Simultaneous UV Spectrophotometric Determination of Cetrizine and Dextromethorphan in Tablet Dosage Form

: Two accurate, precise, sensitve and economical procedures for simultaneous estimation of cetrizine and dextromethorphan in tablet dosage forms have been developed. First method employs formation and solving of simultaneous equations using 230 nm and 280 nm as two analytical wavelengths for both drugs in methanol. The second method is Q -analysis based on measurement of absorptivity at 224 nm (as isobestic point) and 280 nm ( λ max of CTZ). Cetrizine and dextromethorphan at their respective λ max 280 nm and 230 nm and at 224 nm (isobestic point) shows linearity in a concentration range of 10-30 mcg/mL for both the drugs. The recovery studies confirmed accuracy of the proposed methods and low values of standard deviation confirmed precision of the methods. The methods were validated as per ICH guidelines.


Experimental
Elico UV-Visible spectrophotometer (SL 164) was used for spectral measurements with 1 cm matched quartz cells.

Employing simultaneous equations using crammer's rule
Pure drug samples of cetrizine and dextromethorphan were dissolved separately in methanol, so as to give several dilutions of standard in the concentration range of 10 to 30 mcg/mL for both drugs.All dilutions were scanned in the wavelength range of 200-400 nm.
Two wavelengths selected for the formation of simultaneous equations were 280 nm (λ max of CTZ) and 230 nm (λ max of DXM).Similarly, mixed standard solutions were also used and the drugs showed linearity in the range of 10-30 mcg/mL for (CTZ) and (DXM).The absorptivities for the two drugs were presented in the Table 1. Figure 1 represents the overlain spectra of both drugs.The method employs solving of simultaneous equations using crammer's rule and matrices.The simultaneous equations formed were Figure 1.Zero order overlain spectra of CTZ (10 mcg/mL) and DXM (10 mcg/mL) Where A 1 and A 2 are absorbances of sample solution at 230 nm and 280 nm respectively.C 1 and C 2 are the concentrations of DXM and CTZ respectively in sample solution.By substituting the value of C 1 from equation (1) into equation ( 2), the value of C 1 can be obtained.Similarly C 2 can also be obtained.

Procedure for analysis of tablet formulation
The average weight of twenty tablets were determined and then ground to a fine powder.A quantity equivalent to 50 mg of CTZ and 50 mg of DXM were transferred to a 100 mL volumetric flask.The contents were dissolved by using 50 mL of methanol, filtered and made up to volume with the same.The solutions were further diluted with methanol to give concentrations of 5 mcg/mL of CTZ and DXM.Absorbances of these solutions were measured at 280 nm and 230 nm as A1 and A2 respectively and concentrations of these two drugs in the sample were calculated using equation (1) and equation (2).Results of the analysis of the tablet formulations were reported in Table 2.The recovery studies were depicted in Table 3.

Absorbance ratio or q-analysis method
From the overlain spectrum of CTZ and DXM, two wavelengths were selected, one at 224 nm, isobestic point for both the drugs and the other at 280 nm (λ max of CTZ).The absorbances of the standard and sample solutions were prepared in the same manner as in the previous method.The absorptivities for both drugs at the selected wavelength were presented in Table 1.The method employs Q values; the concentrations of drugs in sample solution were determined by using the following formula.Results of the analysis of the tablet formulations were reported in Table 2.The recovery studies were depicted in Table 3.

Results and Discussion
The proposed methods for simultaneous estimation of CTZ and DXM in combined dosage forms were found to be simple, accurate, economical and rapid.In both the methods, the values of coefficient of variation were satisfactorily low and recovery was close to 100% for both the drugs.

Conclusion
The proposed methods are simple, precise, accurate and rapid for the determination of CTZ and DXM in combined tablet dosage forms.These methods can be adopted as an alternative to the existing spectrophotometric methods.Analysis of authentic samples containing CTZ and DXM showed no interference from the common additives and excipients.Hence, recommended procedure is well suited for the assay and evaluation of drugs in pharmaceutical preparations.It can be easily and conveniently adopted for routine quality control analysis.
For CTZ for DXM Absorbance of sample at 224 nm Q 0 = Absorbance of sample at 280 nm Absorptivity of CTZ at 224 nm Q 1 = Absorptivity of CTZ at 280 nm Absorptivity of DXM at 224 nm Q 2 = Absorptivity of DXM at 280 nm A = Absorbance of sample at isobestic point a 1 and a 2 -absorptivities of CTZ and DXM respectively at isobestic point.

Table 1 .
Absorptivity values for cetrizine and dextromethorphan

Table 2 .
Results of commercial formulation analysis

Table 3 .
Recovery studies of CTZ and DXM * Average of three determinations