INTRODUCTION:

Telmisartan, chemically it is 4[(1, 4-dimethyl-2-pyl (2, 6-bi-1H-benzimidazol]-1-yl) methyl] [1, 1-biphenyl]-2-carboxylic acid¹. Amlodipine besylate is chemically 3-Ethyl 5-methyl (4RS)-2-[(2-aminoethoxy)methyl]-4-(2-chloro phenyl)-6-methyl-1,4-dihydropyridine-3,5-dicarboxylate benzene sulphonate². Telmisartan and Amlodipine are introduced into the market in combined dosage form, which is widely used in the treatment of hypertension. Literature review reveals that the methods for Telmisartan and Amlodipine alone or in combined dosage forms are RP-HPLC Method for Estimation of Telmisartan in Tablet dosage form³. Spectrophotometric Simultaneous determination of Hydrochlorothiazide and Telmisartan in Combined Dosage Form⁴. RP-HPLC Method for Simultaneous Estimation of Telmisartan and Amlodipine in Tablet Dosage Forms⁵. Simple and rapid high performance thin layer chromatographic determination of amlodipine in pharmaceutical dosage forms⁶. Stability indicating RP-HPLC method for simultaneous determination of atorvastatin and amlodipine from their combination drug products⁷.

Spectrophotometric method for simultaneous estimation of amlodipine besylate and bisoprolol fumarate in pharmaceutical preparations⁸. Analytical Method Development and Validation of Amlodipine and Hydrochlorothiazide in combined dosage form by RP-HPLC⁹. Simultaneous spectrophotometric estimation of atenolol and amlodipine besylate by multi wavelength method¹⁰. HPLC method development for the simultaneous analysis of amlodipine and valsartan in combined dosage forms and invitro dissolution studies¹¹. Stability indicating RP-HPLC method for simultaneous estimation of valsartan and amlodipine in capsule formulation¹². Simultaneous estimation of amlodipine besylate and lisinopril dihydrate as API and tablet dosage forms¹³. RP-HPLC method for the simultaneous estimation of losartan potassium and amlodipine besylate in tablet formulation¹⁴. Reversed phase liquid chromatographic determination of Ramipril and Amlodipine in tablets¹⁵. Simultaneous determination of metoprolol succinate and amlodipine besylate in pharmaceutical dosage form by HPLC¹⁶.Simultaneous determination of atenolol and amlodipine in tablets by high performance thin layer chromatography¹⁷.

EXPERIMENTAL:

Apparatus

Samples were applied as 8 mm bands by means of a Camag Linomat V automatic samples applicator (Muttenz Switzerland) equipped with a 100 µL syringe.

The distance between the bands was 11.4 mm. Silica gel 60 F₂₅₄ HPTLC plates (20×10 cm, aluminium) were from Merck (Darmstadt, Germany). Densitometric scanning was performed at 251nm with a Camag TLC scanner 3 equipped with Camag Wincats software 1.42 using the deuterium light source and slit dimensions of 4.00 mm × 0.30 mm.

Chemicals

Telmisartan and Amlodipine reference standards was supplied by M/s Microlabs limited, Bangalore, India. HPLC grade chloroform, methanol was purchased from Merck (Mumbai, India). All chemicals were of analytical grade. Commercially available tablets (Stamlo-T of Dr.Reddys Labs, Andhra Pradesh, India), containing 40 mg Telmisartan and 5mg Amlodipine per tablet, were used for analysis. Standard solutions (1 mg mL-1) were prepared in methanol.50 microlitre of the above solution was diluted with 950 microlitre of methanol (50 mcg/ml)

Chromatographic conditions

Chromatography was performed on 20 × 10 cm aluminum HPTLC plates coated with 0.2 mm layers of silica gel 60 F₂₅₄ (Merck). Before use plates were washed with methanol and dried in an oven at 120°C for 20 min. ascending development of the plate with a migration distance of 50 mm was performed at 23± 2°C using chloroform: methanol: Formic acid (85:15:5 v/v/v) as the mobile phase and a Camag twin-trough chamber previously saturated with mobile phase for 20 min. the average development time was 5 minutes.

Calibration

Mixed working standard solutions equivalent to,2 4, 6, 8, 10, 12, 14,16,18 µL were separately stopped on the TLC plate in order to obtain final concentrations at 400, 800, 1200, 1400, 1600, 2000, 2400, 2800, 3200 ng spot^-1 for both drugs respectively. The plates were developed in a 20 × 10 cm twin through chamber using 20 mL freshly prepared mobile phase.

Analysis of Tablet Formulation

The tablets were weighed, triturated and the average weight was calculated. 225 mg of sample was diluted with 10 ml of methanol and filtered through Whatman filter paper no. 41. The above stock was diluted in the ratio of 1:10 with methanol which was used as the working standard solution. The 8µL solution was spotted on the HPTLC plate and the concentrations were calculated from the calibration graph.

Recovery study

The accuracy of the proposed method was evaluated by the addition of a standard drug solution at three different concentration levels at 50, 100, and 150% of linearity for both drugs.

RESULTS AND DISCUSSION:

A number of experimental parameters, such as mobile phase composition, scan modes and detection wavelengths, were optimized during method development in order to provide accurate, precise and reproducible results for the simultaneous determination of Amlodipine and Telmisartan.

Table 1.Calibration graphs of Amlodipine and Telmisartan

Parameter

HPTLC

Telmisartan

Amlodipine

Linearity range

Regression equation

Slope

Intercept

Coefficient of correlation

Limit of detection (LOD)

Limit of quantitation (LOQ)

600-1400 ng/ml

1.844

1761

0.998

100 ng/ml

300 ng/ml

800-2400 ng/ml

1.644

1126

0.997

200 ng/ml

600 ng/ml

Table 2: Assay and Recovery studies of Amlodipine and Telmisartan

Brand name	Compound	% Assay	% Recovery
HPTLC	Telmisartan	99.90	100.5
HPTLC	Amlodipine	99.18	99.6

Maximum separation was achieved (Amlodipine Rf 0.47, Telmisartan Rf 0.61) and minimum tailing were obtained when using a mobile phase composition of chloroform: methanol: formic acid (85:15:5 v/v/v) respectively (Fig. 1). Table 1 shows that correlation coefﬁcients were 0.998 for Amlodipine and 0.997 for Telmisartan. The LOD values were 200 ng/spot and 100 ng/spot, while LOQ values were 600 ng/spot and 300 ng/spot for both Amlodipine and Telmisartan respectively. The proposed method was used for the determination of both drugs in tablets and results are also shown in Table 2. Good recoveries and standard deviations were observed.

CONCLUSION:

A method was developed for the determination of tablets which is simple, quick, reliable, inexpensive and simple. The results indicate that the described method can be used for quantitative analysis of the compound.

ACKNOWLEDGEMENT:

The authors are thankful to Central Research Facility, Sri Ramachandra University, Chennai for encouragement and providing Support to carry out this research work.

REFERENCES:

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Received on 31.10.2012 Modified on 09.11.2012

Asian J. Research Chem. 5(11): Nov., 2012; Page 1385-1387