High-performance liquid chromatographic assay for acetaminophen and phenacetin in the presence of their metabolites in biological fluids

Determination of paracetamol in pure and pharmaceutical dosage forms by pulse perturbation technique

A new procedure for kinetic determination of paracetamol in pharmaceuticals is proposed. The method is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system being in a stable non-equilibrium stationary state close to the bifurcation point. In the case considered as the matrix system, the Bray-Liebhafsky oscillatory reaction is used. The response of the matrix system to the perturbations by different concentrations of paracetamol is followed by a Pt-electrode. Proposed method relies on the linear relationship between maximal potential shift, DeltaEm, and the logarithm of added paracetamol amounts. It is obtained in optimized experimental conditions for variable amounts of paracetamol in the range 0.0085 and 1.5 micromol. The sensitivity and precision of proposed method were quite good (0.0027 micromol as the limit of detection and 2.4% as R.S.D.). Some aspects of possible chemical interactions between paracetamol and matrix are discussed. Applicability of the proposed method to the direct determination of paracetamol in pharmaceutical formulations was demonstrated.

Spectrofluorimetric determination of paracetamol in pharmaceuticals and biological fluids

A spectrofluorimetric method for the determination of paracetamol is presented, based on the oxidation of the analyte to give the fluorophore 2,2'-dihydroxy-5,5'-diacetyldiaminebiphenyl. Sodium hypochlorite was used as an oxidizing reagent and the optimum pH was found to be 10.0 (sodium carbonate-boric acid buffer solution). The linear concentration range of application was 0.1-100.0 micrograms ml-1 of paracetamol, the detection limit 0.01 micrograms ml-1 and the relative standard deviation 1.2%. The method has been satisfactorily applied to the determination of paracetamol in pharmaceutical formulations and biological fluids.

High-performance liquid chromatographic determination of pentamidine in plasma

This report describes the analysis of pentamidine by isocratic reversed-phase high-performance liquid chromatography (HPLC) using a commercially available compound (melphalan) as the external standard. Previously described assays use ion-pairing HPLC, an internal standard (hexamidine) that is not readily available, and require a relatively large sample size. In the present assay, pentamidine was extracted from plasma using solid-phase extraction and was analyzed using a C18 column and a mobile phase containing 18% acetonitrile, 2% methanol, 0.2 M ammonium acetate and 0.5% triethylamine. The identity of the eluting peaks was verified using a diode array detector. The extraction yield of pentamidine was 82%. The limit of detection was 8.6 ng/ml with a sample size of 100 microliters. The inter-day and intra-day coefficients of variation ranged between 0.3% and 10% with an average of 5%. This method was applied to study the pharmacokinetics of pentamidine in rodents.

Rapid high-performance liquid chromatographic assay of acetaminophen in serum and tissue homogenates

The quantitation of a hepatorenal toxic drug, acetaminophen, in blood and target organ tissues is needed for toxicokinetic and distribution studies. A rapid, sensitive and simple method is described to assay acetaminophen in rat serum and liver or kidney homogenates by reversed-phase high-performance liquid chromatography, using an octadecyl (3 micron particle size) Apex column, a mobile phase consisting of a mixture of distilled water-acetonitrile (86:14) and ultraviolet detection at 245 nm. Short retention times of ca. 3.75 and 6.25 min are observed for acetaminophen and the internal standard (sulfamerazine), respectively. A sensitivity of 50 ng/ml is easily achieved for 100-microliter serum and liver or kidney homogenate samples. The proposed method proved to have satisfactory recovery, precision and accuracy. The preliminary results obtained with human plasma of volunteers and of patients treated with various drugs show that the assay, with a sensitivity of 25 ng/ml, would be of considerable interest in clinical monitoring of acetaminophen.

The oxidation of p-phenetidine by horseradish peroxidase and prostaglandin synthase and the fate of glutathione during such oxidations

The oxidation of p-phenetidine by horseradish peroxidase and prostaglandin synthase was investigated. The existence of a free radical intermediate formed during enzymatic oxidation was supported by a ratio of hydrogen peroxide: p-phenetidine consumed of 1:2 in the horseradish peroxidase system. Furthermore in both enzyme systems a rapid oxidation of added glutathione was observed and in the presence of the thiol there was a decreased removal of p-phenetidine. This suggests the reduction of a p-phenetidine radical by glutathione generating p-phenetidine and a thiyl radical. The latter react with oxygen and a rapid oxygen uptake was observed during enzymic oxidation in the presence of thiols. That p-phenetidine radicals were produced during horseradish peroxidase catalyzed oxidation of p-phenetidine was supported by experiments using the spin probe OXANOH. This was oxidized to its stable free radical form (OXANO.) in an enzyme- and substrate-dependent reaction and the EPR signal obtained was not decreased by SOD (80 micrograms/ml) or benzoate (10-100 mM). TLC characteristics of the products of the oxidation of p-phenetidine by both enzymes were almost identical inferring a similar mechanism of oxidation. Two of the metabolites were characterized by mass spectrometry and by comparison with reference compounds prepared by chemical oxidation. One metabolite was identified as 4,4'-diethoxyazobenzene, which further supports a radical mechanism, and the other was a p-phenetidine trimer which could exist in both oxidized and reduced forms. On the basis of these observations a mechanism for the oxidation of p-phenetidine and the fate of glutathione during such oxidations is proposed.

Rapid thin-layer chromatography of various weak analgesics in saliva

A thin-layer chromatographic method was developed to analyze phenacetin, 4-amino-phenazone and N-methyl-4-aminophenazone (5 and 1.25 micrograms/ml); bucetin (4-ethoxy-beta-hydroxybutyranilide), propyphenazone and N-acetyl-4-aminophenazone (2.5 and 1.25 micrograms/ml); phenazone (15 and 1.25 micrograms/ml); and N-acetylsalicylamide (0.25 micrograms/ml). The method was designed to study the bioavailability of different commercial tablets from salivary concentration data.