It's strongly recommended not to consume them in the same week.
Cocaine works strongly on the dopamine receptors and extremly subtle on the serotonine release.
If you combine E with C at the same time you'll remain with a wakeful vision, and a blunt weak ecstasy feeling. The down of coke truly intrerrups with your E trip as well. While your serotonine is fully up, you'll hardly notice it because it is overpowered by the effects coke. Nevertheless the down the days is way more terrible and for some it's easier to gain addiction.
You CAN combine coke with amphetamine, you'll safe your serotonine for later. But you should be careful with your central nervous system. Since they both stimulate breath and heart frequence, blood pressure. And both are broken down by the liver and kidney.