Pharmacokinetics and excretion of phenol red in the channel catfish

1. Disposition of phenol red was examined in channel catfish (Ictalurus punctatus) after oral or intravascular (i.v.) dosing at 10 mg/kg body weight. 2. Phenol red was not detectable in plasma, urine, or bile after oral administration. 3. After i.v. dosing, plasma concentrations of phenol red were best described by a two-compartment pharmacokinetic model with distribution and elimination half-lives of 2.3 and 21 min, respectively. The apparent volume of distribution at steady state (Vss) was 225 ml/kg and total body clearance (Clb) was 658 ml/h per kg. Plasma protein binding was 19%. 4. Biliary excretion was the primary route of elimination of phenol red; in 24 h, 55% of the i.v. dose was excreted in bile compared with 24% in urine. No metabolites were detected in these fluids. 5. The use of anaesthesia during dosing had no effect on the quantitative excretion of phenol red by renal or biliary routes.