Medications and Drugs
GENERIC NAME: levodopa-carbidopa
BRAND NAME: Sinemet
DRUG CLASS AND MECHANISM: Levodopa-carbidopa is a
combination of
two drugs, levodopa and carbidopa. Levodopa-carbidopa is used
in the
treatment of Parkinson's disease. Parkinson's disease is
believed to be
related to low levels of dopamine in certain parts of the
brain. When
levodopa is taken orally, it crosses 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.
PRESCRIPTION: yes
GENERIC EQUIVALNET AVAILABLE: yes
PREPARATIONS: Oval tablets (doses stated are for
levodopa/carbidopa): 100mg/10mg, 200mg/20mg, 200mg/25mg, 250mg/
25mg, and a
sustained-release preparation (Sinemet CR) containing 200mg/50mg.
STORAGE: Tablets should be kept at room temperature, 15-
30°C
(59-86°F).
PRESCRIBED FOR: Levodopa-carbidopa is indicated for the
management of Parkinson's disease.
DOSING: Levodopa-carbidopa 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.
DRUG INTERACTIONS: The use of amantadine (Symmetrel),
benztropine (Cogentin), procyclidine (Kemadrin), or
trihexyphenidyl
(Artane) with levodopa-carbidopa can enhance the anti-
Parkinson's effects
of levodopa. Droperidol, haloperidol (Haldol), loxapine
(Loxitane),
metoclopramide (Reglan), phenothiazines such as prochlorperazine
(Thorazine); thioxanthenes as thiothixene (Navane) inhibit
dopamine in the
brain. 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 levodopa-
carbidopa and
can increase the risk of side effects.
Phenytoin (Dilantin) can increases the break-down of levodopa-
carbidopa,
reducing its effectiveness.
Use of levodopa-carbidopa 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 levodopa-carbidopa
therapy.
The side effects associated with levodopa, including dizziness
upon
rising, confusion, movement disorders, nausea, and
hallucinations, all can
be increased by selegiline (Eldepryl).
PREGNANCY: Although there are no human studies that have
examined the effects of levodopa-carbidopa on the fetus, animal
studies
have shown adverse effects. Therefore, in prescribing levodopa-
carbidopa
for a pregnant woman, the physician must weigh the potential
risks to the
fetus against the potential benefits to the mother.
NURSING MOTHERS: Levodopa is distributed into breast
milk. It
also may inhibit production of milk. It is generally
recommended that
levodopa-carbidopa should not be given to women who are breast-
feeding.
SIDE EFFECTS: Most patients receiving levodopa-carbidopa
experience side effects, but these are usually reversible.
Occasional
involuntary movements are the most common of the serious side
effects of
levodopa-carbidopa therapy. These may include chewing, gnawing,
twisting,
tongue or mouth movements, head bobbing, or movements of the
feet, hands,
or shoulder. These may respond to a reduction in the dose.
Muscle
twitching, dizziness, muscle jerks during sleep, and hand
tremor also may
occur. Various psychiatric disturbances may occur during
levodopa-carbidopa therapy. Such disturbances include memory
loss,
anxiety, nervousness, agitation, restlessness, confusion,
inability to
sleep, nightmares, daytime tiredness, mental depression or
euphoria.
Gastrointestinal side effects are common in patients receiving
levodopa-carbidopa. Nausea, vomiting, loss of appetite, and
weight loss
may occur. 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.
Infrequently, patients may develop a drop in white blood cell
count
during levodopa-carbidopa therapy. This is a cause to
temporarily, if not
permanently, stop treatment.
Reference: FDA Prescribing Information
Last Editorial Review: 8/12/2000
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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