Magali Benjamim de Araújo

Multivariate optimization and validation of an analytical methodology by RP-HPLC for the determination of losartan potassium in capsules

This paper describes the optimization and validation of an analytical methodology for the determination of losartan potassium in capsules by HPLC using 2(5-1) fractional factorial and Doehlert designs. This multivariate approach allows a considerable improvement in chromatographic performance using fewer experiments, without additional cost for columns or other equipment. The HPLC method utilized potassium phosphate buffer (pH 6.2; 58 mmol L(-1))-acetonitrile (65:35, v/v) as the mobile phase, pumped at a flow rate of 1.0 mL min(-1). An octylsilane column (100 mm x 4.6mm i.d., 5 microm) maintained at 35 degrees C was used as the stationary phase. UV detection was performed at 254 nm. The method was validated according to the ICH guidelines, showing accuracy, precision (intra-day relative standard deviation (R.S.D.) and inter-day R.S.D values <2.0%), selectivity, robustness and linearity (r=0.9998) over a concentration range from 30 to 70 mg L(-1) of losartan potassium. The limits of detection and quantification were 0.114 and 0.420 mg L(-1), respectively. The validated method may be used to quantify losartan potassium in capsules and to determine the stability of this drug.

Analytical Validation of Quantitative High-Performance Liquid Chromatographic Methods in Pharmaceutical Analysis: A Practical Approach

Analytical validation is an essential component in allowing a laboratory to ensure routine acceptable performance of analytical methods. Despite the considerable amount of important published work on this subject, diversity still prevails in the employed methodologies because validation of an analytical method depends on the specific purpose of that method. This can lead to difficulties in validation approaches and the interpretation of results. Aiming to assist in the planning of validation methods, we discuss relevant approaches of various parameters in quantitative high-performance liquid chromatographic methods and validation fields in pharmaceutical analysis. Moreover, this article provides several up-to-date examples that should be useful as an introduction to analytical validation for practical applications in academic research or the industrial sector.

A discriminating dissolution method for glimepiride polymorphs

Glimepiride, an oral antidiabetic drug, is practically insoluble in water and exists in two polymorphic forms, I and II, of which form II has higher solubility in water. Because the dissolution rate of drugs can depend on the crystal form, there is a need to develop discriminating dissolution methods that are sensitive to changes in polymorphic forms. In this work, a dissolution method for the assessment of 4 mg glimepiride tablets was developed and validated. The optimal dissolution conditions were 1000 mL of phosphate buffer (pH 6.8) containing 0.1% (w/v) of sodium dodecyl sulfate as the dissolution medium and a stirring speed of 50 rpm using a paddle apparatus. The results demonstrated that all the data meet the validation acceptance criteria. Subsequently, tablets containing forms I and II of glimepiride were prepared and subjected to dissolution testing. A significant influence of polymorphism on the dissolution properties of glimepiride tablets was observed. These results suggested that the raw material used to produce glimepiride tablets must be strictly controlled because they may produce undesirable and unpredictable effects.

Lamivudine Salts with Improved Solubilities

To optimize solubility of drugs, current strategies mainly focus on engineering and screening of smart crystal phases. Two salts of the anti-human immunodeficiency virus (HIV) drug lamivudine--namely, lamivudine hydrochloride and lamivudine hydrochloride monohydrate, were prepared in the course of screening the crystallization conditions of lamivudine duplex, an uncommon DNA-mimic, double-stranded helical structure made up of partially protonated drug pairs. Here, water solubilities of lamivudine hydrochloride, lamivudine hydrochloride monohydrate, and lamivudine duplex are reported. The aqueous solubility of this anti-HIV drug was significantly increased in both salts and also in lamivudine duplex in relation to the water solubility of lamivudine form II. In comparison with the lamivudine form II incorporated into therapeutic formulations, the drug solubility was increased at a temperature of 299 ± 2 K by factors of 1.2, 3.3, and 4.5 in lamivudine hydrochloride, lamivudine hydrochloride monohydrate, and lamivudine duplex, respectively, demonstrating that this solid-state property of lamivudine can be improved by crystal engineering strategies. Solubility profiles were understood on the basis of structural and solvent-solute interaction approaches. At last, correlations between solubility and crystal structures allowed for a rational approach to understand how this physicochemical feature could be enhanced by engineering new salts of the drug.

Solid state chemistry of the antibiotic doxycycline: structure of the neutral monohydrate and insights into its poor water solubility†

The active pharmaceutical ingredient (API) doxycycline (DOX) is a broad-spectrum antibiotic mainly used in the treatment of respiratory and urinary tract infections and, like many drugs, its efficacy may be affected by the crystal form. Up to now, only the crystal structure of doxycycline hyclate (DOX·HYC) (generic name of brand names such as DORYX®, PERIOSTAT®, ATRIDOX®, and VIBRAMYCIN®) has been reported. This study presents the single-crystal X-ray diffractometry structural characterisation of another crystal form, doxycycline monohydrate (DOX·H2O) (generic name of brand names such as MONODOX® and ORACEA®). The DOX·H2O structure was compared with the known DOX·HYC one in terms of intra- and intermolecular geometries, and their melting temperature, water solubility and dissolution rate were measured. These data allowed us to establish relationships between solid state properties related to the pharmaceutical performance of the two DOX crystal variants and their supramolecular structures for the first time. Both hyclate and monohydrate forms crystallise the DOX molecules as zwitterions in which their dimethylamine groups are protonated and one of their hydroxyl groups is deprotonated. Whereas two conformers were observed in the DOX·HYC (i.e., the amine group is next to the enolate in one of them (T1) and beside the carbonyl in the other one (T2)), only one (T2) was found in DOX·H2O. Additionally, in the hyclate form, the presence of ethanol in the crystal lattice could be related to a rotation around the C–C bond of the amide group, directing the oxygen toward the amine group in one (T1) of the two conformers present in this solid state phase. Meanwhile, in the other crystallographically independent molecule (T2), the amide nitrogen is on the same side as the amine. However, only the conformer similar to T1 in DOX·HYC was observed in DOX·H2O. The crystal packing of DOX·H2O was stabilised by several intermolecular hydrogen bonds, with each drug entity interacting with another two DOX and three water molecules in such a way that a compact supramolecular network was formed. This structure was saturated in terms of hydrogen bonding, which could be related to its lower solubility and dissolution rate relative to DOX·HYC.

Analysis of chlorthalidone polymorphs in raw materials and tablets and the effect of forms I and II on the dissolution properties of drug products

Chlorthalidone (CTD) is an antihypertensive drug and exhibits four crystalline forms: I, II, III and IV. In this paper, the incidence of CTD polymorphs in raw materials and in tablets as well as the solubility and dissolution properties of forms I and II have been studied. Raw materials were named as A, B, C, D, and E and tablets as Reference, G1, G2 and S. Using powder X-ray diffraction and infrared spectroscopy analyses we found that A, B, E, Reference and G1 contain CTD form I; C, D and S contain predominantly form II; and G2 contain a mixture of both forms. Solubility experiments showed that form II is up to 49% more soluble than form I and dissolution studies showed a significantly effect of the polymorphism on the dissolution of CTD from tablets. Based on these results, it was concluded that only the CTD form I is acceptable for preparation of tablet form. Moreover, we proposed the polymorphic quality control of CTD raw materials and tablets.

Dissolution test optimization for meloxicam in the tablet pharmaceutical form

Meloxicam is a broadly used drug in the therapeutics for the osteoarthritis and rheumatoid arthritis treatments in adults, and it is available in the Brazilian market, as tablet and capsule pharmaceutical forms. The present work aimed to establish conditions for accomplishment of the dissolution test of 15 mg meloxicam tablets (A and B test products), compared with the reference product, since there is no monograph about dissolution assays for meloxicam in official summaries. To optimize the conditions several parameters were tested and, according to obtained results, the use of pH 7.5 phosphate buffer (900mL, at 37 ± 0.5oC) as dissolution medium, paddle method (apparatus 2), stirring speed of the dissolution medium at 100 rpm and collect time of 60 minutes were considered satisfactory. The samples were quantified by UV spectrophotometric method at 362 nm. The products presented kinetics of first-order. Dissolution efficiency values were of 83.25, 83.73 and 88.10% for the A, B and reference products, respectively. Factors f1 and f2 were calculated and similarity of the tested medicines was demonstrated. The dissolution test was validated presenting selectivity, linearity, precision and accuracy within of the acceptance criteria.

The form II of the antihypertensive drug chlorthalidone

Racemic mixtures of chlorthalidone (CTD) have been structurally elucidated in three crystal forms (space group P), namely, Form I, Form III (both true polymorphs) and a chloroform solvate. Here, we have structurally characterized the Form II, which, in contrast to the known forms, individual crystals are pure enantiomers. However, the Form II bulk product from spontaneous chiral resolution upon crystallization contains a mixture of crystals as a conglomerate, half of which consists solely of the (R)-enantiomer, the other half the (S)-enantiomer. Form II was solved in the space group P21 with one (R)-enantiomer unit in its asymmetric unit resembling that of Form III in terms of the chlorobenzenesulfonamide moiety conformation. Even though the (R)-enantiomer has been chosen for the single-crystal structure determination experiment, chiral chromatography and optical rotation data have inferred the conglomerate nature of Form II. Concerning the crystal packing of Form II, all hydrogen bonding functionalities of the sulfonamide group are saturated into the assembly of helical ribbons growing along the [010] direction, a supramolecular motif which is not found in the known crystal phases of the drug. Moreover, Form II shows packing similarity to the chloroform solvate mainly because the hydrogen bonding patterns of their isoindolinyl functionalities. The isoindolinyl stacking also occurs similarly in Form II and in the solvate form, with bends between the planes calculated through those moieties of stacked molecules of ca. 28° and 24°. In summary, we believe that the structural knowledge of Form II concerns new outlooks not only into the solid-state properties of CTD but also into its medicinal chemistry, e.g., regarding pharmacological profiles of the conglomerate.

In vitro evaluation of transdermal nicotine delivery systems commercially available in Brazil

The aim of this study was to develop and validate a method for evaluating the release and skin permeation from transdermal nicotine patches using the vertical diffusion cell (VDC). The VDC is an experimental apparatus employed in research, development, and the pharmaceutical field because it can simulate conditions closest to those established in clinical trials. Two transdermal nicotine delivery systems marketed in Brazil to release 14 mg over 24 hours were evaluated. Release studies were carried out using a regenerated cellulose dialysis membrane and permeation studies were carried out using excised porcine ear skin. The results indicated that nicotine release from both evaluated patches follows Higuchis release kinetics, while skin permeation studies indicated zero-order release kinetics. Nicotine release rates were different between both evaluated patches, but drug permeation rates were not significantly different. According to validation studies, the method was appropriate for evaluating in vitro performance of nicotine patches. The proposed method can be applied to in vitro comparative studies between different commercial nicotine patches and may be used as an auxiliary tool in the design of new transdermal nicotine delivery systems.

Development and validation of an UV-derivative spectrophotometric method for determination of glimepiride in tablets

Glimepiride is an oral antidiabetic drug widely used in treatment of type 2 diabetes. This work proposed the development and validation of a derivative UV spectrophotometric method for determination of glimepiride in tablets. The quantification of glimepiride in 5×10-3 mol L-1 NaOH was performed by using a wavelength interval of 8 nm in the range of 220-300 nm. The amplitude values obtained in the second-derivative spectra were arbitrary units of the peak height from the central zero base line to the signals obtained at 279.0, 257.5 and 256.3 nm for quantification of Amaryl® tablets 1 mg, Amaryl® tablets 2 mg and Amaryl® tablets 4 mg, respectively. The method was completely validated according to the International Conference on Harmonization (ICH) guidelines, showing accuracy, precision, selectivity, robustness and linearity. The validated method is suitable for quality control applications, since it does not use polluting reagents, it is simple and has low-cost.