G. Solomonraj

The estimation of acetylsalicylic acid and salicylate in biological fluids by gas-liquid chromatography

A gas‐liquid chromatographic method is described for the simultaneous separation and determination of acetylsalicylic acid (ASA) and salicylic acid (SA) in biological fluids. The salicylates are completely extracted from deproteinized plasma or urine at pH 2 with ether containing p‐toluic acid as the internal standard. The silylated derivatives are formed using bis(trimethylsilyl) trifluoroacetamide and separated at 150° on preconditioned 100–120 mesh Gas‐Chrom Q coated with 5% OV17 packed into a 6 ft, 1/4 inch o.d. glass column in a gas chromatograph with a flame ionization detector and integrator. Detector response is linear over the range from 0–2 mg ml−1 for SA and from 0–100 μg ml−1 for ASA. The time required for the analysis of SA alone or with ASA is about 80 min, the analysis of ASA alone requires about 20 min. The precision of the method is 1 % or better for drug concentrations above 10 μg ml−1. The limits of detectability for SA and ASA are 1 and 2 μg ml, respectively.

Analysis of warfarin in plasma by high-pressure liquid chromatography

An improved high-pressure liquid chromatography method for the estimation of warfarin in plasma was developed. Plasma was acidified and extracted with ethylene dichloride spiked with methylated warfarin [3-(alpha-acetonylbenzyl)-4-methoxy-coumarin] as internal standard. The residue, redissolved in dioxane, was chromatographed on a reversed-phase column using a mobile phase of 40% dioxane in water (pH 4.2) on a high-pressure liquid chromatograph fitted with an UV absorbance detector. Recoveries from extraction, quantitated using tracer amounts of [14C]warfarin and methylated [14C]warfarin were 92.2 +/- 3.16% and 82.33 +/- 1.03%, respectively. The standard curve was linear between o.625 and 5.0 microng/ml. Detection was sensitive to approximately 0.5 microng/ml and specific without the inter ference of normal plasma constituents and warfarin metabolites.

Metabolism of [14C]Paracetamol and its Interactions with Aspirin in Hamsters

1. The metabolism of [14C]paracetamol (150 mg/kg) and its interactions with aspirin (200 mg/kg) were studied in male hamsters. 2. Aspirin was found to slow the rate of paracetamol absorption from the gastro-intestinal tract, but did not affect the rate of elimination. 3. Metabolism studies showed that greater than 80% of the radioactivity was excreted in the urine in 24 h. Paper chromatography of the urine separated the radioactivity into five peaks, four of which were identified as paracetamol and its glucuronide, sulphate and mercapturate conjugates. 4. The other peak, comprising of less than 10% of the total radioactivity, was a mixture of two or more other metabolites. A major component was isolated and characterized as methyl 2-hydroxy-5-acetamidophenyl sulphone. 5. Aspirin inhibited the metabolism of paracetamol by the sulphate conjugation pathway.

Fate of [14C]warfarin in guinea-pigs: effect of a concomitant single dose of salicylate.

When a single dose of sodium salicylate (177·8 mg kg−1, by mouth) was given with [14C] warfarin (1 mg kg−1, i.p.) to guinea‐pigs, the salicylate depressed the blood concentrations of 14C for 6 h. At 1 h, salicylate increased the distribution of 14C in the liver and brain, but at 1 and 6 h it was decreased in the blood and kidney. A significant portion of the 14C was excreted into the bile, but was subject to enterohepatic circulation and then excreted by the kidney. There was an enhancement of the biliary elimination of 14C in the first 5 h after salicylate and a decrease in 14C concentration in blood; the proportion of warfarin to its metabolites excreted in the urine and bile was unchanged. Salicylate displaced serum protein bound [14C]warfarin in vitro. Salicylate increases the initial biliary elimination of warfarin by displacing some of that bound to plasma protein. This facilitated uptake of warfarin by the liver where it was metabolized. This effect of salicylate did not modify the hypoprothrombinaemia produced by warfarin.