PHARMACOLOGY

Pharmacotherapeutic Group:  Muscle relaxants, alpha₂ adrenergic agonist

Pharmacodynamic properties: Tizanidine a α₂ adrenergic agonist is a centrally acting muscle relaxant structurally related to clonidine. It reduces spasticity by increasing presynaptic inhibition of motor neurons and has no direct effect on skeletal muscle, the neuromuscular junction or on monosynaptic spinal reflexes.

Pharmacokinetic properties:

Absorption: Absorbed from the GI tract (oral); Peak plasma concentrations: 1-2 hour, Bioavailability: 40%

Distribution: Protein binding: 30% .Elimination half-life: 2-4 hr

Metabolism: Extensive hepatic first pass metabolism mainly via the CYP 450 isoenzyme CYP1A2.

Elimination: Via urine (mainly as inactive metabolites)

INDICATIONS

Migraine, back pain, spasm, multiple sclerosis, cramps, injury, spasticity

 DOSE

 Spasticity
Adult: >18 years: Initially, 2 mg once daily increased according to response by 2 mg increments at intervals of at least 3-4 days up to 24 mg daily in 3-4 divided doses. Max: 36 mg/day 

Painful muscle spasm associated with musculoskeletal conditions.

Adult: >18 year: 2-4 mg tid

CONTRAINDICATIONS

Hypersensitivity, concomitant ciprofloxacin or fluvoxamine or other potent CYP1A2 inhibitors.

 SPECIAL PRECAUTIONS

Hepatic or renal insufficiency. Children, elderly, pregnancy and lactation. Monitor LFT regularly. Stop treatment if liver enzymes are raised persistently >3 times upper limit of normal range. Avoid abrupt withdrawal of therapy.

 ADVERSE DRUG REACTIONS

Severe AEs: Hepatitis

Common AEs: Drowsiness, fatigue, dizziness, insomnia, headache, anxiety, nausea, dryness of mouth, GI disturbances, hypotension, bradycardia, muscle pain and weakness, transient increase in serum transaminases, hallucinations.

 DRUG INTERACTIONS

Potentiates hypotensive effect of antihypertensives. Increased CNS effects with alcohol and CNS depressants. Increased bradycardia with β-blockers and digoxin. Increased serum concentration of tizanidine with CYP1A2 inhibitors.

 PRESENTATION

Each box is supplied with 10 strips of 10 tabs packed in blisters.