Acinetobacter Rt sided infective endocarditis

Dear Doctors,

Recently there was an ex - IVDU that presented with infective endocarditis for the second time within 3 months
His last intravenous drug usage was about 8 years ago. His recent echo confirms a vegetation over his tricuspid valve.
and his blood culture came back as positive for acinetobacter which is sensitive to ceftazidime,unasyn and cefoperazone but resistant to gentamicin. Initially he was started on iv ceftazidime and iv gentamicin but since the acinetobacter is resistant to gentamicin, the physician has stopped the gentamicin and continued him on 6 weeks of ceftazidime with further testing of the organism's sensitivity to amikacin with the intention of giving amikacin together with ceftazidime should the organism be senstive to amikacin. Is monotherapy adequate? should amikacin be added
The patient is afebrile since antibiotic commencent but the vegetation is still present . Should ceftazidime be changed to sulperazone or a cerbapenem?

thank you