Vortex-assisted liquid-liquid microextraction combined with liquid chromatography tandem mass spectrometry for simultaneous determination of cardiovascular drugs in human plasma.

Hypertension and dyslipidemias are among the main risk factors for the development of cardiovascular diseases, which are responsible for the death of approximately 17 million people each year. There are several drugs available for the treatment of these diseases. Therefore, methods for the simultaneous analysis of several of these drugs are useful in a wide range of situations. In this context, this study aimed to develop a modern method for the simultaneous determination of eight cardiovascular drugs in human plasma. A vortex-assisted liquid-liquid microextraction (VALLME) procedure, combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Mass spectrometry conditions, chromatographic separation, and sample preparation were optimized. For VALLME optimization, pH, sodium chloride concentration, volume of buffer solution, extraction solvent (type and volume), and vortex stirring time were evaluated. The method proved to be simple, fast, and environmentally friendly since low volumes of organic solvent were employed. Furthermore, the VALLME procedure required small sample volume, which is desirable when large volumes are scarce. Suitable recoveries and lower limits of quantification were achieved with a chromatographic run of only 8 min. The method was validated, showing to be selective, precise, and accurate. Furthermore, the analytical curves were well fitted to the selected models and the matrix effect did not affect method reliability. The developed method was successfully applied for the analysis of plasma samples obtained from volunteers attending a hospital service.

UHPLC for quality evaluation of genuine and illegal medicines containing sildenafil citrate and tadalafil.

One of the highest incidences of illegal drug products is related to phosphodiesterase-5 inhibitors, used in treatment of erectile dysfunction, including those containing sildenafil citrate and tadalafil. In this context, comprehensive evaluation of the quality of genuine and illegal medicines was performed. A simple and rapid ultra-high performance liquid chromatography (UHPLC-UV) method to quantify sildenafil and tadalafil in the presence of six degradation products was developed and validated. Sildenafil and tadalafil were submitted to forced degradation. The separation was carried out on a Kinetex C18 (50 × 2.1 mm; 1.7 µm) column with mobile phase composed of acetonitrile and aqueous triethylamine solution. The calibration curves were linear in the range of 14-126 µg mL-1 for sildenafil citrate and 4-36 µg mL-1 for tadalafil and the method proved to be selective, precise, accurate and robust. Sildenafil degraded in oxidative media, whereas tadalafil degraded in acidic, alkaline and oxidative environment. The chemical structures and the mechanisms for the formation of the main degradation products were proposed by UHPLC coupled to tandem mass spectrometry. The UHPLC-UV method was applied in the pharmaceutical analysis of genuine and seized medicines. Some of them did not meet quality standards, mainly due to contents below specifications and the large variation on contents between units within a batch.

A simple and sensitive HPLC-FL method for simultaneous determination of angiotensin II receptor antagonists in human plasma.

Angiotensin II receptor antagonists are one of the most widely used classes of antihypertensive drugs. In this study, an HPLC fluorescence method after protein precipitation (PPT) extraction was developed and validated for determination of olmesartan, losartan, irbesartan, and valsartan in human plasma. The separation was carried out on a Luna cyano (250 × 4.6 mm i.d.; 5 µm particle size) column and the mobile phase was composed of acetonitrile and 0.1 % phosphoric acid in gradient elution, at a flow rate of 1.2 mL min-1. A PPT method was optimized by a two-level factorial design with triplicate at the central point. The parameters that could affect the extraction (sample volume and acetonitrile/plasma volume ratio) were evaluated and the method was compared to microextraction by packed sorbent (MEPS) and liquid-liquid extraction (LLE). The developed method allowed the simultaneous quantification of the analytes employing a simple and cheap sample preparation method and a short chromatographic run (13 min). This method was fully validated showing selectivity, precision, accuracy, and linearity over the range of 25.0-1500.0 ng mL-1 for olmesartan and valsartan, 25.0-2500.0 ng mL-1 for irbesartan, and 35.0-2500.0 ng mL-1 for losartan. Finally, the method was successfully applied in the analysis of human plasma from volunteers.

Stability-indicating UHPLC method for determination of nevirapine in its bulk form and tablets: identification of impurities and degradation kinetic study.

Nevirapine (NVP), a non-nucleoside reverse transcriptase inhibitor, is a drug widely used in the treatment of Acquired Immunodeficiency Syndrome (AIDS). The evaluation of NVP stability is of fundamental importance in order to guarantee drug product efficacy, safety and quality. In this study, NVP active pharmaceutical ingredient (API) and tablets were subjected to a detailed study of forced degradation, employing several degrading agents (acid, alkaline, water, metal ions, humidity, heat, light and oxidation agents). In order to determine NVP and the degradation products formed, a stability-indicating UHPLC method using fused core column was developed and validated. The separation was carried out using a Poroshell 120C18 column (100×2.1mm i.d.; 2.7µm particle size) and the mobile phase was composed of acetonitrile and water in a gradient elution, at a flow rate of 0.2ml/min. Chemical structures and mechanisms for the formation of three degradation products were proposed by means of LC/MS-MS. Also, NVP degradation kinetic was studied and its order of degradation evaluated. NVP was degraded in acidic and oxidative conditions and the degradation profile for NVP tablets and API were similar. The stability-indicating method proved to be selective for NVP and its degradation products. Calibration curve was linear in the range of 8-48µg/ml and the method showed to be precise, accurate and robust for both NVP API and tablets, with detection and quantification limits of 0.092µg/ml and 0.174µg/ml, respectively.

Development and validation of an HPLC method for the simultaneous determination of artesunate and mefloquine hydrochloride in fixed-dose combination tablets

The present study developed and validated an HPLC method for the simultaneous determination of artesunate (AS) and mefloquine hydrochloride (MQ) in fixed-dose combination tablets, according to ICH guidelines. The chromatographic separation was carried out on an XBridge C18 (250 x 4.6 mm i.d., 5 µm particle size, Waters) analytical column. The mobile phase included a 0.05 M monobasic potassium phosphate buffer (pH adjusted to 3.0 with phosphoric acid) and acetonitrile (50 + 50, v/v). The flow rate was 1.0 mL/min, and the run time was 13 minutes. A dual-wavelength approach was employed: AS detection was performed at 210 nm and MQ was detected at 283 nm, using a diode array detector. Stability of sample solutions was evaluated for 8 hours after preparation, during which time the solutions remained stable. Youden's test was employed to evaluate robustness. The method proved to be linear (r²>0.99), precise (RSD<2.0%), accurate, selective, and robust, proving to be appropriate for routine drug quality control analysis.

Um método por cromatografia a líquido de alta eficiência para a determinação simultânea de artesunato (AS) e cloridrato de mefloquina (MQ) em comprimidos em dose fixa combinada foi desenvolvido e validado, de acordo com as normas do ICH. A separação cromatográfica foi realizada com uma coluna analítica XBridge C18 (250 x 4,6 mm d.i., partículas de 5 µm, Waters). A fase móvel foi constituída de tampão fosfato monobásico de potássio 0,05 M (pH ajustado para 3,0 com ácido fosfórico) e acetonitrila (50 + 50, v/v). O fluxo da fase móvel foi de 1,0 mL/min e o tempo de corrida foi de 13 minutos. Utilizaram-se dois comprimentos de onda: a detecção do AS foi realizada em 210 nm e a de MQ foi realizada em 283 nm, utilizando-se um detector de arranjo de diodos. A estabilidade das soluções padrão e amostra foi avaliada por 8 horas após sua preparação e as soluções permaneceram estáveis nesse período. O teste de Youden foi empregado para a avaliação da robustez do método. O método se mostrou linear (r²>0,99), preciso (DPR<2,0%), exato, seletivo e robusto, sendo adequado para análises rotineiras de controle de qualidade dos medicamentos.