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Table 2 Metabolic ratio for codeine O-demethylation following administration of a single oral dose to a population of horses of differing breeds and ages. The metabolic ratio calculated as (codeine AUC0 − ∞)/(morphine AUC0 − ∞ + M3G AUC0 − ∞ + M6G AUC0 − ∞)

From: Functional phenotyping of the CYP2D6 probe drug codeine in the horse

Age (years) Breed Number Metabolic ratio
Mean ± SD Median Range
0–5 Paint
QH
SB
TB 28 0.029 ± 0.029 0.019 0.002–0.119
WB 1 0.004 ± 0.00 NA NA
6–10 Paint 1 0.026 ± 0.00 NA NA
QH 2 0.023 ± 0.027 0.023 0.004–0.042
SB 1 0.023 ± 0.00 NA NA
TB 17 0.048 ± 0.038 0.037 0.012–0.147
WB 5 0.016 ± 0.016 0.010 0.006–0.045
11–15 Paint
QH 7 0.019 ± 0.010 0.017 0.007–0.036
SB 1 0.072 ± 0.00 NA NA
TB 7 0.021 ± 0.022 0.013 0.005–0.067
WB 4 0.015 ± 0.012 0.011 0.005–0.033
16–20 Paint
QH 2 0.011 ± 0.004 0.011 0.009–0.014
SB
TB 9 0.012 ± 0.008 0.008 0.003–0.017
WB 2 0.012 ± 0.003 0.012 0.010–0.014
21–25 Paint 1 0.037 ± 0.00 NA NA
QH 2 0.018 ± 0.005 0.018 0.014–0.021
SB 1 0.029 ± 0.00 NA NA
TB 4 0.018 ± 0.007 0.019 0.009–0.024
WB 2 0.027 ± 0.023 0.027 0.011–0.044
26–30 Paint
QH 1 0.032 ± 0.00 NA NA
SB 1 0.014 ± 0.00 NA NA
TB 1 0.025 ± 0.00 NA NA
WB