Drugs online research references
Eur J Clin Pharmacol. 1980 Aug;18(2):151-17.
Decreased tyramine sensitivity after discontinuation of amitriptyline therapy. An index of pharmacodynamic half-life.
Ghose K.
A combined pharmacodynamic and pharmacokinetic approach was made to study the pharmacodynamic half-life (Pd1/2) of amitriptyline (AT). Six depressed patients were treated with 150 mg of amitriptyline as a single oral dose at night for six or more weeks. Decreased tyramine sensitivity (DTS), an index of this drug's pharmacological activity, was determined serially at various intervals after the last dose. Plasma concentrations of AT and nortriptyline (NT) were also estimated at above intervals. It was possible to detect DTS for 228-300 h after the last oral dose and the mean Pd1/2 of this decline of pharmacodynamic effect was observed to be 135 h. However, no measurable amount of AT or NT was present after 84 h and the mean elimination plasma half-life (t1/2) of AT and NT were 37.7 and 38.9 h, respectively. (In this study, pharmacokinetic parameters of NT were directly related with those of AT.) Prolonged pharmacodynamic effect of this drug after discontinuation should be borne in mind in order to avoid drug interactions and autonomic complications, especially after overdosage. Pd1/2, as assessed by DTS, correlated directly with the t1/2 (r = 0.91) and inversely with the plasma clearance rate (r = 0.60) of NT. DTS test can be used as an alternative technique to assess the biological activity of a drug which inhibits noradrenaline reuptake mechanism and/or blocks alpha-adrenoceptors at the peripheral neuronal sites, especially, where facilities to measure plasma concentrations of such drugs are limited.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7428796&dopt=Abstract
Ther Drug Monit. 1983;5(3):279-92.
Liquid chromatographic separation of antidepressant drugs: I. Tricyclics.
Beierle FA, Hubbard RW.
A simple normal-phase (silica), high-performance liquid chromatographic (HPLC) assay of amitriptyline (AMI), doxepin (DOX), imipramine (IMI), nortriptyline (NORT), desmethyldoxepin (DESDOX), desipramine (DESIP), and protriptyline (PRO) in serum with no coelution is described here. Trimipramine and promazine were used as internal standards. Extraction of the 1.0-ml serum samples (collected in plastic) was done with Bond-Elut C18 columns. The compounds of interest were eluted with 10 mM methanolic ammonium acetate. The eluates were evaporated at 56-58 degrees C and reconstituted with 200 microliters of the mobile phase. The mobile phase was absolute ethanol-acetonitrile-tert-butylamine (98:2:0.05, vol/vol/vol). Detection of eluted drugs was at 254 nm at 0.01 absorbance units full scale (AUFS), except for PRO, which was detected at 229 nm at 0.02 AUFS. Absolute recoveries were 87-97%. A 5-micron silica (4.6 X 250 mm) HPLC column was used; results with a 10-micron silica column (3.9 X 300 mm) are also presented. Peak height ratios with trimipramine were linear for each analyte between 25 and 1200 ng/ml. Peak height ratios with promazine as the internal standard were linear for each analyte between 25 and 600 ng/ml. Detection limits under the conditions described were 2 ng/ml for AMI, DOX, and IMI, 4 ng/ml for NORT, DESDOX, and DESIP, and 10 ng/ml for PRO. Coefficients of within-day and day-to-day variation at three concentration levels were less than 9.8% and less than 11.2%, respectively. The hydroxylated metabolites of IMI, DES, NORT, and the cis isomer of DOX are discussed. Steady-state daily dosages and corresponding serum levels are presented for 69 patients. The total assay time was less than 10 min for DESIP and 12 min for PRO. This assay can be used in correlating serum levels with clinical effects, compliancy, and pharmacokinetic studies.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6636256&dopt=Abstract
J Anal Toxicol. 1990 Sep-Oct;14(5):273-6.
Urinary tricyclic antidepressant screening: comparison of results obtained with Abbott FPIA reagents and Syva EIA reagents.
Meenan GM, Barlotta S, Lehrer M.
Department of Pathology, Long Island Jewish Medical Center, New Hyde Park, New York 11042.
Human urine was tested for tricyclic antidepressants with fluorescence polarization immunoassay (FPIA) reagents on Abbott's ADx system and with EIA reagents on Syva's ETS system. A 75-ng/mL imipramine calibrator cutoff was used with the ADx system and a 300-ng/mL nortriptyline calibrator cutoff with the ETS system. The ETS system was adapted to analyze tricyclic antidepressant (TCA) samples using the Syva Emittox serum TCA assay. Negative urine was spiked with various tricyclic and tetracyclic antidepressants, phenothiazines, and other medications with potential to interfere with the assays. Verification of samples was performed by thin-layer chromatography and gas chromatography/mass spectrometry. The different compounds were added to urine at concentrations of 200, 400 and 1,000 ng/mL. At 1,000 ng/mL all TCA compounds tested gave positive results with the ADx and ETS systems. However, some non-TCA medications spiked at 1,000 ng/mL gave false positive results with both systems. The tetracyclic antidepressants did not cross-react and gave negative results. Clomipramine-spiked urine at 400 ng/mL yielded a false negative result on the ETS system.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2263060&dopt=Abstract
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