Oxandrolone will also undergo 17aa first pass metabolism by the liver, whilst its negative effects are mild compared to other AAS.
2.2.2 Metabolism
In marked contrast with other oral AASs that are metabolised extensively, oxandrolone is relatively resistant to liver biotransformation.[13,14] Approxi- mately 28% of oxandrolone is excreted unchanged and unconjugated in the urine.[13,15] Metabolites of oxandrolone are 17-epioxandrolone and 16α- and 16β-hydroxyoxandrolone. The presence of an unu- sual δ-lactone group and lack of a 4-ene function in the A ring of oxandrolone may contribute to its greater stability against metabolic transformation. Hydroxylation is mostly suppressed during phase I metabolism,[13] and no glucuronidation occurs be- cause of steric hindrance of the 17β–hydroxyl group with the glucuronic acid moiety in phase II transfor- mation. Instead, oxandrolone is preferentially sulphated to 17-epioxandrolone. The lack of appre- ciable biotransformation and the high degree of pro- tein binding result in oxandrolone having higher plasma levels than methyltestosterone.[11]
Source:
https://www.doping.nl/media/kb/7120/Orr et al 2004.pdf