ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 2, с. 201-209
DEVELOPMENT AND VALIDATION OF STABILITY INDICATING CHROMATOGRAPHIC METHOD FOR DETERMINATION OF IMPURITIES IN MAPROTILINE PHARMACEUTICAL TABLETS
© 2015 Svetlana Lj. DuriC*, Daniela C. NaskoviC*, Dragan T. VeliCkoviC**,
Dragan M. MilenoviC*,1
*Zdravlje-Actavis company Vlajkova street 199, 16000 Leskovac, Serbia
1E-mail: firstname.lastname@example.org **College of Agriculture and Food Technology
Cirila i Metodija street 1, 18400 Prokuplje, Serbia Received 04.03.2013; in final form 25.12.2013
A simple, sensitive and accurate HPLC method has been developed and validated for determination impurities in maprotiline solid dosage forms. Chromatographic separation was achieved on Lichrospher RP Select B column (250 mm x 4.6 mm i.d., particle size 5 ^m, maintained at 40°C) by a mobile phase consisted of ammonium hydrogen carbonate (pH 8.1; 0.05 M)—acetonitrile—methanol—tetrahydrofuran (20 : 80 : 32 : 4.5, v/v/v/v) and a flow rate of 1.0 mL/min. The detection wavelength was set at 215 nm and injection volume was 10 p.L. The drugs were subjected to oxidation, hydrolysis, photolysis and heat to apply stress conditions. The degradation products, when any, were well resolved from the pure active substance with significantly different retention time values, thus proved the stability indicating power of the method. The method met the International Conference on Harmonisation (ICH) regulatory requirements. The results demonstrated that the method would have a great value when applied in quality control and stability studies for maprotiline tablets.
Keywords: development, stability indicating, validation, maprotiline.
Maprotiline (N-methyl-9,10-ethanoanthracene-9(10H)-propanamine) is a tetracyclic antidepressant, which is distinguished from conventional tricyclic antidepressants only by an ethylene bridge upon its molecular skeleton, creating a fourth ring. It has been used in antidepressant therapy and has sedative as well as anti-aggressive properties. Maprotiline acts by blocking noradrenaline uptake and appears to have no influence on serotonin metabolism. In addition, the drug is a weak central acetylcholine antagonist [1, 2].
Maprotiline is slowly, but completely absorbed from the gastrointestinal tract . The main metabolic degradation pathway of the drug is demethylation, resulting in the active metabolite N-desmethylmaprotiline. In addition, N-oxidation into maprotiline N-oxide and hy-droxylation followed by conjugation also occur. The drug is excreted in urine and faeces, mainly as metabolites .
Adverse effects of maprotiline (drowsiness, dry mouth) are largerly the same as for tricyclic antidepressants, but there seems to be a higher incidence of skin rashes. However, most of the side-effects of maprotiline
are mild and usually disappear with continued treatment or after reduction in dosage .
Several methods for the determination of mapro-tiline in biological samples have been published. Recommended analytical methods for maprotiline involve mainly GC in combination with a nitrogen-phosphorus detector [4-6], HPLC with UV [7-9], diod-array as well as fluorescence detectors [10-12], HPLC with chemiluminescence , spectophotometric, spec-trofluorimetric [1, 14], and TLC . Methods included in the United States Pharmacopoeia and European Pharmacopoeia address only the analysis of maprotiline drug substance and tablets without impurities determination in solid dosage forms [16, 17].
Five impurities are identified for maprotiline HCl in the European Pharmacopoeia: A, B, C, D and E. Three of them, A, B and D, were available for us. The structures of these five impurities, as well as maprotiline • HCl, are presented below.
Chemical structures of maprotiline hydrochloride (a) and its impurities (b, c). (b) - A: R = CH=CH—CH=O, 3-(9,10-ethanoanthracen-9(10H)-yl)prop-2-enal; C: R = CH2-CH2-CH2-NH2, 3-(9,10-ethanoanthra-cen9(10H)-yl)propan-1-amine; D: R = CH=CH-CH2-NH-CH3, 3-(9,10-ethanoanthracen-9(10H)-yl)-methylprop-2-en-1-amine; E: R = CH2-CH2-CH2-N(CH3)2, 3-(9,10-ethanoanthracen-9(10H)-yl)-N, N-dimethylpropan-1-amine. (c) — B: 3-(9,10-etha-noanthracen-9(10H)-yl)-N-[3-(9,10-ethanoanthracen-9(10H)-yl)propyl]-N-methylpropan-1-amine.
Some of these impurities were determined to be possible degradants of maprotiline in the drug product. As such, a method for the determination of these impurities was required. Therefore, a method was developed and validated to this end.
Validation of the method for impurities determination in maprotiline tablets will be performed according to the ICH requirements, after stress testing on the drug tablets under a variety of conditions, including hydrolysis (at various pH), oxidation, photolysis and termal degradation . Results of stability testing are important in developing proper manufacturing process, selecting proper packaging, storage conditions, product's shelf life, and determining the expiration date.
Chemicals and reagents. The maprotiline hydro -chloride, working certified standard, was purchased from Sifavitor S.R.L. (Italy). Impurities A and B were purchased from LGC GmbH (Luckenwalde, Germany), and impurity D was purchased from European Directorate for the Quality of Medicine&Health Care (EDQM) — Council of Europe (Strasbourg, France). Methanol and acetonitrile (HPLC gradient grade) were purchased from J.TBaker (Deventer, Holland). Ammonium hydrogen carbonate, ammonium hydroxide, hydrochloric acid, sodium hydroxide and hydrogen peroxide used were of analytical reagent grade. Tetrahydrofu-ran was purchased from J.TBaker (Deventer, Holland).
Purified water was obtained with a Arium Laboratory Equipment (RO, UV) by Sartorius AG (Gottingen, Germany). The mobile phase was filtered through a 0.45 ^m Sartorius membrane filter (Gottingen, Germany).
Equipment. The HPLC system consisted of a de-gasser G1379A, a bin pump G1312A, an automatic injector G1313A, thermostated column compartment G1316A and a diod-array detector G1315B, all 1100 Series, from Agilent Technologies, controlled by an HP Chemstation software (Waldbroon, Germany). Ultrasonic bath was from Elma, Transsonic 470/H (Singen, Germany). Analytical balance was from Sartorius AG, CP224S—OCE (Gottingen, Germany); accuracy of the balance ±0.0001 g.
Chromatographic conditions. All chromatographic experiments were performed in the isocratic mode. The mobile phase was constituted of ammonium hydrogen carbonate (pH 8.1, 0.05 M, adjusted with 2 M of ammonium hydroxide)—acetonitrile—methanol— tetrahydrofuran (20 : 80 : 32 : 4.5, v/v/v/v). The mobile phase was delivered at 1.0 mL/min. UV detection was made at 215 nm. The volume of injection was fixed at 10 ^L. All analyses were performed at 40°C. The separation was carried out on a Lichrospher RP Select B column (250 mm x 4.6 mm i.d., particle size 5 ^m), from Merck.
Preparation of solutions. Stock solution of maprotiline hydrochloride (1.0 mg/mL) was prepared in mobile phase by using ultrasonic bath for 15 min. Solutions of maprotiline and related compounds (Impurities A, B and D) were prepared in methanol. These solutions were further diluted with the mobile phase to obtain working standard solutions of suitable concentrations (0.002 mg/mL). The solutions were adequately diluted with mobile phase to study accuracy, precision, linearity, limits of detection and quantification. Test and placebo solutions of maprotiline tablets were prepared according to tablet composition in adequate concentration.
Generation of stress samples. The reactions were carried out at a drug concentration of1.0 mg/mL (calculated as maprotiline hydrochloride tablets powder). The stress conditions were as follows:
i. Stress study under hydrolytic condition: acidic hydrolysis — maprotiline tablets powder in 1 M HCl was exposed at room temperature for 24 h; alkaline hydrolysis — maprotiline tablets powder in 1 M NaOH was exposed at room temperature for 1 h.
ii. Stress study under oxidative condition: maprotiline tablets powder in 3% H2O2 were stored at room temperature for 1 h.
iii. Stress study under light: maprotiline tablets were exposed to ICH recommended light conditions (UV and VIS — min 400 W h/m2 and min 2.4 million lux h).
<D О Й ce -О
50 40 30 20 10 0
50 40 30 20 10 0
50 40 30 20 10 0
50 40 30 20 10 0
Fig. 1. Method selectivity for maprotiline and its impurities with initial mobile phase.
iv. Thermal stress: maprotiline tablets powder was subjected to dry heat at 70°C for 72 h.
RESULTS AND DISCUSSION
Selection of chromatographic conditions. A simple, sensitive and rapid isocratic HPLC method was presented for the quantification of three known impurities in maprotiline solid dosage forms. Using this method, a good separation with adequate resolution was obtained for maprotiline and its three impurities.
The primary interest in solvent selectivity is the manipulation of peak resolution in a chromatogram during method development. The classical aproach towards methods development in reversed-phase chroma-tography involves three solvents that are miscible with water, result in different selectivities and have also otherwise reasonably favorable properties (e.g. for UV detection): acetonitrile, methanol and tetrahydrofuran.
Due to high pK value of maprotiline (pK = 10.5) suitable pH value of mobile phase was achieved by using ammonium bicarbonate. Initial mobile phase was
50 40 30 20 10
0 5 1 10 1 15 1 20 25
Fig. 2. Separation of maprotiline and its impurities after adding a small amount of tetrahydrofuran to initial mobile phase.
without tetrahydrofuran. Retention times for impurities A, B, D and maprotiline were below 15 min with flow rate of 2 mL/min (2.04, 14.13, 9.22, 9.69, respec-tivelly). Bu
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