Previous studies that have evaluated
fish oil preparations in patients with
IgA nephropathy (IgAN) have produced a wide range of conclusions. Proposed explanations for these discordant results have not provided a unifying hypothesis. Results from two clinical trials were analyzed to examine whether there is a dosage-dependent effect of
Omacor, a purified preparation of
omega-3 fatty acids, in patients with IgAN. Whether changes in the level of
proteinuria and plasma
phospholipid fatty acid profiles were dependent on the dose of
Omacor factored by body size was determined. In a post hoc analysis of the first trial results, correlations were found between (1)
phospholipid eicosapentaenoic acid (EPA)/
arachidonic acid (AA) and
docosahexaenoic acid (DHA)/AA ratios and the dosage of
Omacor, expressed as milligrams per kilogram of
body weight (r = 0.78, P < 0.001 for EPA/AA; r = 0.86, P < 0.001 for DHA/AA), (2)
phospholipid EPA/AA and DHA/AA levels and percentage change in urine
protein/
creatinine ratio after 21 to 24 mo of
therapy (r = -0.50, P = 0.02 for EPA/AA; r = -0.52, P = 0.01 for DHA/AA), and (3) dosage of
Omacor per kilogram of
body weight and change in
proteinuria after 21 to 24 mo (r = -0.50, P = 0.02). A similar relationship was observed between urine
protein/
creatinine ratio and dosage of
Omacor per kilogram of
body weight in trial 2 (r = -0.38, P < 0.001). It is concluded from these data that the effect of
Omacor on
proteinuria in patients with IgAN is dosage dependent and is associated with a dosage-dependent effect of
Omacor on plasma
phospholipid EPA and DHA levels.