Baclofen is used for treatment of the spasticity of spinal origin that is a common sequela of
spinal cord injury and
multiple sclerosis; spasticity occurs in about 50% of patients affected by these disorders. In open-label studies of oral
baclofen, the
drug improved spasticity in 70-87% of patients; additionally, improvement in
spasms was reported in 75-96% of patients. In double-blind, crossover, placebo-controlled trials,
baclofen was reported to be effective, producing statistically significant improvements in spasticity.
Tizanidine is the antispasticity
drug that has been most widely compared with oral
baclofen; studies have generally found the two drugs to have equivalent efficacy. However,
tizanidine has better tolerability, in particular weakness was reported to be occur less frequently with
tizanidine than with
baclofen. The main adverse effects of oral
baclofen include: sedation or
somnolence, excessive weakness,
vertigo and psychological disturbances. The incidence of adverse effects is reported to range from 10% to 75%. The majority of adverse effects are not severe; most are dose related, transient and/or reversible. The main risks of oral
baclofen administration are related to withdrawal:
seizures, psychic symptoms and
hyperthermia can occur. These symptoms improve after the reintroduction of
baclofen, usually without sequelae. When not related to withdrawal; these symptoms mainly present in patients with brain damage and in the elderly. The limited data on
baclofen toxicity in patients with renal disease suggest that administration of the
drug in these persons may carry an unnecessarily high risk. Intrathecal
baclofen is indicated for use in patients with spasticity of spinal origin unresponsive to treatment with maximum doses of oral
baclofen,
tizanidine and/or
dantrolene. The benefits of continuous intrathecal
baclofen infusion have been demonstrated: >80% and >65% of patients have improvement in tone and
spasms, respectively. The main risks of intrathecal
baclofen infusion are symptoms related to overdose or withdrawal; the latter is more important because of the associated severe effects on clinical status and the possibility of death, but it is responsive to rapid treatment. Overdose primarily arises from
drug test doses or human error during refill and programming of the pump, and withdrawal most commonly occurs as a result of a problem with the delivery system. Since the adverse consequences do not exceed the benefits of oral and intrathecal
baclofen for patients with spinal spasticity, the benefit/risk assessment is favourable.