Bringing prescription medication into a new country can be tricky, and having your medication sent to you could become a time consuming and frustrating process. If you're planning to be in the country for as long as 8 months it might be easier to see an English speaking doctor in Vietnam to get a local prescription and advice on which pharmacies are most trustworthy.
In Vietnam's large cities like Hanoi, it is relatively easy to get medication over the counter and without a prescription. Have you checked if this is the case with your medication?
If you're concerned about the quality of the medication, Expat Arrivals has a page on medicines and pharmacies in Vietnam which will give you useful tips on how to make sure your medication isn't expired or a counterfeit. Why not ask your employer for advice on which pharmacy and doctor you should use?