Muscle Relaxants
Key Points
- Skeletal muscle relaxants reduce muscle spasm and spasticity through CNS-mediated mechanisms.
- Two categories: antispasticity agents (baclofen, tizanidine) for neurological conditions, and antispasm agents (cyclobenzaprine) for acute musculoskeletal injury.
- All cause CNS depression — drowsiness, dizziness, and orthostatic hypotension are common.
- Baclofen must not be stopped abruptly — hallucinations and seizures can result.
Pathophysiology
Spasticity results from upper motor neuron lesions (multiple sclerosis, spinal cord injury, stroke) disrupting normal inhibitory control of lower motor neurons. Antispasticity drugs act within the CNS to reduce this excessive motor neuron activity.
Acute muscle spasm (injury, strain) results from peripheral muscle overuse or injury. Antispasm drugs like cyclobenzaprine act on the brainstem to reduce this tonic activity.
Classification
| Type | Drug | Primary Mechanism | Key Indication |
|---|---|---|---|
| Antispasticity | Baclofen | Inhibits spinal cord reflex arcs (GABA-B agonist) | Multiple sclerosis, spinal cord injury |
| Antispasticity | Tizanidine | Alpha-2 adrenergic agonist → presynaptic inhibition | Spasticity (increased muscle tone) |
| Antispasm | Cyclobenzaprine (Flexeril) | Reduces tonic somatic activity at brainstem | Acute musculoskeletal pain/spasm |
Nursing Assessment
NCLEX Focus
All muscle relaxants cause CNS depression. Assess fall risk, baseline mental status, and blood pressure before administration. Do not give with alcohol or other CNS depressants.
- Assess baseline muscle tone, spasticity severity, and pain level.
- Assess gait stability and fall risk — all agents cause sedation and dizziness.
- Assess blood pressure and orthostatic changes (all agents → orthostatic hypotension).
- Assess renal function before baclofen (renally excreted — reduce dose if impaired).
- Assess hepatic function before tizanidine (hepatotoxicity risk).
- Screen for concurrent CNS depressants, alcohol use, and antidepressant use (cyclobenzaprine).
Nursing Interventions
- Administer oral agents with food or milk if GI upset occurs.
- Instruct patient to rise slowly to standing to prevent orthostatic hypotension.
- Warn against driving or operating machinery during initial treatment.
- Do NOT stop baclofen abruptly — taper gradually to prevent withdrawal seizures and hallucinations.
- Do NOT stop amantadine or cyclobenzaprine abruptly — report behavioral changes.
- Counsel patients to avoid alcohol and other CNS depressants.
Baclofen Abrupt Withdrawal
Abrupt discontinuation of baclofen can cause life-threatening withdrawal: hallucinations, high fever, muscle rigidity, and seizures. Always taper dose gradually under provider supervision.
Pharmacology
| Drug | Key Nursing Considerations |
|---|---|
| Baclofen | Do not stop abruptly (seizures, hallucinations); renally excreted (reduce dose if CrCl impaired); monitor for confusion and muscle weakness; intrathecal route requires close monitoring |
| Cyclobenzaprine (Flexeril) | Structurally similar to TCAs; contraindicated with MAOIs; serotonin syndrome risk with SSRIs/SNRIs; use cautiously in elderly (5 mg starting dose); for acute use only (≤2–3 weeks) |
| Tizanidine | Monitor LFTs (hepatotoxicity); causes bradycardia and hypotension; avoid alcohol; geriatric dosage adjustment needed |
Clinical Judgment Application
Clinical Scenario
A patient with multiple sclerosis has been taking baclofen 20 mg three times daily and was recently prescribed a different antispasticity agent. The patient asks if they can just stop the baclofen today.
- Recognize Cues: Patient attempting abrupt discontinuation of baclofen.
- Analyze Cues: Abrupt baclofen withdrawal can cause seizures and hallucinations — this is a safety priority.
- Prioritize Hypotheses: Withdrawal risk requires immediate education to prevent life-threatening outcome.
- Generate Solutions: Explain necessity of tapering; contact provider for a tapering schedule.
- Take Action: Instruct patient not to stop abruptly; document and notify provider; create a tapering plan.
- Evaluate Outcomes: Patient tapers safely without withdrawal symptoms.
Related Concepts
- common-neurological-disorders-recognition-and-priority-care — MS and spinal cord injuries are primary indications.
- fall-prevention — CNS depression and orthostatic hypotension increase fall risk with muscle relaxants.
- pain-management — Muscle relaxants as adjuncts in multimodal pain management.
- nursing-care-priorities-for-neuromuscular-impairment — Spasticity management within the broader neuromuscular care framework.
Self-Check
- What is the key difference between a drug used for spasticity versus one used for acute muscle spasm?
- Why is baclofen contraindicated for abrupt discontinuation?
- What drug interaction risk must the nurse assess before administering cyclobenzaprine?