Authorization and Toxicity of Veterinary Drugs and Plant Protection Products: Residues of the Active Ingredients in Food and Feed and Toxicity Problems Related to Adjuvants

Chemical substances applied in animal husbandry or veterinary medicine and in crop protection represent substantial environmental loads, and their residues occur in food and feed products. Product approval is governed differently in these two sectors in the European Union (EU), and the occurrence of veterinary drug (VD) and pesticide residues indicated by contamination notification cases in the Rapid Alert System for Food and Feed of the EU also show characteristic differences. While the initial high numbers of VD residues reported in 2002 were successfully suppressed to less than 100 cases annually by 2006 and on, the number of notification cases for pesticide residues showed a gradual increase from a low (approximately 50 cases annually) initial level until 2005 to more than 250 cases annually after 2009, with a halt occurring only in 2016. Main notifiers of VD residues include Germany, Belgium, the UK, and Italy (63, 59, 42, and 31 notifications announced, respectively), and main consigning countries of non-compliances are Vietnam, India, China, and Brazil (88, 50, 34, and 23 notifications, respectively). Thus, countries of South and Southeast Asia are considered a vulnerable point with regard to VD residues entering the EU market. Unintended side effects of VDs and plant protection products may be caused not only by the active ingredients but also by various additives in these preparations. Adjuvants (e.g., surfactants) and other co-formulants used in therapeutic agents and feed additives, as well as in pesticide formulations have long been considered as inactive ingredients in the aspects of the required main biological effect of the pharmaceutical or pesticide, and in turn, legal regulations of the approval and marketing of these additives specified significantly less stringent risk assessment requirements, than those specified for the active ingredients. However, numerous studies have shown additive, synergistic, or antagonistic side effects between the active ingredients and their additives in formulated products; moreover, toxicity has been evidenced for various additives. Therefore, toxicological evaluation of surfactants and other additives is essential for proper environmental risk assessment of formulations used in agriculture including animal husbandry and plant protection.

Pharmacokinetic evaluation of different generic triclabendazole formulations in heifers

AIMS

To assess the comparative drug systemic exposure of a reference (RF) and four test (Test I, Test II, Test III and Test IV) formulations of triclabendazole (TCBZ) in heifers.

METHODS

Thirty Holstein heifers were randomly distributed into five groups (n=6 per group). Animals in the RF group received the reference formulation (Fasinex), and those in the other groups received different commercially available TCBZ formulations (Test I, Test II, Test III and Test IV). All treatments were orally administered at 12 mg/kg bodyweight. The concentrations of TCBZ metabolites in plasma between 0 and 168 hours after treatment were quantified by high-performance liquid chromatography (HPLC).

RESULTS

Triclabendazole sulphoxide (TCBZ.SO) and TCBZ-sulphone (TCBZ.SO₂) were the only analytes recovered in plasma. Only the Test I formulation did not differ from the RF for all pharmacokinetic parameters measured for either metabolite (p>0.8). The TCBZ.SO area under the concentration vs. time curve for Test II formulation (268.9 µg.h/mL) was lower, and for Test III (619.9 µg.h/mL) and Test IV (683.4 µg.h/mL) was higher, than the RF (418.1 µg.h/mL) (p<0.005).

CONCLUSION

Based on the currently available bioequivalence criteria, the only test formulation under evaluation that could be considered equivalent to the RF was the Test I formulation, which demonstrated an equivalent systemic exposure for the active TCBZ.SO metabolite. This comparison of TCBZ pioneer and test formulations in cattle raises awareness of the need for further quality control for drug approval in the veterinary pharmaceutical field in many regions of the world.

Feasibility of interspecies extrapolation in determining the bioequivalence of animal products intended for intramuscular administration

To examine the validity of extrapolating parenteral product bioequivalence determinations across target animal species, the relative bioavailability of two injectable formulations of ampicillin trihydrate (PolyflexR, a water-based suspension, and Ampi-kel 10R, an oil-based suspension) was examined in calves, sheep and swine. Employing products recognized to be bioinequivalent provided an opportunity to explore potential species-by-formulation interactions. As compared with PolyflexR, Ampi-kel 10R exhibited lower area under the curve (AUC) estimates but higher peak concentrations in all target animal species. Nevertheless, marked interspecies differences were noted in the width and bounds of the confidence intervals about the differences in treatment means. Potential physiological and physico-chemical reasons for these findings are discussed.