Telemetry video-electroencephalography (EEG) in rats, dogs and non-human primates: methods in follow-up safety pharmacology seizure liability assessments

Introduction: Non-clinical seizure liability studies typically aim to: 1) confirm the nature of EEG activity during abnormal clinical signs, 2) identify premonitory clinical signs, 3) measure plasma levels at seizure onset, 4) demonstrate that drug-induced seizures are self-limiting, 5) confirm that conventional drugs (e.g. diazepam) can treat drug-induced seizures and 6) confirm the no observed adverse effect level (NOAEL) at EEG. Our aim was to originally characterize several of these items in a three species comparative study.

Methods: Cynomolgus monkey, Beagle dog and Sprague-Dawley rat with EEG telemetry transmitters were used to obtain EEG using the 10-20 system. Pentylenetetrazol (PTZ) was used to determine seizure threshold or as a positive seizurogenic agent. Clinical signs were recorded and premonitory signs were evaluated. In complement, other pharmacological agents were used to illustrate various safety testing strategies.

Results: Intravenous PTZ doses required to induce clonic convulsions were 36.1 (3.8), 56.1 (12.7) and 49.4 (11.7) mg/kg, in Beagle dogs, cynomolgus monkeys and Sprague-Dawley rats, respectively. Premonitory clinical signs typically included decreased physical activity, enhanced physiological tremors, hypersalivation, ataxia, emesis (except in rats) and myoclonus. In Sprague-Dawley rats, amphetamine (PO) increased high (approximately 40-120Hz), and decreased low (1-14Hz) frequencies. In cynomolgus monkeys, caffeine (IM) increased power in high (14-127Hz), and attenuated power in low (1-13Hz) frequencies. In the rat PTZ infusion seizure threshold model, yohimbine (SC and IV) and phenobarbital (IP) confirmed to be reliable positive controls as pro- and anticonvulsants, respectively.

Discussion: Telemetry video-EEG for seizure liability investigations was characterized in three species. Rats represent a first-line model in seizure liability assessments. Beagle dogs are often associated with overt susceptibility to seizure and are typically used in seizure liability studies only if required by regulators. Non-human primates represent an important model in seizure liability assessments given similarities to humans and a high translational potential.