Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Do not operate heavy machinery or drive until you know how this medication affects you.
Identifying the "U 12" Pill
The blue, round pill with the imprint "U" on one side and "12" on the other is identified as Cyclobenzaprine Hydrochloride. It is manufactured by Unichem Pharmaceuticals (USA), Inc. and is classified as a skeletal muscle relaxant. This medication is available only by prescription and is not a federally controlled substance. The pill is typically 7mm in size. The specific strength associated with this imprint is 10 mg.
Primary Uses and Mechanism of Action
Cyclobenzaprine is prescribed as a short-term treatment for muscle spasms associated with acute, painful musculoskeletal conditions. It is intended to be used as an adjunct to rest and physical therapy to relieve pain, tenderness, and stiffness, thereby improving mobility.
Unlike pain relievers that work directly at the site of injury, cyclobenzaprine is a centrally acting muscle relaxant. It works primarily within the central nervous system (CNS), specifically at the brain stem level, to reduce tonic somatic motor activity. This action helps to relieve skeletal muscle spasms of local origin without interfering with overall muscle function. It is important to note that this medication is not effective for muscle spasms caused by central nervous system diseases, such as cerebral palsy.
How to Take Cyclobenzaprine (U 12)
Cyclobenzaprine should be taken exactly as prescribed by a healthcare provider. This medication should only be used for short periods, typically two to three weeks, as its effectiveness for longer use has not been established. The tablets can be taken with or without food. Abruptly stopping the medication after prolonged use can lead to withdrawal symptoms like nausea, headache, and malaise, so a doctor may recommend a gradual dose reduction.
Potential Side Effects and Warnings
Like all medications, cyclobenzaprine has potential side effects. The most common ones are related to its CNS depressant effects.
Common Side Effects
The most frequently reported side effects include:
- Drowsiness: Affects between 29% and 38% of patients.
- Dry Mouth: Reported in 21% to 32% of patients.
- Dizziness:
- Fatigue:
- Headache:
Because cyclobenzaprine can significantly impair mental and physical abilities, patients should avoid driving, operating heavy machinery, or performing other hazardous tasks until they know how the drug affects them.
Serious Warnings and Precautions
There are several serious risks associated with cyclobenzaprine:
- Serotonin Syndrome: A potentially life-threatening condition can occur when cyclobenzaprine is taken with other serotonergic drugs like SSRIs, SNRIs, TCAs, and MAO inhibitors. Symptoms include agitation, hallucinations, rapid heart rate, fever, and muscle stiffness. Immediate medical care is required if these symptoms occur.
- Cardiac Issues: Because cyclobenzaprine is structurally similar to tricyclic antidepressants, it may cause arrhythmias, sinus tachycardia, and other cardiac events. It is contraindicated in patients in the acute recovery phase of a myocardial infarction and those with arrhythmias, heart block, or congestive heart failure.
- Interaction with CNS Depressants: The effects of alcohol, barbiturates, and other CNS depressants are enhanced by cyclobenzaprine, increasing the risk of severe drowsiness and impaired coordination.
Drug Interactions to Be Aware Of
Cyclobenzaprine has significant interactions with several classes of drugs. It should not be used concomitantly with or within 14 days of taking Monoamine Oxidase (MAO) inhibitors, as this combination can lead to hyperpyretic crisis, seizures, and even death. It can also enhance the effects of other CNS depressants and may block the antihypertensive action of certain medications like guanethidine. Patients must inform their doctor of all prescription, over-the-counter, and herbal products they are taking before starting cyclobenzaprine.
For more detailed drug information, you can visit the DailyMed page for Cyclobenzaprine Hydrochloride.
Cyclobenzaprine vs. Other Muscle Relaxants
| Feature | Cyclobenzaprine (Flexeril) | Baclofen (Lioresal) | Tizanidine (Zanaflex) |
|---|---|---|---|
| Mechanism | Acts primarily at the brain stem to reduce tonic motor activity. | Acts at the spinal cord level; a GABA-B agonist. | A centrally-acting alpha-2 adrenergic agonist. |
| Primary Use | Acute, painful musculoskeletal spasms. | Spasticity from multiple sclerosis or spinal cord injury. | Spasticity from multiple sclerosis or spinal cord injury. |
| Common Side Effects | Drowsiness, dry mouth, dizziness. | Drowsiness, weakness, dizziness. | Drowsiness, dry mouth, dizziness, low blood pressure. |
| Duration of Use | Short-term (2-3 weeks). | Can be used long-term. | Can be used long-term. |
| Abuse Potential | Not a controlled substance. | Can cause withdrawal; tapering is required. | Can cause withdrawal; tapering is required. |
Important Considerations for Specific Populations
- Elderly Patients (≥65): The elderly are more susceptible to CNS side effects like hallucinations, confusion, and cardiac events, which can lead to falls. Plasma concentrations of the drug are generally higher in this group. Treatment should be initiated with the lowest effective dose and titrated slowly as needed.
- Patients with Hepatic Impairment: Cyclobenzaprine is extensively metabolized by the liver. In patients with mild hepatic impairment, a lower starting dose should be considered, and it should be used with caution. It is not recommended for patients with moderate to severe hepatic impairment.
- Pregnancy and Nursing: There are no adequate and well-controlled studies in pregnant women. It should be used during pregnancy only if clearly needed. It is not known if cyclobenzaprine is excreted in human milk, so caution should be exercised when administered to a nursing woman.
- Pediatric Use: Safety and effectiveness in patients below 15 years of age have not been established.
Conclusion
The blue round pill imprinted with U 12 is Cyclobenzaprine Hydrochloride, a prescription skeletal muscle relaxant. It is effective for short-term relief of muscle spasms from acute injuries when used with rest and physical therapy. Its primary mechanism involves depressing the central nervous system, which leads to common side effects like drowsiness and dizziness. Due to its potential for serious drug interactions, particularly with MAO inhibitors and other CNS depressants, and risks for specific populations like the elderly, it is crucial to use this medication only under the guidance of a healthcare professional.
