Lack of Evidence for Involvement of P-Glycoprotein in Brain Uptake of the Centrally Acting Analgesic, Tramadol in the Rat

Purpose. Tramadol Hydrochloride is a widely-used centrally acting analgesic drug, which has some features of being a P-gp substrate. The present study evaluates the functional involvement of P-gp in CNS distribution of tramadol. Methods. The possibe involvement of P-glycoprotein in brain distribution of tramadol was evaluated using a pharmacokinetic approach in two groups of Pgp-inhibited and control rats. Six male Sprague-Dawley rats were used in each group to collect plasma and brain at 1, 5, 10, and 30 min following two tramadol doses of 1 and 10 mg/kg. Results. The brain uptake clearances of tramadol in Pgp-inhibited and control rats were 2.47±0.56 and 2.34±0.56 ml min-1g-1, respectively, for 1 mg/kg and 3.50±0.60 and 3.14±1.02 mlmin-1g-1, respectively, for 10 mg/kg dose. The brain-to-plasma concentration ratio (Kp,app) of more than 1 in all the time points following both the high and low dose cases (sometimes more than 3) indicated the brain accumulation of the drug. Linear correlation was found between tramadol dose and both corresponding plasma and brain concentrations, but the presence of a dose-dependency was not confirmed by the data obtained for brain-to-plasma concentration ratio. Conclusion. Considering the results of the previous studies and the present research, it seems that the brain accumulation of tramadol is not affected by P-gp inhibition which implies that there may be some other transport mechanisms involved in BBB transport of tramadol. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page

Simultaneous measurement of formic acid, methanol and ethanol in vitreous and blood samples of postmortem by headspace GC-FID

Abstract Background Formic acid (formate) is the main reason for toxicity and death through methanol poisoning. The simultaneous determination of methanol, ethanol, and formate in the body can help to discover the cause of death and is useful in the diagnosis of acute methanol poisoning. The measurement of formate is not yet available in Iran. With regard to the increasing rate of methanol poisoning and its related mortality in Iran, as well as the main role of formate in methanol poisoning, this study was designed to set up an analytical method for the concurrent determination of ethanol, methanol, and formate. Methods Following the modification of a previously developed gas chromatography method, vitreous and blood samples of 43 postmortem cases with a history of methanol intoxication were collected over a period of 2 years at the Legal Medicine Organization of Mashhad. Thereafter, ethanol, methanol, and formate concentrations were measured by headspace GC/FID. Formate esterification was performed by the methylation of formate with sulfuric acid and methanol. In order to confirm the esterification method for the production of methyl formate, we used gas chromatography with a mass detector (GC/MS) because of its higher sensitivity and accuracy. Furthermore, the correlations between formate and methanol concentrations in blood and vitreous samples, and between formate and methanol were investigated. Results A significant relationship was found only between methanol concentrations in blood and vitreous samples (P < 0.03). Conclusions In postmortems, with the passage of time since alcohol ingestion, the measurement of only methanol concentration cannot determine the degree of toxicity or the cause of death. Therefore, using the present analytical method and measurement of formic acid, we can estimate the degree of toxicity and cause of death

A RAPID AND SENSITIVE HPLC-FLUORESCENCE METHOD FOR DETERMINATION OF MIRTAZAPINE AND ITS TWO MAJOR METABOLITES IN HUMAN PLASMA

A rapid and sensitive HPLC method has been developed for the quantification of mirtazapine (MRZ), a noradrenergic and specific serotonergic inhibitor antidepressant (NaSSA) and its two major metabolites N-desmethylmirtazapine (NDM) and 8-hydroxymirtazapine (8-OHM) in human plasma. The separation was achieved using Chromolith C18 columns and a mobile phase of acetonitrile: phosphate buffer (pH=3, 20:80, v/v) in isocratic mode at a flow rate of 2 ml/min. A fluorescence detector was set at 290 and 350 nm for excitation and emission, respectively. Zolpidem was used as the internal standard. Liquid-liquid extraction was applied for sample clean up. All analytes were eluted in less than 5 minutes with LOQ of 1 ng/ml for MRZ and 2 ng/ml for both NDM and 8-OHM . The developed method was successfully applied to quantify MRZ and its metabolites in plasma of a healthy volunteer