The pill stamped with R179 is a generic form of Tizanidine Hydrochloride in a 2 mg dose. It belongs to a group of medications known as skeletal muscle relaxants and is prescribed to manage spasticity, muscle spasms, cramping, and tightness.
Physical Identification
If you need to verify this pill visually, look for the following characteristics:
- Active Ingredient: Tizanidine Hydrochloride (2 mg equivalent base)
- Imprint Code: R179 debossed on one face
- Reverse Side: Features a single bisecting score line allowing the tablet to be broken in half
- Color & Shape: White to off-white, oval shape with flat, beveled edges
- Size: Approximately 8.00 mm
- Control Class: Non-controlled prescription drug
Uses & Mechanism of Action
Primary Indications
Tizanidine is prescribed to manage increased muscle tone and muscle spasms associated with conditions such as:
- Multiple Sclerosis (MS)
- Spinal cord injuries or spinal trauma
- Traumatic brain injury or stroke-related spasticity
How It Works (Mechanism of Action)
Tizanidine is a centrally acting adrenergic receptor agonist.
Instead of acting directly on the skeletal muscles themselves, it works within the central nervous system (CNS) – primarily in the spinal cord. By stimulating central receptors, it increases presynaptic inhibition of motor neurons. This reduces the transmission of nerve signals that cause excessive muscle contraction, thereby relaxing the muscle without causing a major loss in underlying muscle strength.
Dosage & Administration
- Disclaimer: Always follow your prescribing healthcare provider’s exact instructions.
- Initial Starting Dose: Typically 2 mg orally every 6 to 8 hours as needed.
- Titration: Because tizanidine causes significant drowsiness and drops in blood pressure, doctors usually start at 2 mg and gradually increase the dose by 2 mg to 4 mg at a time, spaced over several days or weeks.
- Maximum Dose: Peak effect occurs 1 to 2 hours after a dose and dissipates between 3 to 6 hours. The maximum recommended daily dose is generally 36 mg in a 24-hour period (and no single dose should exceed 8 mg to 12 mg).
Crucial Note on Food (Pharmacokinetics)
Food significantly affects how your body absorbs tizanidine. Taking the tablet with food increases the overall exposure (AUC) and peak absorption rate compared to taking it on an empty stomach.
- Rule: Pick one method – always take it with food, or always take it without food. Do not alternate back and forth, as this will lead to unpredictable swings in drug effectiveness and side effects.
Potential Side Effects
While tizanidine is effective at relieving painful spasms, its central action leads to noticeable sedative effects.
Category – Common Side Effects
- Most Common (>10%) – Extreme drowsiness (somnolence), sedation, dizziness, dry mouth, fatigue, and general weakness (asthenia).
- Gastrointestinal – Constipation, nausea, vomiting, or mild stomach upset.
- Cardiovascular – Low blood pressure (hypotension) and abnormally slow heart rate (bradycardia).
- Other – Mild confusion, nervousness, or urinary frequency/tract inflammation. |
Critical Warnings & Contraindications
Major Drug Interaction: Contraindicated Medications
Tizanidine is metabolized in the liver by the enzyme CYP1A2. Drugs that strongly block this enzyme slow down tizanidine’s breakdown, causing severe toxicity, extreme low blood pressure, and profound sedation.
DO NOT take tizanidine if you are taking:
- Fluvoxamine (an SSRI antidepressant)
- Ciprofloxacin (a fluoroquinolone antibiotic)
Low Blood Pressure & Fainting (Orthostatic Hypotension)
Because tizanidine is structurally related to the blood pressure drug clonidine, it causes a drop in blood pressure. Getting up too fast from a lying or sitting position can lead to severe dizziness, lightheadedness, or fainting (syncope). Always stand up slowly.
Liver Toxicity
Tizanidine can cause hepatocellular liver injury. Doctors will often check liver function tests (ALT/AST) before starting the medication and periodically during treatment (especially during the first month). Contact a physician immediately if you experience yellowing skin/eyes (jaundice), dark urine, upper-right stomach pain, or unexplained nausea/vomiting.
Hallucinations & Psychosis
Visual hallucinations or vivid visual disturbances occur in approximately 3% of patients taking tizanidine. If you see things that are not there, stop the drug and contact your prescriber.
Rebound Effect (Do Not Stop Abruptly)
If you have been taking tizanidine regularly at higher doses, do not stop taking it suddenly. Sudden withdrawal can trigger a rebound reaction characterized by high blood pressure (hypertension), tachycardia (rapid heart rate), hypertonia (severe muscle tightness), and tremors. Doses must be tapered down slowly under medical supervision.
General Precautions
- Driving & Heavy Machinery: Due to severe sedation and impaired reflexes, avoid driving, operating machinery, or performing dangerous tasks until you know how the 2 mg dose affects you.
- Alcohol & Central Nervous System Depressants: Avoid alcohol, opioids, sleep aids, or tranquilizers while taking tizanidine. They have an additive effect that can cause dangerous respiratory depression or loss of consciousness.
- Kidney Impairment: People with reduced renal function clear the drug much slower. Smaller initial doses and careful monitoring are required.
- Pregnancy & Breastfeeding: Tizanidine should only be used during pregnancy if the benefit outweighs potential fetal risk. It is unclear if tizanidine passes into breast milk, so consult your doctor before nursing.