Tizanidine Clonidine

Hypotension Tizanidine is an 2-adrenergic agonist (eg, clonidine) and can produce... 

Drug abuse and dependence Tizanidine is closely related to clonidine, which is often abused in combination with narcotics and is known to cause symptoms of rebound upon abrupt withdrawal. 

Clonidine and other imidazoline compounds have also been shown to reduce muscle spasms by their central nervous system activity. Tizanidine is perhaps the most thoroughly studied clonidine analog. It is an agonist at a2-adrenergic receptors, but reduces spasticity at doses that result in significantly less hypotension than clonidine. 

Tizanidine (Zanaflex) Tizanidine is used primarily for treating spasticity.14,24 This drug is similar to clonidine, but has less vasomotor effects and is therefore less likely to cause hypotension and other cardiovascular problems. As indicated earlier, tizanidine stimulates alpha-2 receptors in the spinal cord, which results in decreased excitatory input onto the alpha motor neuron. Decreased excitation of the alpha motor neuron results in decreased spasticity of the skeletal muscle supplied by that neuron. 

Tizanidine (zanaflex, others) is an a2 agonist with some properties similar to those of clonidine. 

Mechanism of action The spasmolytic drugs act by several mechanisms. Three of the drugs act in the spinal cord. Diazepam facilitates GABA-mediated presynaptic inhibition, and baclofen acts as a GABAg agonist. Tizanidine, an imidazoline related to clonidine, reinforces both presynaptic and postsynaptic inhibition in the cord. All three drugs reduce the tonic output of the primary spinal motoneurons. 

Hypotension may occur with tubocurarine and with the spasmolytic drug tizanidine. In the case of tubocurarine, the decrease in blood pressure may be due partly to histamine release and also to ganglionic blockade. Tizanidine causes hypotension via alpha2 adrenoceptor activation like its congener clonidine. The answer is (D). 

D. Tizanidine is structurally related to clonidine but has low affinity for alpha-1 receptors. 

D. Tizanidine is similar to clonidine (see p 169) in addition, SA and AV nodal dysfunction was reported after an overdose. 

Tizanidine may increase the effects of antihypertensive drugs. There are two case reports of severe hypotension with iisinoprii. The manufacturer of tizanidine contraindicates the concurrent use of 02-adrenergic agonists (e.g. clonidine). 

Tizanidine alone can cause hypotension, an efTeet whieh is usually minimised by titration of the dose. Patients should be warned about this effeet. Because of this, the manufacturers caution that tizanidine might inerease the effects of antihypertensive drugs, including diuretics, and recommend caution on concurrent use. This is a prudent precaution. The US manufacturer specifically states that tizanidine (an (X2-adrenergic agonist that is structurally related to clonidine) should not be used with other otj-adren-ergic agonists [e.g. clonidine, methyldopa]. ... 

Structure very similar structure to clonidine. See differences in Figures 89.13 (tizanidine) and 89.14 (clonidine). 

Tizanidine and clonidine are both alpha-2 agonists. As evidenced by their differing effects on blood pressure, the specific pharmacodynamic profiles of the two drugs differ somewhat. This may be due to variation in the agonist activity at the specific alpha-2 receptor subtypes A, B, and C [26,27]. 

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