How Mirapex works
Patients with PD have a lack of a chemical called dopamine in the brain. This is caused by the death of nerve cells that produce dopamine, a neurotransmitter or chemical messenger that sends signals between nerve cells in the brain. One of the processes regulated by dopamine signaling is movement. The reduction in dopamine in the brain results in a progressive loss of control over movement as well as other non-motor symptoms.
Mirapex is part of a class of drugs called “dopamine agonist”. It is a substance that has similar properties to dopamine and can fulfill some of the dopamine’s functions in the brain. It is thought that it can act as a substitute for dopamine in the brains of PD patients, relieving some of the motor symptoms caused by the lowered levels of dopamine.
Mirapex is frequently taken alongside levodopa, a chemical that is converted to dopamine by the body. Levodopa is the main treatment used for PD once the disease has progressed. However, with extended use, many patients experience significant “off” periods when the symptoms of the disease return before another dose of levodopa can be taken. It can extend the length of time levodopa is active for.
Mirapex in clinical trials
Immediate release Mirapex was approved by the U.S. Food and Drug Administration (FDA) for the treatment of PD in January 1997. A range of clinical studies was conducted prior to approval, but there were three key trials that resulted in the drug being approved. Two of these were conducted in early stage PD patients, and the third in advanced PD patients. The primary end point of the trials was the change in score on the four-part Unified Parkinson’s Disease Rating Scale (UPDRS) over the course of the treatment.
The first early stage PD trial enrolled patients with little to no exposure to levodopa, and assessed the effect of a six-month period of Mirapex treatment compared to a placebo, following a seven-week dose escalation period. The second trial had participants who had not received levodopa treatment but could be on other PD medication. It consisted of a six-week dose escalation of Mirapex followed by a four-week maintenance period compared to a placebo. Both studies showed a significant improvement in UPDRS scores.
In advanced PD patients, a six-month Mirapex treatment (following a seven-week dose escalation) resulted in a significant two-hour reduction in “off” time per day, compared to the placebo group.
The extended release formulation of Mirapex was approved in February 2010. The approval was following two clinical studies that demonstrated a benefit of extended release Mirapex in early stage and advanced stage PD.
The early stage PD study involved patients that had not had levodopa treatment previously. Patients received either extended release Mirapex, immediate release Mirapex, or a placebo for a total of 33 weeks. Levodopa was permitted during the trial period if the symptoms became too severe, which occurred for 21 percent of patients treated with placebo but only seven percent of those on extended release Mirapex. Furthermore, a significant improvement was seen in UPDRS scores in the patients treated with extended release Mirapex compared to those given placebo.
Patients with advanced PD experiencing motor fluctuations on levodopa therapy received either extended release Mirapex, immediate release Mirapex, or a placebo for a seven-week dose titration period followed by a 26-week maintenance period. After 33 weeks, there was a significant improvement in UPDRS score in patients treated with extended release Mirapex compared to those given placebo.
The following side effects are commonly seen in early PD patients treated with Mirapex: somnolence (sudden episodes of falling asleep), nausea, constipation, dizziness, fatigue, hallucinations, dry mouth, muscle spasms, and peripheral edema.
In advanced PD patients, common side effects include dyskinesia (impaired voluntary movements), nausea, constipation, hallucinations, headache, and anorexia (loss of appetite) due to the concurrent levodopa treatment.
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