Tizanidine (Page 5 of 6)
13 NONCLINICAL TOXICOLOGY
13.1 Carcinogenesis, Mutagenesis, Impairment Of Fertility
Tizanidine was administered to mice for 78 weeks at oral doses up to 16 mg/kg/day, which is 2 times the maximum recommended human dose (MRHD) on a mg/m 2 basis. Tizanidine was administered to rats for 104 weeks at oral doses up to 9 mg/kg/day, which is 2.5 times the MRHD on a mg/m 2 basis. There was no increase in tumors in either species.
Tizanidine was negative in in vitro (bacterial reverse mutation [Ames] , mammalian gene mutation, and chromosomal aberration test in mammalian cells) and in vivo (bone marrow micronucleus, and cytogenetics) assay.
Impairment of fertility
Oral administration of tizanidine resulted in reduced fertility in male and female rats following doses of 30 and 10 mg/kg/day, respectively. No effect on fertility was observed at doses of 10 (male) and 3 (female) mg/kg/day, which are approximately 8 and 3 times, respectively, the MRHD on a mg/m 2 basis).
14 CLINICAL STUDIES
Tizanidine’s capacity to reduce increased muscle tone associated with spasticity was demonstrated in two adequate and well controlled studies in patients with multiple sclerosis or spinal cord injury (Studies 1 and 2).
Single-Dose Study in Patients with Multiple Sclerosis with Spasticity
In Study 1, patients with multiple sclerosis were randomized to receive single oral doses of drug or placebo. Patients and assessors were blind to treatment assignment and efforts were made to reduce the likelihood that assessors would become aware indirectly of treatment assignment (e.g., they did not provide direct care to patients and were prohibited from asking questions about side effects). In all, 140 patients received placebo, 8 mg or 16 mg of tizanidine hydrochloride.
Response was assessed by physical examination; muscle tone was rated on a 5 point scale (Ashworth score), with a score of 0 used to describe normal muscle tone. A score of 1 indicated a slight spastic catch while a score of 2 indicated more marked muscle resistance. A score of 3 was used to describe considerable increase in tone, making passive movement difficult. A muscle immobilized by spasticity was given a score of 4. Spasm counts were also collected.
Assessments were made at 1, 2, 3 and 6 hours after treatment. A statistically significant reduction of the Ashworth score for tizanidine hydrochloride compared to placebo was detected at 1, 2 and 3 hours after treatment. Figure 2 below shows a comparison of the mean change in muscle tone from baseline as measured by the Ashworth scale. The greatest reduction in muscle tone was 1 to 2 hours after treatment. By 6 hours after treatment, muscle tone in the 8 and 16 mg tizanidine hydrochloride groups was indistinguishable from muscle tone in placebo treated patients. Within a given patient, improvement in muscle tone was correlated with plasma concentration. Plasma concentrations were variable from patient to patient at a given dose. Although 16 mg produced a larger effect, adverse events including hypotension were more common and more severe than in the 8 mg group. There were no differences in the number of spasms occurring in each group.
Figure 2: Single Dose Study—Mean Change in Muscle Tone from Baseline as Measured by the Ashworth Scale ± 95% Confidence Interval (A Negative Ashworth Score Signifies an Improvement in Muscle Tone from Baseline)
Seven-Week Study in Patients with Spinal Cord Injury with SpasticityIn a 7-week study (Study 2), 118 patients with spasticity secondary to spinal cord injury were randomized to either placebo or tizanidine hydrochloride. Steps similar to those taken in the first study were employed to ensure the integrity of blinding.
Patients were titrated over 3 weeks up to a maximum tolerated dose or 36 mg daily given in three unequal doses (e.g., 10 mg given in the morning and afternoon and 16 mg given at night). Patients were then maintained on their maximally tolerated dose for 4 additional weeks (i.e., maintenance phase). Throughout the maintenance phase, muscle tone was assessed on the Ashworth scale within a period of 2.5 hours following either the morning or afternoon dose. The number of daytime spasms was recorded daily by patients.
At endpoint (the protocol-specified time of outcome assessment), there was a statistically significant reduction in muscle tone and frequency of spasms in the tizanidine hydrochloride treated group compared to placebo. The reduction in muscle tone was not associated with a reduction in muscle strength (a desirable outcome) but also did not lead to any consistent advantage of tizanidine hydrochloride treated patients on measures of activities of daily living. Figure 3 below shows a comparison of the mean change in muscle tone from baseline as measured by the Ashworth scale.
Figure 3: Seven Week Study—Mean Change in Muscle Tone 0.5 to 2.5 Hours After Dosing as Measured by the Ashworth Scale ± 95% Confidence Interval (A Negative Ashworth Score Signifies an Improvement in Muscle Tone from Baseline)
16 HOW SUPPLIED/STORAGE AND HANDLING
16.2 Tizanidine Tablets
Tizanidine Tablets USP, 2 mg are white to off white, oval, flat, beveled edged tablets debossed with “R179” on one side and “bisecting score” on other side. The tablets are available as follows:
50268-759-15 (10 tablets per card, 5 cards per carton)
Tizanidine Tablets USP, 4 mg are white to off white, oval, flat, beveled edged tablets debossed with “R180” on one side and “quadrisecting score” on other side. The tablets are available as follows:
50268-760-15 (10 tablets per card, 5 cards per carton)
Store at 25°C (77°F); excursions permitted to 15-30°C (59-86°F) [see USP Controlled Room Temperature].
Dispensed in Unit Dose Package. For Institutional Use Only.
17 PATIENT COUNSELING INFORMATION
Serious Drug Interactions
Advise patients they should not take tizanidine hydrochloride if they are taking fluvoxamine or ciprofloxacin because of the increased risk of serious adverse reactions including severe lowering of blood pressure and sedation. Instruct patients to inform their physicians or pharmacists when they start or stop taking any medication because of the risks associated with interaction between tizanidine hydrochloride and other medicines.
Tizanidine hydrochloride Dosing
Tell patients to take tizanidine hydrochloride exactly as prescribed (consistently either with or without food) and not to switch between tablets and capsules. Inform patients that they should not take more tizanidine hydrochloride than prescribed because of the risk of adverse events at single doses greater than 8 mg or total daily doses greater than 36 mg. Tell patients that they should not suddenly discontinue tizanidine hydrochloride, because rebound hypertension and tachycardia may occur.
Effects of Tizanidine Hydrochloride
Warn patients that they may experience hypotension and to be careful when changing from a lying or sitting to a standing position. Tell patients that tizanidine hydrochloride may cause them to become sedated or somnolent and they should be careful when performing activities that require alertness, such as driving a vehicle or operating machinery. Tell patients that the sedation may be additive when tizanidine hydrochloride is taken in conjunction with drugs (baclofen, benzodiazepines) or substances (e.g., alcohol) that act as CNS depressants. Remind patients that if they depend on their spasticity to sustain posture and balance in locomotion, or whenever spasticity is utilized to obtain increased function, that Tizanidine hydrochloride decreases spasticity and caution should be used.
Pulaski, TN 38478
Mfg. Rev. 11/16
PACKAGE LABEL PRINCIPAL DISPLAY PANEL SECTION
50 Tablets (5 x 10) Unit Dose
STOP: Tizanidine Tablets are not
interchangeable with Tizanidine Capsules
Each tablet contains:
2.288 mg tizanidine hydrochloride USP,
equivalent to 2 mg tizanidine base.
Refer to package insert for prescribing
Store at controlled room temperature 15°-30°C
KEEP THIS AND ALL MEDICATION OUT OF THE
REACH OF CHILDREN.
Pulaski, TN 38478
A Product of AvKARE
Mfg. Rev. 04/12
AV 08/17 (P)
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