Some drugs are eliminated by more than one elimination pathway, and these elimination pathways may be saturable.

After administration of increasing doses, the saturable pathway becomes saturated and larger fraction of the dose will be eliminated through the first-order pathway.

In presence of more than one saturable elimination pathway, these pathways usually have different capacities. This makes the fraction of dose that goes through each of the pathways different after administration of different doses.

Salicylic acid is metabolized through five different pathways two of them are saturable.

Salicylic acidAspirin

SU and SPG are the major metabolites after administration of smaller aspirin or salicylic acid doses. However after large doses these pathways are saturated and larger amounts of the other metabolites are detected.