Is an intramuscular injection with Voltaren (diclofenac) and Muscoril (cyclobenzaprine) safe?

Safety of Intramuscular Injection with Voltaren and Muscoril

Intramuscular (IM) co-administration of Voltaren (diclofenac) and Muscoril (cyclobenzaprine) is not recommended due to safety concerns including risk of tissue necrosis, cardiovascular events, and lack of evidence supporting this combination.

Risks of Intramuscular Diclofenac (Voltaren)

Serious Local Complications

• IM diclofenac has been associated with severe tissue necrosis at injection sites
• Cases of necrotizing fasciitis have been reported following IM diclofenac injections, with some resulting in death 1
• Streptococcal myositis with extensive muscle necrosis has occurred after IM diclofenac administration 2

Systemic Risks

• NSAIDs including diclofenac carry cardiovascular risks including thrombotic events, myocardial infarction, and stroke 3
• Anaphylactic reactions, though rare, have been reported after IM diclofenac administration 4
• The FDA requires a black box warning for all NSAIDs including diclofenac regarding cardiovascular and gastrointestinal risks 3

Alternative Administration Routes

Oral Administration

• Oral diclofenac is effective for pain management with fewer injection-related complications
• A study comparing IM vs oral diclofenac showed that while IM provides more rapid analgesia, oral administration may be preferable when circumstances allow 5
• The number needed to treat is 8 cases receiving IM rather than oral diclofenac to achieve one additional case of 50% pain reduction within 30 minutes 5

Recommended Approach for Pain Management

• For acute pain requiring immediate relief, consider:
  1. Oral diclofenac as first-line when possible
  2. If parenteral administration is necessary, IV diclofenac is preferred over IM due to lower risk of tissue necrosis 6
  3. For severe pain requiring IM administration, use proper technique and avoid mixing medications in the same syringe

Specific Concerns with Muscoril (Cyclobenzaprine)

• No guidelines support the co-administration of cyclobenzaprine with diclofenac via IM route
• Mixing medications in the same injection increases risk of:
  • Local reactions
  • Chemical incompatibility
  • Altered drug absorption rates
  • Increased risk of tissue damage

Evidence-Based Recommendations

1. Avoid IM administration when possible

   • Guidelines strongly recommend against intramuscular glucocorticosteroids for conditions like allergic rhinitis due to potential serious side effects 3
   • This caution can be extended to other IM medications when alternatives exist

2. If parenteral administration is necessary:

   • Consider IV diclofenac when available and appropriate
   • Administer medications separately if both must be given parenterally
   • Use proper injection technique to minimize tissue damage

3. Monitor for complications:

   • Watch for signs of tissue necrosis, infection, or systemic reactions
   • Severe pain at injection site may be an early warning sign of tissue damage

Conclusion

While diclofenac can be effective for pain management via multiple routes, the IM administration carries significant risks including tissue necrosis. Co-administration with Muscoril via the same IM injection is not supported by evidence and may increase risks. Oral administration of both medications separately is a safer alternative when appropriate for the clinical situation.