Pharmacology Guide
Motor Control
Last Updated:
Carbidopa/L-Dopa (Sinemet) | Levodopa (L-Dopa) | Bromoc
Carbidopa/L-Dopa
| Sinemet |
Mechanism of Action
|
Levodopa, the metabolic precursor of dopamine, crosses the blood-brain barrier, and is converted to dopamine in the brain. This replaces the dopamine that has been lost in Parkinson s disease. |
Therapeutic Use
|
All types of Parkinsonism. Is being investigated for use with post-anoxic (oxygen deprivation to the brain) intention myoclonus. |
Absorption
|
Variable absorption depending on gastric pH, rate of gastric emptying and presence of food in the G.I. Tract. Peak plasma concentration of levodopa is reached in 2 hours. |
Metabolism
|
Levodopa is decarboxylated to dopamine. Carbidopa reduces the amount of levodopa required to produce a given effect by about 75%. |
Half-life
|
1-2 Hours for levodopa. |
Average Daily Dose (adult)
|
200-1200 mg of levodopa. |
Adverse Effects
|
Dyskinesias (impairment of normal movement). Nausea, confusion and dizziness. |
Drug Interaction
|
Symptomatic postural hypotension has occurred when Sinemet is added to the treatment of a patient receiving antihypertensive drugs. Phenothiazines and butyrophenones may reduce the therapeutic effects of levodopa. |
Contraindication
|
MAO inhibitors. Contraindicated in patients with a known hypersensitivity to any component of this drug. |
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Bromocriptine
| Parlodel |
Mechanism of Action
|
Parlodel is a dopamine receptor agonist, which activates post-synaptic dopamine receptors. A nonhormonal agent that inhibits the release of the hormone prolactin by the pituitary gland. |
Therapeutic Use
|
Treatment of Parkinson s disease, hyperprolactinemia and acromegaly (excessive bone growth). |
Absorption
|
Poorly absorbed from the G.I. tract. |
Metabolism
|
Completely metabolized in the liver prior to excretion and metabolites are excreted in the bile. |
Half-life
|
7 Hours. |
Average Daily Dose (adult)
|
3.75-40 mg |
Adverse Effects
|
Nausea, headache, dizziness, fatigue, lightheadedness, vomiting, abdominal cramps, nasal congestion, constipation, diarrhea and drowsiness. |
Drug Interaction
|
Alcohol may potentiate effects and dopamine receptor antagonists such as chlorpromazine or haloperidol will block action of bromocriptine. |
Contraindication
|
Uncontrolled hypertension and sensitivity to any ergot alkaloids. |
Baclofen
|
Lioresal |
Mechanism of Action
|
GABAB receptor agonist. Activation of these receptors reduces the release of excitatory neurotransmitters. |
Therapeutic Use
|
Reduce muscle spasms such as that occurring in multiple sclerosis and diseases of the spinal cord. |
Absorption
|
Well absorbed. Peak effect 2-3 hours . |
Metabolism
|
35% of the drug is excreted unchanged in the urine and feces. |
Half-life
|
3-4 Hours. |
Average Daily Dose (adult)
|
100-150 mg/day in four divided doses. |
Adverse Effects
|
Drowsiness, slight nausea, occasional mental disturbances such as confusion, euphoria and depression. Hypotension has been noted following overdose. |
Drug Interaction
|
Increased sedation with other CNS depressants such as benzodiazepines. |
Contraindication
|
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Dantrolene
|
Dantrium |
Mechanism of Action
|
It acts by decreasing the release of calcium from the sarcoplasmic reticulum thereby interfering with muscle contraction. |
Therapeutic Use
|
Muscle spasticity associated with chronic disorders, such as MS, CP, spinal cord injury, TBI and stroke. It is also used for the treatment of malignant hyperthermia. |
Absorption
|
Slow and incomplete after oral administration. |
Metabolism
|
Probably metabolized by hepatic microsomal enzymes. and eliminated in the urine and bile. |
Half-life
|
8.7 hours. |
Average Daily Dose (adult)
|
4-8 mg/kg/day oral, 2.5 mg/kg intravenous. |
Adverse Effects
|
The most prominent adverse effect is dose dependent muscle weakness. Other side effects include: drowsiness, dizziness, malaise, fatigue and diarrhea. Transient elevation of liver enzymes may also occur. Symptoms of hepatitis have been reported in 0.5% of the patients receiving the drug. |
Drug Interaction
|
Muscle relaxants. Should not be used together with calcium channel blockers such as verapamil. |
Contraindication
|
Respiratory muscle weakness or liver disease. |
These brief pharmaceutical summaries do not include all information important for patient use and should not be used as a substitute for professional medical advice. Consult the prescribing doctor and read package inserts before using these or any other medications or supplements.
CDER
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
National Institutes of Health
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Wolf, A.P. & Gleckman, A.D. (1995). Sinemet and brain injury: Functional versus statistical change and suggestions for future research designs. Brain Injury . 9(5), 487.
