Can oral antibiotics be successful in treating endocarditis?

No. Oral antibiotics are not recommended for treatment of endocarditis due to any organisms. Treatment requires 2 to 6 weeks of intravenous antibiotics sometimes in combination depending on the infecting organism and whether on native or prosthetic heart valve.
Usually Not. Treatment of the majority of organisms that cause endocarditis consists of intravenous antibiotics for 4-6 weeks. Eradication can prove difficult and valve damage is a possible consequence of inadequate treatment.