The FDA has approved Crexont (Amneal), an extended-release capsule formulation of carbidopa/levodopa, for treatment of Parkinson's disease (PD), postencephalitic parkinsonism, and parkinsonism associated with carbon monoxide or manganese intoxication. Crexont contains a combination of immediate-release carbidopa/levodopa granules and extended-release levodopa pellets. An extended-release carbidopa/levodopa oral capsule (Rytary) has been available from the same manufacturer for years; the patent for Rytary expires in 2025.

The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems. No disease-modifying drugs are available for treatment of PD.

View the Comparison Table: Drugs for Parkinson's Disease

The FDA has approved opicapone (Ongentys – Neurocrine), a peripherally-acting reversible catechol-O-methyltransferase (COMT) inhibitor, for oral use as an adjunct to carbidopa/levodopa in adults with Parkinson’s disease (PD) who experience "off" episodes. It is the third COMT inhibitor to be approved for this indication; tolcapone (Tasmar, and generics) and entacapone (Comtan, and generics) were approved earlier. Opicapone has been available in Europe since 2016.

The FDA has approved istradefylline (Nourianz — Kyowa Kirin), an oral adenosine A_2A receptor antagonist, for use as an adjunct to carbidopa/levodopa in adults with Parkinson's disease (PD) who experience "off" episodes. Istradefylline is the first adenosine A_2A receptor antagonist to be approved in the US; it has been available in Japan since 2013.

The FDA has approved Inbrija (Acorda), an orally inhaled dry-powder formulation of levodopa, for intermittent treatment of "off" episodes in patients with Parkinson's disease (PD) being treated with carbidopa/levodopa (Sinemet, and others).

The motor symptoms of Parkinson's disease (PD) are caused primarily by degeneration of dopaminergic neurons in the substantia nigra. The nonmotor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems.

View the Comparison Table: Drugs for Parkinson's Disease

The FDA has approved the monoamine oxidase type B (MAO-B) inhibitor safinamide (Xadago – US Worldmeds) as an adjunct to levodopa/carbidopa for management of "off" episodes in patients with Parkinson’s disease (PD). It is the first reversible MAO-B inhibitor to be approved for this indication. Selegiline (Eldepryl, and others) and rasagiline (Azilect, and generics), two irreversible MAO-B inhibitors, have been used alone and as adjuncts to levodopa/carbidopa for many years. Safinamide is not approved for use as monotherapy.

The FDA has approved Duopa (Abbvie), a carbidopa/levodopa enteral suspension, for treatment of motor fluctuations in patients with advanced Parkinson's disease (PD). It has been available in Europe since 2001.

In patients with advanced PD, emptying of the stomach may be delayed and unpredictable, which can affect the rate and amount of absorption of carbidopa/levodopa and its efficacy. To bypass the stomach, the new formulation is delivered through a nasojejunal (NJ) tube or percutaneous endoscopic gastrostomy with jejunal (PEG-J) tube.

A randomized, double-blind, active-controlled, 12-week trial in 66 levodopa-responsive patients with advanced PD and motor complications found that Duopa reduced daily mean "off" time from baseline significantly more than oral immediate-release carbidopa/levodopa (by 4.04 hours vs 2.14 hours). Mean "on" time without troublesome dyskinesia increased by 4.11 hours with the new formulation and by 2.24 hours with immediate-release tablets.1

Duopa is available in a 100-mL single-use cassette containing 4.63 mg of carbidopa and 20 mg of levodopa per mL. It should be administered over 16 hours through a NJ or PEG-J tube with the CADD-Legacy 1400 portable infusion pump. Patients should be switched to oral immediate-release carbidopa/levodopa before starting Duopa; the labeling has instructions for conversion from immediate-release tablets to Duopa. The maximum recommended daily dose of levodopa is 2000 mg (1 cassette/day). Patients must also take oral immediate-release carbidopa/levodopa in the evening after disconnecting the pump. The medication cassette should be stored in the refrigerator and removed 20 minutes before administration.

One month's supply of Duopa costs $6054;2 PEG-J tube insertion and administration-related expenses will significantly increase the cost of treatment.3

1. CW Olanow et al. Continuous intrajejunal infusion of levodopa-carbidopa intestinal gel for patients with advanced Parkinson's disease: a randomised, controlled, double-blind, double-dummy study. Lancet Neurol 2014; 13:141.
2. Approximate WAC. WAC = wholesaler acquisition cost or manufacturer's published price to wholesalers; WAC represents a published catalogue or list price and may not represent an actual transactional price. Source: AnalySource® Monthly. July 5, 2015. Reprinted with permission by First Databank, Inc. All rights reserved. ©2015. www.fdbhealth.com/policies/drug-pricing-policy.
3. F Valldeoriola et al. Cost analysis of the treatments for patients with advanced Parkinson's disease: SCOPE study. J Med Econ 2013; 16:191.

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The FDA has approved a new formulation of carbidopa/levodopa (Rytary – Impax) in extended-release capsules for treatment of Parkinson’s disease (PD).

The motor symptoms of Parkinson's disease (PD) are caused primarily by progressive degeneration of dopaminergic neurons in the substantia nigra. The non-motor symptoms of the disease are thought to be caused by degeneration of other neurotransmitter systems.

Gabapentin enacarbil (Horizant – GlaxoSmithKline), a new extended-release (ER) tablet formulation of gabapentin, has been approved by the FDA for treatment of moderate-to-severe restless legs syndrome (RLS). The immediate-release (IR) formulation of gabapentin (Neurontin,and others), which is approved for treatment of epilepsy and postherpetic neuralgia, has been used for many years to treat RLS. Another ER tablet formulation of gabapentin (Gralise) has been approved by the FDA for treatment of postherpetic neuralgia.

Parkinson’s disease (PD) is caused primarily by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat PD because it does not cross the blood-brain barrier.