Imprinted ß-ketoenamine-linked covalent organic frameworks as dispersive sorbents for the fluorometric determination of timolol.

Timolol accompanied the formation of fluorescent ß-ketoenamine-linked covalent organic frameworks (COFs) via the Sc(Tof)3-catalyzed condensation of derivated carbaldehyde and hydrazide in a 1,4-dioxane/mesitylene porogen to construct timolol-imprinted COFs (TICOFs). With high imprinting factors, the synthesis-optimized TICOFs were characterized by fluorescence, UV-Vis spectrometry, X-ray diffraction, N2 adsorption/desorption analyses, scanning electron microscopy, and FTIR spectrometry. The TICOF fluorescence measured at 390 nm/510 nm is dynamically quenched by timolol and was thus utilized to quantify timolol in a linear range of 25-500 nM with a LOD of 8 nM. The TICOF recovered 99.4% of 0.5% timolol maleate in a commercial eye drop (RSD = 1.1%, n = 5). In addition, TICOF was used as a dispersive sorbent to recover 95% of 2.0 nM timolol from 20 mg of TICOF in 25 mL phosphate buffer. Dilution factors of 25 and 75 were the maximum tolerated proportions of the urine and serum matrix spiked with 2.0 nM timolol to reach recoveries of 92.4% and 90.3%, respectively.

Quantitative determination of oxprenolol and timolol in urine by capillary zone electrophoresis.

A simple capillary zone electrophoretic method with UV detection has been developed for the quantitative determination of the beta-adrenoreceptor antagonists (beta-blockers) oxprenolol and timolol in human urine, preceded by a solid-phase extraction step. The electrophoretic separation was performed on a 78 cm x 75 microm I.D. fused-silica capillary (effective capillary length: 70 cm). The electrolyte consisted of a Na2B4O7-H3BO3 (50 mM), pH 9. The introduction of the sample was made hydrostatically for 20 s and the running voltage 25 kV at the injector end of the capillary. Photometric detection was used at a wavelength of 229 nm for oxprenolol and 280 nm for timolol. Under these conditions oxprenolol migrated at 4.76+/-0.05 min and timolol at 4.97+/-0.05 min. The solid-phase extraction methods were optimised for each beta-blocker and provided recoveries of 72.8% for timolol and 94.52% for oxprenolol. Good resolution from the endogenous compounds present in the urine matrix were achieved for both compounds. The method was applied to the determination of both beta-blockers in pharmaceutical formulations and urine samples obtained from hypertensive patients after the ingestion of a therapeutic dose (in a 24-h time interval after the ingestion). The quantitative results were compared with results previously obtained at our laboratories by HPLC and were found to be in good agreement. Good reproducibility, linearity, accuracy and quantitation limits (in urine) of 0.19 microg/ml for timolol and 0.20 microg/ml for oxprenolol were obtained, allowing the method to be applied to pharmacokinetic studies of these compounds.

Gas chromatography-mass spectrometric analysis of clenbuterol from urine.

Clenbuterol which is mostly used as an anabolic agent. It is also used for treatment of asthma. Clenbuterol was analysed from urine by using gas chromatography-mass spectrometry. GC-MS parameters were determined. Timolol was used as an internal standard. Extraction and derivatisation procedure of clenbuterol from urine were developed. Clenbuterol was extracted by using diethylether/ter-butanol (4:1; v:v) and pH 12 K2CO3/KHCO3 (3:2; w:w) buffer. MSTFA/NH4I (1 ml/10 mg) mixture was used for derivatization of clenbuterol. Selected ions of clenbuterol-bis-TMS were m/z: 405, 337, 336, 335, 300, and 227. Extraction yield and minimum detection limit of clenbuterol from urine were identified. Extraction yield was 94.30% and minimum detection was found 0.02 ng ml(-1) urine. It has been concluded that the GC-MS method is sensitive, accurate, precise, and reproducible for analysing of clenbuterol from urine.

Screening and confirmatory analysis of beta-agonists, beta-antagonists and their metabolites in horse urine by capillary gas chromatography-mass spectrometry.

A method for the screening and confirmatory analysis of beta-agonists and -antagonists in equine urine is described. Following initial enzymic hydrolysis, the basic drugs and metabolites are extracted using Clean Screen DAU or Bond Elut Certify cartridges, and analysed as their trimethylsilyl ether or 2-(dimethyl) silamorpholine derivatives by capillary gas chromatography-mass spectrometry. The method proved to be very sensitive and selective for basic drugs. After administration of therapeutic doses of propranolol, metoprolol, timolol, isoxsuprine and clenbuterol to thoroughbred horses, the parent compound/metabolites could be detected in urine for upto 14-120 h depending on the drug.

Timolol metabolism and debrisoquine oxidation polymorphism: a population study.

1. The metabolism of orally administered timolol (T) to its ring cleavage ethanolamine (TE) and glycine (TG) products was studied in 108 unrelated hypertensive patients. 2. Statistically significant correlations between the 0-8 h urinary debrisoquine/4-hydroxy-debrisoquine ratio and the T/TE (rs = 0.74, P less than 0.001), T/TG (rs = 0.42, P less than 0.001) and T/TE + TG (rs = 0.49, P less than 0.001) ratios were found. 3. The log10 T/TE, T/TG and T/TE + TG ratios from poor metabolisers of debrisoquine (PMs) were grouped at the upper end of a unimodal distribution. 4. These results indicate that timolol metabolism is partly under monogenic control of the debrisoquine-type. 5. The mean +/- s.d. plasma timolol concentration in PMs (82 +/- 43 ng ml-1) was double that in extensive metabolisers (45 +/- 19 ng ml-1) (P = 0.011). The clinical significance of this observation remains to be established.

Pharmacokinetics and beta-blocking effects of timolol in poor and extensive metabolizers of debrisoquin.

We studied the pharmacokinetics and beta-blocking effects of a single, oral 20 mg dose of timolol in six poor metabolizers (PMs) and six extensive metabolizers (EMs) of debrisoquin. The plasma timolol concentration was significantly higher in PMs than in EMs. There was a fourfold difference in mean AUC (1590 +/- 1133 vs. 394 +/- 239 ng X hr/ml; P less than 0.01) and a twofold difference in mean t1/2 (7.5 +/- 3 vs. 3.7 +/- 1.7 hours; P less than 0.01), reflecting differences in oral clearance (13.1 +/- 7.8 vs. 48.5 +/- 23.2 L/hr; P less than 0.01). The degree of beta-blockade was greater in PMs than in EMs at 12 hours (30.9% vs. 18.2%; P less than 0.05) and at 24 hours (28.3% vs. 13.1%; P less than 0.05). In the group as a whole the metabolic ratio correlated positively with both kinetic data and beta-blockade, but some overlap was observed. Hence timolol metabolism appears to be subject to debrisoquin-type polymorphism, which results in interphenotypic variation in plasma concentration and beta-blocking effect.

Urinary metabolites of timolol from humans and laboratory animals. Syntheses and beta-adrenergic blocking activities.

Syntheses are reported for three metabolites (2-4) of timolol (1) formed by oxidative metabolism of the morpholine ring. GLC-MS comparisons are presented which establish that the two metabolites whose structures were previously in question are identical with their synthetic counterparts 2 and 3. In 2, metabolic oxidation of the 4-morpholinyl group of 1 had occurred at the carbon next to oxygen to give the 2-hydroxy-4-morpholinyl moiety, whereas in 3, the morpholine of 1 has been oxidized one step further and then ring opened to produce the N-(2-hydroxyethyl)glycine substituent. Biological testing of synthetic samples of the three major metabolites from human urine (3, 4, and 6) indicated that only 4, in which the morpholine moiety has been degraded to a 2-hydroxyethylamino group, had significant beta-adrenergic blocking activity (one-seventh that of timolol in anesthetized dogs).

Timolol metabolism in man and laboratory anamals.

The two major urinary metabolites of 14C-timolol in man, involving oxidation and hydrolytic cleavage of the morpholine ring, are also observed in both Sprague-Dawley rats and CRCD-1 mice. These are the N-T(4-[3-(1,1-dimethylethyl)amino]-2-hydroxypropoxy)-1,2,5-thiadiazol-3-ylT-N-(2-hydroxyethyl)glycine and 1-(1,1-dimethylethylamino-3-([4-(2-hydroxyethylamino)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol. The former was previously identified erroneously as the isomeric compound 1-(1,1-dimethylethylamino)-3-([4-(N-2-hydroxyethylglycolamido)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol. Rats and mice had two additional metabolites in common, 1-[(1,1-dimethylethyl)amino]-3-([4-(2-hydroxy-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol and a compound now proposed to be the corresponding morpholino lactone 1-[1,1-dimethylethyl)-amino]-3-([4-(2-oxo-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol but for which the corresponding isomeric morpholino lactam structure 1-[(1,1-dimethylenthyl)-amino]-3-([4-(3-oxo-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy))-2-propanol was tentatively proposed in an earlier publication. A metabolite observed in the rat, but not in the other species studied, was 4-(4-morpholinyl)-1,2,5-thiadiazol-3-ol-1-oxide. The metabolic pattern in these rodents does not change significantly after repeated doses. A scheme summarizing the metabolic fate of timolol in man and laboratory animals is presented.