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Isocarboxazid

Isocarboxazid is a hydrazine monoamine oxidase inhibitor (MAOI) antidepressant medication used to treat severe or treatment-resistant depression in patients who have not responded to other therapies. Approved by the U.S. Food and Drug Administration (FDA) in 1959 and marketed under the brand name Marplan, it works by irreversibly inhibiting the enzyme monoamine oxidase, which increases the levels of neurotransmitters such as serotonin and norepinephrine in the brain. Due to its potential for serious drug and food interactions—particularly with tyramine-rich foods that can cause hypertensive crises—it is typically reserved as a last-line treatment option. Introduced by Roche Laboratories as one of the earliest MAOIs, isocarboxazid has been largely supplanted by safer alternatives like selective serotonin reuptake inhibitors (SSRIs) but remains available for cases where other antidepressants fail.

Medical Uses

Indications

Isocarboxazid is approved by the U.S. Food and Drug Administration (FDA) for the treatment of major depressive disorder (MDD) in adults. Its efficacy has been established in outpatient adults with MDD, particularly those exhibiting atypical features—like hypersomnia, hyperphagia, leaden paralysis, or interpersonal rejection sensitivity—or non-endogenous and treatment-resistant forms unresponsive to selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), or tricyclic antidepressants (TCAs). Due to its side effect profile, isocarboxazid is reserved as a last-line option for these specific depression subtypes where first- and second-line therapies have failed, leveraging its role as a monoamine oxidase inhibitor (MAOI) for enhanced efficacy in such cases. It is indicated for adults only, with no established efficacy or safety in pediatric populations. In addition to core depressive symptoms, isocarboxazid addresses co-occurring anxiety manifestations, including anxious , panic attacks, and phobic symptoms that often accompany MDD. Clinical trials have demonstrated its superiority over in reducing these anxiety-related features alongside in anxious depressives. Off-label, isocarboxazid has been investigated for potential use in , particularly for negative symptoms or comorbid , with early clinical studies exploring its adjunctive role in chronic schizophrenic patients alongside antipsychotics like . Limited evidence from such trials suggests possible benefits in anergic or depressive aspects of schizophrenia, though it remains unapproved for this indication and is not routinely recommended. Further exploration has occurred in other and anxiety disorders, such as and , supported by observational data on symptom relief.

Dosage

Isocarboxazid is typically initiated at a dose of 10 mg orally twice daily. Dosage may be increased by 10 mg increments every 2 to 4 days, if tolerated, aiming for 40 mg per day (divided into 2 to 4 doses) by the end of the first week; further increases of up to 20 mg per week can be made if necessary, but the maximum recommended daily dose is 60 mg. Once an optimal therapeutic response is achieved, the dosage should be gradually reduced to the lowest effective amount that maintains benefit, typically 10 to 20 mg per day in divided doses. The full effect may require 3 to 6 weeks of to become apparent. The medication is administered orally and can be taken with or without food, though taking it with food may help reduce gastrointestinal upset. Daily doses should be divided into 2 to 4 administrations to minimize side effects. Elderly patients may require caution and dose adjustments due to age-related kidney, liver, or heart conditions, with subsequent adjustments based on response and tolerability. Discontinuation should involve gradual tapering over 2 to 4 weeks to avoid withdrawal effects. During initiation and any dose adjustments, patients require regular monitoring of blood pressure to detect potential hypertensive crises, along with psychiatric evaluations to assess therapeutic response and side effects.

Pharmacology

Pharmacodynamics

Isocarboxazid is a non-selective, irreversible inhibitor of (MAO) enzymes, targeting both MAO-A and MAO-B isoforms. By covalently binding to these enzymes, it prevents the oxidative of monoamine neurotransmitters, thereby inhibiting their breakdown. This mechanism underlies its primary therapeutic action as an . The inhibition of MAO by isocarboxazid leads to elevated levels of several monoamines in the and periphery, including serotonin, norepinephrine, , epinephrine, , and trace amines such as and . These increases occur because MAO normally catalyzes the of these compounds; blocking this process enhances their availability for . Specifically, the accumulation of serotonin, norepinephrine, and in synaptic clefts potentiates monoaminergic signaling, which is thought to contribute to mood stabilization and efficacy, with therapeutic effects typically emerging after 3 to 6 weeks of treatment due to adaptive changes in receptor sensitivity and downstream signaling pathways. In addition to its antidepressant properties, isocarboxazid exhibits potential anti-panic and effects, likely mediated by enhanced noradrenergic transmission that modulates and anxiety circuits. It demonstrates no significant direct for serotonin, adrenergic, or other receptors, distinguishing its action from drugs that target receptors directly. Due to the irreversible nature of its binding, isocarboxazid depletes functional MAO enzymes, with pharmacological effects persisting until new enzyme synthesis occurs, typically requiring 7-14 days for recovery.

Pharmacokinetics

Isocarboxazid is readily absorbed from the after , achieving peak plasma concentrations within 1–2 hours. Its is low, consistent with other hydrazine-based inhibitors. The drug is widely distributed throughout the body, including crossing the blood-brain barrier to exert its central effects. The volume of distribution has not been well characterized, though it exhibits high similar to analogous agents like and tranylcypromine. Isocarboxazid undergoes rapid hepatic metabolism primarily through , yielding largely inactive metabolites such as . Elimination occurs mainly via renal excretion of these metabolites, with approximately 42.5% of the administered dose recovered in within 24 hours (predominantly as ) and about 22% via the intestinal tract. The plasma elimination is short, ranging from 1.5 to 4 hours due to swift metabolism. However, the functional extends to 7–14 days because of its irreversible inhibition of , during which time resynthesis is required for recovery. Factors such as advanced age and impaired hepatic function can decrease clearance, thereby prolonging the and elevating plasma concentrations.

Side Effects

Common Side Effects

Isocarboxazid, a , is associated with several common side effects that are typically mild and dose-related, arising from its effects on levels and autonomic function. These effects often diminish with continued use or dose adjustment, though monitoring is recommended. Orthostatic hypotension, caused by enhanced noradrenergic activity leading to changes upon standing, affects approximately 4% of patients in clinical trials, manifesting as or ; it can be managed by rising slowly and, if persistent, reducing the dose. and nervousness, linked to elevated monoamine levels, occur in 4-6% and 1-2% of patients respectively, often addressed by timing doses earlier in the day to minimize disruption. Gastrointestinal issues, attributed to anticholinergic-like properties, include dry mouth in 6-9% of patients, constipation in 4-7%, and in 4-6%; these are commonly alleviated with , , or symptomatic treatments like sugarless gum for . Other frequent effects encompass (6-15%), drowsiness (up to 4%), and tremors (4%), all reported in placebo-controlled trials and generally resolving with time or dose . is noted in postmarketing reports, while , such as decreased or impotence, affects 1-10% of users, with management involving lifestyle adjustments or dose optimization. Overall, these side effects lead to discontinuation in a minority of cases, primarily due to or dry mouth, and most improve without intervention.

Serious Side Effects

Isocarboxazid, a (MAOI), can precipitate a , a potentially life-threatening condition triggered by ingestion of tyramine-rich foods (such as aged cheeses or certain wines) or sympathomimetic agents. Symptoms typically include severe occipital , , , , , sweating, , and , often accompanied by elevations exceeding 180/120 mmHg, which carries risks of intracranial bleeding, , or . Immediate discontinuation of the drug and initiation of antihypertensive therapy are essential if a crisis occurs. Serotonin syndrome represents another severe adverse reaction, arising from interactions with serotonergic medications like selective serotonin reuptake inhibitors (SSRIs), and is characterized by , muscle rigidity, , autonomic instability, , , and potentially seizures or ; this syndrome is rare but can be fatal without prompt intervention. Concomitant use with SSRIs such as sertraline has been documented to induce this syndrome, necessitating a washout period of at least two weeks after discontinuing most SSRIs (or five weeks for ) before starting isocarboxazid. Hepatotoxicity occurs infrequently with isocarboxazid, with a low incidence of elevated liver enzymes (less than 1%) that may progress to or mimicking . Periodic liver function monitoring is advised, and the drug should be discontinued at the first signs of hepatic dysfunction. A black box warning highlights the increased risk of suicidality associated with isocarboxazid and other antidepressants, particularly in children, adolescents, and young adults (ages 18-24) during initial treatment for major depressive disorder, with short-term studies showing a 4% incidence compared to 2% with placebo. Close monitoring for worsening depression or emergent suicidal thoughts is required, especially in the first few months of therapy. In patients with , isocarboxazid may induce a manic or hypomanic switch, exacerbating mood instability and potentially leading to full . Long-term use has been linked to rare cases of , manifesting as that may require supplementation (25 mg/day) and drug discontinuation.

Contraindications and Interactions

Contraindications

Isocarboxazid is absolutely contraindicated in patients with due to the risk of from accumulated pressor amines. It is also prohibited in those with congestive , uncontrolled , or recent , as these cardiovascular conditions heighten the potential for severe pressor effects and complications like or . Additionally, a history of hepatic disease or abnormal liver function tests represents an absolute contraindication, given the drug's potential to cause . Isocarboxazid is contraindicated in patients with known to the drug. It is also contraindicated in those with severe renal impairment. The drug must not be used concurrently with other inhibitors (MAOIs) or initiated within 14 days of discontinuing another MAOI, owing to the risk of severe, potentially fatal interactions leading to . is another absolute , as isocarboxazid can increase the risk of through its effects on . For special populations, use is prohibited in children under 16 years, as and have not been established. There are no adequate and well-controlled studies in women. Isocarboxazid should be used during only if the potential benefit justifies the potential risk to the . It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when isocarboxazid is administered to a woman. In elderly patients with comorbidities, use requires careful risk-benefit assessment to avoid complications like .

Drug and Food Interactions

Isocarboxazid, a (MAOI), interacts with -containing foods, potentially leading to a characterized by severe , , , and potentially fatal elevations in . Patients must adhere to a low- , avoiding aged cheeses (e.g., cheddar, ), cured or fermented meats (e.g., , , ), , soy products (e.g., , ), overripe bananas, broad (fava) beans, and yeast extracts (e.g., ). This restriction applies during treatment and for at least two weeks afterward, as levels in these foods can be potentiated by MAO inhibition, disrupting normal regulation. Concurrent use with serotonergic medications, such as selective serotonin reuptake inhibitors (SSRIs like or sertraline), serotonin-norepinephrine reuptake inhibitors (SNRIs like ), and (e.g., ), is contraindicated due to the risk of , which manifests as , rigidity, , autonomic instability, and potentially or death. A washout period of at least five weeks is required after discontinuing and two weeks for other SSRIs or SNRIs before initiating isocarboxazid; similarly, a two-week interval is advised post-isocarboxazid before starting these agents. and other serotonin agonists should be avoided entirely during therapy. Sympathomimetic agents, including amphetamines, , (found in many over-the-counter decongestants), and other stimulants, are contraindicated as they can provoke a severe pressor response, exacerbating and risking cardiovascular events. This arises from isocarboxazid's inhibition of monoamine breakdown, leading to excessive norepinephrine release and amplified . Isocarboxazid has over 250 documented major or contraindicated interactions with other drugs, including opioids (e.g., meperidine, which can cause fatal respiratory depression, , or ), tricyclic antidepressants (TCAs like amitriptyline), , bupropion, and certain anesthetics. Meperidine specifically carries a high risk of severe, potentially lethal reactions and should be avoided for two to three weeks after MAOI discontinuation. Additional interactions include (in cough syrups) and St. John's wort, both of which heighten effects. Alcohol consumption is contraindicated with isocarboxazid, as it may intensify , resulting in enhanced , drowsiness, and impaired concentration or coordination. Excessive intake should also be limited to prevent additive hypertensive effects. In all cases of suspected interactions, immediate medical intervention is essential, with monitoring recommended during co-administration risks.

History

Development

Isocarboxazid was developed in the 1950s by Hoffmann-La Roche as a hydrazine derivative of the monoamine oxidase inhibitor (MAOI) class, building on the unexpected antidepressant effects observed with iproniazid, an antitubercular agent synthesized earlier by the same company. The compound emerged from efforts to create safer alternatives to iproniazid, which had shown mood-elevating properties in tuberculosis patients but carried significant risks. It was patented under U.S. Patent 2,908,688, filed on May 31, 1957, and issued on October 13, 1959. This positioned it as a non-selective, irreversible MAOI capable of inhibiting both MAO-A and MAO-B enzymes, thereby elevating levels of neurotransmitters like serotonin, norepinephrine, and dopamine in the brain. Early research focused on screening hydrazine derivatives for MAO inhibitory activity, with demonstrating potent effects in biochemical assays between 1956 and 1958. during this period revealed antidepressant-like behaviors, including reversal of reserpine-induced ptosis and in , which mimicked depressive states and confirmed the compound's potential to counteract monoamine depletion. These preclinical findings, conducted at Roche Laboratories in , established isocarboxazid's pharmacological profile as a broad-spectrum MAOI, distinct from its antitubercular predecessors by prioritizing psychiatric applications. Initial concerns arose regarding , an issue inherited from hydrazine-based compounds like , prompting the integration of liver function monitoring protocols even in early testing phases to mitigate risks of and hepatic injury. Clinical trials in the late advanced isocarboxazid toward therapeutic use, with phase evaluations demonstrating efficacy particularly in endogenous characterized by melancholic features. Key double-blind studies published in 1959 and 1961, including controlled assessments in hospitalized patients, reported response rates exceeding 60%, with significant improvements in mood, energy, and compared to . For instance, a trial in the Journal of Mental Science involving depressed inpatients showed marked symptom relief in the majority of participants after four weeks of treatment at doses of 30-60 mg daily. These results solidified isocarboxazid's role as an early , leading to its market introduction under the Marplan in 1959, though ongoing vigilance for adverse effects like tempered its initial rollout.

Regulatory Approval

Isocarboxazid received approval from the on July 1, 1959, for the treatment of , initially marketed under the brand name Marplan by Hoffman-La Roche. In 1998, as part of the Drug Efficacy Study Implementation () review process, the FDA evaluated existing data and , confirming the drug's effectiveness for this indication while emphasizing its risks, leading to approval of updated labeling. Post-approval regulatory actions included the addition of a black box warning in 2007, highlighting the increased risk of suicidal thinking and behavior in children, adolescents, and young adults treated with isocarboxazid and other antidepressants, based on clinical trial analyses showing elevated suicidality during initial treatment months. In 2004, the FDA revoked a prior temporary exemption under DESI regulations, which had permitted continued pending efficacy resolution, thereby finalizing isocarboxazid's with requirements for revised labeling on contraindications and warnings. After initial marketing by , production of Marplan was discontinued but later resumed following its acquisition by Validus Pharmaceuticals in 2007. As of 2025, it is marketed by Lifsa Drugs LLC. Internationally, isocarboxazid was approved in and the during the , similar to its U.S. timeline, and remains available in these markets for . It is not approved by the for use in the . Currently, in the United States, isocarboxazid is marketed solely as the brand-name Marplan in 10 mg tablets, with no generic equivalent available, and it is rarely prescribed due to safer therapeutic options. Labeling continues to mandate strict warnings and on tyramine-containing food interactions to prevent hypertensive crises.

References

  1. [1]
    Isocarboxazid - LiverTox - NCBI Bookshelf - NIH
    Apr 8, 2020 · Isocarboxazid is a monoamine oxidase inhibitor (MAO inhibitor) used in therapy of severe depression. Isocarboxazid therapy is associated with rare instances of ...
  2. [2]
    Isocarboxazid: MedlinePlus Drug Information
    ### Summary of Isocarboxazid (MedlinePlus)
  3. [3]
    Monoamine Oxidase Inhibitors (MAOI) - StatPearls - NCBI Bookshelf
    The different types of MAOIs approved by the FDA include isocarboxazid, phenelzine, selegiline, and tranylcypromine.[9] When patients are prescribed ...
  4. [4]
    Isocarboxazid | C12H13N3O2 | CID 3759 - PubChem - NIH
    It is used in the treatment of major depression, dysthymic disorder, atypical disorder, panic disorder and the phobic disorders. It was first introduced by ...
  5. [5]
    [PDF] brand of isocarboxazid tablets Suicidality and Antidepressant Drugs
    Patients with major depressive disorder (MDD), both adult and pediatric, may experience worsening of their depression and/or the emergence of suicidal ideation ...
  6. [6]
    Monoamine oxidase inhibitors in the treatment of atypical depression
    In a 6-week, double-blind study outpatients diagnosed as suffering from atypical depression were treated with either isocarboxazid or placebo.
  7. [7]
    MAO inhibitors for treatment-resistant depression - ScienceDirect.com
    Currently considered third-line medications for treatment-resistant depression, they are markedly underutilized.
  8. [8]
    (PDF) The Monoamine Oxidase Inhibitor Isocarboxazid is a ...
    Aug 10, 2025 · Treatment with isocarboxazid is considered to be a relevant option in treatment-resistant depression and we are today much better prepared than ...
  9. [9]
    An Efficacy Study of Isocarboxazid and Placebo in Depression, and ...
    Isocarboxazid was more effective than placebo in major, but not in minor, depression. It was significantly more effective in depression classified as endogenous ...Missing: resistant | Show results with:resistant
  10. [10]
    Combined drug therapy of chronic schizophrenics ... - PubMed
    Controlled evaluation of placebo, dextro-amphetamine, imipiramine, isocarboxazid and trifluoperazine added to maintenance doses of chlorpromazine.
  11. [11]
    Antidepressants - PubMed
    Antidepressants: Comparison of Clinical Effects in Anergic Schizophrenia and the Depressed States ... Isocarboxazid*; Monoamine Oxidase Inhibitors*; Nialamide* ...
  12. [12]
    Isocarboxazid: Uses, Interactions, Mechanism of Action - DrugBank
    Jun 13, 2005 · Isocarboxazid is indicated for the treatment of the enduring and debilitating symptoms of depression that have not responded to other antidepressant drugs.
  13. [13]
    Isocarboxazid Dosage Guide + Max Dose, Adjustments - Drugs.com
    Nov 6, 2024 · Usual Adult Dose for Depression. Initial dose: 10 mg orally 2 times a day. Increase in 10 mg increments every 2 to 4 days, until 40 mg/day ...
  14. [14]
  15. [15]
    Isocarboxazid (oral route) - Side effects & dosage - Mayo Clinic
    Isocarboxazid may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and ...Missing: anxiety panic phobias
  16. [16]
    Isocarboxazid - an overview | ScienceDirect Topics
    Isocarboxazid is an inhibitor of monoamine oxidase (MAO). Furthermore, it binds irreversibly and non-selectively to MAO-A and MAO-B which are two isoforms of ...
  17. [17]
    Trace Amine - an overview | ScienceDirect Topics
    Metabolism of trace amines occurs rapidly, primarily via oxidative deamination by monoamine oxidase (MAO; EC 1.4.3.4), with both MAO-A and MAO-B isoforms ...Trace Amine-Associated... · Functional Roles of Trace...
  18. [18]
    Human plasma melatonin is elevated during treatment ... - PubMed
    Tranylcypromine, a nonselective MAO inhibitor given in doses of 20-40 mg/day for 3 weeks, significantly elevated plasma melatonin to 10.6 +/- SD 2.0 pg/ml.
  19. [19]
    [PDF] brand of isocarboxazid tablets - accessdata.fda.gov
    Nov 1, 2018 · Suicidality and Antidepressant Drugs. Antidepressants increased the risk compared to placebo of suicidal thinking and behavior.Missing: off- | Show results with:off-
  20. [20]
    Isocarboxazid - Prescriber's Guide
    Side effects are generally immediate, but immediate side effects often disappear in time. Notable Side Effects. Dizziness, sedation, headache, sleep ...Missing: course | Show results with:course
  21. [21]
    Isocarboxazid (Professional Patient Advice) - Drugs.com
    Sep 29, 2025 · Isocarboxazid is FDA approved for the treatment of depression in children ≥16 years of age. - The possibility of a suicide attempt is ...
  22. [22]
    Isocarboxazid - an overview | ScienceDirect Topics
    Consequently, the breakdown of the biogenic amines dopamine, norepinephrine, and serotonin is prevented, thereby increasing the concentration of these ...Missing: epinephrine melatonin trace
  23. [23]
    Isocarboxazid Side Effects: Common, Severe, Long Term - Drugs.com
    Dec 6, 2024 · Isocarboxazid may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and ...
  24. [24]
    Sertraline and isocarboxazid cause a serotonin syndrome - PubMed
    Sertraline and isocarboxazid cause a serotonin syndrome. J Clin Psychopharmacol. 1994 Apr;14(2):144-5. doi: 10.1097/00004714-199404000-00010.
  25. [25]
    Isocarboxazid Disease Interactions - Drugs.com
    Depressed patients, usually those with bipolar disorder, may experience a switch from depression to mania or hypomania. Therapy with MAOI antidepressants ...
  26. [26]
    Isocarboxazid - an overview | ScienceDirect Topics
    The MAO inhibitory effects of isocarboxazid may persist for a substantial period after discontinuation. To avoid potentiation, terminate isocarboxazid 10 d ...
  27. [27]
    Label: MARPLAN- isocarboxazid tablet - DailyMed
    If tolerated, dosage may be increased by increments of one tablet (10 mg) every 2 to 4 days to achieve a dosage of four tablets daily (40 mg) by the end of the ...
  28. [28]
    Isocarboxazid (Marplan) Use During Pregnancy - Drugs.com
    Oct 21, 2025 · Advice and warnings for the use of Isocarboxazid (Marplan) during pregnancy. FDA Pregnancy Category C - Risk cannot be ruled out.
  29. [29]
    Isocarboxazid and Alcohol/Food Interactions - Drugs.com
    You should avoid the use of alcohol while being treated with isocarboxazid, as alcohol may increase some of the nervous system side effects.
  30. [30]
    Drug Interactions - Marplan® (isocarboxazid) | MAOI Antidepressant
    Administration of MARPLAN with certain drugs and foods may result in hypertensive crisis. Blood pressure should be followed closely in patients taking MARPLAN ...<|control11|><|separator|>
  31. [31]
    Marplan (isocarboxazid) dosing, indications, interactions, adverse ...
    Depression. 10 mg PO q6-12hr, increase by 10 mg/day q2-4d to 40 mg/day PO divided q6-12hr by end of first week. After first week, may increase by up to 20 ...
  32. [32]
    [PDF] The History of the Discovery of Antidepressants from 1950s Until ...
    Abstract: The 1950s saw the clinical introduction of the first two specifically antidepressant drugs: iproniazid, a mono- amine-oxidase inhibitor that had ...
  33. [33]
    Isocarboxazid - an overview | ScienceDirect Topics
    Imipramine was a derivative of chlorpromazine and was first tested in clinical trials in schizophrenia. While no relevant antipsychotic effects were noted ...
  34. [34]
    [PDF] Marplan DESI Approval - accessdata.fda.gov
    We remind you of your Phase 4 commitment specified in your submission dated February 18, and. August 6(b)(4)(CC)-----------------t, along with any completion ...
  35. [35]
    Isocarboxazid; Drugs for Human Use; Drug Efficacy Study ...
    Apr 16, 2004 · FDA has reviewed all available evidence and concludes that isocarboxazid is effective for the indication in the labeling conditions listed in ...
  36. [36]
    Isocarboxazid - Oral - MyHealth Alberta
    Uses. This medication is used to treat depression. Isocarboxazid belongs to a class of drugs known as monoamine oxidase inhibitors (MAO inhibitors). It works ...Missing: indications | Show results with:indications<|control11|><|separator|>
  37. [37]
    Isocarboxazid | Drugs - BNF - NICE
    View isocarboxazid information, including dose, uses, side-effects, renal impairment, pregnancy, breast feeding, contra-indications and monitoring ...
  38. [38]
    Generic Marplan Availability - Drugs.com
    Oct 8, 2025 · Last updated on Oct 8, 2025. Marplan is a brand name of isocarboxazid, approved by the FDA in the following formulation: MARPLAN (isocarboxazid ...