from RXlist.com
Quote:
he imidazoline chemical structure of tizanidine is related to that of the anti-hypertensive drug clonidine and other a2-adrenergic agonists. Pharmacological studies in animals show similarities between the two compounds, but tizanidine was found to have one-tenth to one-fiftieth (1/50) of the potency of clonidine in lowering blood pressure.....
DRUG INTERACTIONS
In vitro studies of cytochrome P450 isoenzymes using human liver microsomes indicate that neither tizanidine nor the major metabolites are likely to affect the metabolism of other drugs metabolized by cytochrome P450 isoenzymes.
Acetaminophen: Tizanidine delayed the Tmax of acetaminophen by 16 minutes. Acetaminophen did not affect the pharmacokinetics of tizanidine.
Alcohol: Alcohol increased the AUC of tizanidine by approximately 20% while also increasing its Cmax by approximately 15%. This was associated with an increase in side effects of tizanidine. The CNS depressant effects of tizanidine and alcohol are additive.
Fluvoxamine: Clinically significant hypotension (decreases in both systolic and diastolic pressure) has been reported with concomitant administration of fluvoxamine following single doses of 4 mg (see DRUG INTERACTIONS, CONTRAINDICATIONS).
Caution is recommended when considering concomitant use of tizanidine with other inhibitors of CYP1A2, such as, antiarrhythmics (amiodarone, mexiletine, propafenone), cimetidine, fluoroquinolones (ciprofloxacin, norfloxacin), rofecoxib, oral contraceptives, and ticlopidine.
Oral Contraceptives: No specific pharmacokinetic study was conducted to investigate interaction between oral contraceptives and tizanidine, but retrospective analysis of population pharmacokinetic data following single and multiple dose administration of 4 mg tizanidine showed that women concurrently taking oral contraceptives had 50% lower clearance of tizanidine than women not on oral contraceptives.....
izanidine is an a2-adrenergic agonist (like clonidine) and can produce hypotension. In a single dose study where blood pressure was monitored closely after dosing, two-thirds of patients treated with 8 mg of tizanidine had a 20% reduction in either the diastolic or systolic BP. The reduction was seen within 1 hour after dosing, peaked 2 to 3 hours after dosing and was associated, at times, with bradycardia, orthostatic hypotension, lightheadedness/dizziness and rarely syncope. The hypotensive effect is dose related and has been measured following single doses of > 2 mg.
Clinically significant hypotension (decreases in both systolic and diastolic pressure) has been reported with concomitant administration of fluvoxamine following single doses of 4 mg (see DRUG INTERACTIONS, CONTRAINDICATIONS, ADVERSE REACTIONS).
The chance of significant hypotension may possibly be minimized by titration of the dose and by focusing attention on signs and symptoms of hypotension prior to dose advancement. In addition, patients moving from a supine to a fixed upright position may be at increased risk for hypotension and orthostatic effects.
Caution is advised when tizanidine is to be used in patients receiving concurrent antihypertensive therapy and should not be used with other a2-adrenergic agonists.
Prolongation of the QTinterval and bradycardia were noted in chronic toxicity studies in dogs at doses equal to the maximum human dose on a mg/m2 basis. ECG evaluation was not performed in the controlled clinical studies.
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I suggest you plug Tizanidine (Zanaflex) into the drug checker website, I have in Useful Websites here. Put it up against all the meds you are taking. That is the best way. I have an explanation of Prolongation of QT on the Useful websites thread at Chronic Pain here. Please check that out too.
Zanaflex is not usually used, until other muscle relaxant drugs fail. It is safe, but you must use it carefully, and be monitored closely by your doctor.
An EKG before therapy is started will reveal if you have a genetic tendency to prolongation of QT. (heart rhythm issues). This issue is silent, so it must be looked for.
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All truths are easy to understand once they are discovered; the point is to discover them.-- Galileo Galilei
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Weezie looking at petunias 8.25.2017
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