drug question

I'm a new grad nurse, so please don't judge my question too harshly. I want to know about interactions between ondansetron and SSRIs. My understanding is that the only site they are both competing for is the 5-HT3 receptor, and ondansetron has a greater affinity for that receptor. Is this correct? What does this mean in terms of efficacy for the SSRI?

Also, I understand the there is an increase in risk of QT prolongation but that it is dose dependent. What is the standard as far as this is concerned?

Should both of the drugs' half-lives be taken into consideration in scheduling, thereby increasing their individual effectiveness? I understand this would be tricky if the ondansetron is prn.

Any info/experiences welcomed.

edit: I'm having a hard time finding scholarly articles with evidence of QT prolongation of these drugs at therapeutic levels. Anyone? Is the QT prolongation thing blown out of proportion?