Table 4.

Stability data for metformin and rosuvastatin in human plasma under various storage conditions.

Compound	Calculated Concentration (ng mL−1)
Metformin	50		1250		2500
	Mean ± S.D.(n = 3)	%Era	Mean ± S.D.(n = 3)	%Era	Mean ± S.D.(n = 3)	%Era
Ambient temperature/4 h	50.4 ± 1.9	0.9	1271.5 ± 8.2	1.7	2522 ± 138	0.01
−20 °C/4 weeks	49.7 ± 2.1	−0.6	1260.1 ± 0.80	0.8	2412 ± 18	−0.04
−20 °C/4 Freeze-thaw cycles	51.21 ± 0.81	2.4	1282.3 ± 2.6	2.6	2386 ± 24	−0.05
Rosuvastatin	2.5		25		50
Ambient temperature/4 h	2.509 ± 0.0089	0.4	24.72 ± 0.11	−1.1	49.4 ± 3.4	−0.9
−20 °C/4 weeks	2.457 ± 0.045	−1.7	24.53 ± 0.15	−1.9	50.2 ± 3.2	0.4
−20 °C/4 Freeze-thaw cycles	2.435 ± 0.031	−2.6	24.94 ± 0.42	−0.2	49.5 ± 2.4	−1.0

^a %E_r: relative percentage error = (overall mean assayed concentration − added concentration)/(added concentration) × 100.