Can you please suggest treatment of dos (distal subungual onychomycosis)?

Fungus. Using those terms suggests that you have seen someone for a diagnosis. Your treating physician should have done that. However, having said that i find great results with a laser in my office . I personally don't like Lamisil (terbinafine) due to side effects - even as low as they may be.
Keep the nail cut . Short, apply a topical antifugal. If you don't see improvement consider taking Lamisil (terbinafine) pulse dosed.