Tramadol is a weak μ-opioid receptor agonist, releases serotonin, and inhibits the reuptake of norepinephrine. While its analgesic action is thus rather distinct from opioids per se, tramadol is a synthetic analog of the phenanthrene alkaloid codeine. Tramadol is converted to O-desmethyltramadol, a significantly more potent μ-opioid agonist. The euphoria and respiratory depression of opioids are mainly caused by the μ1 and μ2 receptors; the addictive nature of tramadol, as well as other opioids, is due to these effects, but tramadol's serotonergic and noradrenergic effects may also contribute to possible dependence. The opioid agonistic effect of tramadol and its major metabolite(s) is almost exclusively mediated by μ-opioid receptors. This further distinguishes tramadol from opioids in general (including morphine), which do not possess tramadol's degree of subtype selectivity and are much stronger opiate-receptor agonists.
Medical uses
Tramadol is used similarly to codeine, to treat moderate to moderately severe pain. Pharmacologically, Tramadol is similar to levorphanol (albeit with much lower μ-agonism), as both agents are also NMDA-antagonists with SNRI activity. Dextropropoxyphene (Darvon) & M1-like molecule tapentadol (Nucynta, a new synthetic atypical opioid made to mimic the agonistic properties of tramadol's metabolite, M1(O-Desmethyltramadol)) also have similar activities. Tramadol is also molecularly similar to venlafaxine (Effexor) and has similar SNRI effects, with antinociceptive effects also observed. It has been suggested that tramadol could be effective for alleviating symptoms of depression, anxiety, and phobias because of its action on the noradrenergic and serotonergic systems, such as its "atypical" opioid activity. However, health professionals have not endorsed its use for these disorders, claiming it may be used as a unique treatment (only when other treatments failed), and must be used under the control of a psychiatrist
In May 2009, the United States Food and Drug Administration issued a Warning Letter to Johnson & Johnson, alleging that a promotional website commissioned by the manufacturer had "overstated the efficacy" of the drug, and "minimized the serious risks". The company which produced it, the German pharmaceutical company Grünenthal GmbH, were alleged to be guilty of "minimizing" the addictive nature and proposed efficacy of the drug, although it showed little abuse liability in preliminary tests. The 2010 Physicians Desk Reference contains several warnings from the manufacturer, which were not present in prior years. The warnings include more compelling language regarding the addictive potential of tramadol, the possibility of difficulty breathing while on the medication, a new list of more serious side effects, and a notice that tramadol is not to be used in place of opiate medications for addicts. Tramadol is also not to be used in efforts to wean addict patients from opiate drugs, nor to be used to manage long-term opiate addiction.
Availability and usage
Tramadol is classified as a central nervous system drug usually marketed as the hydrochloride salt (tramadol hydrochloride); the tartrate is seen on rare occasions, and rarely (in the US at least) tramadol is available for both injection (intravenous and/or intramuscular) and oral administration. The most well known dosing unit is the 50 mg generic tablet made by several manufacturers. It is also commonly available in conjunction with APAP (paracetamol, acetaminophen) as Ultracet, in the form of a smaller dose of 37.5 mg tramadol and 325 mg of APAP. The solutions suitable for injection are used in patient-controlled analgesia pumps under some circumstances, either as the sole agent or along with another agent such as morphine.
Tramadol comes in many forms, including:
- capsules (regular and extended release)
- tablets (regular, extended release, chewable, low-residue and/or uncoated tablets that can be taken by the sublingual and buccal routes)
- suppositories
- effervescent tablets and powders
- ampules of sterile solution for SC, IM, and IV injection
- preservative-free solutions for injection by the various spinal routes (epidural, intrathecal, caudal, and others)
- powders for compounding
- liquids both with and without alcohol for oral and sub-lingual administration, available in regular phials and bottles, dropper bottles, bottles with a pump similar to those used with liquid soap and phials with droppers built into the cap
- tablets and capsules containing (acetaminophen/APAP), aspirin and other agents.
Tramadol has been regularly used in the form of an ingredient in multi-agent topical gels, creams, and solutions for nerve pain, rectal foam, concentrated retention enema, and a skin plaster (transdermal patch) quite similar to those used with lidocaine.
Tramadol has a characteristic and unpleasant taste which is mildly bitter but much less so than morphine and codeine. Oral and sublingual drops and liquid preparations come with and without added flavoring. Also, 50 mg water-soluble tramadol tablets has strawberry-flavouring, no matter which company manufactured it, to distinguish every, same-looking and same sized Mirtazapine sublingual tablets, which has orange flavouring irrespective of the manufacturer. This different flavouring is considered to be a standard. Its relative effectiveness via transmucosal routes (i.e. sublingual, buccal, rectal) is similar to that of codeine, and, like codeine, it is also metabolized in the liver to stronger metabolites (see below).
The maximum dosage per day is 400 mg for oral use and 600 mg for parenteral use. Certain manufacturers or formulations have lower maximum doses. For example, Ultracet (37.5 mg/325 mg tramadol/APAP tablets) is capped at 8 tablets per day (300 mg/day) due to its acetaminophen content. Ultram ER is available in 100, 200, and 300 mg/day doses and is explicitly capped at 300 mg/day as well.
Patients taking SSRIs, SNRIs, TCAs, MAOIs, or other strong opioids (oxycodone, methadone, fentanyl, morphine), as well as the elderly, pediatric, and those with severely reduced renal or hepatic function should consult their doctor regarding adjusted dosing or whether to use tramadol at all.
