unfortunately, there is no official standard of care for chronic bartonellosis - its a poorly understood and under recognised vector born illness in most european countries
in general and in particular in the case of bartonella - single antibiotic therapies have low success rates against chronic infections
most LLMDs who treat it do so with a combination of 2 or more antibiotics
eg a macrolide and rifampicin or rifabutin - often combined with supportive therapies - like biofilm agents or fibrinolytic enzymes
examples here
https://www.treatlyme.net/guide/ultimate-bartonella-treatments-and-treatment-guidei hope its of some help