The disposition and metabolism of zibotentan (ZD4054): an oral-specific endothelin A receptor antagonist in mice, rats and dogs.

Zibotentan (ZD4054) is an oral-specific endothelin A receptor antagonist in development for the treatment of castration-resistant prostate cancer. In a number of preclinical studies, the disposition and metabolism of zibotentan were investigated in mice, rats and dogs. Following oral and intravenous administration, zibotentan was slowly absorbed (maximal concentration at approximately 4 h) and rapidly excreted, with the majority being eliminated by 48 h. The main route of elimination was via the urine in dogs and female rats, but via the faeces in male rats and mice of both sexes. Zibotentan was moderately bound to plasma proteins of all species examined (55-95%), and widely distributed throughout all tissues with the highest concentrations seen in the organs of excretion. Zibotentan was moderately metabolised. Zibotentan was well absorbed, moderately bound to plasma proteins, widely distributed and excreted predominantly via the urine.

Evaluation of the use of UPLC-TOFMS with simultaneous [14C]-radioflow detection for drug metabolite profiling: application to propranolol metabolites in rat urine.

The non-selective beta-adrenergic receptor antagonist propranolol [1-(isopropylamino)-3-(1-naphthoxy)-2-propanol] is metabolised extensively in vivo. Enumerating and identifying the many metabolites that result from multiple biotransformations provides a considerable analytical challenge, greatly aided by efficient chromatography coupled to sensitive mass spectrometric detection. Here the use of the newly introduced high-resolution technique of "ultra performance liquid chromatography" (UPLC) linked to quadrupole time-of-flight mass spectrometry (TOFMS) with simultaneous [(14)C]-radioflow detection was applied to rapid metabolite profiling. [14C]-propranolol, dosed intraperitoneally to rat at 25 mg kg(-1) and 200 microCi kg(-1) was used as a model compound for this evaluation. Some 14 metabolites were detected in the urine by this technique including a number of conjugated metabolites such as sulphates, several isobaric glucuronides and two novel di-glucuronides.

Substandard tuberculosis drugs on the global market and their simple detection.

SETTING: The prevalence of substandard anti-tuberculosis drugs is unknown. To maximize the effectiveness of tuberculosis (TB) control efforts, simple, inexpensive drug quality screening methods are needed. DESIGN: Isoniazid (INH) and rifampin (RMP) single- and fixed-dose combination (FDC) formulations were collected from selected TB programs and pharmacies in Colombia, Estonia, India, Latvia, Russia and Vietnam. Samples were screened using a recently developed thin-layer chromatography (TLC) kit. All abnormal samples and a 40% random sample of normal formulations were further analyzed using confirmatory techniques. Samples outside of 85% to 115% of stated content, and/or containing compounds other than the stated drug, were defined as being substandard. RESULTS: Overall, 10% (4/40) of all samples, including 13% (4/30) RMP samples, contained <85% of stated content. More FDCs (5/24, 21%) than single-drug samples (2/16, 13%) were substandard. A comparison of TLC with the confirmatory analysis for RMP analysis showed a sensitivity of 100% (4/4), a specificity of 92% (24/26), a positive predictive value (PPV) of 67% (4/6), and a negative predictive value (NPV) of 100% (24/24). An analysis of INH showed a specificity of 90% (9/10). However, sensitivity, PPV, and NVP could not be determined. CONCLUSION: A substantial number of anti-tuberculosis drugs from several countries, in particular FDCs, were found to be substandard. Such drugs may contribute to the creation of drug-resistant TB. TLC is an effective, convenient, and inexpensive method for the detection of substandard drugs.

Detection of substandard fixed-dose combination tuberculosis drugs using thin-layer chromatography.

SETTING: A convenience sample of 13 fixed-dose combination (FDC) tuberculosis (TB) drugs from 'The Fixed Dose Combination Project' was analysed in laboratories at the University of Botswana and the US Food and Drug Administration (FDA). OBJECTIVE: To determine actual versus stated content of drugs in these FDCs. DESIGN: Chemical analysis was performed using thin-layer chromatography (TLC) as a screening method, and ultraviolet (UV) spectrophotometry or liquid chromatography (LC) as confirmation. FDCs with content outside of 85-115% of stated concentration were defined as substandard. RESULTS: All 13 FDCs contained the stated drugs. However, four (31%) were substandard, including two (15%) with low rifampicin content, one (8%) with excessive rifampicin, and one (8%) with excessive pyrazinamide. Both FDCs with low rifampicin contained four drugs and failed TLC screening. The FDC with excessive rifampicin was not detected by TLC screening. Using UV as the gold standard, the sensitivity of TLC for low rifampicin was 2/2 (100%), and the specificity was 9/10 (90%). CONCLUSION: This study found that 31% of the FDCs in 'The Fixed Dose Combination Project' had substandard content, irrespective of bioavailability. Low rifampicin content, which can be reliably detected by TLC screening, was identified in both four-drug FDC products and is particularly worrisome. TB drugs should be screened for quality using TLC to optimise treatment outcomes and to prevent increases in acquired drug resistance.

Simple, at-site detection of diethylene glycol/ethylene glycol contamination of glycerin and glycerin-based raw materials by thin-layer chromatography.

This paper describes a rapid, inexpensive thin-layer chromatographic (TLC) method that separates diethylene glycol (DEG) from glycerin and other glycols. Studies with collaborating laboratories of the World Health Organization have shown that about 6% DEG in glycerin and about 2% DEG in acetaminophen (paracetamol) elixirs may be detected by direct visual inspection of the developed TLC sheets. Staining the sheet permits detection of DEG at less than 0.1%. The method costs less than $1.00 per test and takes 20 min by visual inspection, longer when staining is required. The visual method can be performed without laboratory facilities by personnel having little previous training. Samples testing positive by the visual method can be submitted to a laboratory for confirmation and quantitation of DEG.

Rapid screening of marketed paracetamol tablets: use of thin-layer chromatography and a semiquantitative spot test.

Evaluated is the use of thin-layer chromatography (TLC) to determine the quality of paracetamol tablets marketed in Bangladesh. The procedure was carried out using a cheap and rapid TLC method developed by the U.S. Food and Drug Administration. Reported also is a semiquantitative specific spot test for screening paracetamol tablets. The results obtained indicate that, of the 38 brands tested, three were spurious, while 11 were of borderline quality. In some cases, the results were also verified using the British Pharmacopoeia method. The simplified tests described in this article cannot replace the British Pharmacopoeia or U.S. Pharmacopoeia methods but can be employed as initial screening tests.

Quality assurance in weighing.

Weighing is the most used step in any analytical procedure, and the balance is the one essential piece of laboratory equipment in all analyses. Yet weighing is a common source of error in final analytical results and can be difficult to detect. Analysts may become complacent and expect all weighings to be accurate. Our laboratory experienced a problem in weighing and found that the principal error was due to drift. The ensuing investigation into the cause led to a procedure for reducing drift, which, in turn, ensured accurate weighings that have improved quality assurance in our total operations.

Rapid screening of pharmaceuticals by thin-layer chromatography: analysis of essential drugs by visual methods.

A method for rapidly screening pharmaceuticals by thin-layer chromatography has been designed for use in areas with limited resources and by operators with limited training. An apparatus for performing the analysis in a plastic bag under equilibrium conditions was designed. Results can be reproduced by different operators and in different locations. The analysis can be performed without electricity or in a remote area, away from a laboratory. It is especially suited for field use in developing countries. The method is low cost, maintenance-free, fast, and reliable; it also uses limited volumes of solvents. The analyses can be performed without weighing if reference materials can be supplied in tablet form, provided the drug content is listed and only one unit is required for each analysis. All procedures were developed for the analysis of drugs from a partial list of essential drugs established by the World Health Organization. Three drugs were selected and prepared in the form of reference tablets. Comparisons with the analyses of the drugs in standard dosage forms were made by using reference tablets and primary USP standards. Comparable results were obtained, proving that the screening process can be conducted by using reference tablets and without weighing either the sample or the reference. The method has been successfully demonstrated and used in Swaziland, by high school teachers in the United States, and by personnel from the Ministry of Health in Saudi Arabia. Personnel can be trained in a short time to perform screening analysis of drugs.

Drug quality screening in developing countries: establishment of an appropriate laboratory in Swaziland.

A simple, low-cost, accurate thin-layer chromatography (TLC) method has been used to establish the first drug quality screening laboratory in Swaziland. For this purpose, office space at the central medical stores was first converted into a simple laboratory. Basic equipment, supplies, and materials were purchased, existing manpower was trained to perform accurately the TLC procedure, and a system was established for the qualitative/quantitative screening of selected drugs purchased by the Ministry of Health prior to their distribution to user facilities. The TLC method described can be used to set up similar low-cost, drug quality screening laboratories in other developing countries where analytical chemistry expertise is lacking, resources are scarce, and sophisticated analytical laboratories to assess drug quality are not available.