"The US Food and Drug Administration (FDA) has approved pimavanserin tablets (Nuplazid, Acadia Pharmaceuticals) for the treatment of hallucinations and delusions associated with psychosis in Parkinson's disease (PD).
Signs And Symptoms Of Overdosage
There are very few cases of overdose with levodopa reported in the published literature. Based on the available information, the acute symptoms of levodopa and dopa decarboxylase inhibitor overdose can be expected to arise from dopaminergic overstimulation. Doses of a few grams may result in CNS disturbances, with an increasing likelihood of cardiovascular disturbance (e.g., hypotension, tachycardia) and more severe psychiatric problems at higher doses. An isolated report of rhabdomyolysis and another of transient renal insufficiency suggest that levodopa overdose may give rise to systemic complications, secondary to dopaminergic overstimulation.
COMT inhibition by entacapone treatment is dose-dependent. A massive overdose of entacapone may theoretically produce a 100% inhibition of the COMT enzyme in people, thereby preventing the O-methylation of endogenous and exogenous catechols.
In clinical trials, the highest single dose of entacapone administered to humans was 800 mg, resulting in a plasma concentration of 14.1 mcg per mL. The highest daily dose given to humans was 2,400 mg, administered in one study as 400 mg six times daily with carbidopa/levodopa for 14 days in 15 Parkinson's disease patients, and in another study as 800 mg three times daily for 7 days in 8 healthy volunteers. At this daily dose, the peak plasma concentrations of entacapone averaged 2.0 mcg per mL (at 45 min, compared to 1.0 mcg per mL and 1.2 mcg per mL with 200 mg entacapone at 45 min.). Abdominal pain and loose stools were the most commonly observed adverse events during this study. Daily doses as high as 2,000 mg entacapone have been administered as 200 mg 10 times daily with carbidopa/levodopa or benserazide/levodopa for at least 1 year in 10 patients, for at least 2 years in 8 patients and for at least 3 years in 7 patients. Overall, however, clinical experience with daily doses above 1,600 mg is limited.
Management Of Overdosage
Hospitalization is advised, and general supportive measures should be employed, along with immediate gastric lavage and repeated doses of charcoal over time. This may hasten the elimination of entacapone in particular, by decreasing its absorption and reabsorption from the GI tract. Intravenous fluids should be administered judiciously and an adequate airway maintained.
Respiratory, circulatory and renal function should be monitored and appropriate supportive measures employed. Electrocardiographic monitoring should be instituted and the patient carefully observed for the development of arrhythmias; if required, appropriate antiarrhythmic therapy should be given. The possibility that the patient may have taken other drugs, increasing the risk of drug interactions (especially catechol-structured drugs) should be taken into consideration. To date, no experience has been reported with dialysis; hence, its value in overdosage is not known. Hemodialysis or hemoperfusion is unlikely to reduce entacapone levels due to its high binding to plasma proteins.
Pyridoxine is not effective in reversing the actions of Stalevo.
Stalevo is contraindicated in patients:
- Taking nonselective monoamine oxidase (MAO) inhibitors (e.g., phenelzine and tranylcypromine). These nonselective MAO inhibitors must be discontinued at least two weeks prior to initiating therapy with Stalevo.
- With narrow-angle glaucoma.
Last reviewed on RxList: 2/10/2016
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