Indications

Baclofen is a muscle relaxant and antispasmodic that acts on the nerves of the spinal cord to reduce the number and severity of muscle spasms caused by multiple sclerosis or spinal cord disease. It also relieves pain and improves muscle movement. Baclofen has been approved by the FDA for the treatment of pain and certain types of spasticity states (muscle stiffness and tightness) caused by multiple sclerosis, spinal cord injuries, or other spinal cord disorders. It is also used to treat spasticity caused by trauma to the central nervous system through intrathecal administration.

In addition, studies have shown that Baclofen is also helpful in improving conditions such as trigeminal neuralgia, GERD, intractable eructation, paediatric patients with spasticity states associated with cerebral palsy, and nocturnal calf pain spasms associated with lumbar spinal stenosis.

Mechanism of Action

Baclofen is a GABA B agonist. It has been shown that when Baclofen binds to GABA B receptors, it causes hyperpolarisation of neuronal membranes, reduces calcium influx into presynaptic nerve endings and stimulates inhibitory neuronal signalling in postsynaptic neurons, thereby relieving spasticity. In addition, it may act by decreasing the action potential of postsynaptic motor neurons, which in turn inhibits neuronal signalling.

Dosage

Baclofen is available in oral tablets (5 mg, 10 mg, 20 mg) and liquid solution (5 mg/5 mL). Adults typically start with 5 mg three times a day, increasing to 20 mg three times daily. Intrathecal administration begins with a 50 μg test dose, with the effective dose doubled for long-term implantable pump therapy, adjusted based on spasticity origin. Spinal cord spasticity may require 300 to 800 μg daily, while cerebral spasticity is managed with 90 to 703 μg daily. Children's dosing is determined by weight or age. The maximum oral daily dose should not exceed 80 mg.

Side Effects

Baclofen, a muscle relaxant, can cause common side effects in more than 1 in 100 people, such as sleepiness, fatigue, dizziness, weakness, nausea, vomiting, diarrhea, headaches, sleep disturbances, dry mouth, and visual issues like rapid eye movements, blurred vision, or difficulty focusing. It may also lead to excessive sweating, mild rashes, increased urination, and urinary discomfort. Serious side effects, although rare, can affect multiple organ systems and include liver problems (yellowing of the skin or eyes), sleep apnea, and increased muscle spasms. Discontinuation of intrathecal baclofen after prolonged use can lead to serious complications ( Baclofen Withdrawal Syndrome) including hyperthermia, tachycardia, hypertension, seizures, altered mental status and psychomotor agitation..

Less commonly, baclofen can cause neuropsychiatric impairment, hypotension, peripheral edema, dyspnea, hypoventilation, pneumonia, seizures, insomnia, pain, speech alterations, depression, agitation, constipation, diarrhea, changes in urinary frequency, incontinence, impotence, tremors, weakness, amblyopia, urticaria, and itching. Sudden cessation of oral baclofen may result in seizures or hallucinations, so a gradual dose reduction is advised. Patients with a history of stroke may not tolerate baclofen well and may not benefit significantly from its use. It is crucial to consult a healthcare professional if side effects persist or worsen.

References:

[1] MICHAEL I GREENBERG; Robert G H. Baclofen withdrawal following removal of an intrathecal baclofen pump despite oral baclofen replacement.[J]. Journal of toxicology. Clinical toxicology, 2003. DOI:10.1081/clt-120018277.

[2] G H FROMM; C F T. Comparison of L-baclofen and racemic baclofen in trigeminal neuralgia.[J]. Neurology, 1987. DOI:10.1212/wnl.37.11.1725.