Preclinical toxicity and pharmacokinetics of a new orally bioavailable flubendazole formulation and the impact for clinical trials and risk/benefit to patients.

BACKGROUND: Flubendazole, originally developed to treat infections with intestinal nematodes, has been shown to be efficacious in animal models of filarial infections. For treatment of filarial nematodes, systemic exposure is needed. For this purpose, an orally bioavailable amorphous solid dispersion (ASD) formulation of flubendazole was developed. As this formulation results in improved systemic absorption, the pharmacokinetic and toxicological profile of the flubendazole ASD formulation have been assessed to ensure human safety before clinical trials could be initiated. METHODS & FINDINGS: Safety pharmacology, toxicity and genotoxicity studies have been conducted with the flubendazole ASD formulation. In animals, flubendazole has good oral bioavailability from an ASD formulation ranging from 15% in dogs, 27% in rats to more than 100% in jirds. In in vivo toxicity studies with the ASD formulation, high systemic exposure to flubendazole and its main metabolites was reached. Flubendazole, up to high peak plasma concentrations, does not induce Cmax related effects in CNS or cardiovascular system. In repeated dose toxicity studies in rats and dogs, flubendazole-induced changes were observed in haematological, lymphoid and gastrointestinal systems and in testes. In dogs, the liver was an additional target organ. Upon treatment cessation, at least partial recovery was observed for these changes in dogs. In rats, the No Observed Adverse Effect Level (NOAEL) was 5 mg (as base)/kg body weight/day (mg eq./kg/day) in males and 2.5 mg eq./kg/day in females. In dogs, the NOAEL was lower than 20 mg eq./kg/day. Regarding genotoxicity, flubendazole was negative in the Ames test, but positive in the in vivo micronucleus test. CONCLUSIONS: Based on these results, in combination with previously described genotoxicity and reproductive toxicity data and the outcome of the preclinical efficacy studies, it was concluded that no flubendazole treatment regimen can be selected that would provide efficacy in humans at safe exposure.

Legacy data sharing to improve drug safety assessment: the eTOX project.

The sharing of legacy preclinical safety data among pharmaceutical companies and its integration with other information sources offers unprecedented opportunities to improve the early assessment of drug safety. Here, we discuss the experience of the eTOX project, which was established through the Innovative Medicines Initiative to explore this possibility.

Real life juvenile toxicity case studies: the good, the bad and the ugly.

With the growing experience in the conduct of juvenile toxicity studies for multiple classes of compound, the 'case-by-case' approach has become under much more pressure. Instead, a general screen or 'standard design' is now commonly expected by regulatory authorities with more routine inclusion of neurological and reproductive assessments. Minor modifications or additions can be made to the design to address specific questions according to the class of drug or intended clinical use. This drift from a 'case-by-case' approach to a 'standard design' approach is present within certain reviewing divisions of the FDA, often requesting by default a rodent and non-rodent juvenile animal study. However, juvenile animal studies should be designed thoughtfully to fulfil a purpose based on scientific rationale, with each endpoint carefully considered in terms of practicality and interpretability of data generated. Only when using the appropriate strategy and design may juvenile studies add value by (1) identifying potential safety or pharmacokinetic issues for drugs intended for paediatric use, (2) suggesting additional clinical endpoints and (3) adding new information to the product label. As the knowledge from juvenile animal studies in various species grows, a better understanding of the significance/relevance of findings will be achieved.

Hemorrhagic cardiomyopathy in male mice treated with an NNRTI: the role of vitamin K.

Dietary dosing of the non-nucleoside reverse transcriptase inhibitor (NNRTI) TMC125, under development for treatment of HIV-1, resulted in a syndrome in male mice in a previous experiment that was termed hemorrhagic cardiomyopathy. In literature, this syndrome, which was described in rodent species only, was linked to vitamin K deficiency. Two mechanistic studies were conducted, one with dietary administration and a second with gavage. The syndrome was reproduced in only 1 male mouse after continuous dietary dosing, and TMC125 was demonstrated to affect coagulation parameters (prothrombin time [PT], activated partial thromboplastin time [APTT], clotting factors II, VII and XI), particularly in males. This was counteracted by vitamin K supplementation, supporting the hypothesis that the effects were mediated via a vitamin K deficiency. It is therefore concluded that the observed cardiac changes were not caused by a direct cardiotoxic effect but occurred after a state of disabled clotting ability with subsequent effects on mouse cardiac muscle. Therefore, clotting times can be used as adequate safety biomarkers in clinical trials. To date, no changes have been observed at therapeutic doses of TMC125, following human monitoring of PT and APTT. One other NNRTI, Efavirenz (Sustiva), has been reported to cause prolongation of coagulation times in rats and monkeys.

Optimising the design of preliminary toxicity studies for pharmaceutical safety testing in the dog.

A working party, comprising two animal welfare organisations and some 12 pharmaceutical companies in Europe, was established to minimise the use of the dog in safety testing. As first step, the participants defined the major objectives of preliminary dose-range finding/MTD toxicity studies in non-rodents, defined the principles and requirements for this study type and agreed on a proposal for an optimised study design, based on collective experience of conducting such studies in industry, involving an evaluation of 100 individual study data sets. The suggested study design is explained and described, and reflects current best practice in the pharmaceutical industry in Europe. The implementation of such an optimised design is believed to result in a reduction in the overall numbers of animals used for this purpose, without jeopardising the scientific rationale and usefulness of the studies for informing the conduct of later regulatory studies.