How does Mirapex work?
Parkinson’s disease leads to a lack of dopamine in the brain. Dopamine is a neurotransmitter or chemical messenger that sends signals between nerve cells in the brain. Parkinson’s is characterized by the death of nerve cells that produce dopamine. One of the processes regulated by dopamine signaling is movement, so less 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 agonists.” It is a substance that mimics the effect of dopamine by binding to dopamine receptors.
The therapy has similar properties to dopamine and is thought to act as a substitute for dopamine in the brains of Parkinson’s patients to relieve some of the motor symptoms caused by low dopamine levels.
Mirapex is frequently taken alongside levodopa, a medication that is converted to dopamine by the body. Levodopa is the main treatment used for Parkinson’s 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. Mirapex can not only extend the length of time levodopa is active but also reduce the daily dosage of levodopa needed.
Who can take Mirapex?
Mirapex IR was approved for Parkinson’s disease by the U.S Food and Drug Administration (FDA) in June 1997 and by the European Commission in March 1998.
In 2006, Mirapex was approved in the U.S and Europe to treat restless legs syndrome, a neurological condition.
The ER formulation of Mirapex was approved by the FDA in March 2010. It was previously approved in Europe for the same indication in October 2009.
Who should not take Mirapex?
Because Mirapex is eliminated through the kidneys, caution should be taken when prescribing the therapy to those with kidney impairment.
Pregnant women should consult with their doctors to determine if the potential benefit of Mirapex justifies the potential risk to the fetus.
Lactation problems are expected since Mirapex inhibits the secretion of prolactin, the hormone responsible for the production of breast milk. Nursing mothers should carefully consider the health benefits of breastfeeding versus the potential adverse effects on the breastfed infant.
How is Mirapex administered?
Mirapex is taken orally, with or without food, either as IR or ER tablets.
- the starting dose of Mirapex IR is 0.125 mg three times a day, which can be increased every five to seven days up to a maximum daily dose of 4.5 mg, given as 1.5 mg three times a day.
- ER tablets are taken once daily, with a starting dose of 0.375 mg, which can be increased gradually every five to seven days up to a maximum recommended dose of 4.5 mg per day.
How has Mirapex been tested?
Trials for Mirapex IR
A range of clinical studies was conducted prior to Mirapex’s approval, but three Phase 3 trials were key to the therapy getting approved. Two of these were conducted in early-stage Parkinson’s patients, and the third in advanced Parkinson’s patients.
The primary objective of the trials was to measure the change in scores on the four-part Unified Parkinson’s Disease Rating Scale (UPDRS) over the course of the treatment. UPDRS is a questionnaire that evaluates motor and non-motor symptoms related to Parkinson’s.
The first early-stage trial was a placebo-controlled study that enrolled 335 patients with little to no exposure to levodopa. The study 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 included 264 early-stage patients who were not on levodopa but could be on other Parkinson’s medications. It consisted of a six-week dose escalation of Mirapex followed by a four-week maintenance period.
Both studies showed significant improvement in UPDRS scores in patients treated with Mirapex, compared with a placebo.
A Phase 3 trial was conducted in advanced Parkinson’s patients in the U.S. and Canada. The study involved 360 patients who received Mirapex for six months (following a seven-week dose escalation). Results showed a significant two-hour reduction in “off” time per day, compared to the placebo group.
Trials for Mirapex ER
The approval for Mirapex ER followed two clinical studies that showed a benefit of the treatment in both early and advanced stages of Parkinson’s disease.
The early-stage study (NCT00479401) was a placebo-controlled trial in patients who had not received levodopa previously. Participants received either Mirapex ER, Mirapex IR, or a placebo for a total of 33 weeks. Levodopa was allowed during the trial period if the symptoms became too severe, which occurred in 21% of the patients on the placebo and 7% of those on Mirapex ER. A significant improvement was seen in UPDRS scores in patients treated with Mirapex ER compared to those given the placebo.
A randomized, double-blind, placebo-controlled trial was also conducted in patients with advanced disease. Patients experienced motor fluctuations on levodopa therapy and received either Mirapex ER, Mirapex IR, 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 scores in patients treated with Mirapex ER compared to those given the placebo.
What are common side effects?
The following side effects are common in early-stage Parkinson’s patients treated with Mirapex:
- somnolence (sudden episodes of falling asleep)
- dry mouth
- muscle spasms
- peripheral edema (swelling of the hands or feet)
In advanced disease patients, common side effects include:
- dyskinesia (uncontrolled involuntary movements)
- anorexia due to concurrent levodopa treatment
Dopamine antagonists, which are used to turn down dopamine activity, may reduce the effectiveness of Mirapex. Among those are neuroleptics, also known as antipsychotic treatments, that are used to treat many psychiatric conditions.
Last updated: March 23, 2022, by Teresa Carvalho, MSc
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