For GSH-px, the effect was largest in females (4.52 SMD, 95% CI, 2.98 to 6.07) and the unknown group had the smallest (2.60 SMD, 95% CI, 1.71 to 3.48) effect on GSH-px levels (χ2 = 234.85, Τ2 = 2.39, I2 = 80.8%, d.f. = 45, p<0.0005; Fig 6A). The Balb/c strain showed the largest (11.92 SMD, 95% CI, 3.10 to 20.74) and Albino the smallest (1.58 SMD, 95% CI, 0.21 to 2.96) effect on GSH-px (χ2 = 234.85, Τ2 = 2.39, I2 = 80.8%, d.f. = 45, p<0.0005; Fig 6B). Stratifying the data according to the dose of drug, model duration, rodent type, route of administration and animal age, had no significant impact on the change in GSH-px level.