The pill debossed with the imprint R179 is a generic formulation of Tizanidine Hydrochloride (2 mg). It is a prescription-only skeletal muscle relaxant primarily used to manage muscle spasticity, which involves severe stiffness, cramping, or rigid muscle spasms.
Pill Identification
Before taking any medication, verifying its physical attributes ensures you are taking the correct drug and dosage.
- Imprint: R179
- Strength: 2 mg (expressed as tizanidine base)
- Color: White to off-white
- Shape: Oval / Elliptical
- Features: Flat, beveled edges. One side features the “R179” debossing, while the reverse side has a single bisecting score line, allowing it to be split into two equal 1 mg halves if required by a physician.
- Manufacturer: Par Pharmaceutical Inc. (or affiliated generic distributors)
Mechanism of Action
Tizanidine is a central alpha-2 adrenergic receptor agonist. Unlike some muscle relaxants that work directly on muscle fibers, tizanidine works directly within the central nervous system (the brain and spinal cord).
- Receptor Binding: Tizanidine binds to presynaptic adrenergic receptors in the spinal cord.
- Inhibition of Neurotransmitters: This binding increases presynaptic inhibition, effectively reducing or blocking the release of excitatory amino acids (like glutamate and aspartate).
- Reduction of Motor Neuron Activity: By reducing these excitatory signals, tizanidine calms the overactive polysynaptic pathways in the spinal cord.
- The Result: The frequency and intensity of spinal motor neuron firing decrease, which reduces muscle stiffness and spasms without entirely knocking out voluntary muscle strength.
Its chemical structure is closely related to the anti-hypertensive medication clonidine, meaning it can also inherently lower blood pressure.
Dosage and Administration
Because tizanidine has a short duration of action, it is categorized as a short-acting drug. Its effects peak roughly 1 to 2 hours after a dose and wear off within 4 to 6 hours.
- Targeted Dosing: Treatment is usually reserved for specific daily activities or times when muscle relaxation and symptom relief are most critical (e.g., before physical therapy or right before bed to prevent painful nighttime spasms).
- Typical Titration Schedule: Doctors generally start adults on a low dose of 2 mg (one R179 pill) taken up to 3 times a day. The dosage can be gradually increased by 2 mg to 4 mg at each step, based on patient response, up to a maximum single dose of 8 mg, and a maximum daily total of 24 mg.
- The Food Effect (Crucial Nuance): Food significantly changes how your body absorbs tizanidine. Taking it with a meal increases its peak concentration in your blood. Because of this, you must choose one way to take it—either consistently with food or consistently on an empty stomach. Alternating back and forth can cause sudden spikes in side effects or a drop in how well the medication works.
Side Effects
Because tizanidine suppresses certain central nervous system functions, side effects are common, dose-dependent, and usually peak within 2 to 3 hours of administration.
Common Side Effects
- Somnolence (Severe Drowsiness): Occurs in nearly half of all patients.
- Dry Mouth (Xerostomia): Extremely common; can be managed by sipping water or chewing sugarless gum.
- Dizziness and Lightheadedness
- Asthenia: Unusual tiredness or muscle weakness.
- Constipation
Serious Side Effects (Require Immediate Medical Attention)
- Severe Hypotension: A dangerous drop in blood pressure, often accompanied by fainting (syncope) or a slow heart rate (bradycardia).
- Hepatotoxicity: Liver injury or elevated liver enzymes. Signs include yellowing of the skin/eyes (jaundice), dark urine, or severe right-sided abdominal pain.
- Hallucinations or Psychosis: Seeing or hearing things that aren’t there, or experiencing severe confusion.
Warnings and Drug Interactions
Absolute Contraindications (Do Not Mix)
Tizanidine is primarily broken down in the liver by an enzyme called CYP1A2. Taking tizanidine with potent CYP1A2 inhibitors blocks this enzyme, causing tizanidine levels in the bloodstream to skyrocket dangerously. Concomitant use with the following medications is strictly contraindicated:
- Fluvoxamine (an SSRI antidepressant)
- Ciprofloxacin (a fluoroquinolone antibiotic)
Key Warnings
- Hypotension Risk: Tizanidine can cause significant drops in both systolic and diastolic blood pressure. This risk is amplified when moving quickly from a lying to a standing position (orthostatic hypotension). Caution is advised if you already take blood pressure medications.
- The Danger of Sudden Discontinuation: Never stop taking the R179 pill cold turkey if you have been taking it consistently. Sudden withdrawal can trigger a rebound effect characterized by severe hypertension (high blood pressure), tachycardia (rapid heart rate), and extreme muscle rigidity. A healthcare professional will provide a structured taper schedule to step down safely.
- Sedation: Avoid driving, operating heavy machinery, or participating in hazardous activities until you know exactly how the R179 pill affects your alertness.
Special Precautions
- Alcohol Consumption: Alcohol increases the central nervous system depressant effects of tizanidine. Drinking while taking this medication can cause profound, dangerous drowsiness and a severe drop in blood pressure.
- Reduced Muscle Tone: Because tizanidine reduces muscle tone, patients must take extra care during activities where muscle tone is relied upon to maintain physical balance and posture (such as walking up stairs).
- Liver and Kidney Disease: If you have a history of renal (kidney) insufficiency or hepatic (liver) impairment, your body will clear this drug much slower. Doctors will typically use heavily reduced initial doses and monitor liver function enzymes closely.
- Pregnancy and Breastfeeding: Tizanidine should only be used during pregnancy if the potential benefits clearly outweigh the risks to the fetus. It is currently unknown if tizanidine passes into human breast milk, so nursing mothers should exercise extreme caution.