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Tizanidine: Difference between revisions
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'''Tizanidine''' (known by the trade names '''Zanaflex''' and '''Trinex''' among others) is a [[depressant]] substance of the imidazoline class closely related to [[clonidine]]. Tizanidine is primarily used primarily as an antispasmodic drug. Tizanidine's effectivness is similar to that of [[baclofen]] or [[diazepam]] <ref> Wagstaff AJ, Bryson HM. Tizanidine. A review of its pharmacology, clinical efficacy and tolerability in the management of spasticity associated with cerebral and spinal disorders. Drugs. 1997 Mar;53(3):435-52. doi: 10.2165/00003495-199753030-00007. PMID: 9074844. </ref>. | '''Tizanidine''' (known by the trade names '''Zanaflex''' and '''Trinex''' among others) is a [[depressant]] substance of the imidazoline class closely related to [[clonidine]]. Tizanidine is primarily used primarily as an antispasmodic drug. Tizanidine's effectivness is similar to that of [[baclofen]] or [[diazepam]] <ref> Wagstaff AJ, Bryson HM. Tizanidine. A review of its pharmacology, clinical efficacy and tolerability in the management of spasticity associated with cerebral and spinal disorders. Drugs. 1997 Mar;53(3):435-52. doi: 10.2165/00003495-199753030-00007. PMID: 9074844. </ref>. | ||
Tizanidine is a central | Tizanidine is a central α<sub>2</sub> adrenergic agonist. The relationship between the α<sub>2</sub> receptor agonism and the spasmolytic function of tizanidine is not fully understood <ref> Katzung, Bertram G. (30 November 2017). Basic & clinical pharmacology. Katzung, Bertram G. (Fourteenth ed.). New York. p. 487. ISBN 9781259641152. OCLC 1015240036 </ref> . | ||
While recreational use is extremely rare, some users take tizanidine for its standalone sedative effects or to potentiate the effects of [[opiates]]. In higher doses, tizanidine is capable of inducing [[hallucinations]], [[psychosis]], and [[delirium]] <ref> pmhdev. [https://web.archive.org/web/20121111213511/http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000106/ Tizanidine]. PubMed Health. Archived from [https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000106/ the original] on 11 November 2012. </ref>. | While recreational use is extremely rare, some users take tizanidine for its standalone sedative effects or to potentiate the effects of [[opiates]]. In higher doses, tizanidine is capable of inducing [[hallucinations]], [[psychosis]], and [[delirium]] <ref> pmhdev. [https://web.archive.org/web/20121111213511/http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000106/ Tizanidine]. PubMed Health. Archived from [https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000106/ the original] on 11 November 2012. </ref>. | ||
==Chemistry== | ==Chemistry== | ||
Tizanidine is 2,1,3-Benzothiadiazole substituted at C-4 by a Delta(1)-imidazolin-2-ylamino group and at C-4 by a chloro group. It is an agonist at | Tizanidine is 2,1,3-Benzothiadiazole substituted at C-4 by a Delta(1)-imidazolin-2-ylamino group and at C-4 by a chloro group. It is an agonist at α<sub>2</sub>-adrenergic receptor sites. It is a benzothiadiazole and a member of imidazoles<ref>National Center for Biotechnology Information. "PubChem Compound Summary for CID 5487, Tizanidine" PubChem, https://pubchem.ncbi.nlm.nih.gov/compound/Tizanidine. </ref>. | ||
==Pharmacology== | ==Pharmacology== | ||
Tizanidine is an [[imidazoline]] derivative and centrally acting | Tizanidine is an [[imidazoline]] derivative and centrally acting α<sub>2</sub> [[adrenergic]] [[agonist]] closely related to Clonidine. Tizanidine inhibits the release of excitatory amino acids from spinal interneurons. As a result, Tizanidine enhances the presynaptic inhibition of motor neurons. | ||
Tizanidine also has some affinity for the | Tizanidine also has some affinity for the α<sub>1</sub> receptors, but to a lesser than Clonidine, which may explain why its cardiovascular effects are so much milder than that of Clonidine<ref> Ghanavatian S, Derian A. Tizanidine. [Updated 2021 Aug 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519505/ </ref>. Tizanidine has approximately one tenth to one fifteenth of the blood pressure lowering effect of clonidine <ref> Katzung, Bertram G. (30 November 2017). Basic & clinical pharmacology. Katzung, Bertram G. (Fourteenth ed.). New York. p. 487. ISBN 9781259641152. OCLC 1015240036 </ref> . | ||
Tizanidine has also been found to have [[anticonvulsant]] effects against strychnine-induced seizures but not against [[GABA]]-induced seizures. The | Tizanidine has also been found to have [[anticonvulsant]] effects against strychnine-induced seizures but not against [[GABA]]-induced seizures. The α<sub>2</sub> receptor mediated inhibition of inter-neuronal activity appears to be the cause of Tizanidine's anti-convulsant properties <ref> Denizbaşi A, Berkman K, Ozyazgan S, Eşkazan E. The effect of tizanidine on maximal electroshock seizures (MES) in mice. Gen Pharmacol. 1999 Apr;32(4):513-6. doi: 10.1016/s0306-3623(98)00249-3. Erratum in: Gen Pharmacol 2000 Jun;34(6):443. PMID: 10323494. </ref> <ref> Amabeoku G, Chandomba R. Strychnine-induced seizures in mice: the role of noradrenaline. Prog Neuropsychopharmacol Biol Psychiatry. 1994 Jul;18(4):753-63. doi: 10.1016/0278-5846(94)90082-5. PMID: 7938564. </ref>. | ||
Tizanidine has an oral bioavailability of 20-34% and an elimination half-life of 2.5 hours. It attains steady-state concentration within 24-48 hours after administration <ref>Ghanavatian S, Derian A. Tizanidine. [Updated 2021 Aug 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519505/ </ref> | Tizanidine has an oral bioavailability of 20-34% and an elimination half-life of 2.5 hours. It attains steady-state concentration within 24-48 hours after administration <ref>Ghanavatian S, Derian A. Tizanidine. [Updated 2021 Aug 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519505/ </ref> | ||
The table below compares the selectivity of Tizanidine and other drugs to the imidzaoline-receptor and the | The table below compares the selectivity of Tizanidine and other drugs to the imidzaoline-receptor and the α<sub>2</sub> receptors in rats. Tizanidine has a significantly greater selectivity to the imidazoline receptor than clonidine. The imidazoline receptor selectivity of tizanidine may be responsible for its unique pharmacological profile<ref>Muramatsu I, Kigoshi S. Tizanidine may discriminate between imidazoline-receptors and alpha 2-adrenoceptors. Jpn J Pharmacol. 1992 Aug;59(4):457-9. doi: 10.1254/jjp.59.457. PMID: 1331591.. Retrieved from https://pubmed.ncbi.nlm.nih.gov/1331591/ </ref>. | ||
{| class="wikitable" | {| class="wikitable" | ||
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! Drug | ! Drug | ||
! Imidazoline receptors Ki (nM) | ! Imidazoline receptors Ki (nM) | ||
! | ! α<sub>2</sub> Receptors Ki (nM) | ||
|- | |- | ||
| Tizanidine | | Tizanidine | ||