Of three anti-emetics (ativan, benadryl, (diphenhydramine) and zofran) used on a pediatric oncology floor, why is ativan used?

Depends: Ativan (lorazepam) is not classically considered an anti-emetic. It may be used to help calm a child and could be given in small doses to enhance the actions of other medications. I also think the primary reason to use Ativan (lorazepam) is that it is the drug of choice to give someone who is having a seizure. It is possible that small doses of Ativan (lorazepam) could cause retrograde amnesia where the child would forget the event.

It works for some: Each of the three drugs you listed work by targeting a different mechanism to help battle chemotherapy-induced nausea. It is not uncommon for a patient to require a schedule of all three, depending on the chemo being administered and the individual patient. Ativan can help with anxiety, but it is also an anti-emetic. Reglan (metoclopramide) is also commonly given with Benadryl to help fight nausea.

Because it works: Why lorazepam is effective as an anti-emetic is not clear. In individuals that have had problems with chemotherapy-induced nausea and vomiting (CINV), anxiety can be a major issue leading to anticipatory vomiting (vomiting on arrival to the hospital before anything is done). It's anti-anxiety effect may be its most important action in theses cases.

Ativan: My understanding is that it can be effective for nausea/vomiting that is induced by chemotherapy. It can also help to relax the patient.