Introduction
According to statistics from the World Health Organization (WHO), there are approximately 10 million newly diagnosed cancer patients worldwide each year, and the incidence rate is still rapidly increasing, posing a serious threat to people’s lives ( Cao et al., 2021 ; Sung et al., 2021 ). In this context, tyrosine kinase inhibitors have become the primary first-line therapeutic choice for cancer treatment ( Choi et al., 2022 ; Macia et al., 2013 ; Mercadante et al., 2022 ). As a result of cachexia, cancer patients often experience a range of complications, with pain being one of the most common symptoms that reduces a patient’s quality of life. It is estimated that around 70% of patients with advanced cancer suffer from severe pain ( Li, Han & Liu, 2022 ; Motono et al., 2021 ). Consequently, the combination of tyrosine kinase inhibitors and analgesics is frequently employed as a treatment strategy in clinical settings. However, there are various reports on the effectiveness of combination therapy. Some claim that the combination of both can increase efficacy, while others suggest that they may interact with each other and lead to toxicity and other complications ( Shinde et al., 2014 ; Gadgeel et al., 2007 ; Varrassi et al., 2022 ; Yang et al., 2019 ; Zhao et al., 2017 ). Therefore, further research is needed on the combination of both.

Tramadol is a synthetic codeine analogue that has obvious analgesic effects and low addiction potential. It has become one of the preferred central analgesics for the treatment of cancer pain, replacing morphine or pethidine in clinical settings ( Barbosa et al., 2016 ; Miotto et al., 2017 ; Zarghami, Masoum & Shiran, 2012 ). However, as a µ-opioid receptor agonist and norepinephrine reuptake inhibitor, tramadol can cause common opioid side effects such as gastrointestinal reactions and central nervous system stimulation. It can also easily cause serious side effects such as epilepsy, severe hypotension, hypoglycemia, and adrenal insufficiency ( Senthilkumaran et al., 2017 ; Günther et al., 2018 ; Ventura, Carvalho & Dinis-Oliveira, 2018 ).

Tramadol is mainly eliminated through CYP in the liver, and at least 23 metabolites have been identified ( Grond & Sablotzki, 2004 ; Jamali et al., 2017 ; Perez Jimenez et al., 2016 ; Wu et al., 2001 ). Among these, O-desmethyl tramadol can be produced by CYP2D6 pathway metabolism from tramadol. O-desmethyl tramadol has an affinity more than 700 times higher than that of tramadol, and is the substance that primarily activates opioid receptors ( Allegaert et al., 2015 ; De La Gastine et al., 2022 ; Gillen et al., 2000 ; Gong et al., 2014 ). In addition, CYP3A4 and CYP2B6 are also involved in the metabolism of tramadol, and they produce N-desmethyl tramadol, which has no pharmacological activity ( Al-Qurain et al., 2021 ; Grond & Sablotzki, 2004 ; Grond & Sablotzki, 2004 ). Therefore, the diverse function of CYP can affect the metabolism of tramadol and lead to differences in efficacy. Since most tyrosine kinase inhibitors are also metabolized through the CYP pathway, there may be drug-drug interactions (DDIs) with tramadol ( Abdelhameed et al., 2019 ; Ding et al., 2013 ; Jolibois, Schmitt & Royer, 2019 ). As there are limited reports on this potential interaction, it is essential to investigate this further.

In this study, we screened several representative tyrosine kinase inhibitors to identify potential drug interactions and unveil the underlying mechanism. In addition, considering that Sprague Dawley (SD) rats are common used in the experiment of pharmacokinetics and the homologous gene similarity with human, we used SD rats to carry out the related experiments. The results are expected to provide a theoretical basis for the precise application of tramadol.