U will be much better on tenofovir which is way more potent than etv and it has no resistance whatsoever
Your message is very brief, so it is hard to comment, but I will try.
When you say your father previously tested "negative" , we assume you mean his hbvdna was undetectable. But recently, his hbvdna is again detectable. It would be useful for you to give us the exact number of his hbvdna. It seems from this rise, your doctor decided that he has become drug resistance to Entecavir, hence he switched him to Viread, Tenofovir.
The drug resistance rate of Entecavir is usually very low. Usually doctors would make sure that your father has not missed taking his medication, and they would also test the hbvdna again in about a month time to confirm the rise. A cause for drug resistance to Entecavir may be due to the fact that your father is previously drug resistance to Lamivudine,
Tenofovir and Entecavir are two different drugs, so you cannot compare the dosage.