ObjectiveGlycogen storage disease type Ib (GSD-Ib) is a very rare disease complicated by neutropenia with consequent recurrent bacterial infections. Treatment with Filgrastim is not always effective.The low CD4 count observed in our patient is likely the underlying cause of this treatment failure. This low value was previously examined in a small-scale study. Therefore, adding sulfamethoxazole-trimethoprim (SMX-TMP) might be a good strategy.MethodsWe present the case of a male patient with GSD-Ib. He has severe neutropenia (380/mm3) with recurrent infections. Despite neutrophil improvement with Filgrastim, he developed three severe infections requiring hospitalization. Lymphocyte phenotyping showed a deficit in T CD4 + cells (280/mm3) which led us to HIV testing returning negative. Based on this finding we initiated prophylaxis with SMX-TMP.ResultsSince the start of SMX-TMP along with Filgrastim, the patient was not admitted to the hospital for any bacterial infection.ConclusionTo date, no study has examined the significance of incorporating antibiotic prophylaxis for neutropenic patients with GSD-Ib based on CD4 count, akin to the approach of adding SMX-TMP to antiretroviral therapy for HIV patients. Cotrimoxazole is empirically prescribed without assessing the CD4 count or conducting a comparative analysis of the advantages of its addition to Filgrastim. Such practices could potentially exert a significant influence on the disease’s presentation and severity.