L-Dopa-carbidopa (Sinemet): Side Effects, Dosage & Uses

What is levodopa-carbidopa, and how does it work (mechanism of action)?

Carbidopa-levodopa is a combination of two
drugs, levodopa and carbidopa. Carbidopa-levodopa is used in the treatment of
Parkinson’s disease. Parkinson’s disease is believed to be caused by low levels
of dopamine in certain parts of the brain. When levodopa is taken orally, it
crosses into the brain through the "blood- brain barrier." Once it crosses, it
is converted to dopamine. The resulting increase in brain dopamine
concentrations is believed to improve nerve conduction and assist the movement
disorders in Parkinson disease. Carbidopa does not cross the blood-brain
barrier. Carbidopa is added to the levodopa to prevent the breakdown of levodopa
before it crosses into the brain. The addition of carbidopa allows lower doses
of levodopa to be used. This reduces the risk of side effects from levodopa such
as
nausea and vomiting. This combination medicine was approved by the FDA in
1988.

What brand names are available for levodopa-carbidopa?

Sinemet, Sinemet CR, Parcopa

Is levodopa-carbidopa available as a generic drug?

GENERIC AVAILABLE: Yes

Do I need a prescription for levodopa-carbidopa?

Yes

What are the uses for levodopa-carbidopa?

Carbidopa-levodopa is used for the management of
Parkinson’s disease.

What are the side effects of levodopa-carbidopa?

Most patients receiving carbidopa-levodopa experience
side effects, but these usually are reversible.

Gastrointestinal side effects are common in patients receiving
carbidopa-levodopa and these include:

Patients may experience dizziness upon standing up, associated with a drop in
blood pressure. Fortunately, the body develops tolerance to this side effect
within a few months.

Other important side effects of carbidopa-levodopa therapy include:

memory loss,
anxiety,
nervousness,
agitation,
restlessness,
confusion,
inability to sleep,
nightmares,
daytime tiredness,
mental depression or
euphoria.

Occasional involuntary movements
are the most common of the serious side effects of carbidopa-levodopa therapy, and these are:

muscle twitching,
dizziness,
muscle jerks during sleep,
hand tremor,
chewing,
gnawing,
twisting,
tongue or
mouth movements,
head bobbing, or
movements of the feet, hands, or shoulder which may respond to a reduction in the dose.

Infrequently, patients may develop a drop in white blood cell count during
carbidopa-levodopa therapy. This is a significant reason to temporarily, if not
permanently, stop treatment.

What is the dosage for levodopa-carbidopa?

Carbidopa-levodopa is taken several times per day. It may be
administered with food to reduce the likelihood of nausea; however, a
high-protein diet may reduce its absorption. The initial dose using regular
tablets is 25/100 mg three times daily. The dose may be increased by one tablet
every day or every other day until 8 tablets of 25/100 mg daily is reached.
Alternatively 10/100 mg three or four times daily may be used initially and
increased by one tablet daily or every other day until a total of eight tablets
daily is reached. The dose of controlled release tablets is 50/200 mg twice
daily and may increase up to 1.6 grams levodopa daily. Controlled release tablet
should be given at least 6 hours apart.

Which drugs or supplements interact with levodopa-carbidopa?

The use of
the following drugs with carbidopa-levodopa can enhance the anti-Parkinson’s effects of levodopa:

amantadine (Symmetrel),
benztropine (Cogentin),
procyclidine (Kemadrin), or
trihexyphenidyl (Artane)

The following drugs can inhibit dopamine in the brain and shouldn’t be used in combination with levodopa:

Droperidol,
haloperidol (Haldol),
loxapine (Loxitane),
metoclopramide (Reglan),
phenothiazines such as prochlorperazine (Thorazine); and
thioxanthenes as thiothixene (Navane).

These drugs, therefore, can worsen Parkinson’s disease
and reverse the beneficial effects of levodopa. Methyldopa (Aldomet) and
reserpine also can interfere with the beneficial actions of carbidopa-levodopa
and can increase the risk of side effects.

The occurrence of postural
hypotension (reduced blood pressure when standing from a sitting or lying down
position) may increase when carbidopa-levodopa is combined with drugs that
reduce blood pressure. Phenytoin (Dilantin) can increase the break-down of
carbidopa-levodopa, reducing its effectiveness. Use of carbidopa-levodopa with
monoamine oxidase inhibitors (MAOI‘s) antidepressants, for example,
isocarboxazid (Marplan), phenelzine (Nardil), tranylcypromine (Parnate), and
procarbazine (Matulane), can result in severe and dangerous elevations in blood
pressure. MAOI’s should be stopped 2-4 weeks before starting carbidopa-levodopa
therapy.

The side effects associated with levodopa, including dizziness upon
rising, confusion, movement disorders, nausea, and hallucinations, all can be
increased by selegiline (Eldepryl).

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Is levodopa-carbidopa safe to take if I’m pregnant or breastfeeding?

Although there are no human studies that have examined the
effects of carbidopa-levodopa on the fetus, animal studies have shown adverse
effects. Therefore, in prescribing carbidopa-levodopa for a
pregnant woman, the
treating physician must weigh the potential risks to the fetus against the potential
benefits to the mother.

Levodopa is distributed into
breast milk. It also may
inhibit production of milk. It is generally recommended that carbidopa-levodopa
should not be given to women who are breast- feeding.

What else should I know about levodopa-carbidopa?

What preparations of levodopa-carbidopa are available?

Tablets (carbidopa/levodopa): 10/100, 25/100 mg. Tablets
(Controlled Release): 25/100 and 50/200 mg.

How should I keep levodopa-carbidopa stored?

Tablets should be kept at room temperature, 15-30 C (59-86
F).