Population pharmacokinetics of levodopa in patients with Parkinson's disease treated with tolcapone

OBJECTIVE: To use pharmacostatistical models to evaluate the overall exposure of patients with Parkinson's disease to levodopa in the presence and absence of tolcapone. METHODS: Four hundred twelve patients with Parkinson's disease with fluctuating and nonfluctuating responses to levodopa participated in three multicentered, parallel, double-blind, placebo-controlled dose-finding studies and received either placebo or tolcapone in addition to levodopa-decarboxylase inhibitor therapy. Sparse blood samples were obtained from 393 patients for levodopa and 3-O-methyldopa assay, and the data were analyzed with use of the NONMEM program. RESULTS: The fraction of levodopa metabolized to 3-O-methyldopa was substantially reduced by the co-administration of tolcapone (by 65%, 74%, and 84% with tolcapone doses of 50, 200, and 400 mg, respectively, in fluctuators, and by 50% and 90% with doses of 200 and 400 mg, respectively, in nonfluctuators). This led to an overall reduction in levodopa clearance (CL) of approximately 15% to 25% in fluctuators and 20% to 30% in nonfluctuators. Because this was partly compensated for by a reduction in levodopa dose in these studies, the total daily exposure of patients to levodopa was only slightly increased (11% to 16%). The peak-trough fluctuations of plasma levodopa (Cmax-Cmin) were reduced in both populations in a dose-dependent fashion. CONCLUSIONS: Tolcapone effectively inhibited the formation of 3-O-methyldopa and resulted in a decrease in levodopa CL. The consequent increase in levodopa bioavailability was mostly offset by reductions in levodopa dose. It is possible that decreased fluctuations in plasma levodopa concentrations rather than increased levodopa exposure may explain the clinical benefits obtained with tolcapone.     

A sensitive fluorimetric method for determination of platelet-bound and plasma free serotonin.

A sensitive and specific fluorimetric assay for blood platelet-bound and plasma free serotonin is described. Serotonin is concentrated and purified on Amberlite CG-50 resin, eluted by 0.15 mol/l HCl and its native fluorescence is read at 295/350 nm. The good recovery (90% about), reproducibility and sensitivity (the smallest amount detectable is 5 ng) make the assay particularly useful for the detection of free serotonin in plasma. The whole procedure is rapid enough to permit the analysis of 15--20 samples within one working day and thus the method is suitable for routine determination of serotonin in biological specimens.     

Semiautomatic bioluminescence determination of glycerol using a computer controlled luminescence analyser (Berthold LB 950 T)

A semiautomatic determination of glycerol is described, in which luminescence produced by bacterial NADH-linked luciferase is measured by an automatic luminescence analyser (Berthold LB 950 T). The glycerol determination is based on the enzymatic conversion of glycerol to 3-phosphoglycerate, made irreversible by the presence of arsenate. NADH, formed in the glycerol-3-phosphate and glyceraldehyde-3-phosphate dehydrogenase reactions, is subsequently determined by the bacterial luciferase system. Stable kinetics of light emission were obtained by reducing the catalytic concentration of NAD(P)H: FMN oxidoreductase from 85 U/1 to 8.5 U/1. This method was applied to serum samples and validated by comparison with an enzymatic fluorimetric method. The new method is approximately 10 times more sensitive than the fluorimetric one. Moreover, it is simpler, more convenient, less time consuming and also less expensive than spectrophotometric, fluorimetric or radiochemical methods used for glycerol determination.     

Simultaneous determination of lidocaine and its principal metabolites by liquid chromatography on silica gel, with aqueous eluent

We describe the simultaneous determination of lidocaine and its pharmacologically active metabolites, monoethylglycinexylidide and glycinexylidide, in plasma by "high-performance" liquid-chromatography. By use of a bare ( unbonded ) silica gel with aqueous eluents, separations of organic amines such as lidocaine and its metabolites, which are very difficult and have a poor peak symmetry on bonded reversed-phase packings, were easily accomplished with a good peak symmetry. The method is sufficiently precise, sensitive, and specific. Analytical recoveries of all compounds were greater than 90%; CVs for reproducibility were less than 5% for all compounds; the lower detection limits were 0.1 mg/L or less. This method can be used to monitor the concentrations of these compounds in plasma and to prevent the concentration-related side-effect(s).     

Analysis of total urinary catecholamines by liquid chromatography: methodology, routine experience and clinical interpretations of results

A simple routine method is described for simultaneous assay of total urinary adrenaline, noradrenaline and dopamine. The catecholamines are pre-purified on a small ion-exchange column, separated by reversed phase ion-pair liquid chromatography, and are quantitated by electrochemical detection. The method was routinely applied to 422 urines. Elevated values were found in four urine specimens obtained from patients with histologically proven phaeochromocytomas. Virtually no interference by endogenous or exogenous compounds was found. Values for urinary catecholamines determined by fluorimetric analysis agreed with those obtained by high pressure liquid chromatography with electrochemical detection. Within-day CVs for the compounds ranged from 5.2-11.9%, between-day CVs from 3.3-6.6%. The normal range (95% confidence level) was 20-230 micrograms/24 h for noradrenaline and 1-35 micrograms/24 h for adrenaline.     

Simultaneous electrochemical determination of levodopa and piroxicam using a glassy carbon electrode modified with a ZnO–Pd/CNT nanocomposite

A highly conductive electrochemical sensor was constructed for the simultaneous electrochemical determination of levodopa and piroxicam by modification of a glassy carbon electrode with a ZnO–Pd/CNT nanocomposite (GCE/ZnO–Pd/CNTs). The ZnO–Pd/CNT nanocomposite was synthesized by the sol–gel procedure and was characterized by EDAX, MAP and SEM. The sensor was shown to improve the oxidation signal of levodopa and piroxicam by ∼70.2-fold and ∼41.5-fold, respectively. This marks the first time that the electrochemical behavior of levodopa and piroxicam have been investigated at the surface of GCE/ZnO–Pd/CNTs. The voltammogram showed a quasi-reversible signal and an irreversible redox signal for electro-oxidation of levodopa and piroxicam, respectively. The GCE/ZnO–Pd/CNTs showed a linear dynamic range of 0.6 to 100.0 μM (at a potential of ∼180 mV) and 0.1 to 90 μM (at a potential of ∼480 mV) with detection limits of 0.08 and 0.04 μM for the determination of levodopa and piroxicam, respectively. GCE/ZnO–Pd/CNTs were then applied for the determination of levodopa and piroxicam in real samples.

A highly conductive electrochemical sensor was constructed for the simultaneous electrochemical determination of levodopa and piroxicam by modification of a glassy carbon electrode with a ZnO–Pd/CNT nanocomposite (GCE/ZnO–Pd/CNTs).     

高效液相色谱法测定人血清中褪黑素的浓度

目的用反相高效液相色谱法测定血清中褪黑素的含量。方法采用荧光检测器检测20例自愿者血清中的褪黑素。结果血清中褪黑素最低检测浓度为0.5pg·ml-1,检测限0.2pg,褪黑素在1.0～500pg·ml-1之间呈线性关系,回归方程Y=65744.7x-220.6(r=0.9989,P<0.05),回收率>94.7%,日间、日内变异系数均在10%以下。结论用反相高效液相色谱法测定血清中褪黑素的含量灵敏、快速、准确,为褪黑素在体内代谢等研究提供方法,对临床合理补充外源性褪黑素具有指导性。     

Novel biotinylated acridinium derivatives: new reagents for fluorescence immunoassays and proteomics

BACKGROUND: The favorable properties of acridinium derivatives over conventional fluorescent probes have attracted considerable interest. These conjugates have found wide utility in tests developed for medical diagnosis providing at least comparable sensitivity to radioimmunoassay (RIA) and enzyme immunoassay (EIA) procedures. METHODS: In this paper we describe the synthesis, luminescent properties and immunoassay applications of two novel biotinylated acridinium derivatives, 9-(2-biotinyl-oxyethyl)-carboxylate-10-methyl-acridinium triflate, BOCMAT and 9-(2-biotinyl-amidoethyl)-carboxylate-10-methyl-acridinium triflate, BACMAT. RESULTS: The chemiluminescence efficiency of the novel reagents is high in polar aprotic solvents and attains detection limits down to 7.28 x 10(-8) M, while the fluorescence efficiency has its maximum in aqueous solutions with detection limits down to 1.94 x 10(-10) M. The above novel compounds were applied in the fluorimetric determination of solid phase-immobilized biotinylated mouse IgG and the detection limit was found to be approximately 1 microg/assay ( approximately 7 pmol/assay). CONCLUSIONS: The new streptavidin-based detection reagents were synthesized can be used for the development of highly sensitive solid-phase fluorescence-based immunoassays and may find important applications in proteomics.     

Clinical trial on the use of cytidine diphosphate choline in Parkinson's disease

Thirty patients with Parkinson's disease, treated with levodopa for the past few years, concomitantly received 500 mg of cytidine diphosphate choline (CDPC) daily for 30 days. Significant improvements in some of the neurologic signs and in several electrophysiologic parameters measuring the traction reflex and the active contraction were observed. A greater stability of therapeutic response between doses of levodopa was also seen, although the incidence of dyskinesia increased. In a second stage of CDPC treatment, also lasting 30 days, the dose of levodopa was reduced by one-third, and the incidence of dyskinesia dropped to its previous level, but the therapeutic response remained stable. Addition of CDPC produced significant increases in plasma concentrations of dopa and homovanillic acid, with no modifications in tyrosine or 3-O-methyldopa concentrations. A significant increase in the number of lymphocytic dopaminergic receptors also occurred.     

A liquid chromatographic method for the determination of AY-25,712, a lipid-lowering agent, in serum

We report a sensitive and specific method for the determination of AY-25,712 concentrations in rat, dog and human serum by liquid chromatography with UV detection. The detection limit is 25 ng/mL, based on 2 mL of serum or plasma. The method has been validated in human volunteers receiving single oral doses of AY-25,712 (25 to 900 mg).