Get your patient on Carbidopa And Levodopa - Carbidopa And Levodopa tablet, Extended Release (Carbidopa And Levodopa)

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 carbidopa and levodopa tablets and carbidopa and levodopa extended-release tablets are different, appropriate adjustments should be made, as shown in Table 2.

Table 2: Approximate Bioavailabilities at Steady State•

• This table is only a guide to bioavailabilities since other factors such as food, drugs, and inter-patient variabilities may affect the bioavailability of carbidopa and levodopa.

^† The extent of availability of levodopa from carbidopa and levodopa extended-release tablets was about 70-75% relative to intravenous levodopa or standard carbidopa and levodopa tablets in the elderly.

‡  The extent of availability of levodopa from carbidopa and levodopa tablets was 99% relative to intravenous levodopa in the healthy elderly.

Dosage with carbidopa and levodopa extended-release tablets 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 carbidopa and levodopa extended-release tablets ). The interval between doses of carbidopa and levodopa extended-release tablets should be 4-8 hours during the waking day. (See CLINICAL PHARMACOLOGY, Pharmacodynamics. )

A guideline for initiation of carbidopa and levodopa extended-release tablets is shown in Table 3.

Table 3: Guidelines for Initial Conversion from Carbidopa and Levodopa Tablets to Carbidopa and Levodopa Extended-Release Tablets

•For dosing ranges not shown in the table see DOSAGE AND ADMINISTRATION, Initial Dosage — Patients currently treated with conventional carbidopa levodopa preparations.

Patients currently treated with levodopa without a decarboxylase inhibitor: Levodopa must be discontinued at least twelve hours before therapy with carbidopa and levodopa extended-release tablets is started. Carbidopa and levodopa extended-release tablets 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 carbidopa and levodopa extended-release tablets 50 mg/200 mg b.i.d.

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

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 carbidopa and levodopa extended-release tablets 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 carbidopa and levodopa extended-release tablets (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 carbidopa and levodopa extended-release tablets 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.

Because Parkinson's disease is progressive, periodic clinical evaluations are recommended; adjustment of the dosage regimen of carbidopa and levodopa extended-release tablets may be required.

Anticholinergic agents, dopamine agonists, and amantadine can be given with carbidopa and levodopa extended-release tablets. Dosage adjustment of carbidopa and levodopa extended-release tablets may be necessary when these agents are added.

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

Sporadic cases of hyperpyrexia and confusion have been associated with dose reductions and withdrawal of carbidopa and levodopa tablets or carbidopa and levodopa extended-release tablets. Patients should be observed carefully if abrupt reduction or discontinuation of carbidopa and levodopa extended-release tablets is required, especially if the patient is receiving neuroleptics. (See WARNINGS .)

If general anesthesia is required, carbidopa and levodopa extended-release tablets 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.

Parkinson's disease is a progressive, neurodegenerative disorder of the extrapyramidal nervous system affecting the mobility and control of the skeletal muscular system. Its characteristic features include resting tremor, rigidity, and bradykinetic movements. Symptomatic treatments, such as levodopa therapies, may permit the patient better mobility.

Current evidence indicates that symptoms of Parkinson's disease are related to depletion of dopamine in the corpus striatum. Administration of dopamine is ineffective in the treatment of Parkinson's disease apparently because it does not cross the blood-brain barrier. However, levodopa, the metabolic precursor of dopamine, does cross the blood-brain barrier, and presumably is converted to dopamine in the brain. This is thought to be the mechanism whereby levodopa relieves symptoms of Parkinson's disease.

When levodopa is administered orally, it is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the central nervous system. For this reason, large doses of levodopa are required for adequate therapeutic effect, and these may often be accompanied by nausea and other adverse reactions, some of which are attributable to dopamine formed in extracerebral tissues.

Since levodopa competes with certain amino acids for transport across the gut wall, the absorption of levodopa may be impaired in some patients on a high protein diet.

Carbidopa inhibits decarboxylation of peripheral levodopa. It does not cross the blood-brain barrier and does not affect the metabolism of levodopa within the central nervous system.

Since its decarboxylase inhibiting activity is limited to extracerebral tissues, administration of carbidopa with levodopa makes more levodopa available for transport to the brain.

Patients treated with levodopa therapy for Parkinson's disease may develop motor fluctuations characterized by end-of-dose failure, peak dose dyskinesia, and akinesia. The advanced form of motor fluctuations (‘on-off’ phenomenon) is characterized by unpredictable swings from mobility to immobility. Although the causes of the motor fluctuations are not completely understood, in some patients they may be attenuated by treatment regimens that produce steady plasma levels of levodopa.

Carbidopa and levodopa extended-release tablets contains either 50 mg of carbidopa and 200 mg of levodopa, or 25 mg of carbidopa and 100 mg of levodopa in an extended-release dosage form designed to release these ingredients over a 4-to 6-hour period. With carbidopa and levodopa extended-release tablets there is less variation in plasma levodopa levels than with carbidopa and levodopa immediate release tablets, the conventional formulation. However, carbidopa and levodopa extended-release tablets are less systemically bioavailable than carbidopa and levodopa tablets and may require increased daily doses to achieve the same level of symptomatic relief as provided by carbidopa and levodopa tablets.

In clinical trials, patients with moderate to severe motor fluctuations who received carbidopa and levodopa extended-release tablets did not experience quantitatively significant reductions in ‘off’ time when compared to carbidopa and levodopa tablets. However, global ratings of improvement as assessed by both patient and physician were better during therapy with carbidopa and levodopa extended-release tablets than with carbidopa and levodopa tablets. In patients without motor fluctuations, carbidopa and levodopa extended-release tablets, under controlled conditions, provided the same therapeutic benefit with less frequent dosing when compared to carbidopa and levodopa tablets.

Carbidopa reduces the amount of levodopa required to produce a given response by about 75% and, when administered with levodopa, increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid.

Elimination half-life of levodopa in the presence of carbidopa is about 1.5 hours. Following carbidopa and levodopa extended-release tablets, the apparent half-life of levodopa may be prolonged because of continuous absorption.

In healthy elderly subjects (56-67 years old) the mean time-to-peak concentration of levodopa after a single dose of carbidopa and levodopa extended-release tablets 50mg/200mg was about 2 hours as compared to 0.5 hours after standard carbidopa and levodopa tablets. The maximum concentration of levodopa after a single dose of carbidopa and levodopa extended-release tablets was about 35% of the standard carbidopa and levodopa tablets (1151 vs. 3256 ng/mL). The extent of availability of levodopa from carbidopa and levodopa extended-release tablets was about 70-75% relative to intravenous levodopa or standard carbidopa and levodopa tablets in the elderly. The absolute bioavailability of levodopa from carbidopa and levodopa extended-release tablets (relative to I.V.) in young subjects was shown to be only about 44%. The extent of availability and the peak concentrations of levodopa were comparable in the elderly after a single dose and at steady state after t.i.d. administration of carbidopa and levodopa extended-release tablets 50mg/200mg. In elderly subjects, the average trough levels of levodopa at steady state after the extended-release tablet were about 2 fold higher than after the standard carbidopa and levodopa tablets (163 vs. 74 ng/mL).

In these studies, using similar total daily doses of levodopa, plasma levodopa concentrations with carbidopa and levodopa extended-release tablets fluctuated in a narrower range than with carbidopa and levodopa tablets. Because the bioavailability of levodopa from carbidopa and levodopa extended-release tablets relative to carbidopa and levodopa tablets is approximately 70-75%, the daily dosage of levodopa necessary to produce a given clinical response with the sustained-release formulation will usually be higher.

The extent of availability and peak concentrations of levodopa after a single dose of carbidopa and levodopa extended-release tablets 50 mg/200 mg increased by about 50% and 25%, respectively, when administered with food.

At steady state, the bioavailability of carbidopa from carbidopa and levodopa tablets is approximately 99% relative to the concomitant administration of carbidopa and levodopa. At steady state, carbidopa bioavailability from carbidopa and levodopa extended-release tablets 50 mg/200 mg is approximately 58% relative to that from carbidopa and levodopa tablets.

Pyridoxine hydrochloride (vitamin B ₆ ), in oral doses of 10 mg to 25 mg, may reverse the effects of levodopa by increasing the rate of aromatic amino acid decarboxylation. Carbidopa inhibits this action of pyridoxine.

Geriatric: A study in eight young healthy subjects (21-22 yr) and eight elderly healthy subjects (69-76 yr) showed that the absolute bioavailability of levodopa was similar between young and elderly subjects following oral administration of levodopa and carbidopa. However, the systemic exposure (AUC) of levodopa was increased by 55% in elderly subjects compared to young subjects. Based on another study in forty patients with Parkinson’s disease, there was a correlation between age of patients and the increase of AUC of levodopa following administration of levodopa and an inhibitor of peripheral dopa decarboxylase. AUC of levodopa was increased by 28% in elderly patients (≥ 65 yr) compared to young patients (< 65 yr). Additionally, mean value of C _max for levodopa was increased by 24% in elderly patients (≥ 65 yr) compared to young patients (< 65 yr) (see PRECAUTIONS, Geriatric Use ).

The AUC of carbidopa was increased in elderly subjects (n=10, 65-76 yr) by 29% compared to young subjects (n=24, 23-64 yr) following IV administration of 50 mg levodopa with carbidopa (50 mg). This increase is not considered a clinically significant impact.