SINEMET CR (carbidopa-levodopa sustained release) 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 CR (carbidopa-levodopa sustained release) contains carbidopa and levodopa in a 1:4 ratio as either the 50-200 tablet or the 25-100 tablet. The daily dosage of SINEMET CR (carbidopa-levodopa sustained release) must be determined by careful titration. Patients should be monitored closely during the dose adjustment period, particularly with regard to appearance or worsening of involuntary movements, dyskinesias or nausea. SINEMET CR (carbidopa-levodopa sustained release) should not be chewed or crushed.

Standard drugs for Parkinson's disease, other than levodopa without a decarboxylase inhibitor, may be used concomitantly while SINEMET CR (carbidopa-levodopa sustained release) is being administered, although their dosage may have to be adjusted.

Since carbidopa prevents the reversal of levodopa effects caused by pyridoxine, SINEMET CR (carbidopa-levodopa sustained release) can be given to patients receiving supplemental pyridoxine (vitamin B₆).

Initial Dosage

Patients currently treated with conventional carbidopa-levodopa preparations: Studies show that peripheral dopa-decarboxylase is saturated by the bioavailable carbidopa at doses of 70 mg a day and greater. Because the bioavailabilities of carbidopa and levodopa in SINEMET and SINEMET CR (carbidopa-levodopa sustained release) are different, appropriate adjustments should be made, as shown in Table 2.

Table 2: Approximate Bioavailabilities at Steady State^†

Dosage with SINEMET CR (carbidopa-levodopa sustained release) should be substituted at an amount that provides approximately 10% more levodopa per day, although this may need to be increased to a dosage that provides up to 30% more levodopa per day depending on clinical response (see DOSAGE AND ADMINISTRATION, Titration with SINEMET CR (carbidopa-levodopa sustained release) ). The interval between doses of SINEMET CR should be 4-8 hours during the waking day. (See CLINICAL PHARMACOLOGY, Pharmacodynamics.)

A guideline for initiation of SINEMET CR (carbidopa-levodopa sustained release) is shown in Table 3.

Table 3 Guidelines for Initial Conversion from SINEMET to SINEMET CR (carbidopa-levodopa sustained release)

Patients currently treated with levodopa without a decarboxylase inhibitor: Levodopa must be discontinued at least twelve hours before therapy with SINEMET CR is started. SINEMET CR (carbidopa-levodopa sustained release) should be substituted at a dosage that will provide approximately 25% of the previous levodopa dosage. In patients with mild to moderate disease, the initial dose is usually 1 tablet of SINEMET CR (carbidopa-levodopa sustained release) 50-200 b.i.d.

Patients not receiving levodopa: In patients with mild to moderate disease, the initial recommended dose is 1 tablet of SINEMET CR (carbidopa-levodopa sustained release) 50-200 b.i.d. Initial dosage should not be given at intervals of less than 6 hours.

Titration with SINEMETCR

Following initiation of therapy, doses and dosing intervals may be increased or decreased depending upon therapeutic response. Most patients have been adequately treated with doses of SINEMET CR (carbidopa-levodopa sustained release) that provide 400 to 1600 mg of levodopa per day, administered as divided doses at intervals ranging from 4 to 8 hours during the waking day. Higher doses of SINEMET CR (carbidopa-levodopa sustained release) (2400 mg or more of levodopa per day) and shorter intervals (less than 4 hours) have been used, but are not usually recommended.

When doses of SINEMET CR (carbidopa-levodopa sustained release) are given at intervals of less than 4 hours, and/or if the divided doses are not equal, it is recommended that the smaller doses be given at the end of the day.

An interval of at least 3 days between dosage adjustments is recommended.

Maintenance

Because Parkinson's disease is progressive, periodic clinical evaluations are recommended; adjustment of the dosage regimen of SINEMET CR (carbidopa-levodopa sustained release) may be required.

Addition of Other Antiparkinson Medications

Anticholinergic agents, dopamine agonists, and amantadine can be given with SINEMET CR (carbidopa-levodopa sustained release) . Dosage adjustment of SINEMET CR may be necessary when these agents are added.

A dose of carbidopa-levodopa immediate release 25-100 or 10-100 (one half or a whole tablet) can be added to the dosage regimen of SINEMET CR (carbidopa-levodopa sustained release) in selected patients with advanced disease who need additional immediate-release levodopa for a brief time during daytime hours.

Interruption of Therapy

Sporadic cases of a symptom complex resembling Neuroleptic Malignant Syndrome (NMS) have been associated with dose reductions and withdrawal of SINEMET or SINEMET CR (carbidopa-levodopa sustained release) .

Patients should be observed carefully if abrupt reduction or discontinuation of SINEMET CR (carbidopa-levodopa sustained release) is required, especially if the patient is receiving neuroleptics. (See WARNINGS.)

If general anesthesia is required, SINEMET CR (carbidopa-levodopa sustained release) may be continued as long as the patient is permitted to take oral medication. If therapy is interrupted temporarily, the patient should be observed for symptoms resembling NMS, and the usual dosage should be administered as soon as the patient is able to take oral medication.

No. 3919— SINEMET CR 50-200 (carbidopa-levodopa) Sustained-Release Tablets containing 50 mg of carbidopa and 200 mg of levodopa, are dappled-purple in color, oval, compressed tablets, that are coded "521" on one side and plain on the other. They are supplied as follows:

NDC 0006-3919-68 bottles of 100.

No. 3918— SINEMET CR 25-100 (carbidopa-levodopa) Sustained-Release Tablets containing 25 mg of carbidopa and 100 mg of levodopa, are dappled-purple in color, oval, compressed tablets, that are coded "601" on one side and plain on the other. They are supplied as follows:

NDC 0006-3918-68 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. January 2011

Last reviewed on RxList: 3/28/2011
This monograph has been modified to include the generic and brand name in many instances.