Twenty batches of polyvalent antivenom produced at the Instituto Clodomiro Picado were analyzed for turbidity, both before and after freezing-thawing and lyophilization. Eight batches became turbid upon freezing-thawing, and this change correlated with high levels of cholesterol, triglycerides and lipoproteins, especially β-lipoprotein. Since normal horse serum does not become turbid after freezing-thawing, despite the fact that it has high lipoprotein levels, the possibility was raised that phenol, used as a preservative during serum fractionation, might affect lipoproteins, inducing the appearance of turbidity after freezing-thawing. This hypothesis was tested by fractionating a sample of hyperimmune serum either without phenol or using two different phenol concentrations (0.1 g/dl and 0.25 g/dl). Results showed that, although the three samples had the same cholesterol and triglyceride levels before fractionation, only the one having 0.25 g/dl phenol became turbid upon freezing-thawing, containing a diffuse lipoprotein band on electrophoresis. This finding suggests that turbidity in equine antivenoms depends on the interaction of at least three factors: (a) freezing, (b) high initial cholesterol and lipoprotein concentration in the serum, and (c) addition of phenol during fractionation of serum.
