Combining two serotonin reuptake inhibitors is not a smart idea. There are far too many pharmacological factors to consider when you go about abusing reuptake inhibitors all willy-nilly, especially when there may be concurrent chronic treatment with e.g. a SSRI or SNRI. Chronic SSRI treatment in particular is known to greatly alter the functioning of many serotonergic drugs.
For the uneducated, cocaine is not only a dopamine reuptake inhibitor, it is also a serotonin-norepinephrine reputake inhibitor too. It has a great effect on all three monoamine pathways and isn't exactly a "clean" drug. On top of the reuptake inhibition is a sodium channel block responsible for numbing and also for messing with cardiac currents. There are other as of yet uncharted receptors it binds to, I'm sure, but those are the major ones. My point being: only the dopamine (and to a lesser extent, norepinephrine) reuptake inhibition is sought out in a psychostimulant, usually. Elevated serotonin levels are certainly part of the cocaine experience but they are not on their own pleasurable.
In the best case the cocaine will only be mildly potentiated (because of the SSRI), but some aspects of it could be dulled entirely if there is a strong SNRI working, which will instead stop cocoaine from binding to the transporters to work its magic. There's also the whole QT interval elongation to conisder as mentioned above, probably due to the sodium-channel effects of cocaine - cocaine & other local anesthetics like lidocaine are known for playing havoc with heart rythyms if not carefully prescribed and monitored.
If you want to play it safe, don't combine cocaine and antidepressants! You shouldn't be doing blow if you're on antidepressants anyway! How do you think you're gonna feel on the tail end of your cokeout?
In the end my advice is basically: if you're going to do cocaine, make sure you've got a clean system. Don't run the risk of a heart attack for some lines of bloe and a 20 minute high. If you want a stimulant then get some amphetamine or (m)ethylphenidate, (even caffeine), geeez. And if you wanna feel real good, spend your money on MDMA, 2c-*, DOx or LSD instead. Coca is not a happy plant to be investing in at the moment, what with the nonsense in Mexico and the whole dewormer scandal.