The optimum daily dosage of levodopa + carbidopa must be determined by careful titration according to individual requirements, response and tolerance. Titration and dosage adjustment should be made in small steps and the dosage ranges recommended should usually not be exceeded. Treatment with levodopa should not be stopped abruptly.
Levodopa + carbidopa tablets are available in a ratio of 4:1 or 10:1 of levodopa to carbidopa to provide facility for fine dosage titration for each patient.
General Dosing Recommendation: Studies show that peripheral dopa decarboxylase is saturated by carbidopa at doses between 70 and 100 mg per day. Patients receiving less than this amount of carbidopa are more likely to experience nausea and vomiting.
Patients should be carefully monitored during the dosage adjustment period since both therapeutic and adverse effects are seen more rapidly with levodopa + carbidopa than with levodopa alone. Involuntary movements, particularly blepharospasm, are a useful early sign of excess dosage in some patients, thus requiring dose reduction.
Since parkinsonian syndrome is progressive, the patient's clinical condition should be evaluated periodically and therapy should be adjusted as necessary.
Patients not receiving levodopa: Usual Initial Dose: One tablet (levodopa 100 mg + carbidopa 25 mg) three times a day; Dosage may be increased by one tablet every day or every other day, as necessary, until a dosage equivalent of eight tablets of levodopa 100 mg + carbidopa 25 mg a day is reached.
Maximum Recommended Dose: 2 g of levodopa and 200 mg of carbidopa.
Some patients, including those with postencephalitic parkinsonism, are more sensitive to levodopa and require specially careful dosage adjustment.
Maintenance: Therapy should be individualized and adjusted according to the desired therapeutic response. At least 70 to 100 mg of carbidopa per day should be provided for optimal inhibition of extracerebral decarboxylation of levodopa.
When more levodopa is required, levodopa 250 mg + carbidopa 25 mg should be substituted at a dosage of one tablet three or four times a day. If necessary, the dosage of levodopa 250 mg + carbidopa 25 mg may be increased by half to one tablet every other day to a maximum of eight tablets a day. Clinical experience with a total daily dose greater than 200 mg carbidopa is limited.
Patients receiving levodopa: Discontinue levodopa at least 12 hours (24 hours for slow-release preparations) before starting therapy with levodopa + carbidopa.
Levodopa + carbidopa should be given as the first morning dose after a night without any levodopa. The dose of levodopa + carbidopa should be approximately 20% of the previous daily dose of levodopa.
Patients taking less than 1,500 mg of levodopa a day should be started on one tablet of levodopa 100 mg + carbidopa 25 mg three or four times a day based on patient need. The recommended starting dose for most patients taking more than 1,500 mg levodopa a day is one tablet of levodopa 250 mg + carbidopa 25 mg tablet three or four times a day.
Patients receiving levodopa with another decarboxylase inhibitor: When transferring a patient to levodopa + carbidopa from levodopa combined with another decarboxylase inhibitor, discontinue dosage at least 12 hours before levodopa + carbidopa is started.
Start with a dosage of levodopa + carbidopa that will provide the same amount of levodopa as contained in the other levodopa + decarboxylase inhibitor combination.
Patients receiving other antiparkinsonian agents: Current data indicate that other antiparkinsonian agents may be continued when levodopa + carbidopa is introduced, although dosage adjustment of levodopa + carbidopa may be necessary.
Or, as prescribed by a physician.