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	R 2	k (min−1)	t 90 (h)	t 50 (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