Sulfadimethoxine in giant freshwater prawns (Macrobrachium rosenbergii): an attempt to estimate the withdrawal time by a population pharmacokinetic approach.

The fates of sulfadimethoxine (SDM) for different routes of administration were investigated in muscle tissue of giant freshwater prawns, Macrobrachium rosenbergii, following either intramuscular (i.m.) or gavage administration at a dosage of 50 mg/kg body weight (b.w.). The depletion patterns of SDM were also examined after medicated feed treatment at the feeding concentration of 10 g/kg of feed twice a day at a rate of 1% of total b.w. for five consecutive days. The concentration of SDM in prawn muscle tissue was measured using a high-performance liquid chromatography (HPLC) equipped with ultraviolet detector. Noncompartmental analyses were used to estimate basic pharmacokinetic parameters for the i.m. and gavage data, while a population model was developed to analyze the entire data set including the feed group. Using the Monte Carlo simulations, the withdrawal times (WT) for the orally administered SDM in feed supplement were determined. Maximum concentration of SDM was significantly higher in the i.m. than in the gavage group, and the area under the curve (AUC) value for relative bioavailability following gavage administration was 25.6%. Using Monte Carlo simulation, for a maximum residue limit (MRL) of 0.1 µg/g, the WT for muscle after oral administration of SDM in feed was estimated to be 67 h, while for a MRL of 0.2 µg/g, the WT was estimated to be of 54 h.

Muscle tissue kinetics of oxytetracycline following intramuscular and oral administration at two dosages to giant freshwater shrimp (Macrobrachium rosenbergii).

The giant river shrimp (Macrobrachium rosenbergii), a native species of Thailand, is either exported for commercial purposes or supplied to meet the local requirements in Thailand. Limited pharmacokinetic information of the major antibiotic, oxytetracycline (OTC), is available for this freshwater shrimp. The purpose of the present study was to investigate the muscle tissue kinetics of OTC in M. rosenbergii following either intramuscular (i.m.) or oral (p.o.) administration at two dosages of 11 and 22 mg/kg body weight (b.w.). The concentration of OTC in shrimp tissues was measured using high-performance liquid chromatography (HPLC) equipped with a fluorescence detector. Muscle tissue concentrations were below the detection limit (LOD, 0.1 microg/g) after 96 and 120 h, following i.m. and p.o. administration, respectively. Peak muscle concentrations (C(max)) were 3.47 and 1.73 microg/g after i.m. and p.o. administration at a single dose of 11 mg/kg b.w. whereas they were 6.03 and 2.51 microg/g at a single dose of 22 mg/kg b.w., respectively. A noncompartment model was developed to describe the pharmacokinetics of OTC in the giant freshwater shrimp. The terminal half-lives of OTC were 28.68 and 28.09 h after i.m. and p.o. administration at a single dose of 11 mg/kg b.w., but 29.95 and 27.03 h at a single dose of 22 mg/kg b.w., respectively. The relative bioavailability was 82.32 and 64.67% following i.m. and p.o. administration, respectively. Based on the pharmacokinetic data, i.m. and p.o. administration with OTC at a dose of 11 mg/kg b.w. would be appropriate for use in giant freshwater shrimp farming. To avoid the OTC residue in shrimp muscle, it should take at least seven half-lives (8 days) to wash out the drug from the muscle of M. rosenbergii.