The white pill stamped with the imprint R180 is identified as Tizanidine Hydrochloride 4 mg. Manufactured by Dr. Reddy’s Laboratories (and distributed by various pharmaceutical vendors), it is the generic equivalent of the brand-name skeletal muscle relaxant Zanaflex.
Physical Identification
Characteristic Specification
- Imprint Code –
R180(debossed on one side) - Scoring – Quadrisecting score (cross score dividing it into 4 equal 1 mg quarters) on the reverse
- Active Ingredient – Tizanidine Hydrochloride (4 mg tizanidine base)
- Color – White to off-white
- Shape – Oval / Elliptical (flat, beveled edge)
- Size – Approximately 11 mm
- Drug Class – Centrally acting adrenergic receptor agonist / Skeletal muscle relaxant
- Controlled Status – Non-controlled prescription drug (Rx required)
Mechanism of Action
Tizanidine works as a centrally acting adrenergic receptor agonist in the central nervous system (CNS):
- Presynaptic Inhibition: Tizanidine selectively binds to pre-synaptic adrenergic receptors in the spinal cord.
- Reduction of Excitatory Amino Acids: By stimulating these receptors, it reduces the release of excitatory amino acids (such as glutamate and aspartate) from spinal interneurons.
- Polysynaptic Pathway Suppression: This action increases presynaptic inhibition of motor neurons, specifically targeting polysynaptic spinal pathways.
- Muscle Tone Reduction: The overall effect reduces hyperactive spinal reflexes and muscle tone without directly weakening skeletal muscle fibers or disrupting the neuromuscular junction.
Because its chemical structure is related to the antihypertensive drug clonidine, tizanidine also exhibits mild blood-pressure-lowering (hypotensive) properties.
Indications & Clinical Dosing
Indications
Tizanidine is FDA-approved for the management of spasticity—a condition characterized by stiff, rigid, or involuntary muscle spasms resulting from spinal cord injury, multiple sclerosis (MS), or acquired brain injuries.
Dosing Guidelines
Because tizanidine has a short duration of effect (peak concentrations occur around 1.5 hours and drop rapidly), dosing is titrated to manage spasms during specific functional activities.
- Initial Starting Dose: 2 mg to 4 mg taken orally as a single dose.
- Titration Schedule: Doses may be increased gradually by 2 mg to 4 mg per dose at intervals of 1 to 4 days until satisfactory reduction of spasticity is achieved.
- Frequency: Can be repeated every 6 to 8 hours as needed, up to a maximum of 3 doses in 24 hours.
- Maximum Daily Limit: Do not exceed 36 mg in a single 24-hour period.
- Food Effect Warning: Capsules and tablets react differently to food. Food can significantly increase the peak concentration and rate of absorption of tizanidine tablets. It is critical to maintain a consistent routine – either always take the tablet with food or always take it on an empty stomach.
Side Effects
Because tizanidine acts directly on the CNS and vascular receptors, side effects are common, particularly at higher doses.
Most Common Side Effects
- Somnolence / Sedation: Extreme drowsiness occurs in up to 45%–90% of patients depending on the dosage.
- Dry Mouth (Xerostomia): Experienced by over 70% of users.
- Asthenia: Unexplained weakness, tiredness, or loss of energy.
- Dizziness & Lightheadedness: Often tied to postural blood pressure drops.
Serious Adverse Effects
- Severe Hypotension (Low Blood Pressure) & Bradycardia: Significant drops in blood pressure, fainting (syncope), or slowed heart rate.
- Hepatotoxicity (Liver Damage): Tizanidine can cause hepatocellular liver injury. Monitoring of liver function enzymes (AST/ALT) is typically required at baseline and periodic intervals.
- Hallucinations / Psychosis: Visual or auditory hallucinations or confusion can occur, particularly in elderly patients.
- Severe Hypersensitivity: Anaphylaxis, hives, facial swelling, or severe skin eruptions (e.g., Stevens-Johnson syndrome).
Precautions & Contraindications
Absolute Contraindications
- Concomitant Strong CYP1A2 Inhibitors: Tizanidine is strictly contraindicated with potent inhibitors of the liver enzyme CYP1A2, notably fluvoxamine (Luvox) and ciprofloxacin (Cipro). Combining these dramatically raises tizanidine serum levels (AUC increases up to 33-fold), causing profound hypotension, severe sedation, and motor impairment.
- Known Hypersensitivity: History of allergic reaction to tizanidine or any of the tablet’s inactive components (e.g., anhydrous lactose).
Major Warnings & Precautions
- Withdrawal Hyper-Rebound: Stopping tizanidine abruptly – especially after prolonged use or high daily doses – can cause rebound hypertension, tachycardia, hypertonia, and tremors. Doses must be tapered gradually (by 2 mg to 4 mg per day) under medical supervision.
- Hepatic Impairment: Exercise extreme caution in patients with preexisting liver disease, as tizanidine clearance is significantly reduced.
- Renal Impairment: Patients with renal insufficiency clear the drug more slowly and require lower individual doses with careful blood pressure monitoring.
- Central Nervous System Depressants: Concomitant use with alcohol, benzodiazepines, opioids, or sedatives produces additive CNS depression and respiratory risks.
Safety & Pill Verification Notice
If you possess a white oval pill stamped R180 with a cross-score on the back, verify its appearance carefully before handling. Do not take unverified prescription medications or adjust muscle relaxant dosages without consulting a licensed physician or pharmacist.