PFC after olanzapine-fluoxetine treatment was unique and may contribute to the profound antidepressive effect of the olanzapine and fluoxetine therapy in TRD.

Evaluation of LY203647 on cardiovascular leukotriene D4 receptors and myocardial reperfusion injury.

In vitro studies have shown LY203647 to be a selective antagonist of contractile responses to leukotriene (LT) D4 and LTE4 in guinea pig ileum, trachea and lung parenchyma. In pithed rat, i.v. injection of LTD4 produced pressor responses that were selectively antagonized by LY203647 in a dose-dependent manner [ED50 7.5 (6.0-9.5) mg/kg, i.v.]. In normal anesthetized rats and dogs, LTD4 reduced aortic blood flow and stroke volume in association with systemic vasoconstriction, variable blood pressure responses and no change in cardiac rate. LTD4 did not alter myocardial contractility corrected for alterations in afterload. Pretreatment of rats and dogs with LY203647 (1-10 mg/kg, i.v.) produced dose-related inhibition of the myocardial and systemic hemodynamic effects of LTD4, whereas coadministration of LY203647 reversed established myocardial depression and systemic and pulmonary vasoconstriction during continuous infusion of LTD4 in dogs. LY203647 (10 mg/kg over 90 min, i.v.) infusion in normal dogs abolished or greatly antagonized hemodynamic responses to LTD4 for 6 hr. In subsequent experiments, myocardial infarct size was measured after 1 hr of occlusion of the circumflex coronary artery and 5 hr of reperfusion. LY203647 (10 mg/kg over 90 min, i.v.) treatment did not alter cardiovascular parameters when compared to time-related alterations observed in control dogs. ST segment deviation and the intensity and duration of cardiac arrhythmias associated with coronary artery occlusion and reperfusion also were similar between groups. Resultant infarct sizes were 46 +/- 1 and 45 +/- 1% of the left ventricular mass placed at risk in control and LY203647-treated dogs, respectively. Present data illustrate the prominent cardiac and systemic hemodynamic effects of LTD4 and indicate that LY203647 produces selective and sustained antagonism of cardiovascular LTD4 receptors. Lack of containment of infarction by LY203647 suggests that endogenous cysteinyl-LT do not contribute to reperfusion injury of ischemic myocardium.

Antagonism of leukotriene B4 receptors does not limit canine myocardial infarct size.

Injection of leukotriene (LT)B4 (0.1-3 micrograms/kg i.v.) in normal anesthetized dogs produced dose-related leukopenia that was accompanied by arterial hypotension and tachycardia at higher tested doses. LTD4 (0.1-3 micrograms/kg i.v.), in contrast, increased arterial blood pressure, lowered cardiac rate and produced little change in arterial blood leukocyte count. Continuous infusion of LY255283 [(1-(5-ethyl-2-hydroxy-4-(6-methyl-6-(1H-tetrazol-5-yl)- heptyloxy)phenyl)ethanone] (0.33 mg/kg/min i.v.), a selective LTB4 receptor antagonist, resulted in near complete inhibition of leukopenic, hypotensive and tachycardic responses to LTB4 (3 micrograms/kg i.v.) challenge over a 6-hr test period. Persistent antagonism of canine LTB4 receptors was associated with high circulating levels of LY255283 that were bound extensively to plasma proteins. In subsequent experiments, myocardial infarct size was measured following 1 hr of occlusion of the circumflex coronary artery and 5 hr of reperfusion in control dogs infused with vehicle, and in dogs receiving LY255283 (0.33 mg/kg/min i.v.). Drug and vehicle were infused continuously beginning 15 min before coronary artery occlusion. LY255283 treatment essentially did not alter base-line cardiovascular parameters or myocardial oxygen demand when alterations were compared to time-related changes observed in control dogs. LY255283 infusion also did not alter the degree of myocardial ischemia or the intensity and duration of cardiac arrhythmias associated with coronary artery occlusion and reperfusion. Resultant infarct sizes were 43 +/- 5% of the left ventricle placed at risk in control dogs and 32 +/- 5% in dogs given LY255283; this difference was not statistically significant. The extent of left ventricle placed at risk was similar between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism, disposition, and pharmacokinetics of a potent anticonvulsant, 4-amino-N-(2,6-dimethylphenyl)benzamide (LY201116), in rats.

The metabolism, disposition, and pharmacokinetics of 4-amino-N-(2,6-dimethylphenyl)benzamide (LY201116) have been studied in rats. 14C-LY201116 was well absorbed (approximately 94%) from the gastrointestinal tract following oral administration. Of the dose administered, 64.5% was excreted in the urine and 29% in the bile; with the majority being excreted during the first 24 hr. Peak plasma levels of LY201116 were observed at 0.75 hr, whereas peak plasma concentrations of radioactivity were seen at 2 hr after dosing. Maximum levels of radioactivity were observed at 2 hr in all of the tissues studied. The elimination of radioactivity from the tissues was monophasic with a mean half-life of 3.4 hr. Biotransformation of LY201116 in rats was investigated by quantitating and isolating metabolites from urine and plasma. The major route of metabolism was N-acetylation to form 4-(acetylamino)-N-(2,6-dimethylphenyl)benzamide (ADMP), and subsequent hydroxylation to form 4-(acetylamino)-N-(2-hydroxymethyl-6-methylphenyl)benzamide (HADMP). Two hr after oral dosing with 14C-LY201116, ADMP and HADMP comprised 92% of the total radioactivity in the plasma. The major urinary metabolite, accounting for 63% of the radioactivity in the urine, was HADMP. The elimination of LY201116 from the systemic circulation following iv administration was monophasic, with a terminal t1/2 of 9.4 min. The volume of distribution was 911 ml/kg and the plasma clearance was 66.9 ml/min/kg.

Methylphenidate plasma concentrations in chronically and acutely treated latency-age children.

In 5 latency-age boys, methylphenidate plasma concentrations following multiple doses of methylphenidate were consistently higher than those obtained after a single dose. Pharmacological and clinical implications are discussed.

Metabolism of the prodrug DEGA (N-(2,6-dimethylphenyl)-4-[[(diethylamino)acetyl]amino]benzamide) to the potent anticonvulsant LY201116 in mice. Effect of bis-(p-nitrophenyl)phosphate.

In mice, the diethylglycineamide analogue of LY201116, DEGA (N-(2,6-dimethylphenyl)-4-[[(diethylamino)acetyl]amino]benzamide), is metabolized by consecutive N-deethylations for form MEGA and GA; the monoethylglycineamide and glycineamide analogues of LY201116, respectively. All of these compounds are in turn hydrolyzed to form LY201116 [4-amino-N-(2,6-dimethylphenyl)benzamide]. LY201116 is N-acetylated to form the N-acetyl metabolite, NAC. NAC is also deacetylated to reform LY201116. All of the above compounds inhibit maximal electroshock-induced seizures (MES) in mice. After oral administration, the potencies of these compounds were similar at their time of peak anticonvulsant effect. However, the MES ED50 values for the above compounds 5 min after iv dosing were 43, 13, 2, and 0.5 mg/kg for DEGA, MEGA, GA, and LY201116, respectively. Similar plasma levels of LY201116 were produced in mice 5 min after iv dosing with the respective ED50 values of the above compounds, which suggested that all of the compounds produced their anticonvulsant effects via LY201116. The in vivo metabolism of DEGA and MEGA but not GA to LY201116 was inhibited by the acylamidase inhibitor bis-(p-nitrophenyl) phosphate (BNPP). Mice predosed with BNPP were not protected by DEGA and MEGA from MES-induced seizures and the plasma samples contained little or no LY201116. The metabolism of GA to LY201116 was not inhibited by BNPP, and GA was an active anticonvulsant in BNPP-pretreated mice. The apparent iv potency of DEGA increased dramatically with time after dosing, again suggesting time-dependent, metabolically mediated liberation of the more potent anticonvulsant LY201116.

Discovery and anticonvulsant activity of the potent metabolic inhibitor 4-amino-N-(2,6-dimethylphenyl)-3,5-dimethylbenzamide.

Compound 2 [4-amino-N-(2,6-dimethylphenyl)benzamide] is an effective anticonvulsant in several animal models. For example, following oral administration to mice, it antagonized maximal electroshock (MES) induced seizures with an ED50 of 1.7 mg/kg. During drug disposition studies with 2, we found that it was rapidly metabolized by N-acetylation. Thirty minutes after oral administration of 1.7 mg/kg of 2 to mice, plasma concentrations of parent drug and the N-acetyl metabolite 5 were 1.09 and 0.41 microgram/mL, respectively. Six hours postadministration the concentrations were 0.23 and 0.22 microgram/mL, respectively. In order to sterically preclude or diminish the rate of metabolic N-acetylation, we synthesized analogues of 2 possessing either one (3) or two (4) methyl groups ortho to the 4-amino substituent. Both compounds antagonized MES-induced seizures after administration to mice; oral ED50 values for 3 and 4 were 3.5 and 5.6 mg/kg, respectively. Compound 3 was rapidly metabolized by N-acetylation. However, 4 provided exceptionally high and long-lived plasma concentrations of parent drug; no N-acetyl metabolite could be detected. While 2 and 3 had no pharmacologically relevant effects on hexobarbital-induced sleeping time in mice, 4 was a potent, dose-dependent potentiator of sleeping time. Oral administration of 375 micrograms/kg led to a 61% increase in sleeping time relative to control values. Thus, 4 represents one of the most potent potentiators of hexobarbital-induced sleeping time described to date.

Pharmacokinetics, metabolism, and disposition of 6-chloro-2,3,4,5-tetrahydro-3-methyl-1H-3-benzazepine (SK&F 86466) in rats and dogs.

The pharmacokinetics and metabolism of 6-chloro-2,3,4,5-tetrahydro-3-methyl-1H-3-benzazepine (SK&F 86466) have been studied in rats and dogs. Using radiolabeled SK&F 86466, it was shown that the compound was completely absorbed from the gastrointestinal tract following oral administration. Most of the administered radioactivity (approximately 80%) was excreted in urine with the remainder excreted in feces via the bile. Very little of the parent compound was excreted unchanged in the urine. The major urinary metabolite, accounting for about 55% of the dose in rat and 35% in dog, was the N-oxide. N-Demethylation also occurs in both species, and in the rat approximately 20% of the dose is metabolized by this route. The plasma concentration vs. time curves following iv administration were analyzed using a two-compartment open model. The distribution phase half-life was 0.24 hr in the rat and 0.37 hr in the dog. In both species the terminal half-life was approximately 2 hr. The volume of distribution at steady state in the rat was 12.1 liters/kg and in the dog was 8.2 liters/kg. About 55% of the drug in plasma was bound to protein in both species so that the volume of distribution of the free drug was 27 liters/kg in the rat and 19 liters/kg in the dog. The clearance of SK&F 86466 from blood was very high in both the dog (56 ml/min/kg) and the rat (191 ml/min/kg). Since less than 1% of the compound was excreted unchanged in urine, the clearance was almost entirely metabolic.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas-chromatographic quantification of methylphenidate in plasma with use of solid-phase extraction and nitrogen-sensitive detection.

The gas-chromatographic assay for methylphenidate described here involves isolation by solid-phase extraction and quantification by thermionic nitrogen-phosphorus detection. Methylphenidate and the internal standard, ethylphenidate, are extracted from plasma by partition onto C2 reversed-phase packing. Methylphenidate and ethylphenidate are eluted, dried, derivatized with trifluoroacetic anhydride, and gas-chromatographed, with nitrogen-sensitive detection. The standard curve for the assay is linear in the range 5-100 micrograms/L. The within-run CV is less than 4%, the between-run CV less than 6%. Mean analytical recovery of methylphenidate was greater than 90%. The smallest measurable concentration is 2 micrograms/L. The sensitivity, reproducibility, and economy of this assay make it suitable for clinical monitoring and pharmacokinetic studies.