Sample preparation by salts precipitation and quantitation by high-performance liquid chromatography with UV detection of selected drugs in biological fluids

Determination of serum glucose by horseradish peroxidase-catalysed imidazole chemiluminescence coupled to a micro-flow-injection system

The reactivity of flow-injection (FI)-horseradish peroxidase (HRP)-catalysed imidazole chemiluminescence (CL) was studied for continuous determination of hydrogen peroxide (H(2)O(2)) and serum glucose with immobilized glucose oxidase. Light emission by the HRP-catalysed imidazole CL was obtained when immobilized HRP, alkaline imidazole (in Tricine solution, pH 9.3) and H(2)O(2) were reacted at room temperature. The optimal pH for the CL reaction was 9.3 and the optimal concentration of imidazole was 100 micromol/L. When no imidazole was added, the light intensity of the same H(2)O(2) specimen decreased to a level that could not be quantitatively determined. The spectrum of the light emitted by imidazole CL was in the range 400-600 nm with a peak at 500 nm. The calibration equation for determination of H(2)O(2) was y = 9860x(2) + 3830x + 11,700, where y = light intensity (RLU) and x = concentration of H(2)O(2) (micromol/L). The detection limit of H(2)O(2) was 5 pmol, and the reproducibility of the H(2)O(2) assay was 2.3% of the coefficient of variation (H(2)O(2) 48 micromol/L, n = 13). The CL method was successfully applied to assay glucose after on-line generation of H(2)O(2) with the immobilized glucose oxidase column, resulting in good reproducibility (CV = 3.3% and 1.0% for the standard glucose and the control serum, respectively).

Rapid and sensitive high performance liquid chromatographic method for the determination of itraconazole and its hydroxy-metabolite in human serum

Published high performance liquid chromatographic (HPLC) methods for the determination of itraconazole (ITZ) in biological matrices are labor intensive, extraction-based procedures which operate at a pH approaching the limit of column tolerance, and unless modified, cannot measure its hydroxy-metabolite (OH-ITZ). A protein precipitation-based method requiring no solvent extraction and utilizing a base-deactivated C18 analytical column to minimize peak tailing is described herein. Calibration curves for OH-ITZ and ITZ were linear from 25-1500 ng ml-1 (r2 > or = 0.999). Intra-assay relative standard deviations (R.S.D.) were below 12%. Inter-assay R.S.D. were below 14%. This method provides a rapid means for the accurate and precise determination of both OH-ITZ and ITZ concentrations in human serum.

Intestinal absorption of aspartame decomposition products in adult rats

The dipeptide sweetener aspartame (N-L-alpha-aspartyl-L-phenylalanine, 1-methyl ester; alpha-APM) is relatively stable in dry powder form. However, when exposed to elevated temperature, extremes of pH and/or moisture, alpha-APM is converted into a variety of products. In aqueous solution alpha-APM decomposes to yield methanol, two isomeric forms of L-aspartyl-L-phenylalanine (Asp-Phe) [alpha-Asp-Phe and beta-Asp-Phe], and APM's diketopiperazine cyclo-Asp-Phe. Depending on beverage storage conditions, individuals drinking alpha-APM-sweetened beverages may consume small quantities of these three compounds. Relatively little has been published about the metabolism of beta-Asp-Phe and cyclo-Asp-Phe. We compared the absorption and metabolism of alpha-Asp-Phe, beta-Asp-Phe, and cyclo-Asp-Phe with that of L-phenylalanine (Phe) in adult rats. Steady-state perfusion studies of rat jejunum indicated rapid carrier-assisted uptake of Phe and alpha-Asp-Phe, but only slow passive diffusion of beta-Asp-Phe and cyclo-Asp-Phe from the lumen. Homogenates of rat intestinal mucosa, liver, and cecal contents, as well as homogenates of pure cultures of Escherichia coli B, catalyzed the hydrolysis of alpha-Asp-Phe, but not cyclo-Asp-Phe. Homogenates of E coli and rat cecal contents, but not homogenates of rat liver or intestinal mucosa catalyzed the hydrolysis of beta-Asp-Phe.

Serum concentrations of salicylate and naproxen during concurrent therapy in patients with rheumatoid arthritis

The kinetic interaction between salicylate and naproxen was investigated in 25 rheumatoid arthritis patients. Kinetic interactions were tested in serum after patients had been on each drug regimen for 1 month. Salicylate decreased serum naproxen concentration from 89.5 mg/liter to 65.9 mg/liter (P less than 0.001) and increased serum naproxen clearance by 56%. Naproxen had minimal effect on serum salicylate concentrations.

Plasma and urine diketopiperazine concentrations in normal adults ingesting large quantities of aspartame

In aqueous solution, aspartame can cyclicize to form its corresponding diketopiperazine (3-carboxymethyl-6-benzyl-2,5-diketopiperazine; DKP) and methanol. We measured plasma and urinary concentrations of DKP in samples obtained from six normal adult subjects ingesting 2.2 mg DKP/kg body weight. The DKP was administered as part of a dose of 200 mg aspartame/kg body weight. DKP concentrations in plasma were below the detection limit (less than 1 microgram/ml) of the high-pressure liquid chromatographic method at each time interval after ingestion at which they were measured. Mean (+/- SD) total urinary DKP excreted during the first 24-hr period after dosing was 6.68 +/- 1.30 mg (4.83 +/- 0.23% of the ingested DKP dose). Approximately 44% of the total DKP excreted was excreted in the first 4 hr after dosing.

A controlled study of concurrent therapy with a nonacetylated salicylate and naproxen in rheumatoid arthritis

Previous studies of combinations of nonsteroidal drugs used in the treatment of rheumatoid arthritis (RA) have yielded conflicting results. We used standard methods to measure disease activity and high pressure liquid chromatography to measure plasma drug concentrations. We used doses of choline magnesium trisalicylate, adjusted to achieve therapeutic serum salicylate concentrations, and naproxen in a randomized, double-blind, placebo-controlled cross-over study of full dose trisalicylate (CMT), full dose naproxen (N), full dose of both (CMT-N), and half dose of both (cmt-n) to examine their relative efficacy and toxicity in treating RA. CMT-N was statistically superior to all other treatments in only 1 of 12 efficacy variables, but was equal to N and better than CMT or cmt-n for 7 variables. There were minimal differences among treatments for the other 4 efficacy variables. The mean percentage difference for the efficacy variables between CMT-N and N was 3%, between CMT-N and CMT was 10.6%, and between CMT-N and cmt-n was 10.5%. Thirteen percent of patients manifested toxic reactions during the initial open dose-adjustment salicylate run-in phase. During the double-blind phases of the study, CMT-N was more toxic than N, CMT, or cmt-n (7.5% versus 3.4%, 1.8%, and 3.7%, respectively). Tinnitus was more common when full-dose CMT was used; N (N or CMT-N) was associated with increased skin toxicity. Gastrointestinal complaints were equally common with all regimens. CMT-N, although sometimes statistically superior to CMT, N, or cmt-n, showed no clinically important additive or synergistic effect versus N or CMT alone.

Time-dependent inhibition of platelet cyclooxygenase by indomethacin is slowly reversible

Indomethacin has been characterized in vitro as a time-dependent, irreversible inhibitor of cyclo-oxygenase, yet its effects on human platelets have been found to be reversible in vivo. To understand this apparent contradiction, we have investigated the kinetics of recovery of platelet thromboxane production after a single dose of indomethacin. The inhibition of platelet thromboxane production was greater than would be expected from the levels of indomethacin found in the plasma suggesting that the time-dependent inhibition occurs in vivo. Yet recovery of platelet thromboxane production was faster than expected for an irreversible inhibitor, with 50% of control values being regained within 24 hours after ingestion of the drug. When platelets were isolated and resuspended in homologous drug-free plasma, slow recovery of thromboxane production was seen to occur with 50% of control activity regained in 100 minutes. This recovery was much slower than that seen from a competitive inhibitor of cyclo-oxygenase, ibuprofen. Ibuprofen-treated platelets recovered nearly completely immediately on being resuspended in drug-free plasma. When microsomes were isolated from platelets, then treated with indomethacin, no time-dependent recovery of activity was seen. The recovery of cyclo-oxygenase after indomethacin inhibition appears to be limited to the unperturbed enzyme in its natural milieu.

Drug level monitoring: chromatography of some minor groups of drugs

Some important facts about the chromatographic separation of a number of selected categories of drugs are summarized. The data refer to the chromatographic method of choice, stationary phase, mobile phase (carrier gas), detection procedure and (where available) method sensitivity. Also, fundamental instrumental parameters, namely injector, column and detector temperature, carrier gas and mobile phase flow-rate and gradient set-up are reported here. In all cases also the source material used for analysis is specified. The data are presented in table form, each table dealing with a particular category of drugs. The following categories of drugs are being dealt with: anthelmintics, antiarteriosclerotics, antibacterials, anticholinergics and cholinergics, anticoagulants, antidiabetics, antiemetics, antimycotics, antihistamines, antimalarials, antiparasitics, antiparkinsonics, antitussives, antiulcer drugs, antiviral compounds, appetite depressants and immunosuppressives.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

High-performance liquid chromatography with polarographic and voltammetric anodic detection: simultaneous determination of allopurinol, oxipurinol and uric acid in body fluids

Allopurinol, oxipurinol and uric acid have been determined in human serum and urine by liquid chromatography with electrochemical detection. In particular the use of a polarographic detector operating in the oxidative mode, whose principle of detection is based on the property of allopurinol, oxipurinol and uric acid to form insoluble anodic films on mercury, is described. The performance of such a detector is compared with that of a glassy carbon wall-jet detector. Different procedures for sample pretreatment have been evaluated.