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Apokyn

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Apokyn

CLINICAL PHARMACOLOGY

Mechanism Of Action

APOKYN is a non-ergoline dopamine agonist with high in vitro binding affinity for the dopamine D4 receptor, and moderate affinity for the dopamine D2, D3, and D5, and adrenergic α1D, α2B, α2C receptors. The precise mechanism of action of APOKYN as a treatment for Parkinson's disease is unknown, although it is believed to be due to stimulation of post-synaptic dopamine D2-type receptors within the caudate-putamen in the brain.

Pharmacodynamics

Prolongation of the QTc Interval

In a placebo-controlled study in which patients received increasing single doses of APOKYN from 2 mg to up to 10 mg, the mean difference in QTc (measured by Holter monitor) between APOKYN and placebo was 0 msec at 4 mg, 1 msec at 6 mg, and 7 msec at 8 mg. Too few patients received a 10 mg dose to be able to adequately characterize the change in QTc interval at that dose.

In a controlled trial in which patients were administered placebo or a single dose of APOKYN (mean dose of 5.2 mg; range of 2 mg to 10 mg), the mean difference between APOKYN and placebo in the change in QTc was about 3 msec at 20 minutes and 90 minutes. In the entire database, 2 patients (one at 2 mg and 6 mg, one at 6 mg) exhibited large QTc increments ( > 60 msecs from pre-dose) and had QTc intervals greater than 500 msecs acutely after dosing. Doses of 6 mg or less thus are associated with minimal increases in QTc.

Decreases in blood pressure

Dose-dependent mean decrements in systolic blood pressure ranged from 5 mmHg after 2 mg to 16 mmHg after 10 mg. Dose-dependent mean decrements in diastolic blood pressure ranged from 3 mmHg after 2 mg to 8 mmHg after 10 mg. These changes were observed at 20 minutes, and were maximal between 20 and 40 minutes after dosing. Lesser, but still noteworthy blood pressure decrements persisted up to at least 90 minutes after dosing.

Pharmacokinetics

Absorption

Apomorphine hydrochloride is a lipophilic compound that is rapidly absorbed (time to peak concentration ranges from 10 minutes to 60 minutes) following subcutaneous administration into the abdominal wall. After subcutaneous administration, apomorphine appears to have bioavailability equal to that of an intravenous administration. Apomorphine exhibits linear pharmacokinetics over a dose range of 2 mg to 8 mg following a single subcutaneous injection of APOKYN into the abdominal wall in patients with idiopathic Parkinson's disease.

Distribution

The plasma-to-whole blood apomorphine concentration ratio is equal to one. Mean (range) apparent volume of distribution was 218 L (123 L to 404 L). Maximum concentrations in cerebrospinal fluid (CSF) are less than 10% of maximum plasma concentrations and occur 10 minutes to 20 minutes later.

Metabolism and Elimination

The mean apparent clearance (range) is 223 L/hr (125 L/hr to 401 L/hr) and the mean terminal elimination half-life is about 40 minutes (range about 30 minutes to 60 minutes).

The route of metabolism in humans is not known. Potential routes of metabolism in humans include sulfation, N-demethylation, glucuronidation and oxidation. In vitro, apomorphine undergoes rapid autooxidation.

Special Populations

The clearance of apomorphine does not appear to be influenced by age, gender, weight, duration of Parkinson's disease, levodopa dose or duration of therapy.

Renal Impairment

In a study comparing renally-impaired subjects (moderately impaired as determined by estimated creatinine clearance) to healthy matched volunteers, the AUC0-∞ and Cmax values were increased by approximately 16% and 50%, respectively, following a single subcutaneous administration of APOKYN into the abdominal wall. The mean time to peak concentrations and the mean terminal half-life of apomorphine were unaffected by the renal status of the individual. Studies in subjects with severe renal impairment have not been conducted. The starting dose for patients with mild or moderate renal impairment should be reduced [see DOSAGE AND ADMINISTRATION and Use In Specific Populations].

Hepatic Impairment

In a study comparing subjects with hepatic impairment (moderately impaired as determined by the Child-Pugh classification method) to healthy matched volunteers, the AUC0-∞ and Cmax values were increased by approximately 10% and 25%, respectively, following a single subcutaneous administration of APOKYN into the abdominal wall. Studies in subjects with severe hepatic impairment have not been conducted [see DOSAGE AND ADMINISTRATION and Use In Specific Populations].

Drug-Drug Interactions

Carbidopa/levodopa: Levodopa pharmacokinetics were unchanged when subcutaneous APOKYN and levodopa were co-administrated in patients. However, motor response differences were significant. The threshold levodopa concentration necessary for an improved motor response was reduced significantly, leading to an increased duration of effect without a change in the maximal response to levodopa therapy.

Other Drugs Eliminated Via Hepatic Metabolism

Based upon an in vitro study, cytochrome P450 enzymes play a minor role in the metabolism of apomorphine. In vitro studies have also demonstrated that drug interactions are unlikely due to apomorphine acting as a substrate, an inhibitor, or an inducer of cytochrome P450 enzymes.

COMT Interactions

A pharmacokinetic interaction of APOKYN with catechol-O-methyl transferase (COMT) inhibitors or drugs metabolized by this route is unlikely since apomorphine appears not to be metabolized by COMT.

Clinical Studies

The effectiveness of APOKYN in the acute symptomatic treatment of the recurring episodes of hypomobility, “off” episodes (“end-of-dose wearing off” and unpredictable “on/off” episodes), in patients with advanced Parkinson's disease was established in three randomized, controlled trials of APOKYN given subcutaneously (Studies 1, 2, and 3). At baseline in these trials, the mean duration of Parkinson's disease was approximately 11 years. Whereas all patients were using concomitant L-dopa at baseline, 86% of patients were using a concomitant oral dopaminergic agonist, 31% were using a concomitant catechol-ortho-methyl transferase COMT) inhibitor, and 10% were using a concomitant monoamine B oxidase inhibitor. Study 1 was conducted in patients who did not have prior exposure to APOKYN (i.e., APOKYN na´ve) and Studies 2 and 3 were conducted in patients with at least 3 months of APOKYN use immediately prior to study enrollment. Almost all patients without prior exposure to APOKYN began taking an antiemetic (trimethobenzamide) three days prior to starting APOKYN and 50% of patients were able to discontinue the concomitant antiemetic, on average 2 months after initiating APOKYN.

The change from baseline in Part III (Motor Examination) of the Unified Parkinson's Disease Rating Scale (UPDRS) served as the primary outcome assessment measure in each study. Part III of the UPDRS contains 14 items designed to assess the severity of the cardinal motor findings (e.g., tremor, rigidity, bradykinesia, postural instability, etc.) in patients with Parkinson's disease.

Study 1

Study 1 was a randomized, double-blind, placebo-controlled, parallel-group trial in 29 patients with advanced Parkinson's disease who had at least 2 hours of “off” time per day despite an optimized oral regimen for Parkinson's disease including levodopa and an oral dopaminergic agonist. Patients with atypical Parkinson's disease, psychosis, dementia, hypotension, or those taking dopamine antagonists were excluded from participation. In an office setting, hypomobility was allowed to occur by withholding the patients' Parkinson's disease medications overnight. The following morning, patients (in a hypomobile state) were started on study treatment in a 2:1 ratio (2 mg of APOKYN or placebo given subcutaneously). At least 2 hours after the first dose, patients were given additional doses of study medication until they achieved a “therapeutic response” (defined as a response similar to the patient's response to their usual dose of levodopa) or until 10 mg of APOKYN or placebo equivalent was given. At each injection re-dosing, the study drug dose was increased in 2 mg increments up to 4 mg, 6 mg, 8 mg, 10 mg of APOKYN) or placebo equivalent.

Of the 20 patients randomized to APOKYN, 18 achieved a “therapeutic response” at about 20 minutes. The mean APOKYN dose was 5.4 mg (3 patients on 2 mg, 7 patients on 4 mg, 5 patients on 6 mg, 3 patients on 8 mg, and 2 patients on 10 mg). In contrast, of the 9 placebo-treated patients, none reached a “therapeutic response.” The mean change-from-baseline for UPDRS Part III score for APOKYN group (highest dose) was statistically significant compared to that for the placebo group (Table 2).

Table 2: Mean Change from Baseline in UPDRS Motor Score for Intent-to-Treat Population in Study 1

Treatment Baseline UPDRS Motor Score Mean Change from Baseline Difference from placebo
Placebo 36.3 - 0.1 NA
APOKYN 39.7 -23.9 -23.8

Study 2

Study 2 used a randomized, placebo-controlled crossover design of 17 patients with Parkinson's disease who had been using APOKYN for at least 3 months. Patients received their usual morning doses of Parkinson's disease medications and were followed until hypomobility occurred, at which time they received either a single dose of subcutaneous APOKYN (at their usual dose) and placebo on different days in random order. UPDRS Part III scores were evaluated over time. The mean dose of APOKYN was 4 mg (2 patients on 2 mg, 9 patients on 3 mg, 2 patients on 4 mg, and 1 patient each on 4.5 mg, 5 mg, 8 mg, and 10 mg). The mean change-from-baseline UPDRS Part III score for the APOKYN group was statistically significant compared to that for the placebo group (Table 3).

Table 3: Mean Change from Baseline in UPDRS Motor Score for Intent-to-Treat Population in Study 2

Treatment Baseline UPDRS Motor Score Mean Change from Baseline Difference from placebo
Placebo 40.1 - 3.0 NA
APOKYN 41.3 -20.0 - 17.0

Study 3

Study 3 used a randomized withdrawal design in 4 parallel groups from 62 patients (APOKYN-35; Placebo-27) with Parkinson's disease who had been using APOKYN for at least 3 months. Patients were randomized to one of the following 4 treatments dosed once by subcutaneous administration: APOKYN at the usual dose (mean dose 4.6 mg), placebo at a volume matching the usual APOKYN dose, APOKYN at the usual dose + 2 mg (0.2 mL) (mean dose 5.8 mg), or placebo at a volume matching the usual APOKYN dose + 0.2 mL. Patients received their usual morning doses of Parkinson's disease medications and were followed until hypomobility occurred, at which time they received the randomized treatment. APOKYN doses ranged between 2 mg – 10 mg. The mean change-from-baseline for the APOKYN group for UPDRS Part III scores at 20 minutes post dosing was statistically significant compared to that for the placebo group (Table 4). Figure 2 describes the mean change from baseline in UPDRS Motor Scores over time for pooled APOKYN and placebo administration.

Table 4: Mean Change from Baseline in UPDRS Motor Score for Intent-to-Treat Population in Study 4

Treatment Baseline UPDRS Motor Score Mean Change from Baseline Difference from placebo
Placebo (Pooled) 40.6 - 7.4 NA
APOKYN (Pooled) 42.0 -24.2 - 16.8

Figure 2: Mean Change from Baseline in UPDRS Motor Scores of Pooled APOKYN Groups and Placebo Group in Study 3

Mean Change from Baseline in UPDRS Motor Scores of Pooled APOKYN Groups and Placebo Group - Illustration

In Study 3, the mean changes-from-baseline for UPDRS Part III scores at 20 minutes post dosing for the APOKYN and higher dose APOKYN groups were 24 and 25, respectively. This result suggests that patients chronically treated at a dose of 4 mg might derive little additional benefit from a dose increment of 2 mg. There was also an increased incidence of adverse reactions in patients randomized to higher APOKYN dose.

Last reviewed on RxList: 8/8/2014
This monograph has been modified to include the generic and brand name in many instances.

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