Crikey, twice in a week I've wanted to answer differently to shep53...
If it's routine fluke
prevention, probably ok (though not ideal). If you are
treating fluke, then it's pretty suboptimal, I would say.
Treating fluke is quite a hit to their systems, and Heptavac is quite a hit to their systems. So both together is suboptimal, yes. But it's a trade off. If doing only one now means the other doesn't get done for a couple of weeks, probably the least worst option is to do both now.