There is a need
to research the role of Lamotrigine in treating the spinal cord injury pain and neuralgia after nerve section.2 A full pharmacokinetic profile is usually observed before compounds undergo extensive pain model testing. Various parameters in the determination of pharmacokinetic and MAPK inhibitor pharmacodynamic relationships of various new pain drugs include the endpoint chosen (touch/pressure).3 It is always a rational approach to correlate the pharmacokinetic and pharmacodynamic data to draw meaningful conclusions. In this paper, for the peerless evidence we discuss the relationship of plasma drug concentration and the anti-neuropathic pain effect of Lamotrigine on rat. Lamotrigine active pharmaceutical ingredient (LMT-API) was obtained as a gift sample from Dr.Reddy’s Labs, Hyderabad. Remaining all other excipients, chemicals and solvents were procured from local suppliers. Albino rats (National Institute of Nutrition, Reverse Transcriptase inhibitor Hyderabad, India) of either sex, weighing 180–210 g were selected. The experimental protocol has been approved by Institutional Animal Ethical Care Committee (IAEC) of BITS-PILANI, Hyderabad (IAEC/RES/06/03)
as per IAEC/CPCSEA. Human dose was extrapolated to animal dose using the USFDA dose calculator.4 In the study design for pharmacokinetics and pharmacodynamics assessment a number of nine Wistar rats were selected for drug administration. Three animals were used for pharmacokinetic studies and six animals for pharmacodynamic studies. All the animals in every group were administered drug with 1 ml of polyethylene glycol (vehicle). Blood was collected from the retro-orbital sinus after anaesthetizing animal. 0.1 ml of 2.8% sodium citrate was used as an anticoagulant. Blood samples were taken at regular time intervals from 0 h till 24 h following drug administration and plasma Lamotrigine concentration5 were determined using a validated HPLC method with minor modifications. The various pharmacokinetic parameters were calculated by the optimal descriptive model fit using Try Kinetica PK-PD version 5.0 program (USA). Neuropathic
pain was induced in rats by chronic constriction injury many as previously described by Bennett and Xie.6 After this procedure, the animal developed a peripheral neuropathy which resembles the human condition in its response to static, allodynia and hyperalgesia. For spontaneous pain, each rat was placed on a plantar test glass stand (lITC Life sciences, CA, USA) which was set at a neutral temperature. Then foot lifting measurements were made. To quantify for dynamic allodynia, brisk foot withdrawal response to normally innocuous mechanical stimuli was measured by von-Frey filament (lITC Life sciences, CA, USA). In order to quantify cold sensitivity for cold allodynia, brisk foot withdrawal in response to acetone application was measured.