M. De Smet

Expert system for pharmaceutical analysis : I. Selection of the detection system in high-performance liquid chromatographic analysis: UV versus amperometric detection

The usefulness of amperometric detection in pharmaceutical analyses was investigated for different groups of drugs. The UV response at 254 nm and that at the absorption maximum of the solute were compared with the electrochemical signal obtained. The minimum detectable concentration (nanograms on-column) of each substance is reported for the three different detection systems. This comparison was performed for 72 drugs (local anaesthetics, antipyretics, tricyclic antidepressants, sulphonamides, sex hormones, beta-adrenoceptor blocking agents, phenothiazines, alkaloids, diuretics and penicillins). The median limit of detection of the amperometric detector (see definition in the text) is 1.0 ng on-column and the median gain in sensitivity, compared with UV detection is 22.5.

Expert system for the selection of high-performance liquid chromatographic methods in pharmaceutical analysis : Validation of the rules for the selection of the mobile phase

The rules for the selection of the mobile phase and the validation performed on 44 pharmaceutical preparations, containing one to five active compounds, are described. These rules are incorporated into an expert system, called LABEL, for the selection of high-performance liquid chromatographic methods in pharmaceutical analysis. A single stationary phase type is used, namely a nitrile or cyanopropyl (CN) column, which can be used in both normal-phase (NP) and reversed-phase (RP) chromatography. Three mobile phase systems were evaluated on this column type: NP, RP with water and RP with buffer. LABEL selects one of these three systems on the basis of the rules incorporated for the mobile phase selection, checks if the addition of ion-suppressing agents to the eluting agent is necessary and finally gives the starting composition of the mobile phase in each of the three systems. For this selection the number of compounds in the sample, the acid-base properties and the hydrophobicity of the solutes are the more important factors. The validation of the rules on 44 pharmaceutical preparations resulted in an immediate success in 82% of all cases. In half of the remaining cases, the system proposed can be adapted with a minor change in conditions, so that it can also be used in practice.

High-performance liquid chromatographic determination of vinca-alkaloids in plasma and urine.

A liquid chromatographic method is described for separating and determining vinblastine, vincristine and vindesine in plasma and urine. The drugs are extracted from the biological material using an ion-pair extraction, with sodium octylsulphate as counter-ion at pH 3. The extracts are injected on a reversed-phase system with a cyano column as stationary phase and a mobile phase composed of acetonitrile-phosphate buffer, pH 3 (65:35, vol. %). Stability studies are carried out for stock solutions of the drugs in water at different temperatures and pH values. The stability of these compounds in plasma is also investigated in the presence of an antioxidant. The method is applied to determine drug levels of vindesine and vinblastine in preliminary pharmacokinetic studies, using vincristine as the internal standard.

Determination of vinca alkaloids in mouse tissues by high-performance liquid chromatography

A high-performance liquid chromatographic method is described for the determination of vinblastine in various normal mouse tissues, such as lung, heart, liver, kidney and muscles, and in implanted MO4 tumours. Vincristine was used as the internal standard. Freshly obtained mouse tissue or tumour tissue was frozen at -20 degrees C and then lyophilized. After lyophilisation, the dry tissues were pulverized and homogeneously mixed, and an aliquot was suspended in 0.1 M hydrochloric acid. The drugs of interest were then isolated from this suspension using ion-pair extraction at pH 3 with octylsulphate as counter-ion. The obtained extracts were analysed on a reversed-phase system with a cyanopropyl stationary phase. The detection limit was 1 ng/l in plasma and 10 ng/g in tissue. The extraction recoveries of vincristine and vinblastine were between 45 and 67%, and there were no interferences from blank components. Preliminary pharmacokinetic data for different mouse tissues and tumour implanted in muscle tissue are presented.

Integrating expert systems for high-performance liquid chromatographic method development

Abstract A complex expert system for high-performance liquid chromatographic method development has been obtained by linking several smaller stand-alone expert systems (modules), each representing a part of the entire domain. The modules LABEL, DASH and LIT select initial chromatographic conditions (first guess), the modules LABEL′, DASH′ and LIT′ perform retention optimization and the module SLOPES, which consists of the stand-alone expert systems VARIABLES, DESIRE and CRISE, is used for selectivity optimization. The linking is achieved through a supervisor, that is able to decide which of the former stand-alone expert systems must be activated at each stage of the development. The stand-alone expert systems were implemented by the use of the expert system building tool (ESBT) KES. To allow communication between the modules, they were embedded in C-language programs, without modification of the knowledge of the smaller systems.

High-performance liquid chromatographic determination of navelbine in MO4 mouse fibrosarcoma cells and biological fluids

A high-performance liquid chromatographic method is described for separating and determining navelbine and possible metabolites in plasma, cell culture medium and MO4 cells. Navelbine is extracted from these fluids by ion-pair extraction with sodium octylsulphate as the counter-ion at pH 3. The system uses a cyano column as the stationary phase and a mobile phase of acetonitrile-0.12 M phosphate buffer (pH 3) (60:40, v/v). Application of the method to a study of the pharmacokinetic behaviour of navelbine in MO4 mouse fibrosarcoma cells is reported.

Feasibility Study for the Construction of an Integrated Expert System in High-Performance Liquid Chromatography

Abstract An integrated expert system consisting of several stand-alone expert systems was developed to assist the chromatographer in the determination of optimum high-performance liquid chromatographic conditions, i.e., after a good “first guess”, an elution within a reasonable analysis time and with adequate resolution. The implementation and linking of the systems were performed by means of the expert system building tool KES. The knowledge incorporated in this expert system is described.

Determination of amiodarone and desethylamiodarone in plasma with a standardised extraction and chromatographic optimisation procedure

A previously described optimisation procedure was tested by developing suitable HPLC systems for the determination of amiodarone and desethylamiodarone in plasma. Chromatography is performed on a cyano-column (CN-column) in the reversed-phase mode. The optimisation strategy consists of carrying out a gradient elution from which an appropriate solvent strength for isocratic elution is determined. Binary and ternary mobile phase compositions with the same solvent strength but with different solvent selectivity are then used to evaluate selectivity. The anti-arrhythmic drugs are extracted from plasma using an ion-pair extraction procedure with sodium-n-octylsulphate as ion-pairing agent.

Does the total dysphagia risk score correlate with swallowing function examined by videofluoroscopy

OBJECTIVE The purpose of this study was to correlate the total dysphagia risk score (TDRS) with swallowing function as measured by videofluoroscopy of swallowing using the swallowing performance scale (SPS) and the penetration aspiration scale (PAS). METHODS 63 patients from two different centres treated with radiotherapy for head and neck cancer were evaluated in the current study. Swallowing videofluoroscopies at baseline, 6 and 12 months following radiotherapy were evaluated by two observers. The TDRS of all patients was calculated and correlated with the consensus PAS and SPS scores of the two observers. RESULTS Regarding the PAS scale, we did not observe a significant correlation with the TDRS. Regarding SPS, we found a significant correlation at 6 months (p = 0.01) and a borderline significant correlation at 12 months (p = 0.05). We observed statistically lower SPS scores for patients in the intermediate-risk category when compared to the high-risk category. When we compared low vs high TDRS risk patients, we did not observe a significant difference regarding SPS scores. When comparing low- vs intermediate-risk patients, we observed higher SPS scores in the low-risk group (p = 0.01). When the low- and intermediate-risk patients were grouped together, we observed less swallowing problems as measured by SPS in the low and intermediate group when compared to the high-risk group (p = 0.05) at 6 months. CONCLUSION Patients with high-risk TDRS scores have higher SPS scores when compared to the intermediate group and the intermediate- and low-risk group together. However, low-risk patients in our patient cohort could not be distinguished from high or intermediate-risk patients. Advances in knowledge: TDRS was never correlated with videofluoroscopies in past studies. The hypothesis of this paper was to see if the TDRS could guide us to see which patients are at risk for high scores on SPS and PAS and might need a videofluoroscopic examination in the follow up. Given the poor correlations in our study, however, we cannot recommend the use of the TDRS to select patients who might benefit from the additional information provided by videofluoroscopies.