Dosage Forms. Tablet, Immediate Release: (Carbidopa/Levodopa) 10 mg/100 mg, 25 mg/100 mg, 25 mg/250 mg; Tablet, Extended Release: (Carbidopa/Levodopa) 25 mg/100 mg, 50 mg/200 mg; Orally Disintegrating Tablet: (Carbidopa/Levodopa) 10 mg/100 mg, 25 mg/100 mg, 25 mg/250 mg
Common FDA Label Indication, Dosing, and Titration.
1. Parkinson disease: 10 mg/100 mg po tid, increasing dose (no more often than every 3 d) to therapeutic response; patients generally treated with 400-1600 mg of levodopa per day
1. Restless legs syndrome: 25 mg/100 mg po qhs, may repeat dose if awakening within 2 h
MOA. When levodopa is administered orally, it is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the CNS. For this reason, when given alone, large doses of levodopa are required for adequate therapeutic effect. However, these doses often result in nausea and other adverse reactions. Carbidopa inhibits decarboxylation of circulating levodopa, preventing nausea and allowing more levodopa to reach the CNS. Carbidopa does not cross the blood-brain barrier and does not affect the metabolism of levodopa within the central nervous system.
Drug Characteristics: Carbidopa/Levodopa
Medication Safety Issues: Carbidopa/Levodopa
Drug Interactions: Carbidopa/Levodopa
Adverse Reactions: Carbidopa/Levodopa
Efficacy Monitoring Parameters. Reduction of symptoms of Parkinson disease (extrapyramidal movements, rigidity, tremor, gait disturbances).
Toxicity Monitoring Parameters. Seek medical attention if gastrointestinal bleeding and dyskinesia occur; monitor intraocular pressure in glaucoma patients who take this product.
Key Patient Counseling Points. Patients using concomitant antihypertensive may be at increased risk for postural hypotension.
Clinical Pearls. Since levodopa competes with certain amino acids for transport across the gut wall, the absorption of levodopa may be impaired in some patients on a high protein diet. Parkinson disease is a progressive, neurodegenerative disorder of the extrapyramidal nervous system affecting the mobility and control of the skeletal muscular system. Its characteristic features include resting tremor, rigidity, and bradykinetic movements. Similar symptoms can occur (known as “parkinsonism”) due to manganese or carbon monoxide intoxication, after encephalitic conditions, and idiopathically. All are treated with levodopa/carbidopa at the same doses as used for Parkinson disease.