Tramadol

Oral🕒 Plan

Route dataPsychonautWiki

Bioavailability: 70–90 %

🧬 Receptor activityDC

Mechanism of actionPHDM

Tramadol is a centrally acting μ-opioid receptor agonist and SNRI (serotonin/norepinephrine reuptake-inhibitor) that is structurally related to [codeine] and [morphine]. Tramadol binds weakly to κ- and δ-opioid receptors and to the μ-opioid receptor with 6000-fold less affinity than morphine. Tramadol exists as a racemic mixture consisting of two pharmacologically active enantiomers that both contribute to its analgesic property through different mechanisms: (+)-tramadol and its primary metabolite (+)-O-desmethyl-tramadol (M1) are agonists of the μ opioid receptor while (+)-tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine reuptake. These pathways are complementary and synergistic, improving tramadol's ability to modulate the perception of and response to pain. In animal models, M1 is up to 6 times more potent than tramadol in producing analgesia and 200 times more potent in μ-opioid binding. Tramadol has also been shown to affect a number of pain modulators including alpha2-adrenoreceptors, neurokinin 1 receptors, the voltage-gated sodium channel type II alpha subunit, transient receptor potential cation channel subfamily V member 1 (TRPV1 - also known as the capsaicin receptor), muscarinic receptors (M1 and M3), N-methyl-D-aspartate receptor (also known as the NMDA receptor or glutamate receptor), Adenosine A1 receptors, and nicotinic acetylcholine receptor. In addition to the above neuronal targets, tramadol has a number of effects on inflammatory and immune mediators involved in the pain response. This includes inhibitory effects on cytokines, prostaglandin E2 (PGE2), nuclear factor-κB, and glial cells as well as a change in the polarization state of M1 macrophages.
Tramadol is a racemic mixture (R & S) that has a complicated mechanism of action. It has some mu-opioid receptor action, but this effect is 10 times lower than codeine and 6000 timex lower than morphine. Tramadol also inhibits the reuptake of norepinephrine (NE) and serotonin (5 HT) and produces secondary effects on alpha-2 adrenergic receptors in pain pathways. One isomer has greater effect on 5 HT reuptake and greater affinity for mu-opiate receptors. The other isomer is more potent for NE reuptake and less active for inhibiting 5 HT reuptake. Taken together, the effects of of tramadol may be explained through inhibition of 5 HT reuptake, action on alpha2 receptors, and mild activity on opiate mu-receptors.
The transient receptor potential vanilloid 1 (TRPV1) and the transient receptor potential ankyrin 1 (TRPA1), which are expressed in sensory neurons, are polymodal nonselective cation channels that sense noxious stimuli. Recent reports showed that these channels play important roles in inflammatory, neuropathic, or cancer pain, suggesting that they may serve as attractive analgesic pharmacological targets. Tramadol is an effective analgesic that is widely used in clinical practice. Reportedly, tramadol and its metabolite (M1) bind to mu-opioid receptors and/or inhibit reuptake of monoamines in the central nervous system, resulting in the activation of the descending inhibitory system. However, the fundamental mechanisms of tramadol in pain control remain unclear. TRPV1 and TRPA1 may be targets of tramadol; however, they have not been studied extensively. We examined whether and how tramadol and M1 act on human embryonic kidney 293 (HEK293) cells expressing human TRPV1 (hTRPV1) or hTRPA1 by using a Ca imaging assay and whole-cell patch-clamp recording. Tramadol and M1 (0.01-10 uM) alone did not increase in intracellular Ca concentration ([Ca]i) in HEK293 cells expressing hTRPV1 or hTRPA1 compared with capsaicin (a TRPV1 agonist) or the allyl isothiocyanate (AITC, a TRPA1 agonist), respectively. Furthermore, in HEK293 cells expressing hTRPV1, pretreatment with tramadol or M1 for 5 minutes did not change the increase in [Ca]i induced by capsaicin. Conversely, pretreatment with tramadol (0.1-10 uM) and M1 (1-10 uM) significantly suppressed the AITC-induced [Ca]i increases in HEK293 cells expressing hTRPA1. In addition, the patch-clamp study showed that pretreatment with tramadol and M1 (10 uM) decreased the inward currents induced by AITC. These data indicate that tramadol and M1 selectively inhibit the function of hTRPA1, but not that of hTRPV1, and that hTRPA1 may play a role in the analgesic effects of these compounds.
Tramadol is an effective analgesic substance widely used in medical practice. Its therapeutic action have been mainly attributed to the activation of mu-opioid receptors as well as to the inhibition of neurotransmitter reuptake mechanisms and various voltage- and ligand-gated ion channels of the nociceptive system. As transient receptor potential vanilloid-1 (TRPV1, "the capsaicin receptor") has been shown to function as a central integrator molecule of pain sensation, our aim in the current study was to define the involvement of TRPV1 in the complex mechanism of action of tramadol. To achieve these goals, we used single-cell Ca-imaging as well as fluorescent image plate reader assays on Chinese hamster ovary (CHO) cells heterologously over-expressing TRPV1. We found that (1) tramadol, similar to the well-known TRPV1 agonist, capsaicin, significantly increased [Ca(2+)](i) of TRPV1-CHO cells in a concentration-dependent fashion; (2) its effect was reversibly prevented by the TRPV1 antagonist capsazepine; (3) repeated application of tramadol resulted in marked tachyphylaxis; and (4) tramadol did not modify [Ca(2+)](i) in control (empty vector expressing) CHO cells. Collectively, these findings strongly support the intriguing and novel concept that tramadol acts as an agonist of TRPV1. Considering that activation of TRPV1 on sensory neurons is followed by a local release of vasoactive neuropeptides and a marked desensitization of the afferent fibers (hence termination of pain sensation), our findings may equally explain both the desired analgesic as well as the often-seen, yet "unexpected," local side effects (e.g., initiation of burning pain and erythema) of tramadol.
Tramadol has a dual mechanism of action that includes weak agonistic effects at the mu-opioid receptor as well as inhibition of monoamine (serotonin, norepinephrine) re-uptake. Its major (M1) metabolite mono-O:-desmethyltramadol, which is rapidly formed in vivo, has a markedly higher affinity for mu receptors and may thus contribute to the effects of the parent compound. Furthermore, the pharmacological effects of tramadol appear to be related to the different, but complementary and interactive pharmacologies of its enantiomers.
Tramadol has been used as an analgesic for several decades. mu-Opioid receptors (muORs) are the major receptors that mediate the analgesic effects of opioids. Although muORs have been thought to be one of the sites of action of tramadol, there has been no report that directly proves whether tramadol is an agonist of muOR or not. In this study, we examined the effects of tramadol and its main active metabolite O-desmethyltramadol (M1), on the function of muORs using Xenopus oocytes expressing cloned human muORs. The effects of tramadol and M1 were evaluated using the Ca(2+)-activated Cl(-) current assay method for G(i/o)-protein-coupled receptors by using a muOR fused to G(qi5) (muOR-G(qi5)) in Xenopus oocytes. DAMGO [(D-Ala(2), N-MePhe(4), Gly(5)-ol)-enkephalin] evoked Cl(-) currents in oocytes expressing muOR-G(qi5) in a concentration-dependent manner. Tramadol and M1 also evoked Cl(-) currents in the oocytes expressing muOR-G(qi5); however, relatively higher concentrations (compared to DMAGO) were necessary to induce such currents. Tramadol and M1 had a direct effect on muORs expressed in Xenopus oocytes. Although the monoamine uptake system and several types of ligand-gated ion channels are thought to be one of the targets for tramadol, tramadol-induced antinociception may be mediated at least in part, by the direct activation of muORs.

PharmacodynamicsPHDM

Tramadol modulates the descending pain pathways within the central nervous system through the binding of parent and M1 metabolite to μ-opioid receptors and the weak inhibition of the reuptake of norepinephrine and serotonin. Apart from analgesia, tramadol may produce a constellation of symptoms (including dizziness, somnolence, nausea, constipation, sweating and pruritus) similar to that of other opioids. **Central Nervous System** In contrast to [morphine], tramadol has not been shown to cause histamine release. At therapeutic doses, tramadol has no effect on heart rate, left-ventricular function or cardiac index. Orthostatic hypotension has been observed. Tramadol produces respiratory depression by direct action on brain stem respiratory centres. The respiratory depression involves both a reduction in the responsiveness of the brain stem centres to increases in CO2 tension and to electrical stimulation. Tramadol depresses the cough reflex by a direct effect on the cough centre in the medulla. Antitussive effects may occur with doses lower than those usually required for analgesia. Tramadol causes miosis, even in total darkness. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origin may produce similar findings). Marked mydriasis rather than miosis may be seen with hypoxia in the setting of oxycodone overdose. Seizures have been reported in patients receiving tramadol within the recommended dosage range. Spontaneous post-marketing reports indicate that seizure risk is increased with doses of tramadol above the recommended range. Risk of convulsions may also increase in patients with epilepsy, those with a history of seizures or in patients with a recognized risk for seizure (such as head trauma, metabolic disorders, alcohol and drug withdrawal, CNS infections), or with concomitant use of other drugs known to reduce the seizure threshold. Tramadol can cause a rare but potentially life-threatening condition resulting from concomitant administration of serotonergic drugs (e.g., anti-depressants, migraine medications). Treatment with the serotoninergic drug should be discontinued if such events (characterized by clusters of symptoms such as hyperthermia, rigidity, myoclonus, autonomic instability with possible rapid fluctuations of vital signs, mental status changes including confusion, irritability, extreme agitation progressing to delirium and coma) occur and supportive symptomatic treatment should be initiated. Tramadol should not be used in combination with MAO inhibitors or serotonin-precursors (such as L-tryptophan, oxitriptan) and should be used with caution in combination with other serotonergic drugs (triptans, certain tricyclic antidepressants, lithium, St. John’s Wort) due to the risk of serotonin syndrome. **Gastrointestinal Tract and Other Smooth Muscle** Tramadol causes a reduction in motility associated with an increase in smooth muscle tone in the antrum of the stomach and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased, while tone may be increased to the point of spasm resulting in constipation. Other opioid-induced effects may include a reduction in gastric, biliary and pancreatic secretions, spasm of the sphincter of Oddi, and transient elevations in serum amylase. **Endocrine System** Opioids may influence the hypothalamic-pituitary-adrenal or -gonadal axes. Some changes that can be seen include an increase in serum prolactin and decreases in plasma cortisol and testosterone. Clinical signs and symptoms may be manifest from these hormonal changes. Hyponatremia has been reported very rarely with the use of tramadol, usually in patients with predisposing risk factors, such as elderly patients and/or patients using concomitant medications that may cause hyponatremia (e.g., antidepressants, benzodiazepines, diuretics). In some reports, hyponatremia appeared to be the result of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and resolved with discontinuation of tramadol and appropriate treatment (e.g., fluid restriction). During tramadol treatment, monitoring for signs and symptoms of hyponatremia is recommended for patients with predisposing risk factors. **Cardiovascular** Tramadol administration may result in severe hypotension in patients whose ability to maintain adequate blood pressure is compromised by reduced blood volume, or concurrent administration of drugs such as phenothiazines and other tranquillizers, sedative/hypnotics, tricyclic antidepressants or general anesthetics. These patients should be monitored for signs of hypotension after initiating or titrating the dose of tramadol. **QTc-Interval Prolongation** The maximum placebo-adjusted mean change from baseline in the QTcF interval was 5.5 ms in the 400 mg/day treatment arm and 6.5 ms in the 600 mg/day mg treatment arm, both occurring at the 8h time point. Both treatment groups were within the 10 ms threshold for QT prolongation. Post-marketing experience with the use of tramadol containing products included rare reports of QT prolongation reported with an overdose. Particular care should be exercised when administering tramadol to patients who are suspected to be at an increased risk of experiencing torsade de pointes during treatment with a QTc-prolonging drug. **Abuse and Misuse** Like all opioids, tramadol has the potential for abuse and misuse, which can lead to overdose and death. Therefore, tramadol should be prescribed and handled with caution. **Dependence/Tolerance** Physical dependence and tolerance reflect the neuroadaptation of the opioid receptors to chronic exposure to an opioid and are separate and distinct from abuse and addiction. Tolerance, as well as physical dependence, may develop upon repeated administration of opioids, and are not by themselves evidence of an addictive disorder or abuse. Patients on prolonged therapy should be tapered gradually from the drug if it is no longer required for pain control. Withdrawal symptoms may occur following abrupt discontinuation of therapy or upon administration of an opioid antagonist. Some of the symptoms that may be associated with abrupt withdrawal of an opioid analgesic include body aches, diarrhea, gooseflesh, loss of appetite, nausea, nervousness or restlessness, anxiety, runny nose, sneezing, tremors or shivering, stomach cramps, tachycardia, trouble with sleeping, unusual increase in sweating, palpitations, unexplained fever, weakness and yawning.

Pharmacokinetics

External links