A thin-layer chromatographic method for the determination of acebutolol and its major metabolite in serum

Pharmacokinetics of acebutolol enantiomers in humans

The chiral beta-blocker acebutolol (AC) is marketed as a racemic mixture. Both AC and its major metabolite, diacetotol (DC), are chiral, the S-enantiomer possessing beta-blocking activity. The pharmacokinetics of AC and DC enantiomers was determined in 12 healthy subjects following oral administration of 200 mg of AC. Plasma and urine were collected over a 24-hr period and both AC and DC enantiomers were measured utilizing a stereospecific HPLC assay. Concentrations of S-AC were predominant in both plasma and urine [AUC S:R, 1.20 +/- 0.1; cumulative urinary excretion (sigma Xu) S:R, 1.17 +/- 0.05), which corresponded to a significantly greater oral clearance of R-AC (106 +/- 30 L/h) than S-AC (87 +/- 22 L/h). The Cmax of R-DC was significantly greater than for S-DC (S/R 0.7 +/- 0.1). The half-life (t1/2) of R-DC (6.4 +/- 1.6 h) was significantly shorter than that of S-DC (8.8 +/- 2.4 h). The observed AUC values for R- and S-DC were not significantly different. Renal clearance of R-DC (70 +/- 34 mL/min) was significantly greater than that of S-DC (53 +/- 29 mL/min). The data suggest that the first-pass metabolism of R-AC to R-DC is stereoselective. This metabolism, coupled with the stereoselective renal excretion of R-DC is likely a major contributor to the observed stereoselective disposition of AC and its major metabolite in humans.

Identification and differentiation of beta-blockers and their metabolites in urine by computerized gas chromatography-mass spectrometry

A method for the identification and differentiation of beta-blockers and their metabolites in urine after acid hydrolysis is described. The acetylated extract is analysed by computerized gas chromatography-mass spectrometry. An on-line computer allows rapid detection using ion chromatography with the ions of m/z 72, 86, 98, 140, 151, 159, 200 and 335. The identity of positive signals in the reconstructed ion chromatogram is confirmed by a comparison of the stored entire mass spectra with the reference spectra. The ion chromatogram, the reference mass spectra and the gas chromatographic retention indices (OV-101) are documented. References for the quantitation of the single beta-blockers are cited.

Acebutolol: ten years of experience

During 10 years of clinical use involving almost 3 million patient-years, acebutolol has become established as a remarkably safe and well-tolerated beta-blocking agent, effective in treating essential hypertension and cardiac arrhythmias. The existence of a long-lived active metabolite (diacetolol) confers a 24-hour duration of action, which permits effective use of a once-daily regimen, particularly for hypertension. Acebutolol has low lipid solubility and low protein binding; the former property reduces the risk of central side effects, and the latter means that displacement interactions with other drugs are unlikely. Because acebutolol and its metabolite normally have both renal and hepatic excretion pathways, an alternative pathway is available should either be compromised through disease. Acebutolol is cardioselective, and clinical use has borne out the low incidence of bronchospasm in patients with impaired lung function. The possession of intrinsic sympathomimetic activity (ISA) leads to only modest reductions in cardiac output, which in turn reduces the chance of excessive bradycardia and the likelihood of precipitating heart failure. A combination of selectivity and ISA may be responsible for the low incidence of tiredness and cold extremities observed with acebutolol compared with other beta blockers. The unique pharmacologic and pharmacokinetic profile of acebutolol confers several therapeutic advantages and may be responsible for the generally low level of side effects experienced in clinical use.

Industrial hygiene air monitoring of phenylhydrazine

Two gas chromatographic (GC) methods for the analysis of phenylhydrazine have been examined with phenyl- and rho-chlorophenylhydrazine and a new method using thin-layer chromatography (TLC) was developed. The NIOSH GC method (2-furalphenylhydrazone derivatization), which is classified as "proposed", was found to yield two derivatization peaks, which could only be separated with capillary columns. The other GC method (acetone phenylhydrazone derivatization) gave a single peak, however, of limited stability. In the newly developed TLC method the fluorescamine derivative of phenylhydrazine is separated and detected either visually or with a TLC-fluorescence scanner after fluorescence enhancement with paraffin wax. With ordinary TLC techniques the quantification of phenylhydrazine was possible down to 200 pg per spot. The sensitivity of the TLC method is generally sufficient for the requirements of industrial hygiene air monitoring of phenylhydrazine.

High-pressure liquid chromatography of nadolol and other beta-adrenergic blocking drugs

A high-pressure liquid chromatographic assay was developed for the analysis of the beta-adrenergic blocking agent nadolol as a bulk material or formulated in a tablet. Other beta-adrenergic blocking drugs such as acebutolol, alprenolol, atenolol, metoprolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol can be chromatographed in this system. An ethylsilane column and a mobile phase consisting of 35% methanol-65% aqueous 0.0005 M hydrochloric acid-0.05 M sodium chloride are used. Detection is either at 254 nm with a variable-wavelength detector. As exemplified by nadolol, the drug content can be quantitated with or without atenolol as an internal standard.

Reversed-phase high-performance liquid chromatography with differential pulse polarographic detection for assaying drugs in feed: stability-indicating assay of diacetolol

Reversed-phase high-performance liquid chromatography with differential pulse polarographic detection at a dropping mercury electrode provides a high degree of specificity for stability-indicating assays of drugs in animal feed. The selectivity of this detection system is demonstrated in the assay of diacetolol in feed at concentrations down to 50 microgram/g.

A simple radioimmunoassay of acebutolol in plasma

Antisera against acebutolol were produced in rabbits immunized by means of this drug conjugated with bovine serum albumin. These antisera were used to develop a method of radioimmunoassay for acebutolol. The plasma radioimmunoassay, described here, requires no extraction and is very easy to perform besides being quick, specific and sensitive. As little as 2.97 X 10(-9) mol/l of acebutolol can be detected. This radioimmunoassay is suitable for assaying the large number of samples usually measured in pharmacological studies.

Reliable routine method for determination of perazine in serum by thin-layer chromatography with an internal standard

The use of a high-performance thin-layer chromatography linear chamber and of thioridazine as internal standard increases the performance of thin-layer chromatography (TLC) with direct densitometric scanning, and allows the rapid determination of serum levels of the neuroleptic drug perazine under usual therapeutic conditions. TLC is superior to gas-liquid chromatography in so far as the main metabolite desmethylperazine can be easily separated and detected by the same procedure.

Spectrofluorimetric determination of dipyridamole in serum--a comparison of two methods

Two spectrofluorimetric methods for the determination of dipyridamole in plasma are described. The thin-layer chromatographic-fluoridensitometric method utilizes 1 ml of plasma which is extracted at pH 10 with diethyl ether-dichloromethane (80:20). The organic phase is evaporated to dryness, reconstituted in 250 microliter dichloromethane and 5 microliter are spotted on a silica gel 60 plate. The plate is developed in ethyl acetate-methanol-ammonia (85:10:5), dried, dipped in a paraffin wax solution, dried, and scanned using 380 nm as excitation wavelength, a 430 nm cut-off filter, and collecting all emitted light on the photomultiplier. Quantitation was done by the external standard method, peak heights being measured and a calibration graph constructed. For the spectrofluorimetric method 1 ml of plasma is extracted at pH 10 with 8 ml of hexane-isoamyl alcohol (95:5) and the organic phase used directly for the measurement of the fluorescence intensity (excitation 405 nm, emission 495 nm). Quantitation was done by measuring the fluorescence of standards that were treated as above and constructing a calibration graph of concentration versus fluorescence intensity. Concentrations of unknowns were found by interpolation from this graph. The two methods were found to exhibit good correlation but the spectrofluorimetric method proved to be more amenable to the analysis of a large number of samples.

Evaluation of a modified high-performance liquid chromatography assay for acebutolol and its major metabolite

Extensive modification of an existing high-performance liquid chromatography assay for acebutolol and its major metabolite has markedly improved chromatographic stability eliminating the previous need for frequent adjustment of the eluent composition to accommodate continuous loss of column retention. The eluents now used and avoidance of the requirement for elevated column temperature may be significant factors in the ability to maintain column life over 8 months of continuous use with little decrease in retention. As a result of the improved chromatographic stability full advantage can now be taken of automatic injection devices for the unattended processing of large numbers of samples. A significant modification of the work-up of blood samples has improved precision of the assay in whole blood. Nevertheless, it is recommended that plasma samples rather than whole blood be analyzed, since the plasma assay is faster and still more precise.

[Quantitative determination of drugs by in situ spectrophotometry of chromatograms for pharmacokinetic studies. I. Sulpiride and other benzamides, vincamine, naftazone (author's transl)]

Assays are proposed for sulpiride and other benzamides, vincamine and naftazone in plasma (or blood) and urine with direct UV reflectance spectrophotometry on this are applied directly on TLC along with a calibration curve on each plate. Plasma (or total blood) samples are extracted, and an internal standard is added before aplication; slopes of the obtained calibration curves do not change significantly from plate to plate, thus allowing several determinations on the same plate. The sensitivity is 2 microgram in a 1-ml sample (amount applied 30 ng) for sulpiride and related compounds and about the same for vincamine. Naftazone is determined in plasma with simultaneous reflectance and transmittance spectrophotometric measurements at 520 nm on chromatoplates sprayed with lead acetate, the sensitivity reached is 10 ng in a 1-ml sample (amount applied 0.5 ng). For all drugs studied, the proposed techniques are specific, reliable and sensitive enough and can be used to perform pharmacokinetic studies in human or in animal after administration of doses in the therapeutic range.

High-pressure liquid chromatographic analysis of drugs in biological fluids. V. Analysis of acebutolol and its major metabolite

A high-pressure liquid chromatographic analysis for acebutolol and its major metabolite in blood, plasma and urine is reported. The analysis, in which the above mentioned compounds are chromatographed as ion pairs with dodecyl sulfonic acid, uses a simple and rapid method of sample preparation. The technique is more sensitive and rapid than those previously reported and it has equivalent or better reproducibility. The method is applied to the measurement in blood of acebutolol and its acetyl metabolite after a single oral dose.