Diazepam Classification: Antispastic Agent
Diazepam is classified as an antispastic agent, not an antispasmodic agent. 1, 2, 3
Understanding the Distinction
The classification of muscle relaxants falls into two distinct categories that are often confused in clinical practice:
Antispastic Agents
- Diazepam belongs to this category as a benzodiazepine that acts through the GABAergic system to reduce muscle hypertonicity and involuntary jerks caused by upper motor neuron disorders 2, 3
- The FDA specifically indicates diazepam for "spasticity caused by upper motor neuron disorders (such as cerebral palsy and paraplegia), athetosis, and stiff-man syndrome" 1
- Other antispastic agents include baclofen, tizanidine, and dantrolene sodium 2, 3
- These drugs work centrally to suppress excitation or enhance inhibition in the CNS 2
Antispasmodic Agents
- This separate category includes drugs like cyclobenzaprine, carisoprodol, chlorzoxazone, metaxalone, and methocarbamol 3, 4
- Antispasmodics are primarily used for acute musculoskeletal conditions and "reflex spasm to local pathology (such as inflammation of the muscles or joints, or secondary to trauma)" 1
- These agents do not directly relax skeletal muscle despite their common name "muscle relaxants" 5
Clinical Implications of This Classification
When Diazepam Is Appropriate
- Upper motor neuron disorders causing spasticity (cerebral palsy, paraplegia, multiple sclerosis) 1, 2
- Acute alcohol withdrawal with tremor and agitation 1
- Adjunctive treatment in convulsive disorders 1
Critical Limitations and Warnings
- Diazepam should be avoided during stroke recovery due to deleterious effects on neurological recovery 6, 7
- The FDA states "the effectiveness of diazepam in long-term use, that is, more than 4 months, has not been assessed by systematic clinical studies" 1
- Clinical trials in spasticity typically lasted only 5-14 days, with evidence showing inconsistent benefits even in the short term 5, 8
- For acute radiculopathy, diazepam was actually less effective than placebo (41% vs 79% achieving ≥50% pain relief) 5
Preferred Alternatives Based on Indication
- For focal spasticity: Botulinum toxin is superior to diazepam and should be first-line 6, 7
- For generalized spasticity: Baclofen, tizanidine, or dantrolene are preferred over benzodiazepines 6, 7, 2
- For acute musculoskeletal pain: Non-benzodiazepine muscle relaxants have better evidence than diazepam 5
- For neuropathic pain: Gabapentinoids (pregabalin, gabapentin) are first-line, not benzodiazepines 5
Common Pitfall to Avoid
The most critical error is prescribing diazepam as if it were an antispasmodic for acute musculoskeletal conditions when it is actually an antispastic agent indicated for upper motor neuron disorders 1, 2, 3. This misclassification leads to inappropriate use, increased risk of CNS adverse effects (sedation, dizziness, drowsiness), and potential for dependence without addressing the underlying pathology 5, 4.