UTILITY OF CERTAIN π-ACCEPTORS FOR THE SPECTROPHOTOMETRIC DETERMINATION OF THE ANTIHISTAMINICS TERFENADINE AND ASTEMIZOLE

Two simple, rapid, accurate and sensitive spectrophotometric methods were described for the determination of the antihistaminics, terfenadine (I) and astemizole(II). The methods were based on the reaction of each of terfenadine and astemizole as n-electron donors with either tetrachloro-p-benzoquinone(p-chioranil, CL) or tetrabromo, 1,2-benzoquinone(TBBQ) as T-acceptors, to give highly colored radical anions. The colored products with terfenadine exhibited maximum absorption at 550 nm and 573 nm with CL. and TBBQ, respectively. While astemizole exhibited maximum absorption at 561 nm with CL and 578 nm in case of TBBO, Different assay parameters have been optimized to achieve maximum sensitivity and accuracy for determination of terfenadine and astemizole. Linear relationships between absorption and concentrations have been obtained over the range of 0.05 -1.00 mg mL^-1 of (I) and (II). The mean percentage recoveries from triplicate determinations of nine concentrations lied in the same range  of each drug were 99.45 ±0.902 S D with CL and 99.776 ± 0.781SD with TBBQ in case of terfenadine and 99.99 +0.168 S D with CL and 100.113 ± 0.284 S D with TBBQ in case astemizole. The method has been applied for the determination of terfenadine and astemizole in their tablets. The results obtained were in a good agreement with those obtained by the use of some reported procedures.