Pre-column derivatization with fluorescamine and high-performance liquid chromatographic analysis of drugs. Application to tocainide

Liquid chromatography assay for 5-aminolevulinic acid: application to in vitro assessment of skin penetration via Dermaportation

The purpose of the present study was to develop a reverse-phase high performance liquid chromatographic (HPLC) assay for quantifying 5-aminolevulinic acid (ALA). The assay was applied to study the skin permeation of ALA and the influence of a novel skin penetration enhancement technology. Separation was achieved utilizing a Phenomenex Jupiter C(18) column following fluorescence derivatization with fluorescamine. The assay was linear (r(2)>0.99) with a minimum limit of quantitation of 400 ng/mL. The inter- and intraday variation was 1.6 and 0.9% at the lower end of the linear range and 1.5 and 1.9% at the upper end, respectively. The HPLC assay and fluorescence derivatization procedure is sensitive, simple, rapid, accurate and reproducible and offers advantages with regard to stability of ALA in comparison to other fluorescence derivatization methods. Results from the preliminary skin permeation study demonstrated substantial skin penetration of ALA only when applied with Dermaportation as a skin penetration enhancement device.

Determination of the monoamine oxidase B inhibitor Ro 19-6327 in plasma by high-performance liquid chromatography using precolumn derivatization with fluorescamine and fluorescence detection

A specific high-performance liquid chromatographic (HPLC) method using precolumn derivatization and fluorescence detection was developed for the determination of the monoamine oxidase B inhibitor Ro 19-6327 in human plasma. After extraction of the basified plasma with tert.-butyl methyl ether-1-butanol (8:2, v/v) and back-extraction into dilute phosphoric acid, the solution was neutralized with phosphate buffer and the drug derivatized with fluorescamine. The derivative was chromatographed on a reversed-phase C8 column, using phosphate buffer-acetonitrile (68:32, v/v) as mobile phase, and fluorescence detection (excitation 370 nm, emission 485 nm). The limit of quantification was 1 ng/ml using 1 ml of plasma. The recovery was 79% in the range 5-200 ng/ml and the inter-assay precision was 3.1-7.9% in the range 2-500 ng/ml. The compound proved to be stable in human plasma. Moderate instability was found in rat plasma and, surprisingly, severe instability in dog plasma. Measures for handling unstable dog plasma samples are described. An HPLC method with UV detection was used for the analysis of dog and rat plasma samples, which is also described briefly. The fluorescence method, which was five times more sensitive than the UV method, was successfully applied to a human tolerance study.

Efficacy of class Ib (lidocaine-like) antiarrhythmic agents for prevention of sustained ventricular tachycardia secondary to coronary artery disease

The effects of lidocaine, tocainide and mexiletine were examined in 17 patients with coronary artery disease and chronic, recurrent, sustained ventricular tachycardia (VT) or ventricular fibrillation and inducible VT. Eleven patients presented with sustained VT; 6 patients had had an episode of sudden death from which they had been resuscitated. All patients were refractory to conventional antiarrhythmic agents. Lidocaine prevented induction of VT in only 3 patients (18%). Tocainide prevented induction of VT in only 1 lidocaine-responsive patient. Mexiletine prevented VT induction in 1 patient who had responded to lidocaine but not tocainide. Neither tocainide nor mexiletine was effective in preventing induction of VT in any patient who did not respond to lidocaine. Lidocaine terminated VT in 3 patients, but this did not predict noninducibility with lidocaine, tocainide or mexiletine. Cycle length of VT was prolonged slightly by lidocaine (control 311 +/- 14 ms, lidocaine 361 +/- 26 ms, p less than 0.05), tocainide (344 +/- 16 ms, p less than 0.05) and mexiletine (371 +/- 27 ms, mean +/- standard error of the mean, p less than 0.05). Thus, class lb agents are infrequently effective in preventing induction of VT in this group of patients, electrophysiologic inefficacy of lidocaine is highly predictive of continued inducibility with tocainide and mexiletine, and termination of VT with lidocaine does not correlate with its ability to prevent VT induction.

HPLC electrochemical fluorometric detection of amino acids including tryptophan using 4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole

It has been shown that by electrochemical oxidation 7-nitrobenzo-2-oxa-1,3-diazole-tryptophan (NBD-T) is converted to fluorophores having the same emission and excitation spectra as those for other NBD-amino acids. NBD-dioxindolylalanine was tentatively assumed to be a main electrochemical oxidation product of NBD-tryptophan. A coulochemical cell placed between an analytical column and a fluorometer showed no detrimental effect on the separation of NBD-amino acids by reversed phase HPLC. Highly sensitive fluorescence detection was achieved for amino and imino acids at 10-100 fmol levels. The detection limit for tryptophan was 50 fmol.

Determination of a prodrug of tranexamic acid in whole blood by reversed-phase liquid chromatography after pre-column derivatization with fluorescamine

A sensitive high-performance liquid chromatographic (HPLC) method for a prodrug of tranexamic acid (KABI 2161) in whole blood is described. Since KABI 2161 is rapidly hydrolysed in whole blood the samples are collected directly into the extraction tubes and extracted immediately. After pre-column derivatization with fluorescamine the derivatives are analysed by reversed-phase liquid chromatography on a C(8)-Nucleosil column using an eluent mixture of phosphate buffer and acetonitrile (pH 3). The eluent is monitored by a fluorescence detector. Determinations as low as 10 ng ml(-1) of KABI 2161 in whole blood can be made when 0.5 ml blood is analysed. The precision of the method is 4.1% (RSD) at the 300 ng ml(-1) level and 6.9% (RSD) at the 50 ng ml(-1) level.

Liquid chromatographic determination of mexiletine and tocainide in human plasma with fluorescence detection after reaction with a modified o-phthalaldehyde reagent

A liquid chromatographic procedure for the determination of mexiletine or tocainide in human plasma is described. Plasma, after the addition of a homologue of mexiletine or of tocainide, is extracted with dichloromethane. The extract is evaporated and reconstituted in a non-aqueous o-phthalaldehyde--mercaptoethanol reagent. An aliquot of the solution is chromatographed on a reversed-phase Ultrasphere-octyl column. The peaks are detected by fluorescence (lambda ex = 350 nm and lambda em = 445 nm). The fluorescent derivatives of the drugs and internal standards are stable at room temperature and give symmetrical single peaks. Use of fluorescamine as a reagent to prepare fluorescent derivatives of mexiletine and tocainide prior to chromatography is also evaluated.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Clinical pharmacokinetics of the newer antiarrhythmic agents

This article reviews clinical pharmacokinetic data on 8 new antiarrhythmic agents. Some of these drugs have been studied extensively while others are relatively new, with incomplete data due to limited evaluation. Amiodarone is a class III antiarrhythmic drug which is effective in treating many atrial and ventricular arrhythmias that are refractory to other drugs. Amiodarone accumulates extensively in tissues and its disposition characteristics are best described by models with 3 and 4 compartments. Its apparent volume of distribution is very large (1300 to 11,000L) and its elimination half-life very long (53 days). A delay of up to 28 days from of treatment to onset of antiarrhythmic effect may be observed, and the antiarrhythmic effect may persist for weeks to months following cessation of therapy. Clinically significant drug interactions have been observed with amiodarone and warfarin, digoxin, quinidine and procainamide. Encainide is a class Ic antiarrhythmic drug. Although it has a short elimination half-life (1 to 3h), 2 major metabolites with antiarrhythmic effects accumulate in the plasma of patients during long term therapy. Plasma concentrations of O-demethyl encainide appear to correlate with the antiarrhythmic effect. Flecainide, another class Ic antiarrhythmic agent, has an elimination half-life of 14 hours which makes it suitable for twice daily dosing. Flecainide elimination is prolonged in patients with low output heart failure. Significant drug interactions with digoxin and cimetidine have been reported. Lorcainide is also a class Ic antiarrhythmic drug, the bioavailability of which is nonlinear. Clearance of the drug is reduced during long term therapy. A major active metabolite, norlorcainide, accumulates in the plasma of patients during long term therapy and its concentration exceeds that of lorcainide by a factor of 2. The elimination half-lives of lorcainide (9h) and norlorcainide (28h) allow for once or twice daily dosing. Mexiletine, a class Ib antiarrhythmic drug, is structurally similar to lignocaine (lidocaine). A sustained release formulation provides effective plasma concentrations when administered twice daily. The apparent volume of distribution of mexiletine is 5.0 to 6.6 L/kg, and the elimination half-life varies from 6 to 12 hours in normal subjects and from 11 to 17 hours in cardiac patients. Mexilitine is extensively metabolised but the metabolites are not pharmacologically active. Renal elimination of mexiletine is pH dependent. Drugs which induce hepatic metabolism significantly alter the pharmacokinetics of mexiletine.(ABSTRACT TRUNCATED AT 400 WORDS)