Selegiline and rasagiline: twins or distant cousins?

Parkinson's disease is a complicated disease state that affects patients' quality of life. The first monoamine oxidase (MAO-B) inhibitor for PD, selegiline (Eldepryl), was approved by the Food and Drug Administration (FDA) in 1996, and rasagiline (Azilect) received FDA approval in 2006. At first, pharmacists may assume that rasagiline is just another me-too drug. There are three areas in which the two medications differ from each other: MAO type A inhibitors are found in high concentrations in the intestines, and MAO type B inhibitors are found mostly in the brain. If MAO-A inhibition occurs, the body cannot protect itself from exogenous amines such as tyramine. The absorbed tyramine can cause hypertensive crisis, also known as the cheese reaction. Selegiline's capsule product labeling includes a bolded warning that it "should not be used at daily doses exceeding 10 mg per day because of the risks associated with non-selective inhibition of MAO." It also says, "the selectivity of selegiline for MAO B may not be absolute, even at the recommended daily dose." The fact that rasagiline has the same effect has been challenged by two main-stream studies. Selegiline is a propargyl amphetamine derivative that undergoes extensive first-pass metabolism to L-methamphetamine and L-amphetamine. Rasagiline's major metabolite is amioindan, which has no amphetaminelike properties. Selegiline has been reviewed looking for neuroprotection, but studies have been unable to come to a definite positive neuroprotection conclusion. Proponents of rasagiline's neuroprotective effects also point to clinical studies in humans that demonstrate delayed and reduced need for future use of levodopa. In summary, selegiline and rasagiline look more and more like distant cousins instead of twins.