S.K. Wahba Khalil

High Performance Liquid Chromatographic Analysis of Tolmetin, Indomethacin and Sulindac in Plasma

Abstract Isocratic and gradient reversed phase high-performance liquid chromatographic (HPLC) methods for the quantitation of tolmetin, indomethacin, and sulindac and their respective metabolites in plasma were developed. Only the determination of the parent drugs was possible using the isocratic technique. Specific, simultaneous determination of each drug and its respective metabolites was achieved using the gradient technique. The effect of pH and ionic concentration of the mobile phase on retention time was studied. Statistical analysis demonstrated excellent precision and linearity over the following ranges: 1–40, 0.1–3, and 0.1–3 ug/ml plasma for tolmetin, indomethacin, and sulindac respectively. Both methods have been applied to the analysis of patient samples.

An Isocratic HPLC Method for the Determination of Cephalosporins in Plasma

Abstract An isocratic reversed-phase liquid chromatographic method for the determination of eight cephalosporins in human plasma using UV detection at 254 nm is described. Plasma proteins were precipitated using acetonitrile prior to injection of a 10 μl aliquot onto an octadecylsilane column. The mobile phases consisted of 6–11% acetonitrile in sodium dihydrogen phosphate (0.01M). The minimum detectable limit for each drug was less than 1 γg/ml of plasma. Possible interference from other drugs which might be administered concurrently is discussed. The reproducibility and precision of the method for cephalosporin assay are shown from the analysis of plasma containing 5–500 γg/ml of plasma. The chromatographic behavior of the eight cephalosporins was examined by varying mobile phase conditions.

An HPLC Method for the Determination of Verapamil and Norverapamil in Human Plasma

Abstract A high performance liquid chromatographic method is presented for the determination of verapamil and its metabolite norverapamil in human plasma. Verapamil and norverapamil are extracted from plasma basified with 0.5M dibasic sodium phosphate (pH 9.5) using ethyl acetate containing trimipramine as an internal standard. A reverse-phase cyanopropylsilane column was used with a mobile phase of 65% acetonitrile and 35% 0.02M acetate buffer (pH 7.0). The minimum detectable limit was 2 ng/ml of plasma. The effect of the pH, molarity, and percent acetonitrile of the mobile phase on the capacity factor was studied. Possible interferences from other drugs administered concurrently are presented.

An HPLC Method for the Determination of Diltiazem and Desacetyldiltiazem in Human Plasma

Abstract A high performance liquid chromatographic method is presented for the determination of diltiazem and its metabolite desacetyldiltiazem in human plasma. Diltiazem and desacetyldiltiazem are extracted from plasma basified with 0.5M dibasic sodium phosphate (pH 7.4) using 1% 2-propanol in n-hexane containing diazepam as an internal standard. A reversed phase cyanopropylsilane column was used with a mobile phase of 45% acetonitrile and 55% 0.05M acetate buffer (pH 4.0). The minimum detectable limit was 2ng/ml of plasma. The effect of the pH, molarity, and percent acetonitrile of the mobile phase on the capacity factor was studied. Possible interferences from other drugs administered concurrently are presented.

An HPLC Method for Determination of Atropine in Human Plasma

Abstract A development of a high performance liquid chromatographic method for the determination of atropine in human plasma is presented. Atropine is extracted from plasma basified with 0. 1N sodium hydroxide using chloroform, subsequently subjected to base hydrolysis, followed by derivatization of the generated tropic acid with 4-bromomethyl-7-methoxycoumarin (Br-Mmc). The derivative produced has a strong blue fluorescence at excitation wavelength of 328 nm and emission cutoff filter of 389 nm. d1-Mandelic acid as internal standard (I. S.) was added after hydrolysis. The chromatographic separation was achieved on a reversed phase ODS column with a mobile phase of 33% acetonitrile in 0. 01M ammonium phosphate buffer (pH 5). The minimum quantitative limit was 125 ng/ml of plasma.

Quantitative Analysis of Phenyl-Acetic Acid in Proteus Mirabilis Cultures by High Performance Liquid Chromatography

Abstract A method was developed for the analysis of phenylacetic acid produced by Proteus mirabilis during a 10-day incubation period. A daily sample was acidified and extracted with petroleum ether for 24 hours in a continuous extraction apparatus. The extract of each day was analyzed by reverse-phase liquid chromatography using UV detection at 254 nm. A 10-μl aliquot of the concentrated extract was injected onto an octadecylsilane column. The mobile phase consisted of 20% methanol and 80% sodium acetate buffer, 0.01 M, pH 4.2. This method may be used for screening other microbial fermentations for the production of similar lipophilic acids.

Dietz and associates reply

I would like to comment on the recent paper by Dietz et a!, “Effects of Alcoholism on Acetaminophen Pharmacokinetics in Man” (I Clin Pharmacol 1984;24:205-208). Although their conclusion-that the data are consistent with “results. . . which show that pretreatment with alcohol stimulates the cytochrome P-450 [enzymesj. . . and increases the rate of acetaminophen metabolism”-is correct, it leaves the reader with the impression that the changes observed in the pharmacokinetics were due to increases in cytochrome P-450 activity alone. This, however, is inconsistent with what is known about acetaminophen metabolism and elimination in human beings. The recovery of acetaminophen in urine as the cysteine plus mercapturic acid conjugates (following P-450 metabolism) usually accounts for less than 10% of a therapeutic dose. Even a twofold increase in activity of this quantitatively minor metabolic pathway would have little effect on the overall elimination kinetics of acetaminophen. Conversely, it would not be possible to infer anything about the safety of acetaminophen in alcoholics solely on the basis of data on the overall elimination of the drug. Unfortunately, the authors do not indicate how the apparent volume of distribution (Vd) was determined. The calculation of clearance as the product of Vd and eliminalion rate must therefore be questioned in the absence of

Examination of North Dakota Plants by a Thin Layer Chromatographic Method Used to Identify Cannabis

The plant Cannabis saliva L. is the source of the psychotomimetic drug preparations marijuana and hashish. Due to widespread use of these products, and criminal statutes restricting or prohibiting their possession and/or distribution, it is necessary that law enforcement agencies have a simple yet accurate screening procedure for the presence of Cannabis materials. De Faubert Maunder (1969) has developed a rapid and reasonably specific test for Cannabis in which the suspected material is extracted with petroleum ether, applied to filter paper, allowed to dry, and then treated with a solution of Fast Blue salt B (FBB). If Cannabis has been extracted, a red to violet color rapidly develops, De Faubert Maunder (1969) examined approximately 200 plant materials by this method and found nutmeg and mace, both products of Myristica frugruns Houtt., produced a false positive result. Other plant materials producing false positive results are Agrimony, with color of a much paler hue than that produced by Cannabis, and Henna if an excessively large sample is tested (de Faubert Maunder, 1969b). Thin layer chromatography coupled with Fast Blue salt B (FBB) visualization has been used to resolve the problem of false positives (Forrest and Heacock, 1974). However, when testifying in criminal cases, forensic chemists are often asked by defense attorneys if materials obtained from local plants are able to produce a false positive result when examined by thin layer chromatography and FBB visualization. To help resolve this question, petroleum ether extracts of leaves, flowers and stems prepared from 118 species of plants indigenous to North Dakota (U.S.A.) were examined by a thin layer chromatographic method used to identify Cannabis materials.