Thank you for your query,
Usually Penidure 6 LA to be given once in every 3 weeks at least till the age of 35 years in a diagnosed patient of acute rheumatic fever
or rheumatic heart disease
Only knee joint pain and positive ASO titre is not diagnostic of rheumatic fever.
Further investigations like ESR, CRP, ECG, 2D Echo and physical examination to demonstrate carditis
, skin lesions and neurological symptoms like chorea to be looked.
Jone's criteria is used to diagnose rheumatic fever and after confirmation of the diagnosis, it is better to plan for long term penicillin prophylaxis.
So I advise you to consult Pediatrician
or Pediatric cardiologist for further advise.
Hope I have answered your query.