Rapid reversed-phase high-performance liquid chromatographic assay of diflunisal in biological fluids

High-performance liquid chromatographic method for the simultaneous quantitation of diflunisal and its glucuronide and sulfate conjugates in human urine

A direct high-performance liquid chromatographic (HPLC) assay was developed to simultaneously quantitate diflunisal and its three known metabolites (i.e., the phenolic and acyl glucuronides and the sulfate conjugate) in human urine. Chromatographically pure standards of the diflunisal conjugates were isolated from urine of volunteers following ingestion of multiple doses of diflunisal (500 mg twice daily). Diflunisal, its three conjugates, and an internal standard (naproxen) were separated on a reversed-phase column using gradient elution. The column eluate was monitored fluorometrically (excitation: 258 nm; emission: 428 nm). Urine samples were diluted with phosphate buffer (pH 5.75) and injected onto the column. The limit of detection was approximately 1 microgram/mL for each conjugate and 0.1 microgram/mL for diflunisal. Due to the presence in most urine samples of significant concentrations of rearrangement products of the biosynthetic 1-O-acyl glucuronide of diflunisal, the acyl glucuronide could not be reliably quantitated by direct injection of diluted urine samples. Instead, diflunisal acyl glucuronide was quantitated indirectly following alkaline hydrolysis of the urine samples. The method has been successfully used to investigate the dose-dependent glucuronidation and sulfation of diflunisal in humans.

Reversed-phase high-performance liquid chromatographic assay for the simultaneous determination of diflunisal and its glucuronides in serum and urine. Rearrangement of the 1-O-acylglucuronide

A reversed-phase ion-pair high-performance liquid chromatographic assay for the simultaneous determination of diflunisal and its ester and ether glucuronide in urine and serum has been developed. The determination of the ester glucuronide in serum has not been previously reported. The genuine glucuronide conjugates isolated from urine were used as standards. The ester glucuronide is found to be unstable, especially in neutral and basic solutions, and special precautions therefore have to be taken during sampling and sample treatment. Nine rearrangement/degradation products of the ester glucuronide were detected.

Separation and identification of non-steroidal antirheumatic drugs containing a free carboxyl function using high-performance liquid chromatography

Different methods for the separation and identification of eighteen non-steroidal antirheumatics (non-steroidal, anti-inflammatory drugs) and the application of these methods for systematic toxicological analysis are reviewed. A method for separating these compounds by high-performance liquid chromatography using an RP-18 column and mixtures of acetonitrile and acetate buffers as eluents is presented and the detectability of these substances with respect to their different UV maxima is discussed.

Assay methodology for quantification of the ester and ether glucuronide conjugates of diflunisal in human urine

Diflunisal is a salicylate derivative with analgesic and anti-inflammatory properties. It is excreted in the urine as an ether glucuronide, a 1-O-acyl glucuronide and as unchanged drug. The 1-O-acyl glucuronide rearranges to isomeric esters of glucuronic acid under neutral to alkaline pH conditions. The development of a urine assay for the conjugates enables the elucidation of diflunisal non-linear pharmacokinetics. The assay quantitates the ether and ester glucuronides and free diflunisal in urine at 0.5-1.0 micrograms/ml. Analysis of the glucuronides does not require authentic standards.