EFFECT OF TEMPERATURE ON THE PHARMACOKINETICS OF BENZOCAINE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AFTER BATH EXPOSURES

The pharmacokinetics of benzocaine during bath exposures at I mg/L wer e determined in rainbow trout acclimated at 6 degrees C, 12 degrees C or 18 degrees C for at least 1 month. Individual Gsh were exposed to b enzocaine in a recirculating system for 4 h and pharmacokinetic parame ters were estimated in a unique manner from the concentration of benzo caine in the bath water vs. time curve. Elimination from plasma was al so determined after the 4 h exposure. The uptake clearance and metabol ic clearance increased with increased acclimatization temperatures (up take clearance 581 +/- 179 mL/min/kg at 6 degrees C and 1154 +/- 447 m L/min/kg at 18 degrees C; metabolic clearance 15.2 +/- 4.1 ml/min/kg a t 6 degrees C and 22.3 +/- 4.2 ml/min/kg at 18 degrees C). The apparen t volume of distribution had a trend for increasing with temperature t hat was not significant at the 5% level (2369 +/- 678 mL/kg at 6 degre es C to 3260 +/- 1182 mL/kg at 18 degrees C). The elimination half-lif e of benzocaine in plasma was variable and did not differ significantl y with temperature (60.8 +/- 30.3 min at 6 degrees C to 35.9 +/- 13.0 min at 12 degrees C). Elimination of benzocaine from rainbow trout is relatively rapid and even more rapid at higher acclimatization tempera tures based on calculated metabolic clearances and measured plasma con centrations, but was not evident by measurement of terminal plasma hal f-lifes.