Microchip Isotachophoresis: Analysis of Pharmaceuticals.

Microchip isotachophoresis (µITP) is a miniaturized version of conventional isotachophoresis (ITP) characterized by low sample and buffer consumption and reduced waste production. µITP with universal conductivity detection is suitable for quantitative analysis of relatively simplified samples that contain analyte(s) at relatively high concentration, e.g., pharmaceutical preparations. Here we describe in detail a principle of µITP in terms of reaching highly precise results. A practical use of µITP is shown on the analyses of various pharmaceutical preparations for content of major constituents including active pharmaceutical ingredients as well as pharmaceutical counterions. The pharmaceuticals are treated only minimally prior to the ITP run on a microchip with coupled channels and sample injection channel with 0.9 µL volume. Developed method is suitable for rapid (analysis time up to 10 min), precise (less than 1% RSD of analyte zone length), and accurate (recovery of 98-101%) determination of major pharmaceutical ingredients using a method of internal standard for data evaluation.

Quantitative aspects of microchip isotachophoresis for high precision determination of main components in pharmaceuticals.

Although microchip electrophoresis (MCE) is intended to provide reliable quantitative data, so far there is only limited attention paid to these important aspects. This study gives a general overview of key aspects to be followed to reach high-precise determination using isotachophoresis (ITP) on the microchip with conductivity detection. From the application point of view, the procedure for the determination of acetate, a main component in the pharmaceutical preparation buserelin acetate, was developed. Our results document that run-to-run fluctuations in the sample injection volume limit the reproducibility of quantitation based on the external calibration. The use of a suitable internal standard (succinate in this study) improved the repeatability of the precision of acetate determination from six to eight times. The robustness of the procedure was studied in terms of impact of fluctuations in various experimental parameters (driving current, concentration of the leading ions, pH of the leading electrolyte and buffer impurities) on the precision of the ITP determination. The use of computer simulation programs provided means to assess the ITP experiments using well-defined theoretical models. A long-term validity of the calibration curves on two microchips and two MCE equipments was verified. This favors ITP over other microchip electrophoresis techniques, when chip-to-chip or equipment-to-equipment transfer of the analytical method is required. The recovery values in the range of 98-101 % indicate very accurate determination of acetate in buserelin acetate, which is used in the treatment of hormone-dependent tumors. This study showed that microchip ITP is suitable for reliable determination of main components in pharmaceutical preparations.

Use of collision induced dissociation mass spectrometry as a rapid technique for the identification of pharmacologically active peptides in pharmacopoeial testing.

The applicability of collision induced dissociation mass spectrometry (CID-MS) for the pharmacopoeial identification of pharmacologically active peptides was examined. Two different classes of related peptides were selected, i.e. four synthetic gonadotropin releasing hormone analogues (gonadorelin, goserelin, buserelin and leuprorelin) being either nona- or decapeptides, and human insulin and 2 insulin analogues (insulin lispro and insulin aspart). For all these substances the pharmacopoeial identification currently requires a combination of several partly rather laborious tests using sophisticated equipment. In contrast, CID-MS as a stand alone test can provide increased reassurance about the identity and is rapid and efficient. Moreover, the substance consumption for testing is significantly lower, which is a non-negligible factor for very expensive substances.

Buserelin acetate microparticle dispersion effects drug release and plasma E(1) levels.

We investigated the effect of different dispersion methods on release behavior and efficacy onset following microparticle administration of buserelin acetate (BA) sustained-release injection. In this in vitro release study, the initial dispersion of BA increased with increased stirring speed (p<0.01). Stability of BA was studied over 7 days after BA release. The initial BA release rate was higher (p<0.01) after a 1-min vibration dispersion method (VDM) using a test tube mixer (2000 rpm) compared with the standard dispersion method (SDM) by hand. Without shaking, powder aggregation was observed, and BA release was lower than in either the SDM or VDM methods. In this study using 4-week-old Sprague-Dawley female rats, the initial plasma estrone (E(1)) concentrations were lower (p<0.05) in the VDM method than in the SDM method. Observations by optical microscope and scanning microscope showed no change in microparticle shape or distribution of size induced by SDM, VDM or the ultrasonication dispersion method. These results suggest that different dispersion methods do not change the shape and distribution of microparticle size, but clearly change the BA release rate and the transition in plasma E(1) concentrations that can affect drug efficacy.

Quantification of buserelin in a pharmaceutical product by multiple-injection CZE.

An efficient and rapid separation method based on reversed-polarity multiple-injection CZE (MICZE), has been developed for the quantification of buserelin in a pharmaceutical product. The determinations were performed by serially injecting five standard solutions of buserelin (50-300 microg/mL) and one reference analyte into a Polybrene-coated capillary. All the samples contained goserelin, an analog peptide to buserelin, as internal standard (IS). Immediately after pressure injection, the applied sample plugs were subjected to electrophoresis for 2 min at -25 kV. Consequently, each sample plug became isolated from its neighboring plugs by the BGE, composed of 100 mM phosphate-triethanolamine buffer at pH 3.0 containing 10% v/v ACN. During separation the individual sample components migrated at similar velocities and as distinct zones through the capillary giving 24 peaks, 12 from the analyte and the IS and 12 from the sample matrix. The buserelin content of the pharmaceutical product was determined to be 0.94 +/- 0.05 mg/mL, which is only a slight deviation from the declared concentration (1 mg/mL).

Radioimmunoassay of an analog of luteinizing hormone-releasing hormone, [D-Ser(tBu)]6des-Gly-NH2(10) ethylamide (Buserelin).

A sensitive and specific radioimmunoassay is described for plasma and urinary levels of [D-Ser(tBu)]6des-Gly-NH2(10) ethylamide (buserelin). No appreciable cross-reaction (less than 0.05%) was observed with LH-RH and its analogs other than buserelin fragments (1.6-45%). The sensitivity was 3 pg per tube. At buserelin concentrations of 125, 250 and 500 pg/ml, the intra- and inter-assay coefficients of variation were 7.9, 10.0 and 10.0%, and 19.0, 7.8 and 6.8% respectively. Recovery of buserelin added to plasma was quantitative (62.5 pg/ml, 101.6%; 125 pg/ml, 76.8% and 250 pg/ml, 63.4%). A dose of 5 micrograms buserelin injected subcutaneously into 5 normal male adults, reached a peak plasma level in 45 min (mean value 119.3 +/- 47.3 pg/ml) and remained detectable for at least 4 h. The half disappearance time was 118.8 +/- 26.0 min. Between 9 and 16% of the administered dose was excreted in the urine within 24 h. Buserelin could also be detected in the plasma after intranasal administration of doses of 150, 300 and 450 micrograms. There was a significant difference in the area under the curve (AUC) for plasma levels after subcutaneous injection of 5 micrograms and intranasal administration of 150 micrograms, but not between the AUC values after the three intranasal doses. These results indicate that this method for radioimmunoassay of buserelin is suitable for analyzing the pharmacokinetics and bioavailability of buserelin in man.