Bioaccumulation of trimethoprim, sulfamethoxazole and N-acetyl-sulfamethoxazole in Artemia nauplii and residual kinetics in seabass larvae after repeated oral dosing of medicated nauplii

The pharmacokinetics of trimethoprim (TMP), sulfamethoxazole (SMX) and its metabolite N-acetyl-sulfamethoxazole (N-acetyl-SMX), were studied in Artemi a nauplii as a function of the duration and temperature of their storage, f ollowing their enrichment with the therapeutics using the bioencapsulation technique. A marked decrease in the therapeutic content of the nauplii was observed upon storage at 18 degrees C and 25 degrees C and it was concluded that medicated nauplii should either be administered fresh to fish larvae or after storage for 8 h at 5 degrees C, at the most. Under the latter cond itions, satisfactory levels of TMP and SMX were achieved, high survival rat es and dry weight contents of the nauplii were preserved and minimal leakag e of the therapeutics to the environment was secured. Treatment of seabass larvae with one, three, six or ten doses of medicated Artemia nauplii, show ed that maximum levels of the therapeutics are achieved in fish larvae when 10 doses are used. Following the treatment scheme of oral administration o f 10 doses of medicated Artemia nauplii to fish larvae, the residual kineti cs of TMP, SMX and N-acetyl-sulfamethoxazole were studied in seabass larvae . TMP and SMX showed different kinetic characteristics. A steady state of S MX concentration is considered to be achieved in fish body tissue during th e 5-day medication period. TMP, SMX as well as the metabolite N-acetyl-sulf amethoxazole, were detectable in small amounts in fish body tissue even 100 h-post treatment. These data suggest that oral medication of fish larvae t hrough the use of Artemia nauplii as a carrier of therapeutics, appears to be a quite promising approach to be used as an alternative method of treatm ent, which could minimize some of the problems arising from the methods cur rently in use. (C) 1999 Elsevier Science B.V. All rights reserved.