J.Arthur F. de Silva

Determination of clonazepam and flunitrazepam in blood by electron-capture gas-liquid chromatography

Abstract An electron-capture gas-liquid chromatographic assay was developed for the determination of clonazepam (as its methyl derivative) and of flunitrazepam and its N-desmethyl metabolite in blood. The method was used to measure blood levels in man following single oral 2-mg doses of clonazepam and flunitrazepam, and has a sensitivity limit of 0.5 to 1.0 ng of compound per milliliter of blood.

Determiation of retinoic acid (13-cis- and all-trans-) and aromatic retinoic acid analogs possessing anti-tumor activity, in biological fluids by high-performance liquid chromatography

Abstract A sensitive and specific high-performance liquid chromatographic assay was developed for the determination of 13- cis - and all- trans -retinoic acid in blood or urine with an overall recovery of 90 ± 5.0% and a limit of detection of 10–20 ng/ml of sample. The method provides for rapid and simple quantitation of the compounds using 1 ml of blood. The assay was applied in the determination of blood levels of 13- cis -retinoic acid in the dog following intravenus and oral administration of 9.5 mg/kg and 2.0 mg/kg does, and in man following a single 100-mg oral dose and following divided daily doses totalling 2 mg per kg of body weight. The assay is also applicble with minor modifications to the determination of a series of aromatic retinoic acid analogs of clinical interest as anti-tumor agents.

Determination of flurazepam (dalmaneR) and its major metabolits in blood by electron-capture gas-liquid chromatography and in urine by differential pulse polarography

Abstract A sensitive and specific electron-capture gas chromatographic (EC-GLC) assay was developed for thte determination of flurazepam and its major blood metabolites with a sensitivity limit of 5–10 ng/ml of each compound. The major urinary metabolites are determined by differential pulse polarography. The EC-GLC assay was applied to the determination of blood levels in man following single and multiple 30-mg oral doses of Dalmane. The polarographic assay was used to quantitate the major urinary metabolites in several subjects who received a single 90-mg oral dose of the drug.

Determination of 8-Methoxypsoralen, A Photoactive Compound, in Blood by High Pressure Liquid Chromatography

Abstract A rapid, sensitive, and specific high pressure liquid chromatographic (HPLC) assay was developed for the determination of 8-methoxypsoralen (8-MOP) from blood. The assay involves extraction of 8-methoxypsoralen into n-hexane: 2-propanol (95:5) from blood buffered to pH 9. The overall recovery is 75 ± 5.0% (S.D.), and the sensitivity limit of detection is 10–15 ng/ml of blood, using a 1 ml specimen. The assay was used in the determination of blood levels of 8-methoxypsoralen in a dog following intravenous and oral administration of a 5 mg/kg dose, and in man following single oral 0.56 mg/kg doses of 8-MOP, totalling 40 mg.

Determination of midazolam (versed®) and its metabolites in plasma by high-performance liquid chromatography

A rapid, sensitive and selective high-performance liquid chromatographic (HPLC) assay was developed for the determination of midazolam, 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]- benzodiazepine (I), and its four metabolites in plasma. The assay involves extraction into diethyl ether--methylene chloride (7:3) from plasma buffered to pH 9 and subsequent analysis by reversed-phase HPLC with ultraviolet detection at 254 nm. The overall recovery of I from dog plasma was 94.5 +/- 7.1% and greater than 89.0% for its metabolites. The sensitivity limit of the assay was 50 ng/ml of plasma for all compounds. The HPLC assay was used to determine plasma concentrations of I and its metabolites from selected samples taken from an oral toxicity study in the dog.

Determination of Chlordiazepoxide and Its Metabolites in Plasma by High Pressure Liquid Chromatography

Abstract A rapid, sensitive and specific high pressure liquid chromatographic (HPLC) assay was developed for the determination of chlordiazepoxide and its metabolites from plasma. The assay involves extraction of chlordiazepoxide and its metabolites into diethyl ether from plasma buffered to pH 9. The overall recovery of chlordiazepoxide is 80 ± 5.0% (S.D.) and the sensitivity limit of detection is 50 to 100 ng/ml of plasma, using a 1 ml specimen. The assay was used in the determination of plasma levels of chlordiazepoxide and its metabolites in man following oral administration of chlordiazepoxide. HCl. The chromatographic behavior of other clinically important benzodiazepines and their major metabolites is also reported.

Determination of the anti-inflammatory agent carprofen, (d,l)-6-chloro-α-methylcarbazole-2-actic acid, in blood by high-pressure liquid chromatography

A rapid, sensitive, and specific high-pressure liquid chromatographic (HPLC) assay was developed for the determination of (D,L)-6-chloro-alpha-methylcarbazole-2-acetic acid (carprofen) in blood. The assay involves extraction into diethyl ether from blood buffered to pH 6. The overall recovery of carprofen from blood is 97.3 +/- 5.3% (S.D.), and the sensitivity limit of detection is 100-200 ng/ml of blood using a fluorescence detector with excitation at 240 nm and emission at wavelengths greater than 350 nm. The HPLC assay is amenable to rapid routine analysis of clinical specimens, and the data obtained using this assay showed an excellent correlation coefficient (0.99) compared with a previously published spectrofluorometric assay. The method was used to monitor the blood level-time fall-off profiles in four subjects following single and multiple dose administration of carprofen.

Determination of chlordiazepoxide, diazepam, and their major metabolites in blood or plasma by spectrophotodensitometry.

An analytical procedure was developed for the determination of chlordiazepoxide, diazepam and their major metabolites in blood or plasma. Demoxepam, a metabolite of chlordiazepoxide, is determined by spectrofluorometry after extraction. The remaining compounds are determined by spectrophotodensitometry after thin-layer chromatographic separation. The sensitivity limit of the spectrofluorometric determination of demoxepam is 0.1 to 0.2 microgram while that of the spectrophotodensitometric determination of chlordiazepoxide, diazepam and their N-desmethyl metabolites is 0.05 to 0.2 microgram. The sensitivity and specificity of the assay renders it suitable for monitoring plasma levels of chlordiazepoxide and its major metabolites following single or chronic oral administration of chlordiazepoxide hydrochloride. The sensitivity limit for diazepam and nordiazepam, its major metabolite, renders the assay useful only for the determination of plasma concentrations resulting from high dosage of diazepam. The assay was used to determine chlordiazepoxide and its metabolites following oral administration of Librium. The data showed a significant correlation to those obtained on the same specimens by differential pulse polarography and by radioimmunoassay.

Determination of the carotenoid phytoene in blood by high-pressure liquid chromatography

A sensitive and specific high-pressure liquid chromatographic assay was developed for the determination of phytoene in blood with an overall recovery of 86 +/- 6.0% and a limit of detection of 50-100 ng per ml of blood. This method provides for rapid and simple quantitation of phytoene using 1 ml or less of blood. The assay was used in the determination of phytoene blood levels in the dog following intravenous and oral administration of 10-mg/kg doses.

Determination of the anti-allergenic agent, 2-methoxy-11-oxo-11H-pyrido[2,1-b]quinazoline-8-carboxylic acid, in biological fluids by high-performance liquid chromatography

A rapid, sensitive, and specific high performance liquid chromatographic (HPLC) assay was developed for the determination of 2-methoxy-11-oxo-11H-pyrido-[2,1-b]quinazoline-8-carboxylic acid (I) from biological fluids. The overall recovery from blood and plasma is 69 +/- 10% (S.D.) and 84 +/- 6% (S.D.), respectively, and the sensitivity limit of quantitation is 100 ng/ml by UV absorption and 5 ng/ml by fluorescence detection using a 1 ml specimen. The assay was used in the determination of blood levels of compound in the Rhesus monkey following intravenous administration of a 10 mg/kg dose, and of blood and urine levels of compound I in a dog following intravenous and oral administration of a 1 mg/kg dose.