Amitriptyline pharmacokinetics in experimental spinal cord injury in the rabbit

Abstract

Previous studies have demonstrated that pharmacokinetic behavior of several drugs such as paracetamol, theophylline, and aminoglycosides are significantly altered in spinal cord injured patients. No pharmacokinetic study of amitriptyline has been performed in patients and experimental models of spinal cord injury. Pharmacokinetic parameters of amitriptyline in orally treated rabbits subjected to laminectomy and spinal cord injury compared with those underwent laminectomy alone. Among twenty four male rabbits were included in this study, nine of them subjected to spinal cord injury at the 8th thoracic level by knife severance method and six rabbits underwent laminectomy alone (sham group) and nine rabbits treated as control. All received a single oral dose of amitriptyline (20 mg/kg) 24 h after injury. Blood sampling were done at predetermined times to 36 h after drug administration. Amitriptyline concentration in serum samples was determined by high-performance liquid chromatography. Pharmacokinetic parameters including maximum concentration (Cmax), time to reach maximum concentration (Tmax), half life, and the area under the curve to last detectable concentration time point (AUC0-t) were directly determined from the concentration-time curve. Maximum concentration was observed at 6.5 h after administration in sham group with a concentration of 439.6 ng/ml, whereas in SCI group Tmax was at 2.7 h with a concentration of 2763.9 ng/ml. In control group it was 3.3 h and 396 ng/ml, respectively. In SCI group, AUC was 9465.6 ng.h/ml and half life was 6 h and for control group it was 2817.4 ng.h/ml and 6.4 h, respectively. Statistical analysis of data showed that SCI didn't induce significant changes in amitriptyline pharmacokinetic parameters.

Drug Management of Visceral Pain: Concepts from Basic Research

“…Gabapentinoids have been shown to reduce visceral hypersensitivity in experimental animals as well as symptoms of irritable bowel syndrome in humans [ 104 – 109 ]. Low-dose gabapentin and morphine reduced writhing in rats given intraperitoneal acetic acid at doses which were found to be ineffective as single agents [ 110 ]. Not only do gabapentinoids reduce nociceptive neurotransmission centrally but also improve bowel compliance to distention perhaps through blocking alpha-2 delta subunits in smooth muscle [ 105 , 111 ].…”