thanks for posting your query.
As your brother is having G6PD deficiency
which is an inherited disease causing hemolytic anemia
. Vomiting may be due to viremia/ acute viral illness as people with G6PD deficiency are prone to infections. However, there are some drugs and irritants that may trigger heamolysis and present with abdominal pain
, nausea, and vomiting.
These drugs and substances include primaquine
, salicylates, sulfonamides, methylene blue, pollens and fava beans. for more visit (http://www.g6pd.org/en/G6PDDeficiency/SafeUnsafe/DaEvitare_ISS-it)
Treatment is supportive and transfusions are needed in crisis. Patients are advised to avoid infections drugs or substances that initiate hemolysis
Consult you doctor for further information.
Hope it helps.