Isoprinosine, an in vitro immuno-enhancing agent principally acting by stimulating T-lymphocytes, is one of a number of agents sometimes used in an attempt to prevent recurrent respiratory infections in children, although there are no formal trials for this particular drug. We performed a placebo-controlled double-blind trial to assess the efficacy of isoprinosine (50 mg/kg per day) for 6 weeks followed by 50 mg/kg per day twice weekly for 6 weeks in the prevention of frequent acute respiratory tract infections in 102 children aged 4-8 years. A total of 43 children treated with isoprinosine and 41 with placebo finished the study. Despite a transient increase in the total number of CD3+, CD4+ and CD8+ T-lymphocytes after 6 weeks of daily isoprinosine treatment, there was no difference in the number and length of duration of acute respiratory infections, number of antibiotic courses and number of days with cough, pharyngitis, rhinitis and increased body temperature (> or = 37.0 degrees C and > or = 38.0 degrees C). There were no changes in markers of T- or B-lymphocyte activation (CD25, HLA-DR, CD45RA/RO, CD23).
Conclusion: Attempts at immunomodulation using isoprinosine in the dose and for the duration used may increase the total numbers of both CD4 and CD8 T-lymphocytes but is ineffective in prevention of respiratory tract infections in childhood.