Monamine Oxidase Type B Inhibitors

The next dopaminergic medication we will discuss is a Monamine Oxidase Type B (MAO-B) inhibitor. These medications treat the manifestations of Parkinson’s disease and are often adjunct to levodopa/carbidopa.

Prototype and Other Medications

Medication Classification – Antiparkinson Agent/Monoamine Oxidase-B Inhibitors

The prototype medication for MAO-B inhibitors is selegiline. Another medication in this category is rasagiline.

Expected Pharmacologic Action

Indirect-acting dopamine receptor agonists inhibit the action of the enzyme monoamine oxidase B in the brain and other parts of the body. Monoamine oxidase inactivates several chemical neurotransmitters. MAO-A inactivates epinephrine and norepinephrine. MAO-B inactivates dopamine. A deficiency of dopamine causes Parkinson’s disease. By inhibiting this enzyme, dopamine is not inactivated, and more is available to the brain. Giving MAO-B inhibitors as an adjunct to levodopa/carbidopa prolongs the effects and enhances the effectiveness of both medications.

Adverse Drug Reactions

Insomnia is a major adverse effect specific to selegiline. This can be alleviated by administering the last dose of the day no later than 12 noon. At high doses, selegiline can act like a MAO-A inhibitor and cause a hypertensive crisis as a result of ingesting a medication that contains ephedrine or foods that contains tyramine, such as aged cheese and processed meats. Irritation of oral mucous membranes may also occur with the orally-disintegrating tablet form of the medication.

Interventions

Monitor for insomnia when caring for clients taking selegiline. A change in the prescribed dose or its time of administration may help resolve this manifestation. Monitor blood pressure closely for hypertension. Assist with menu selections so clients know which foods and beverages contain tyramine or caffeine and should be avoided. Carefully evaluate any other medications clients are taking, especially when the provider adds a new medication to the medication regimen. When administering the form of selegiline that dissolves on the tongue, visually inspect the tongue and oral cavity on a regular basis for irritation.

Safety Alert

If clients taking an MAO-B inhibitor suddenly develop a headache, nausea, and vomiting, measure their blood pressure immediately. These manifestations may indicate a hypertensive crisis due to an interaction of the MAOI with another medication or a food containing tyramine.

Administration

Selegiline is available in capsules, tablets, an orally disintegrating form, and a transdermal patch. Give the orally disintegrating form by placing it on the top of the tongue and keep the client from eating or drinking for 5 minutes before or after administration. Give it before the morning meal. Do not give any form of selegiline after noon due to its ability to cause insomnia.

Client Instructions

When telling clients how to take MAO-B inhibitors, make sure they know to take the last dose of the day by noon to prevent insomnia. Advise them to report irritation of the tongue or elsewhere in the oral cavity to the provider. Tell them to notify the provider before taking any new medications because of the number of medications that can interact with selegiline and cause a hypertensive crisis. Reinforce that even over-the-counter medications and herbal supplements may interact with selegiline.

Contraindications and Precautions

Contraindications to the use of MAO-B inhibitors are clients who have hypersensitivity. Use these drugs with caution in clients who have a history of peptic ulcer disease.

Interactions

MAO-B inhibitors interact with many different types of medications. Their use with meperidine, also called Demerol, and other opioids, MAOIs, tricyclic antidepressants, and selective serotonin reuptake inhibitors, also called SSRI antidepressants, may cause a high fever and muscle rigidity. Eating foods that contain tyramine or taking herbal medications, such as ephedra, St. John’s wort, ginseng, or ma huang, may cause severe hypertension. This interaction, however, is less likely with selegiline than with MAOI medications. Antihypertensive medications, diuretics, and general anesthetics may cause hypotension.

Safety Alert

Clients taking any MAOI should notify the provider prior to taking ANY new prescription or over-the-counter medications. Many medications interact with MAOIs and can cause a life-threatening hypertensive crisis if clients take them together.