Intrathecal baclofen is costly. Although useful, it should be considered only for patients with severe functional limitations who have not responded satisfactorily to other therapeutic options.
A pump with a reservoir is surgically implanted in the subcutaneous tissue or subfascial tissue on the abdominal wall. A catheter is threaded into the subarachnoid space, delivering baclofen directly into the cerebrospinal fluid. This allows as much as four times the level of drug to be delivered at only 1% of the oral dose. Keeping serum levels low reduces unwanted cerebral side effects, such as lethargy.
Penn et al.92 conducted a double-blind, placebo-controlled 3-day crossover study in 20 patients—10 with MS and 10 with spinal cord injury. All patients had decreased muscle tone and frequency of spasms while being treated with baclofen. All patients were subsequently enrolled in a long-term open trial of continuous baclofen infusion, with a mean follow-up period of 19 months. Using a standardized scale to assess spasticity, these researchers found that all patients exhibited normal tone and that spasm frequency was diminished to the point that spasms no longer interfered with activities of daily living.93 In 7 of 8 patients, bladder function also improved.92
In cerebral palsy (CP), intrathecal baclofen can effectively treat spasticity in two groups:
The efficacy and tolerability of continuous intrathecal infusion of baclofen can be tested by administering a trial bolus of baclofen by intrathecal injection.99,100 In studies of CP patients, intrathecal baclofen injections in the 25- to 100-µg range led to significant reductions in muscle tone within 2 hours. The effects persisted for 6 hours. Long-term follow-up in CP patients revealed that spasticity remains almost 50% improved after more than 3 years of continuous intrathecal baclofen therapy.101
After a patient undergoes a trial of intrathecal baclofen to establish responsiveness, pump implantation can be considered. Starting doses are 25 µg per day, up to an average of 400–500 µg per day, although doses as high as 1,500 µg per day have been reported.105 The half-life of intrathecal baclofen is approximately 5 hours. Many patients require dose increases in the first 6 months, owing to tolerance.106,107
Most side effects tend to occur during the titration phase. They include drowsiness, headache, nausea, weakness, and hypotension. Overdose can produce reversible coma.108
Other complications may be due to mechanical problems (dislodgment, disconnection, kinking, blockage), pump failure, or infection.
Intrathecal baclofen may improve medically refractory dystonia. Continuous intrathecal baclofen infusion was used with modest success in a case of hereditary generalized dystonia refractory to multiple medications and thalamotomy.102 After pump implantation, baclofen dosage was gradually increased to 450 µg per day. The patient displayed significant improvement on the right side of her body and moderate improvement on the left side.
On an average daily dose of 575 µg per day of intrathecal baclofen, 10 of 12 patients with generalized dystonia had significant reduction in scores for overall dystonia and dystonia in the extremities, trunk, and cervical regions.103 One-year follow-up studies of dystonic patients support the long-term efficacy of intrathecal baclofen for dystonia.104
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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