MAO-B Inhibitors in PD
Monoamine oxidase is an enzyme that breaks down certain neurotransmitters (chemical messengers) in the brain including dopamine, one of the chemicals that are deficient in the brains of Parkinson’s patients. Monoamine oxidase inhibitorsblock this enzyme, preventing the breakdown of dopamine. Therefore there is more dopamine available, leading to fewer motor symptoms.
There are two main MAO – B inhibitors that are used in Parkinson’s disease treatment - selegiline (Eldepryl, Zelapar) andrasagiline(Azilect). In general this group of medications may be used on their own early in the course of the disease to help control the motor symptoms that are typical of Parkinson’s. In fact their use has been shown to delay the need for starting other symptomatic antiparkinsonian drugs such as dopamine replacement or dopamine agonists.
MAO – B inhibitors are also indicated for use in combination with other medications at all stages of PD, early or late. When combined with other medications, MAO – B inhibitors help reduce “off” times patients may have experienced with their existing treatment. Specifically they work to prolong the effects of levodopa therapy thereby improving motor functioning and making activities of daily living easier.
In recent years, there have been a number of studies looking at whether these medications are actually disease modifying. In other words, do they slow down the progression of Parkinson’s? Although these medications are helpful in the treatment of Parkinson’s disease, there is no conclusive clinical trial evidence that they are disease-modifying when it comes to the natural history of this chronic disease.
Selegiline is generally well tolerated but it does have a few side effects including headaches, dry mouth, dizziness and nausea. Because this medication is converted into an amphetamine like by-product, it may also cause insomnia, jitteriness and loss of appetite. Rasagiline is a more potent inhibitor than selegiline and its side effect profile includes headache, nausea and flu-like symptoms. When combined with levodopa therapy, increased dyskinesias (involuntary movements), hallucinations or vivid dreaming may occur.
With older MAO inhibitors (used as anti-depressants) there was significant concern with regards to their interaction with tyramine rich foods (for example aged cheese, beer, red wine, sauerkraut, soy sauce). Eating these foods results in what is known as the “cheese effect” where the person would suffer a hypertensive crisis - an episode of extreme high blood pressure that can result in heart, kidney or brain damage. The newer MAO – B inhibitors are much more selective and can technically be used without dietary restrictions except when they are taken in high doses, a situation where they lose their selectivity.
Drug interactions are a concern with this category of medications. Selegiline is contraindicated if taking meperedine or other opioids. Rasagiline should also not be taken with meperidine or other narcotic medications as well as other drugs such as cyclobenzaprine, mirtazapine and certain cold medications. Rasagiline should also not be taken within 5 weeks of some antidepressants including fluoxetine (Prozac) This list is by no means all inclusive so if you’re taking an MAO – B inhibitor it is important to consult with your physician or pharmacist before taking any other prescribed or over-the-counter medication in order to avoid potentially dangerous interactions.
MAO – B inhibitors do have a role to play in today’s management of Parkinson’s disease. Regardless of whether or not this group of medications is disease modifying, they are still a useful option either as monotherapy or as an adjunct to dopamine replacement.