What muscle relaxant is safer for older adults with potential impaired renal function or other comorbidities?

From the Guidelines

Muscle relaxants like metaxalone should be used with caution in older adults due to potential central nervous system adverse effects, and alternative options should be considered. When selecting a muscle relaxant for older adults, it is essential to weigh the benefits and risks, prioritizing medications with a safer profile 1.

Key Considerations

• Metaxalone has multiple central nervous system adverse effects, including drowsiness, dizziness, and irritability 1, which can be particularly problematic in older adults.
• Older adults are more susceptible to side effects, including increased fall risk, and medications like metaxalone may exacerbate these risks.
• Non-pharmacological approaches, such as physical therapy, gentle stretching, heat therapy, and appropriate rest, should be tried first to minimize the need for medication.

Safer Alternatives

• While specific safer alternatives are not mentioned in the provided study 1, other muscle relaxants like cyclobenzaprine or methocarbamol may be considered, with careful attention to dosing and duration of use.
• It is crucial to start with the lowest possible dose and use these medications for the shortest duration possible, ideally less than 1-2 weeks, to minimize potential side effects.

Important Precautions

• Older adults should always check with their healthcare provider about potential interactions with their existing medications before starting any muscle relaxant.
• Medications should be taken at bedtime to help minimize daytime sedation, and patients should be closely monitored for signs of adverse effects.

From the FDA Drug Label

Age Effects: No specific pharmacokinetic study was conducted to investigate age effects. Cross study comparison of pharmacokinetic data following single dose administration of 6 mg tizanidine showed that younger subjects cleared the drug four times faster than the elderly subjects Tizanidine clearance is reduced by more than 50% in elderly patients with renal insufficiency (creatinine clearance < 25 mL/min) compared to healthy elderly subjects; this would be expected to lead to a longer duration of clinical effect. Tizanidine should be used with caution in renally impaired patients

The muscle relaxor tizanidine may not be safer for older adults due to reduced clearance, which can lead to a longer duration of clinical effect. Key considerations for older adults include:

• Renal insufficiency: Tizanidine clearance is reduced by more than 50% in elderly patients with renal insufficiency.
• Caution: Tizanidine should be used with caution in renally impaired patients 2.

From the Research

Muscle Relaxants for Older Adults

• The use of skeletal muscle relaxants (SMRs) among older adults is associated with sedation and confusion, which may lead to an increased risk of falls and injuries 3.
• A study found that older adults using SMRs have an increased risk of injury, with carisoprodol, methocarbamol, and cyclobenzaprine being associated with a higher risk of injury compared to no use 3.
• Another study found that cyclobenzaprine has the most recent and largest clinical trials demonstrating its benefit, but carisoprodol and metaxalone also appear to be effective, although carisoprodol's usefulness is mitigated by its potential for abuse 4.

Safety of Specific Muscle Relaxants

• Tizanidine is associated with more dry mouth, while baclofen is associated with more weakness 5.
• Dantrolene and chlorzoxazone have been associated with rare serious hepatotoxicity 5.
• Cyclobenzaprine has been found to have a higher risk of adverse medication effects compared to placebo 6.
• Co-prescription of strong CYP1A2 inhibitors and tizanidine increases the risk of tizanidine-associated hypotension 7.

Efficacy of Muscle Relaxants

• There is fair evidence that baclofen, tizanidine, and dantrolene are effective compared to placebo in patients with spasticity 5.
• Cyclobenzaprine, carisoprodol, orphenadrine, and tizanidine are effective compared to placebo in patients with musculoskeletal conditions 5.
• However, a study found that SMRs do not improve outcomes more than placebo in patients with acute low back pain, regardless of age, sex, and baseline severity 6.