Research Article
Comparative Study of Chemical Stability of Two H1 Antihistaminic Drugs, Terfenadine and Its In Vivo Metabolite Fexofenadine, Using LC-UV Methods
Table 2
Percentage degradation and kinetic parameters of terfenadine (TER) and fexofenadine (FEX) at 70°C and different pH.
| | Stress conditions | Degradation (%) | Linear equation y = ax + b | R2 | k (min−1) | t90 (h) | t50 (h) |
| | TER | | 1 M HCl | 21.02 | y = −0.0008x + 3.9036 | 0.9893 | 1.84 × 10−3 | 0.95 | 6.27 | | pH 4.0 | 19.72 | y = −0.0007x + 3.9015 | 0.9683 | 1.61 × 10−3 | 1.08 | 7.16 | | pH 7.0 | 18.44 | y = −0.0007x + 3.9145 | 0.9948 | 1.61 × 10−3 | 1.08 | 7.16 | | pH 10.0 | 17.54 | y = −0.0007x + 3.9300 | 0.9836 | 1.61 × 10−3 | 1.08 | 7.16 | | 1 M NaOH | 16.50 | y = −0.0006x + 3.9258 | 0.9834 | 1.38 × 10−3 | 1.27 | 8.36 | | FEX | | 1 M HCl | 67.32 | y = −0.0036x + 3.9210 | 0.9938 | 8.29 × 10−3 | 0.21 | 1.39 | | pH 4.0 | 67.54 | y = −0.0037x + 3.9680 | 0.9846 | 8.52 × 10−3 | 0.21 | 1.36 | | pH 7.0 | 40.42 | y = -0.0016x + 3.8485 | 0.9724 | 3.68 × 10−3 | 0.47 | 3.14 | | pH 10.0 | 59.14 | y = −0.0028x + 3.9034 | 0.9922 | 6.45 × 10−3 | 0.27 | 1.79 | | 1 M NaOH | 72.98 | y = −0.0043x + 3.9801 | 0.9839 | 9.90 × 10−3 | 0.18 | 1.17 |
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