Evaluation of the pharmacokinetic profile of artesunate, artemether and their metabolites in sheep naturally infected with Fasciola hepatica

The pharmacokinetic (PK) parameters of artesunate, artemether and their metabolites dihydroartemisinin (DHA) and dihydroartemisinin-glucuronide (DHA-glucuronide) were determined in sheep naturally infected with Fasciola hepatica.Sheep were treated either with artesunate (intramuscular (i.m.): 40 and 60 mg/kg) or artemether (i.m.: 40 and 160 mg/kg; oral: 80 mg/kg). Blood samples were withdrawn at selected time points post treatment and the artemisinins were quantified in plasma by liquid chromatography and tandem mass spectrometry (LC-MS/MS). The in vitro effect of the metabolites against F. hepatica was investigated using a phenotype-based assay and scanning electron microscopy (SEM).Following artesunate applications (40 and 60 mg/kg), comparable Cmax (maximal plasma concentration) and AUCs (area under the plasma concentration-time curve) were observed for artesunate (Cmax: 8.4 × 103 and 9.4 × 103 ng/ml; AUC: 6.9 × 105 and 9.7 × 105 ng min/ml), DHA (Cmax: both 2.4 × 103 ng/ml; AUC: 3.7 × 105 and 5.0 × 105 ng min/ml), and DHA-glucuronide (Cmax: 1.7 × 104 and 1.6 × 104 ng/ml; AUC: 2.6 × 106 and 3.3 × 106 ng min/ml). Mean elimination half-lifes (t1/2) of artesunate, DHA and DHA-glucuronide ranged between 58 and 63 min, 94 and 113 min, and 89 and 98 min, respectively. The i.m. oil-based drug formulation liberated artemether slowly and constant levels of artemether and its metabolites were observed during the entire sampling period (24 h). The AUCs of all analytes were significantly higher for the i.m. 160 mg/kg dose compared to i.m. 40 and oral 80 mg/kg doses (P = 0.018). Mean Cmax of artemether (2126 and 426 ng/ml) and DHA-glucuronide (3477 and 1587 ng/ml) were higher following oral compared to i.m. (160 mg/kg) treatments (P > 0.068), whereas Cmax of DHA was significantly higher following i.m. applications (P = 0.0062). DHA rapidly reduced the viability of F. hepatica in vitro, whereas DHA-glucuronide showed no activity. SEM observations revealed only minor and focal tegumental alterations in few of the DHA treated worms.The calculated PK parameters reflect the anthelmintic activity of artesunate and artemether following different routes of application and will aid in the design of future studies with these drugs.