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SINEMET (carbidopa-levodopa) is indicated in the treatment of the symptoms of idiopathic Parkinson's disease (paralysis agitans), post-encephalitic parkinsonism, and symptomatic parkinsonism which may follow injury to the nervous system by carbon monoxide intoxication and/or manganese intoxication. SINEMET (carbidopa-levodopa) is indicated in these conditions to permit the administration of lower doses of levodopa with reduced nausea and vomiting, with more rapid dosage titration, with a somewhat smoother response, and with supplemental pyridoxine (vitamin B6).
In some patients a somewhat smoother antiparkinsonian effect results from therapy with SINEMET (carbidopa-levodopa) than with levodopa. However, patients with markedly irregular ("on-off") responses to levodopa have not been shown to benefit from SINEMET (carbidopa-levodopa) .
Although the administration of carbidopa permits control of parkinsonism and Parkinson's disease with much lower doses of levodopa, there is no conclusive evidence at present that this is beneficial other than in reducing nausea and vomiting, permitting more rapid titration, and providing a somewhat smoother response to levodopa.
Certain patients who responded poorly to levodopa have improved when SINEMET (carbidopa-levodopa) was substituted. This is most likely due to decreased peripheral decarboxylation of levodopa which results from administration of carbidopa rather than to a primary effect of carbidopa on the nervous system. Carbidopa has not been shown to enhance the intrinsic efficacy of levodopa in parkinsonian syndromes.
In considering whether to give SINEMET (carbidopa-levodopa) to patients already on levodopa who have nausea and/or vomiting, the practitioner should be aware that, while many patients may be expected to improve, some do not. Since one cannot predict which patients are likely to improve, this can only be determined by a trial of therapy. It should be further noted that in controlled trials comparing SINEMET (carbidopa-levodopa) with levodopa, about half of the patients with nausea and/or vomiting on levodopa improved spontaneously despite being retained on the same dose of levodopa during the controlled portion of the trial.
DOSAGE AND ADMINISTRATION
The optimum daily dosage of SINEMET (carbidopa-levodopa) must be determined by careful titration in each patient. SINEMET (carbidopa-levodopa) tablets are available in a 1:4 ratio of carbidopa to levodopa (SINEMET (carbidopa-levodopa) 25-100) as well as 1:10 ratio (SINEMET (carbidopa-levodopa) 25-250 and SINEMET (carbidopa-levodopa) 10-100). Tablets of the two ratios may be given separately or combined as needed to provide the optimum dosage.
Studies show that peripheral dopa decarboxylase is saturated by carbidopa at approximately 70 to 100 mg a day. Patients receiving less than this amount of carbidopa are more likely to experience nausea and vomiting.
Usual Initial Dosage
Dosage is best initiated with one tablet of SINEMET (carbidopa-levodopa) 25-100 three times a day. This dosage schedule provides 75 mg of carbidopa per day. Dosage may be increased by one tablet every day or every other day, as necessary, until a dosage of eight tablets of SINEMET (carbidopa-levodopa) 25-100 a day is reached.
If SINEMET (carbidopa-levodopa) 10-100 is used, dosage may be initiated with one tablet three or four times a day. However, this will not provide an adequate amount of carbidopa for many patients. Dosage may be increased by one tablet every day or every other day until a total of eight tablets (2 tablets q.i.d.) is reached.
How to Transfer Patients from Levodopa
Levodopa must be discontinued at least twelve hours before starting SINEMET (carbidopa-levodopa) . A daily dosage of SINEMET (carbidopa-levodopa) should be chosen that will provide approximately 25% of the previous levodopa dosage. Patients who are taking less than 1500 mg of levodopa a day should be started on one tablet of SINEMET (carbidopa-levodopa) 25-100 three or four times a day. The suggested starting dosage for most patients taking more than 1500 mg of levodopa is one tablet of SINEMET (carbidopa-levodopa) 25-250 three or four times a day.
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. When a greater proportion of carbidopa is required, one tablet of SINEMET (carbidopa-levodopa) 25-100 may be substituted for each tablet of SINEMET (carbidopa-levodopa) 10-100. When more levodopa is required, SINEMET (carbidopa-levodopa) 25-250 should be substituted for SINEMET (carbidopa-levodopa) 25-100 or SINEMET (carbidopa-levodopa) 10-100. If necessary, the dosage of carbidopa/levodopa 25-250 may be increased by one-half or one tablet every day or every other day to a maximum of eight tablets a day. Experience with total daily dosages of carbidopa greater than 200 mg is limited.
Because both therapeutic and adverse responses occur more rapidly with SINEMET (carbidopa-levodopa) than with levodopa alone, patients should be monitored closely during the dose adjustment period. Specifically, involuntary movements will occur more rapidly with SINEMET (carbidopa-levodopa) than with levodopa. The occurrence of involuntary movements may require dosage reduction. Blepharospasm may be a useful early sign of excess dosage in some patients.
Addition of Other Antiparkinsonian Medications
Standard drugs for Parkinson's disease, other than levodopa without a decarboxylase inhibitor, may be used concomitantly while SINEMET (carbidopa-levodopa) is being administered, although dosage adjustments may be required.
Interruption of Therapy
Sporadic cases of a symptom complex resembling Neuroleptic Malignant Syndrome (NMS) have been associated with dose reductions and withdrawal of SINEMET (carbidopa-levodopa) . Patients should be observed carefully if abrupt reduction or discontinuation of SINEMET (carbidopa-levodopa) is required, especially if the patient is receiving neuroleptics. (See WARNINGS.)
If general anesthesia is required, SINEMET (carbidopa-levodopa) may be continued as long as the patient is permitted to take fluids and medication by mouth. If therapy is interrupted temporarily, the patient should be observed for symptoms resembling NMS, and the usual daily dosage may be administered as soon as the patient is able to take oral medication.
No. 3916A— SINEMET (carbidopa-levodopa) 25-100 Tablets are yellow, round, uncoated tablets, that are coded "650" on one side and plain on the other. They are supplied as follows:
NDC 0006-3916-68 bottles of 100.
No. 3915 — SINEMET (carbidopa-levodopa) 10-100 Tablets are light dapple-blue, round, uncoated tablets, that are coded "647" on one side and plain on the other. They are supplied as follows:
NDC 0006-3915-68 bottles of 100.
No. 3917 — SINEMET (carbidopa-levodopa) 25-250 Tablets are light dapple-blue, round, uncoated tablets, that are coded "654" on one side and plain on the other. They are supplied as follows:
NDC 0006-3917-68 bottles of 100.
Storage and Handling
Store at 25°C (77°F), excursions permitted to 15-30°C (59-86°F) [see USP Controlled Room Temperature]. Store in a tightly closed container, protected from light and moisture.
Dispense in a tightly closed, light-resistant container.
Manufactured for: Merck Sharp & Dohme Corp., a subsidiary of Merck & Co.,Inc.,Whitehouse Station, NJ 08889, USA. Manufactured By: Mylan Pharmaceuticals, Inc. Morgantown, WV 26505, USA. Issued: January 2011
Last reviewed on RxList: 3/28/2011
This monograph has been modified to include the generic and brand name in many instances.
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