Study of Trimethoprim/Sulfamethoxazole as PCP Prophylaxis in CTD Patients

Inclusion Criteria: * Age 18-65 years with informed consent * SLE, Sjögren syndrome, Polymyositis or Dermatomyositis, defined by consensus classification criteria * concomitant high dose glucocorticoid, defined as \>1mg/kg/d prednisone or equivalent * concomitant cyclophosphamide, cyclosporine or mycophenolate mofetil Exclusion Criteria: * Pregnant or lactating * WBC\< 4×10\^9/L，PLT\<100×10\^9/L * Serum ALT or AST \> 2 times upper limit of normal * Serum creatinine \> 1.5 mg/dL * Severe hepatic, hematological, gastrointestinal, pulmonary, cardiovascular, neurological, endocrine or cerebral disease * Active infection, including HIV, HCV, HBV, tuberculosis or PCP * concomitant antibiotics other than trimethoprim/sulfamethoxazole * Patient with malignancy * Drug allergy, especially trimethoprim/sulfamethoxazole