Tizanidine

RECENT MAJOR CHANGES • Indications and Usage ( 1 ) 11/2024 • Dosage and Administration ( 2.1 , 2.2 , 2.3 , 2.4 , 2.5 , 2.6 ) 11/2024 • Contraindications ( 4 ) 11/2024 • Warnings and Precautions ( 5.1 , 5.2 , 5.4 , 5.5 ) 11/2024

1 INDICATIONS AND USAGE Tizanidine Tablets, USP is a central alpha-2-adrenergic agonist indicated for the management of spasticity. Because of the short duration of therapeutic effect, treatment with Tizanidine Tablets, USP should be reserved for those daily activities and times when relief of spasticity is most important [see Dosage and Administration(2.1) ]. Tizanidine Tablets, USP is a central alpha-2-adrenergic agonist indicated for the management of spasticity. Because of the short duration of therapeutic effect, treatment with Tizanidine Tablets, USP should be reserved for those daily activities and times when relief of spasticity is most important [ see Dosage and Administration (1) ].

2 DOSAGE & ADMINISTRATION 2.1 Dosing Information Tizanidine Tablets, USP tablets may be prescribed with or without food. Once the formulation has been selected and the decision to take with or without food has been made, this regimen should not be altered. Food has complex effects on tizanidine pharmacokinetics, which differ with the different formulations. Tizanidine Capsules and Tizanidine Tablets, USP are bioequivalent to each other under fasting conditions (more than 3 hours after a meal), but not under fed conditions (within 30 minutes of a meal). These pharmacokinetic differences may result in clinically significant differences when switching administration of tablet and capsules and when switching administration between the fed or fasted state. These changes may result in increased adverse events, or delayed or more rapid onset of activity, depending upon the nature of the switch. For this reason, the prescriber should be thoroughly familiar with the changes in kinetics associated with these different conditions [ see Clinical Pharmacology ( 12.3 ) ]. The recommended starting dose is 2 mg. Because the effect of Tizanidine Tablets, USP peaks at approximately 1 to 2 hours post-dose and dissipates between 3 to 6 hours post-dose, treatment can be repeated at 6 to 8 hour intervals, as needed, to a maximum of three doses in 24 hours. Dosage can be gradually increased by 2 mg to 4 mg at each dose, with 1 to 4 days between dosage increases, until a satisfactory reduction of muscle tone is achieved. The total daily dose should not exceed 36 mg. Single doses greater than 16 mg have not been studied. 2.2 Dosing in Patients with Renal Impairment Tizanidine Tablets, USP should be used with caution in patients with renal insufficiency (creatinine clearance < 25 mL/min), as clearance is reduced by more than 50%. In these patients, during titration, the individual doses should be reduced. If higher doses are required, individual doses rather than dosing frequency should be increased [ see Warnings and Precautions ( Error! Hyperlink reference not valid. ) ]. 2.3 Dosing in Patients with Hepatic Impairment Tizanidine Tablets, USP should be used with caution in patients with any hepatic impairment. In these patients, during titration, the individual doses should be reduced. If higher doses are required, individual doses rather than dosing frequency should be increased. Monitoring of aminotransferase levels is recommended for baseline and 1 month after maximum dose is achieved, or if hepatic injury is suspected. [ see Use in Specific Populations ( 8.7 ) ] 2.4 Drug Discontinuation If therapy needs to be discontinued, particularly in patients who have been receiving high doses (20 mg to 36 mg daily) for long periods (9 weeks or more) or who may be on concomitant treatment with narcotics, the dose should be decreased slowly (2 mg to 4 mg per day) to minimize the risk of withdrawal and rebound hypertension, tachycardia, and hypertonia [ see Drug Abuse and Dependence ( 9.3 )]. • Recommended starting dose: 2 mg; dose can be repeated at 6 to 8 hour intervals, up to a maximum of 3 doses in 24 hours ( Error! Hyperlink reference not valid. ) • Dosage can be increased by 2 mg to 4 mg per dose, with 1 to 4 days between increases; total daily dose should not exceed 36 mg ( Error! Hyperlink reference not valid. ) • Tizanidine pharmacokinetics differs between tablets and capsules, and when taken with or without food. These differences could result in a change in tolerability and control of symptoms ( Error! Hyperlink reference not valid. , 12.3 ) • To discontinue Tizanidine Tablets, USP, decrease dose slowly to minimize the risk of withdrawal and rebound hypertension, tachycardia, and hypertonia ( Error! Hyperlink reference not valid. )

3 DOSAGE FORMS AND STRENGTHS • Tablets 2 mg and 4 mg ( 3 ) Tablets Tizanidine tablets USP, 2 mg are white to off-white, round, flat, bevel edged uncoated tablets debossed with "U" and "168" on one side and bisecting score on other side. Tizanidine tablets USP, 4 mg are white to off-white, round, flat, bevel edged uncoated tablets debossed with "U" and "169" on one side and quadrisecting score on other side.

CONTRAINDICATIONS Concomitant use of tizanidine with fluvoxamine or with ciprofloxacin, potent inhibitors of CYP1A2, is contraindicated. Significant alterations of pharmacokinetic parameters of tizanidine including increased AUC, t1/2, C max , increased oral bioavailability and decreased plasma clearance have been observed with concomitant administration of either fluvoxamine or ciprofloxacin. This pharmacokinetic interaction can result in potentially serious adverse events (See WARNINGS and CLINICAL PHARMACOLOGY: Drug Interactions). Tizanidine tablets is contraindicated in patients with known hypersensitivity to Tizanidine tablets or its ingredients.

ADVERSE REACTIONS In multiple dose, placebo-controlled clinical studies, 264 patients were treated with tizanidine and 261 with placebo. Adverse events, including severe adverse events, were more frequently reported with tizanidine than with placebo. Common Adverse Events Leading to Discontinuation Forty-five of 264 (17%) patients receiving tizanidine and 13 of 261 (5%) of patients receiving placebo in three multiple dose, placebo-controlled clinical studies, discontinued treatment for adverse events. When patients withdrew from the study, they frequently had more than one reason for discontinuing. The adverse events most frequently leading to withdrawal of tizanidine treated patients in the controlled clinical studies were asthenia (weakness, fatigue and/or tiredness) (3%), somnolence (3%), dry mouth (3%), increased spasm or tone (2%), and dizziness (2%). Most Frequent Adverse Clinical Events Seen in Association With the Use of Tizanidine In multiple dose, placebo-controlled clinical studies involving 264 patients with spasticity, the most frequent adverse effects were dry mouth, somnolence/sedation, asthenia (weakness, fatigue and/or tiredness) and dizziness. Three-quarters of the patients rated the events as mild to moderate and one-quarter of the patients rated the events as being severe. These events appeared to be dose related. Adverse Events Reported in Controlled Studies The events cited reflect experience gained under closely monitored conditions of clinical studies in a highly selected patient population. In actual clinical practice or in other clinical studies, these frequency estimates may not apply, as the conditions of use, reporting behavior, and the kinds of patients treated may differ. Table 1 lists treatment emergent signs and symptoms that were reported in greater than 2% of patients in three multiple dose, placebo-controlled studies who received tizanidine where the frequency in the tizanidine group was at least as common as in the placebo group. These events are not necessarily related to tizanidine treatment. For comparison purposes, the corresponding frequency of the event (per 100 patients) among placebo treated patients is also provided. Table 1: Multiple Dose, Placebo-Controlled Studies—Frequent (> 2%) Adverse Events Reported for Which Tizanidine Tablets Incidence is Greater than Placebo Event Placebo N = 261 % Tizanidine Tablet N = 264 % Dry Mouth 10 49 Somnolence 10 48 Asthenia* 16 41 Dizziness 4 16 UTI 7 10 Infection 5 6 Constipation 1 4 Liver function tests abnormal <1 3 Vomiting 0 3 Speech disorder 0 3 Amblyopia (blurred vision) <1 3 Urinary frequency 2 3 Flu symptom 2 3 SGPT/ALT increased <1 3 Dyskinesia 0 3 Nervousness <1 3 Pharyngitis 1 3 Rhinitis 2 3 *(weakness, fatigue, and/or tiredness) In the single dose, placebo-controlled study involving 142 patients with spasticity, the patients were specifically asked if they had experienced any of the four most common adverse events: dry mouth, somnolence (drowsiness), asthenia (weakness, fatigue and/or tiredness) and dizziness. In addition, hypotension and bradycardia were observed. The occurrence of these adverse effects is summarized in Table 2. Other events were, in general, reported at a rate of 2% or less. able 2: Single Dose, Placebo-Controlled Study—Common Adverse Events Reported Event Placebo N=48 % Tizanidine Tablet, 8 mg, N=45 % Tizanidine Tablet, 16 mg, N=49 % Somnolence 31 78 92 Dry mouth 35 76 88 Asthenia* 40 67 78 Dizziness 4 22 45 Hypotension 0 16 33 Bradycardia 0 2 10 *(weakness, fatigue, and/or tiredness) Other Adverse Events Observed During the Evaluation of Tizanidine Tizanidine was administered to 1385 patients in additional clinical studies where adverse event information was available. The conditions and duration of exposure varied greatly, and included (in overlapping categories) double-blind and open-label studies, uncontrolled and controlled studies, inpatient and outpatient studies, and titration studies. Untoward events ass …

DRUG INTERACTIONS SECTION Fluvoxamine The effect of fluvoxamine on the pharmacokinetics of tizanidine was studied in 10 healthy subjects. The Cmax, AUC, and half-life of tizanidine increased by 12-fold, 33-fold, and 3-fold, respectively. These changes resulted in significant decreases in blood pressure, increased drowsiness, and psychomotor impairment. (See CONTRAINDICATIONS and WARNINGS ). Ciprofloxacin The effect of ciprofloxacin on the pharmacokinetics of tizanidine was studied in 10 healthy subjects. The Cmax and AUC of tizanidine increased by 7-fold and 10-fold, respectively. These changes resulted in significant decreases in blood pressure, increased drowsiness, and psychomotor impairment. (See CONTRAINDICATIONS and WARNINGS ). CYP1A2 Inhibitors The interaction between tizanidine and either fluvoxamine or ciprofloxacin is most likely due to inhibition of CYP1A2 by fluvoxamine or ciprofloxacin. Although there have been no clinical studies evaluating the effects of other CYP1A2 inhibitors on tizanidine, other CYP1A2 inhibitors, such as zileuton, other fluoroquinolones, antiarrythmics (amiodarone, mexiletine, propafenone and verapamil), cimetidine, famotidine oral contraceptives, acyclovir and ticlopidine, may also lead to substantial increases in tizanidine blood concentrations. (See WARNINGS ) Oral Contraceptives No specific pharmacokinetic study was conducted to investigate interaction between oral contraceptives and tizanidine. Retrospective analysis of population pharmacokinetic data following single and multiple dose administration of 4 mg tizanidine, however, showed that women concurrently taking oral contraceptives had 50% lower clearance of tizanidine compared to women not on oral contraceptives (see PRECAUTIONS ).

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. Fluvoxamine The effect of fluvoxamine on the pharmacokinetics of a single 4 mg dose of tizanidine was studied in 10 healthy subjects. The Cmax, AUC, and half-life of tizanidine increased by 12-fold, 33-fold, and 3-fold, respectively. These changes resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor impairment. (See CONTRAINDICATIONS and WARNINGS ). Ciprofloxacin The effect of ciprofloxacin on the pharmacokinetics of a single 4 mg dose of tizanidine was studied in 10 healthy subjects. The Cmax and AUC of tizanidine increased by 7-fold and 10-fold, respectively. These changes resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor impairment. (See CONTRAINDICATIONS and WARNINGS ). CYP1A2 inhibitors The interaction between tizanidine and either fluvoxamine or ciprofloxacin is most likely due to inhibition of CYP1A2 by fluvoxamine or ciprofloxacin. Although there have been no clinical studies evaluating the effects of other CYP1A2 inhibitors on tizanidine, other CYP1A2 inhibitors, including zileuton, other fluroquinolones, antiarrythmics (amiodarone, mexiletine, propafenone, and verapamil), cimetidine and famotidine, oral contraceptives, acyclovir, and ticlopidine may also lead to substantial increases in tizanidine blood concentrations. Concomitant use of tizanidine with CYP1A2 inhibitors should ordinarily be avoided. If their use is clinically necessary, they should be used with caution (see WARNINGS ). 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. Oral Contraceptives No specific pharmacokinetic study was conducted to investigat …

8 USE IN SPECIFIC POPULATIONS • Pregnancy: Based on animal data, may cause fetal harm (8.1) • Geriatric use: tizanidine hydrochloride should be used with caution in elderly patients because clearance is decreased four-fold (8.5) 8.1 Pregnancy Risk Summary There are no adequate data on the developmental risk associated with use of Tizanidine hydrochloride in pregnant women. In animal studies, administration of tizanidine during pregnancy resulted in developmental toxicity (embryofetal and postnatal offspring mortality and growth deficits) at doses less than those used clinically, which were not associated with maternal toxicity (see Animal Data). In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% - 4% and 15% - 20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown. Data Animal Data Oral administration of tizanidine (0.3 to 100 mg/kg/day) to pregnant rats during the period of organogenesis resulted in embryofetal and postnatal offspring mortality and reductions in body weight at doses of 30 mg/kg/day and above. Maternal toxicity was observed at the highest dose tested. The no-effect dose for embryofetal developmental toxicity in rats (3 mg/kg/day) is similar to the maximum recommended human dose (MRHD) of 36 mg/day on a body surface area (mg/m2) basis. Oral administration of tizanidine (1 to 100 mg/kg/day) to pregnant rabbits during the period of organogenesis resulted in embryofetal and postnatal offspring mortality at all doses. Maternal toxicity was observed at the highest dose tested. Oral administration of tizanidine (10 and 30 mg/kg/day) during the perinatal period of pregnancy (2-6 days prior to delivery) resulted in increased postnatal offspring mortality at both doses. A no-effect dose for embryofetal developmental toxicity in rabbit was not identified. The lowest dose tested (1 mg/kg/day) is less than the MRHD on a mg/m2 basis. In a pre- and postnatal development study in rats, oral administration of tizanidine (3 to 30 mg/kg/day) resulted in increased postnatal offspring mortality. A no-effect dose for pre- and postnatal developmental toxicity was not identified. The lowest dose tested (3 mg/kg/day) is similar to the MRHD on a mg/m2 basis, respectively. 8.2 Lactation Risk Summary There are no data on the presence of tizanidine in human milk, the effects on the breastfed infant, or the effects on human milk production. Animal studies have reported the presence of tizanidine in the milk of lactating animals. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for tizanidine hydrochloride and any potential adverse effects on the breastfed infant from Tizanidine hydrochloride or from the underlying maternal condition. 8.3 Females and Males of Reproductive Potential There are no adequate and well-controlled studies in humans on the effect of tizanidine hydrochloride on female or male reproductive potential. Oral administration of tizanidine to male and female rats resulted in adverse effects on fertility [see Nonclinical Toxicology (13.1)]. 8.4 Pediatric Use Safety and effectiveness in pediatric patients have not been established. Juvenile Animal Toxicity Data Oral administration of tizanidine (0, 1, 3, and 10 mg/kg/day) to juvenile rats from postnatal day (PND) 7 through PND 70 resulted in delayed sexual maturation in males at all doses, reduced body weight gain, delayed sexual maturation in females, and bilateral corneal crystals at the mid and high doses. Corneal crystals were still observed at the mid and high doses after a three-week recovery period. Neurobehavioral deficits were observed on a learning and memory task at the high dose. A no-effect dose for adverse effects on postnatal development not identified. 8.5 Geriatric Use Tizanidine hydrochloride is known to be substantially excreted by the kidn …

Mechanism Of Action Tizanidine is an agonist at α 2 -adrenergic receptor sites and presumably reduces spasticity by increasing presynaptic inhibition of motor neurons. In animal models, tizanidine has no direct effect on skeletal muscle fibers or the neuromuscular junction, and no major effect on monosynaptic spinal reflexes. The effects of tizanidine are greatest on polysynaptic pathways. The overall effect of these actions is thought to reduce facilitation of spinal motor neurons. The imidazoline chemical structure of tizanidine is related to that of the anti-hypertensive drug clonidine and other α 2 -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.

11 DESCRIPTION Should overdose occur, ensure the adequacy of an airway and monitor cardiovascular and respiratory function. Dialysis is not likely to be an efficient method of removing tizanidine from the body [see Description (11) ] . In general, symptoms resolve within one to three days following discontinuation of tizanidine and administration of appropriate therapy. Because of the similar mechanism of action, symptoms and management of tizanidine overdose are similar to that following clonidine overdose. For the most recent information concerning the management of overdose, contact a poison control center. Tizanidine Hydrochloride is a white to slightly yellow crystalline powder. Tizanidine is slightly soluble in water and methanol. Each tizanidine tablet intended for oral administration contains 2.29 mg or 4.58 mg of tizanidine hydrochloride USP, which is equivalent to 2 mg or 4 mg of tizanidine base. In addition, each tablet contains the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, croscarmellose sodium, microcrystalline cellulose and stearic acid. Meets USP Dissolution Test 2. figure

10 OVERDOSAGE A review of the safety surveillance database revealed cases of intentional and accidental tizanidine hydrochloride overdose. Some of the cases resulted in fatality and many of the intentional overdoses were with multiple drugs including CNS depressants. The clinical manifestations of tizanidine overdose were consistent with its known pharmacology. In the majority of cases a decrease in sensorium was observed including lethargy, somnolence, confusion and coma. Depressed cardiac function is also observed including most often bradycardia and hypotension. Respiratory depression is another common feature of tizanidine overdose. Should overdose occur, basic steps to ensure the adequacy of an airway and the monitoring of cardiovascular and respiratory systems should be undertaken. Tizanidine is a lipid-soluble drug, which is only slightly soluble in water and methanol. Therefore, dialysis is not likely to be an efficient method of removing drug from the body. In general, symptoms resolve within one to three days following discontinuation of tizanidine and administration of appropriate therapy. Due to the similar mechanism of action, symptoms and management of tizanidine overdose are similar to that following clonidine overdose. For the most recent information concerning the management of overdose, contact a poison control center.

16 HOW SUPPLIED/STORAGE AND HANDLING 16.1 How Supplied Tizanidine Tablets USP, 2 mg are white to off-white, round, uncoated tablet debossed with '1' & '1' on either side of bisecting score on one side and debossed with '04' on the other side and are supplied as follows: NDC 76420-885-11 in unit-dose blister of 10 tablets. (relabeled from NDC 72578-096-30) NDC 76420-885-30 in bottles of 30 tablets. (relabeled from NDC 72578-096-06) NDC 76420-885-99 in unit-dose blister cartons of 100 (10 x 10) unit-dose tablets (relabeled from NDC 72578-096-77) NDC 76420-885-21 in bottles of 150 tablets. (relabeled from NDC 72578-096-21) NDC 76420-885-00 in bottles of 1000 tablets. (relabeled from NDC 72578-096-10) NDC 76420-885-88 in bottles of 10 tablets. (repackaged from NDC 72578-096-XX) NDC 76420-885-15 in bottles of 15 tablets. (repackaged from NDC 72578-096-XX) NDC 76420-885-60 in bottles of 60 tablets. (repackaged from NDC 72578-096-XX) NDC 76420-885-90 in bottles of 90 tablets. (repackaged from NDC 72578-096-XX) NDC 76420-885-01 in bottles of 100 tablets. (repackaged from NDC 72578-096-XX) Tizanidine Tablets USP, 4 mg are white to off-white, round, uncoated tablet with quadrisecting score on one side and debossed with '1105' on the other side and are supplied as follows: NDC 76420-886-11 in unit-dose blister of 10 tablets. (relabeled from NDC 72578-097-30) NDC 76420-886-30 in bottles of 30 tablets. (relabeled from NDC 72578-097-06) NDC 76420-886-99 in unit-dose blister cartons of 100 (10 x 10) unit-dose tablets (relabeled from NDC 72578-097-77) NDC 76420-886-21 in bottles of 150 tablets. (relabeled from NDC 72578-097-21) NDC 76420-886-03 in bottles of 300 tablets. (relabeled from NDC 72578-097-76) NDC 76420-886-00 in bottles of 1000 tablets. (relabeled from NDC 72578-097-10) NDC 76420-886-88 in bottles of 10 tablets. (repackaged from NDC 72578-097-XX) NDC 76420-886-15 in bottles of 15 tablets. (repackaged from NDC 72578-097-XX) NDC 76420-886-60 in bottles of 60 tablets. (repackaged from NDC 72578-097-XX) NDC 76420-886-90 in bottles of 90 tablets. (repackaged from NDC 72578-0967-XX) NDC 76420-886-01 in bottles of 100 tablets. (repackaged from NDC 72578-097-XX) 16.2 Storage and Handling Store at 20° to 25°C (68° to 77°F) [See USP Controlled Room Temperature]. Dispense in a tight container as defined in the USP with a child-resistant closure.