Dose and administration-period play a key role in the effect of ceftriaxone on neuropathic pain in CCI-operated rats

Introduction An unmet medical need for more effective therapies of neuropathic pain exits. Here modulation of the glutaminergic system represents an unexplored possibility. Down-regulation ofglutamate transporters potentiates pain transmission by delaying the removal of glutamate from the synapse. In the spinal cord, glutamate transporter 1 (GLT-1) is responsible for more than 90% of the glutamate uptake. Ceftriaxone, a β-lactam, is believed to induce the expression of GLT-1 through the transcriptional factor (NF-ºB) pathway, which results in induced promoter activity and thereby increased synthesis of GLT-1 protein. Objectives To evaluate the analgesic effect of ceftriaxone in the Chronic Constriction Injury (CCI) rat model of neuropathic pain and to investigate the pharmacodynamics of ceftriaxone in a chronic dosing regime. Methods In CCI rats, mechanical and thermal hypersensitivity, were determined with von Frey filaments and Hargreaves test, respectively. Groups of rats received ceftriaxone (200, 300 or 400 mg/kg, i.p.) once daily in 7-19 days and the control groups received vehicle. Results From a total of 24 CCI operated rats, 16 rats developed both mechanical (withdrawal threshold ≤3g) and thermal hypersensitivity (latency threshold ≤13 s.). Ceftriaxone alleviated mechanical allodynia and thermal hyperalgesia in CCI operated. Daily dosing of ceftriaxone 200, 300 and 400 mg/kg reached the same withdrawal threshold levels as before the CCI surgery, after 18, 12 and 7 days, respectively. This indicates that the dynamic effect of ceftriaxone is not only dependent of the dose, but also the duration of administration. Thus, it seems that dose exposure above a certain threshold is necessary to induce protein synthesis. Conclusion The CCI model is a useful model to evaluate the anti-nociceptive effects of ceftriaxone. Increased dose do not only elevate effect magnitude but also the rate of with which the effect appears.