The P-I-E-N-O Parkinsn's List Drug Database
baclofen / LioresalTM
CNS DEPRESSANT
Antispasmodic, muscle relaxant
Description: Baclofen is an oral skeletal muscle relaxant. It is a derivative of the inhibitory neurotransmitter gamma- aminobutyric acid (GABA). Clinically, baclofen is used to treat spasticity and improve mobility in patients with multiple sclerosis and other spinal cord lesions by decreasing the number and severity of spasms and relieving associated pain, clonus, and muscle rigidity. Baclofen also improves bowel and bladder function in some of these patients. Baclofen was approved by the FDA in November 1977. On February 28, 1995, the FDA granted approval under a treatment IND to study intrathecal baclofen for the treatment of spasticity of cerebral origin.
Mechanism of Action: Baclofen's mechanism of action is not fully understood, but it is believed that the drug works mainly at the level of the spinal cord to block polysynaptic afferent pathways and, to a lesser extent, monosynaptic afferent pathways. Baclofen may inhibit the transmission of impulses through these pathways by acting as an inhibitory neurotransmitter itself or by hyperpolarizing the primary afferent nerve terminals, which inhibits the release of excitatory neurotransmitters such as glutamate and aspartic acids. Because large doses of baclofen cause CNS depression, it is postulated that the drug works at supraspinal sites as well.
Pharmacokinetics: Baclofen is administered orally and is rapidly and almost completely absorbed, although bioavailability varies from patient to patient. Both the rate and extent of absorption is inversely proportional to the dose. Peak blood concentrations are achieved within 2-3 hours.
Baclofen is distributed throughout the body but only minimally crosses the blood-brain barrier. Protein binding is low. About 15% of a dose is metabolized by the liver. The half-life ranges from 2.5-4 hours. The kidney excretes 70-85% of a dose as unchanged drug and metabolites, and the remainder is excreted via the feces.
CONTRAINDICATIONS/PRECAUTIONS: Baclofen is excreted mainly unchanged in the urine. Patients with renal impairment may require a reduced dose of baclofen to avoid drug accumulation.
Baclofen is relatively contraindicated in patients with cerebral hemorrhage or lesions or a prior cerebrovascular accident (stroke) because of the increased risk of developing CNS, respiratory, or cardiovascular depression; ataxia; or psychiatric disturbances. In addition, elderly patients or patients with pre-existing psychiatric disorders may be more susceptible to baclofen's CNS toxicities.
Baclofen can increase blood glucose concentrations, so it should be used cautiously in patients with diabetes mellitus.
Baclofen has caused deterioration in seizure control and EEG changes in patients with epilepsy. Baclofen should be prescribed cautiously to patients with a history of a seizure disorder.
Baclofen should not be used in patients who require spasticity to maintain upright posture and balance.
Baclofen has been reported to cause positive results on tests for occult blood in the stool, so caution should be taken when prescribing baclofen for patients with peptic ulcer disease.
DRUG INTERACTIONS: Concomitant use of baclofen with other CNS depressants, such as ethanol, opiate agonists, antipsychotics, anxiolytics, certain HA-blockers or sedative/hypnotics, can increase CNS depression.
Baclofen should be administered cautiously to patients receiving antidepressants. In addition to the risk of additive CNS depression, simultaneous use of baclofen and tricyclic antidepressants may cause muscle hypotonia. Concomitant use of baclofen and monoamine oxidase inhibitors (MAOIs) can increase CNS depression and hypotension.
Because baclofen can increase blood glucose concentrations, doses of oral hypoglycemics and/or insulin may need adjustment in patients receiving these drugs concomitantly.
ADVERSE REACTIONS: The most common adverse effects seen with oral baclofen therapy include drowsiness, weakness, dizziness/lightheadedness, headache, nausea/vomiting, hypotension, constipation, lethargy/fatigue, confusion, insomnia, and increased urinary frequency. The most common adverse effects seen with intrathecal administration include those associated with oral therapy, seizures, paresthesias, blurred vision, hypotonia, slurred speech, coma (overdose), hypertension, and dyspnea.
Additional adverse effects of baclofen therapy are given below and divided into different organ systems: Central nervous system: Oral: euphoria, excitement, depression, hallucinations, paresthesias, myalgia, tinnitus, coordination disorder, tremor, rigidity, dystonia, ataxia, nystagmus, strabismus, miosis, mydriasis, diplopia, dysarthria (rare). Intrathecal: respiratory depression, concentration difficulty, decreased coordination, amnesia/forgetfulness, nystagmus, accomodation disorder, anxiety, hypothermia, burning buttocks/feet, cerebellar dysmetria, cerebrovascular accident (stroke), depression, disorientation, unsteady gait/balance alteration, hallucinations, mood lability, paranoia, head/neck pressure, delayed responsiveness, somnolence, dysphagia, vertigo.
Gastrointestinal system: Oral: xerostomia, anorexia, dysgeusia, abdominal pain, diarrhea, positive test for occult blood in stool (rare). Intrathecal: xerostomia, diarrhea/fecal incontinence, anorexia, dehydration, ileus, dysgeusia.
Cardiovascular: Oral: palpitations, angina, excessive diaphoresis, syncope (rare). Intrathecal: bradycardia, deep vein thrombosis, skin flushing, diaphoresis, orthostatic hypotension, pallor, lower extremity edema.
Genitourinary: Oral: enuresis (urinary incontinence), urinary retention, dysuria, impotence, ejaculation dysfunction, nocturia, hematuria (rare). Intrathecal: urinary incontinence, sluggish bladder, bladder spasm, sexual dysfunction.
Respiratory: Oral: dyspnea, nasal congestion. Intrathecal: chest tightness, aspiration pneumonia.
Miscellaneous: Oral: rash, pruritus, ankle edema, weight gain. Intrathecal: septicemia, weight loss, subdural hemorrhage, suicide attempt, suicidal ideation, double vision (diplopia), urticaria of face and hands, alopecia, facial edema.
Lab test alteration: Oral: increased AST, elevated alkaline phosphatase, elevation of blood sugar (hyperglycemia)
PATIENT INFORMATION:
What do baclofen tablets do?
Baclofen (LioresalTM ) is a muscle relaxant. It relieves spasms and cramping of muscles in conditions such as multiple sclerosis. Generic baclofen tablets are available.
What should my doctor, dentist, or pharmacist know before I take baclofen?
They need to know if you have any of these conditions:
How should I take this medicine?
Take baclofen tablets by mouth. Follow the directions on the prescription label. Swallow the tablets with a drink of water. Take your doses at regular intervals. Do not take your medicine more often than directed.
Special precautions for use in children:
This medicine is not for children under 12 years old.
What if I miss a dose?
If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.
What other medicines can interact with baclofen?
Tell your doctor or pharmacist: about all other medicines you are taking, including non-prescription medicines; if you are a frequent user of drinks with caffeine or alcohol; if you smoke; or if you use illegal drugs. These may affect the way your medicine works. Check before stopping or starting any of your medicines.
What side effects may I notice from taking baclofen?
Side effects with baclofen include:
Let your doctor know about these side effects if they do not go away or if they annoy you.
What do I need to watch for while I take baclofen?
Visit your doctor for regular checks on your progress. It may take several days of treatment before you see the full effects of baclofen. Do not suddenly stop taking baclofen. You must gradually reduce the dose or you may get side effects. Ask your doctor for advice.
Baclofen can affect blood sugar levels. If you are diabetic check with your doctor before you change your diet or the dose of your diabetic medicine.
You may get drowsy or dizzy. Do not drive, use machinery, or do anything that needs mental alertness until you know how baclofen affects you. To reduce the risk of dizzy or fainting spells, do not sit or stand up quickly, especially if you are an older patient. Alcohol can make you more drowsy; avoid alcoholic drinks.
Where can I keep my medicine?
Keep out of the reach of children in a container that small children cannot open.
Store at room temperature between 15 and 30C (59 and 86F). Keep container tightly closed. Throw away any unused medicine after the expiration date.
Parkinsn's Archive Treasures Page
John Cottingham is the webmaster of this site.
