The effect of varying percentages of haemodilution with fluosol-DA or normal saline on antipyrine metabolism in the rat.

Antipyrine disposition and metabolism in conscious, unrestrained rats after 25 or 50% haemodilution with Fluosol or normal (0.9% NaCl) saline is reported. Rats received an intravenous antipyrine dose (20 mg kg-1) 0.5, 24, 48, or 72 h after haemodilution and its pharmacokinetic parameters have been compared with non-exchanged control animals. Haemodilution 25% with Fluosol initially depressed antipyrine metabolism for 24 h by decreasing the antipyrine urinary excretion rate constant and the formation rate constants of 4-hydroxyantipyrine (4-OH) and 3-hydroxymethylantipyrine (3-OHME). Metabolism was then increased for 48 and 72 h with a slight increase in all rate constants. Haemodilution 50% with Fluosol produced a similar pattern but with significant increases in the 3-OHME formation rate constant found at 48 and 72 h. Haemodilution 25% with saline reduced 4-OH formation for 48 h. Haemodilution 50% with saline significantly reduced antipyrine urinary excretion at all times. After a significant increase in the 4-OH and 3-OHME formation rate constants at 24 h following 50% haemodilution with saline, the rate constants were significantly decreased at 48 and 72 h. Haemodilution 25% with Flusol significantly reduced the antipyrine Vd at 0.5 and 72 h. After haemodilution 50% with Fluosol, the Vd alternated between values greater and less than control throughout the 72 h. Haemodilution 25 or 50% with saline had little influence on Vd.