Adverse effects most frequently occur at the start of treatment, particularly if the dosage is increased to rapidly, if large doses are administered, and in the elderly patient. However, these effects are often transient and can be alleviated or eliminated by decreasing the dosage; they are seldom severe enough to warrant withdrawal of the medication. In elderly patients or those patients with cerebrovascular disorder or a history of psychiatric illness, more serious adverse reactions may occur, such as hallucinations and confusion.
The most common adverse reactions associated with baclofen are transient drowsiness, daytime sedation, dizziness, weakness and fatigue. Others reported: Central Nervous System:
Headache (<10%), insomnia (<10%), and rarely, euphoria, excitement, depression, confusion, hallucinations, paresthesia, nightmares, muscle pain, tinnitus, slurred speech, coordination disorder, strabismus, miosis, mydriasis, diplopia, dysarthria, epileptic seizures, respiratory depression.
Hypotension (<10%), rare instances of dyspnea, palpitation, chest pain, syncope.
Nausea (approx. 10%), constipation (<10%), and rarely dry mouth, anorexia, taste disorder, abdominal pain, vomiting, diarrhea and positive test for occult blood in stool.
Urinary frequency (<10%), and rarely enuresis, urinary retention, dysuria, impotence, inability to ejaculate, nocturia, hematuria.
Instances of rash, pruritus, ankle edema, excessive perspiration, weight gain, nasal congestion, visual disturbances, hepatic function disorders, and paradoxical increase in spasticity.
Muscular hypotonia of a degree sufficient to make walking or movement difficult may occur, but is usually relieved by readjusting the dosage. For this purpose the daytime may be reduce and the evening dose increased.
Some of the CNS and genitourinary symptoms reported may be related to the underlying disease rather than to drug therapy.