Imidazolines (Clonidine and Tizanidine)

Clonidine (Catapres®, which is available as a tablet or a patch worn on the skin) and tizanidine (Zanaflex®, available as a tablet) are two imidazolines that reduce spasticity through their action on the central nervous system. These drugs typically cause less muscle weakness than do oral baclofen and benzodiazepines. This factor may be valuable when it is important for the patient to retain strength. When compared with dantrolene, tizanidine may be equal or better in controlling spasticity due to MS or strokes; it can also be used in patients with traumatic brain injury. The imidazolines may be combined with baclofen or benzodiazepines, but the combination may worsen the side effects of both. Dantrolene and tizanidine are usually not prescribed together because of the increased risk for liver problems. The most common side effect of the imidazolines is sedation, and these drugs can cause low blood pressure, dry mouth, dizziness, and hallucinations. The use of tizanidine requires regular monitoring of liver function, since a small proportion of patients show some liver damage as a result of taking the drug. People who have liver problems should usually not take tizanidine.

People who are taking tizanidine should not take fluvoxamine (Luvox®) or ciprofloxacin (Cipro® Cipro XR®). When tizanidine is taken with either of these medicines, it can worsen the drop in blood pressure upon standing or the sedation that occurs with tizanidine alone. This combination can also lead to difficulty with movement. People who are taking tizanidine should probably not take the following medicines: zileuton, fluoroquinolones, amiodarone, mexiletine, propafenone, birth control pills, verapamil, cimetidine, famotidine, acyclovir, and ticlopidine. People who take tizanidine should tell all of their healthcare providers and pharmacists when they start or stop taking a new medicine.

People who take the drug, tizanidine (Zanaflex®) need to be aware that there are two forms of the medicine—a pill and a capsule. These two forms of tizanidine should not be substituted for each other. When you pick up your prescription from the pharmacy, check to make sure that the pharmacist gives you the medication in the form that you usually take. If it's not the same form, speak with your pharmacist, and ask to have the prescription filled in the correct form.

When the pill and the capsule are taken at the time that you eat food or immediately afterward, the amount of the medicine that you absorb—that gets into your bloodstream—from these different forms is different, even when the dose of the medicine that you are taking is the same. The same is true if you open the capsules and sprinkle the medicine on applesauce or another food. The difference in forms is enough to change the effectiveness of your medicine and the side effects that you might experience.

Another thing to keep in mind is that you should always take this medicine either with or without food. You should not sometimes take it with food and sometimes when you are fasting—that is, when you havenšt eaten for a few hours. As with the different forms of the medicine, if you switch back and forth between taking your medicine with and without food, this switching is enough to change the effectiveness of your medicine and the side effects that you might experience.

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