chemistry

Pargyline

Pargyline is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pargyline rather than just read about it. In short: Pargyline, sold under the brand name Eutonyl among others, is a monoamine oxidase inhibitor (MAOI) medication which has been used to treat hypertension (high blood pressure) but is no longer marketed. It has also been studied as an antidepressant, but was never licensed for use in the treatment of depression.

Key takeaways

Pargyline belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pargyline to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pargyline from memory before moving on to harder problems.

Reference excerpt

Pargyline, sold under the brand name Eutonyl among others, is a monoamine oxidase inhibitor (MAOI) medication which has been used to treat hypertension (high blood pressure) but is no longer marketed. It has also been studied as an antidepressant, but was never licensed for use in the treatment of depression. The drug is taken by mouth. Side effects of pargyline include orthostatic hypotension among others. It has the potential for serious food and drug interactions with sympathomimetic agents like tyramine that can result in hypertensive crisis. Pargyline acts as a non-selective and irreversible inhibitor of the monoamine oxidases MAO-A and MAO-B. The exact mechanism of the hypotensive effects of pargyline and other MAOIs is unclear. Structurally, pargyline is a benzylamine derivative and is related to selegiline and clorgyline. Pargyline was first described in 1960 and was introduced for medical use in 1963. It was available in the United States and the United Kingdom. The clinical use of pargyline was limited due to its side effects and interactions. The drug remained available in the United States as late as 2000, but was fully discontinued worldwide by 2007.

Medical uses Pargyline is used as an antihypertensive agent in the treatment of hypertension (high blood pressure). The dosage was 12.5 to 200 mg per day. Its onset of action is slow and several weeks of continuous administration are required for the effects to develop fully upon initiation of treatment. The decrease in blood pressure with pargyline is described as impressive and is especially strong when standing. However, the blood pressure decrease with pargyline is often difficult to control adequately. Pargyline shares its mechanism of action, monoamine oxidase inhibition, with a class of antidepressants that includes phenelzine, tranylcypromine, and isocarboxazid, among others. However, unlike other MAOIs, pargyline itself was never licensed for treatment of depression. In any case, the drug was studied in the treatment of depression and was advertised in the 1960s as an antihypertensive agent that also "brightens emotional outlook".

Side effects Orthostatic hypotension (excessively low blood pressure when standing or standing up) is a prominent side effect of pargyline. Other side effects include dry mouth, dizziness, nausea, headaches, increased appetite, nervousness, insomnia, agitation, sedation, manic reactions, and psychotic reactions.

Interactions Pargyline has the potential for serious food and drug interactions due to its MAOI actions. This includes hypertensive crisis with intake of norepinephrine releasing agents like tyramine, amphetamine, and ephedrine. Tyramine is found in high concentrations in certain cheeses and other foods and can result in hypertensive crisis often referred to as the "cheese reaction". Episodes of hypertensive crisis can be severe or fatal and this has greatly limited the clinical use of pargyline. Hypertensive crisis with pargyline is treated intravenously with sympatholytic alpha blockers like phentolamine. Combination of pargyline and the antihypertensive agent methyldopa has been found to result in intense and potentially fatal central nervous system excitation in rodents. This has been said to resemble the effects of amphetamine overdose. The interaction appears to be due to inhibition by pargyline of the metabolism of normally short-lived methyldopa metabolites like α-methyldopamine and α-methylnorepinephrine that act as potent catecholamine releasing agents. Visual hallucinations have been reported with coadministration of pargyline and methyldopa in humans. As such, use of methyldopa in combination with pargyline and other MAOIs is contraindicated. Pargyline is also a disulfiram-like drug and aldehyde dehydrogenase (ALDH) inhibitor similarly to disulfiram and can produce alcohol intolerance-type reactions with alcohol.

Pharmacology

Pharmacodynamics

Monoamine oxidase inhibition Pargyline is a non-selective and irreversible monoamine oxidase inhibitor (MAOI), or an inhibitor of the monoamine oxidase (MAO) enzyme. This enzyme is involved in the metabolism of the monoamine neurotransmitters serotonin, norepinephrine, and dopamine. Pargyline is said to have slight preference or selectivity for inhibition of MAO-B over MAO-A (IC50Tooltip half-maximal inhibitory concentration = 8.20 nM and 11.52 nM, respectively). Using rodent systems however, pargyline showed 2- to 356-fold selectivity for MAO-B inhibition over MAO-A inhibition in different studies (compared to 16- to 6401-fold selectivity with selegiline). In relation to the preceding, pargyline has been referred to as a so-called semi-selective MAO-B inhibitor. It has also been found to show some selectivity for MAO-B inhibition with a single dose but results in non-selective inhibition with continuous administration. Pargyline produces its antihypertensive effects via MAO inhibition. However, the exact mechanism of action by which this occurs is unclear. Pargyline and other MAOIs inhibit the metabolism of norepinephrine and cause accumulation of norepinephrine in the heart, brain, and other adrenergic tissues. Some possibilities include diminished responsiveness to norepinephrine via increased norepinephrine levels in blood vessels and blockade blockade of the release of norepinephrine from peripheral sympathetic neurons. Another possibility is that pargyline increases levels of false neurotransmitters like octopamine and tyramine, which are weaker pressor agents than norepinephrine. However, the involvement of octopamine in the hypotensive effects of pargyline and other MAOIs is uncertain. Yet another possibility is that the hypotensive effects may be due to accumulation of N-acetylserotonin, which shows antihypertensive effects in animals. As of 2018, the precise mechanism of the hypotensive effects of MAOIs still remains unresolved.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Pargyline

Start with the simplest possible case. Write down what Pargyline claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pargyline before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pargyline ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pargyline

In research: Pargyline appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pargyline in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pargyline is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acetaldehyde dehydrogenase inhibitors, Antihypertensive agents, Benzylamines, so understanding it makes those chapters shorter.
In everyday life: Look for Pargyline outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pargyline in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pargyline means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pargyline out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pargyline in simple terms?

Why does Pargyline matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pargyline?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pargyline.