Intracerebral microdialysis coupled to LC-MS/MS for the determination tramadol and its major pharmacologically active metabolite O-desmethyltramadol in rat brain microdialysates.

A rapid and sensitive method involving liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) coupled to an intracerebral microdialysis technique was developed for the determination and pharmacokinetic investigation of tramadol and its major active metabolite O-desmethyltramadol (ODT) in rat brain. The microdialysis samples were separated on a C18 column and eluted with a mobile phase of acetonitrile-water-formic acid (50:50:0.1; v/v/v) at a flow rate of 0.3 mL/min. The ESI-MS/MS spectra were performed in electrospray positive ion mode, and the analytes were detected by multiple reaction monitoring (MRM) of the transitions m/z [M + H]+ 264.3 â†’ 58.2 for tramadol, m/z [M + H]+ 250.3 â†’ 58.3 for ODT, and m/z [M + H]+ 379.4 â†’ 264.0 for ambroxol (internal standard; IS). The total run time was 4.0 min. A lower limit of quantitation (LLOQ) was achieved as 1 ng/mL for tramadol and 0.5 ng/mL for ODT, with excellent linearity over a concentration range of 1 ~ 500 ng/mL (r > 0.99) for tramadol and 0.5 ~ 50 ng/mL for ODT (r > 0.99), respectively. The proposed method was successfully applied to the pharmacokinetic studies of tramadol and ODT in rat brain. Copyright © 2017 John Wiley & Sons, Ltd.

Evaluation of the route dependency of the pharmacokinetics and neuro-pharmacokinetics of tramadol and its main metabolites in rats.

Tramadol hydrochloride is a centrally acting analgesic used for the treatment of moderate-to-severe pain. It has three main metabolites: O-desmethyltramadol (M1), N-desmethyltramadol (M2), and N,O-didesmethyltramadol (M5). Because of the frequent use of tramadol by patients and drug abusers, the ability to determine the parent drug and its metabolites in plasma and cerebrospinal fluid is of great importance. In the present study, a pharmacokinetic approach was applied using two groups of five male Wistar rats administered a 20mg/kg dose of tramadol via intravenous (i.v.) or intraperitoneal (i.p.) routes. Plasma and CSF samples were collected at 5-360min following tramadol administration. Our results demonstrate that the plasma values of Cmax (C0 in i.v. group) and area under the curve (AUC)0-t for tramadol were 23,314.40±6944.85 vs. 3187.39±760.25ng/mL (Cmax) and 871.15±165.98 vs. 414.04±149.25µg·min/mL in the i.v. and i.p. groups, respectively (p<0.05). However, there were no significant differences between i.v. and i.p. plasma values for tramadol metabolites (p>0.05). Tramadol rapidly penetrated the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB) (5.00±0.00 vs. 10.00±5.77min in i.v. and i.p. groups, respectively). Tramadol and its metabolites (M1 and M2) were present to a lesser extent in the cerebrospinal fluid (CSF) than in the plasma. M5 hardly penetrated the CSF, owing to its high polarity. There was no significant difference between the AUC0-t of tramadol in plasma (414.04±149.25µg·min/mL) and CSF (221.81±83.02µg·min/mL) in the i.p. group. In addition, the amounts of metabolites (M1 and M2) in the CSF showed no significant differences following both routes of administration. There were also no significant differences among the Kp,uu,CSF(0-360) (0.51±0.12 vs. 0.63±0.04) and Kp,uu,CSF(0-∞) (0.61±0.10 vs. 0.62±0.02) for i.v. and i.p. pathways, respectively (p>0.05). Drug targeting efficiency (DTE) values of tramadol after i.p. injection were more than unity for all scheduled time points. Considering the main analgesic effect of M1, it is hypothesized that both routes of administration may produce the same amount of analgesia.

Regulation of cerebral CYP2D alters tramadol metabolism in the brain: interactions of tramadol with propranolol and nicotine.

1. Cytochrome P450 2D (CYP2D) protein is widely expressed across brain regions in human and rodents. We investigated the interactions between tramadol, a clinically used analgesic, and brain CYP2D regulators, by establishing concentration-time curves of tramadol and O-desmethyltramadol (M1) in rat cerebrospinal fluid (CSF) and plasma, as well as by analyzing the analgesia-time course of tramadol. 2. Propranolol (20 µg, intracerebroventricular injection), CYP2D inhibitor, prolonged the elimination t1/2 of tramadol (40 mg/kg, intraperitoneal injection) in the CSF; meanwhile, lower Cmax and AUC0-∞ values of M1 were observed. Nicotine (1 mg base/kg, subcutaneous injection, seven days), brain CYP2D inducer, induced a shorter Tmax and elevated Cmax of M1 in CSF. No differences in the peripheral metabolism of tramadol were observed following propranolol and nicotine pretreatment. Nicotine increased areas under the analgesia-time curve (AUC) for 0-45 min and 0-90 min of tramadol, which was attenuated by propranolol administration. The analgesic actions of tramadol positively correlated with cerebral M1 concentration. 3. The results suggest that the regulation of brain CYP2D by xenobiotics may cause drug-drug interactions (DDIs) of tramadol. Brain CYPs may play an important role in DDIs of centrally active substances.

Effects of intracisternal tramadol on cerebral and spinal neuronal cells in rat.

BACKGROUND: The aim was to investigate whether tramadol had toxic effect on cerebral neurons and/or spinal cord neurons when it was administered into the cerebrospinal fluid. Due to lipid peroxidation (LPO) and myeloperoxidation (MPO) levels are not specific predictors of neuronal damage, these biochemical markers of tissue damage were evaluated together with the histopathological findings of apoptosis. METHODS: Forty eight Wistar rats were anesthetized and the right femoral artery was cannulated. Mean arterial pressures, and heart rates, arterial carbon dioxide tension, arterial oxygen tension, blood pH were recorded. When the free cerebrospinal fluid flow was seen; 0.04 mL normal saline (Group Sham) or diluted tramadol in 0.04 mL volume (Group T1, T2, T0.5 and T0.1) was administered within 30 seconds from the posterior craniocervical junction of rats. For the Control Group, the free cerebrospinal fluid flow was seen but nothing was injected in it. After 7 days, following the sacrification of the rats, brain tissue, cervical and lumber segments of spinal cord were collected for the histopathological and biochemical examination. RESULTS: There was not a statistically significant difference among all groups regarding the brain LPO levels (P=0.485). The LPO levels of the cervical segment of spinal cord and the lumbar segment of spinal cord were also similar (P=0.146, P=0.939, respectively). The mean MPO levels of the cervical and the lumbar segments of spinal cord were similar among all groups (P=0.693, P=0.377, respectively). There were not any statistically significant difference regarding the total number of red neurons of the brain tissue and the cervical and lumbar segments of spinal cord among all groups (P=0.264, P=0.202, P=0.780, respectively). CONCLUSION: Tramadol had no neurotoxic effect on brain and on spinal cord tissue when administered by the intracisternal route in cerebrospinal fluid in rats.

Pharmacokinetics of tramadol in rat plasma and cerebrospinal fluid after intranasal administration.

We have evaluated the potential of intranasal administration of tramadol. The pharmacokinetic behaviour of tramadol in rat plasma and cerebrospinal fluid (CSF) after intranasal administration was determined and compared with those after intravenous and oral administration. Serial plasma and CSF samples were collected for 6 h, and the drug concentrations were assayed by an HPLC-fluorescence method. The plasma absolute bioavailability values of tramadol after intranasal and oral administration were 73.8% and 32.4%, respectively, in conscious rats. The Cmax (maximum concentration) value after the intranasal dose was lower (P<0.05), and the MRT (mean retention time) was longer (P<0.05) than the values obtained after intravenous administration. A pharmacokinetic study of tramadol in plasma and CSF was undertaken in anaesthetized rats. The absolute bioavailability values in plasma and CSF after intranasal administration were 66.7% and 87.3%, respectively. The Cmax values in plasma and CSF after a nasal dose were lower (P<0.05) than after the intravenous dose. The values of Cmax and AUC0-->6 h in plasma and CSF after intranasal administration were higher than after the oral dose. The mean drug-targeting efficiency after intranasal administration was significantly greater than after the oral dose. In conclusion, intranasal administration of tramadol appeared to be a promising alternative to the traditional administration modes for this drug.

Tramadol concentrations in blood and in cerebrospinal fluid in a neonate.

Based on blood and cerebrospinal fluid samples collected in a full-term neonate, the penetration of tramadol in the central nervous system is described. Following intravenous administration of tramadol, a lag time of about 4 h was observed until full blood-brain equilibration was achieved. This pharmacokinetic observation is in line with a recent pharmacodynamic evaluation of the central opioid effects of tramadol in adults.