Oxidase inhibitors

Antidepressant drugs of various classes (tricyclics, MAO inhibitors, SSRIs) have broad efficacy in generalized anxiety and in panic disorder, but SSRIs are now the treatments of choice (2,3). Selegiline has been used to treat Parkinson s disease. Other drugs that have MAO inhibitory activity, but are not used as such, include deb-risoquine, linezolid, and isoniazid. 

The monoamine oxidase inhibitors epitomize cyclical fashions in drug use and the impact of adverse effects. They were the first psychotropic drugs for which a clear biochemical action was defined. Early excitement was quickly tempered by reports of liver toxicity with the hydrazine derivatives, leading to synthesis of the cyclopropylamine drug, tranylcypromine, which in turn elicited the food and drug interactions that led to an overall decline in popularity. 

Then in the 1980s there was a reappraisal of the benefit-to-harm balance of the MAO inhibitors. This spawned both a search for safer and more selective or rapidly 

There have been many studies of the efficacy and toxicity of selective inhibitors of MAO type A (SEDA-16, 7 SEDA-17,16 SEDA-18,16). 

The adverse effects of the MAO inhibitors include hepatocellular damage, similar to that which led to the withdrawal of the earlier hydrazine derivatives, hypotension, often a pronounced adverse effect (possibly due to 

Because of the improved tolerability and safety of newer antidepressants, MAOIs are not currently used as first-line agents. However, MAOIs remain excellent medications for patients whose symptoms do not respond to the newer antidepressant drugs. Patients with atypical depression, characterized by oversleeping and overeating, show a preferential response to MAOI therapy compared with TCAs (Liebowitz et al. 1984 Quitkin et al. 1979 Ra-varis etal. 1980 Zisook 1985). 

Monoamine oxidase A (MAO A) acts selectively on the substrates norepinephrine and serotonin, whereas monoamine oxidase B (MAO B) preferentially affects phenylethylamine. Both MAO A and MAO B oxidize dopamine and tyramine. MAO A inhibition appears to be most relevant to the antidepressant effects of these drugs. Drugs that inhibit both MAO A and MAO B are called non-selective. The MAOI antidepressants currently available in the United States are nonselective inhibitors. Because tyramine can be metabolized by either MAO A or MAO B, drugs that selectively inhibit one of these enzymes but not the other do not require dietary 

Drug Reversible inhibition Enzyme selectivity Indication 

MAOI=monoamine oxidase inhibitor MAO=monoamine oxidase. Selective at lower doses, nonselective at higher doses. 

Another important characteristic of M AOIs is the production of reversible versus irreversible enzyme inhibition. An irreversible inhibitor permanently disables the enzyme. This means that MAO must be resynthesized, in the absence of the drug, before the activity of the enzyme can be reestablished. Resynthesis of the enzyme may take up to 2 weeks. For this reason, an interval of 10-14 days is required after discontinuing irreversible inhibitors and before instituting treatment with other antidepressants or permitting the use of contraindicated drugs or the consumption of contraindicated foods. On the other hand, a reversible inhibitor can move away from the active site of the enzyme, making the enzyme available to metabo-hze other substances. The reversibility and selectivity of the currently available MAOIs are summarized in Table 2-4. 

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Patients receiving monoamine oxidase inhibitors (MAOI) as antidepressant therapy have been especially subject to the hypertensive effects of vasoactive amines (52). These dietary amines have also been impHcated as causative agents ia migraine. Other aaturaHy occurring alkaloids (qv) have been recognized for centuries as possessing neurological stimulant and depressant properties. 

Monoamine—Oxidase Inhibitors. In the mid-1950s, tuberculosis patients with depression being treated with iproniazid (42) were occasionally reported to become euphoric. This observation led to the discovery of irreversible monoamine—oxidase (MAO) inhibiting properties. Hydrazine and nonhydrazine-related MAO inhibitors were subsequentiy shown to be antidepressants (122). Three other clinically effective irreversible MAO inhibitors have been approved for treatment of major depression phenelzine (43), isocarboxazid (44), and tranylcypromine (45). 

Monoamine Oxidase Inhibitors. MAOIs inactivate the enzyme MAO, which is responsible for the oxidative deamination of a variety of endogenous and exogenous substances. Among the endogenous substances are the neurotransmitters, norepinephrine, dopamine, and serotonin. The prototype MAOI is iproniazid [54-92-2] (25), originally tested as an antitubercular dmg and a close chemical relative of the effective antitubercular, isoniazid [54-85-3] (26). Tubercular patients exhibited mood elevation, although no reHef of their tuberculosis, following chronic administration of iproniazid. In... 

Normally, dietary tyramine is broken down in the gastrointestinal tract by MAO and is not absorbed. In the presence of MAOI, however, all of its potent sympathomimetic actions are seen. Other side effects of MAOI include excessive CNS stimulation, orthostatic hypotension, weight gain, and in rare cases hepatotoxicity. Because the monoamine oxidase inhibitors exhibit greater toxicity, yet no greater therapeutic response than other, newer agents, clinical use has been markedly curtailed. The primary use for MAOIs is in the treatment of atypical depressions, eg, those associated with increased appetite, phobic anxiety, hypersomnolence, and fatigues, but not melancholia (2). 

Pharmacologically useful isoxazoles (B-82MI41600) include antibacterial sulfonamides (614), (615) and (616), semisynthetic penicillins (617), (618), (619) and (620), semisynthetic cephalosporin (621), anabolic steroid (622), the monoamine oxidase inhibitor (623) (used in psychotherapy), antiinflammatory agent (624) and antitumor agent (625). 

Pargyline hydrochloride (Eutonyl, (V-methyl-n-propargylbenzylamine hydrochloride) [306-07-0] M 195.7, m 154-155 , 155 , pK 6.9. Recrystd from EtOH-Et20 and dried in vacuo. It is very soluble in H2O, in which it is unstable. The free base has b 101-103°/ 1mm. It is a glucuronyl transferase inducer and a monoamine oxidase inhibitor, [von Braun et al. Justus Liebigs Ann Chem 445 205 1928, Yeh and Mitchell Experientia 28 298 1972 Langslrom et al. Science 225 1480 1984.]... 

Incorporation of the phenethyl moiety into a carbocyclic ring was at first sight compatible with amphetamine-like activity. Clinical experience with one of these agents, tranylcypromine (79), revealed the interesting fact that this drug in fact possessed considerable activity as a monamine oxidase inhibitor and as such was useful in the treatment of depression. Decomposition of ethyl diazoacetate in the presence of styrene affords a mixture of cyclopropanes in which the trans isomer predominates. Saponification gives acid 77. Conversion to the acid chloride followed by treatment with sodium azide leads to the isocyanate, 78, via Curtius rearrangement. Saponification of 78 affords tranylcypromine (79). 

MAO (monoamine oxidase) inhibitor. An agent that blocks one of the enzymes that deaminates amines. 

Therapeutic Function Xanthine oxidase inhibitor gout therapy Chemical Name 1 H-pyra2olo[3,4-d] pyrimidin4-ol Common Name —... 

Therapeutic Function Antidepressant monoamine oxidase inhibitor Chemical Name 4-Pyridinecarboxylic acid 2-(1-methylethyl)hydrazide Common Name —... 

Anti-gout Drugs. Figure 1 Xanthine oxidase-catalyzed reactions. Xanthine oxidase converts hypoxanthine to xanthine and xanthine to uric acid, respectively. Hypoxanthine and xanthine are more soluble than uric acid. Xanthine oxidase also converts the uricostatic drug allopurinol to alloxanthine. Allopurinol and hypoxanthine are isomers that differ from each other in the substitution of positions 7 and 8 of the purine ring system. Although allopurinol is converted to alloxanthine by xanthine oxidase, allopurinol is also a xanthine oxidase inhibitor. Specifically, at low concentrations, allopurinol acts as a competitive inhibitor, and at high concentrations it acts as a noncompetitive inhibitor. Alloxanthine is a noncompetitive xanthine oxidase inhibitor. XOD xanthine oxidase. 

Monoamine oxidases Inhibitors Depressive illness Parkinson s disease Neuroprotection neurorescue... 

Monoamine Oxidases and their Inhibitors. Table 4 Nonselective and selective monoamine oxidase inhibitors... 

Youdim MB, Edmondson D, Tipton KF (2006) The therapeutic potential of monoamine oxidase inhibitors. Nat Rev Neurosci 7(4) 295-309... 

The term pasaon flower is used to denote many of the approximately 400 species of the herb. F saon flower has been used in medicine to treat pain, anxiety, and insomnia. Some herbalists use the herb to treat symptoms of parkinsonism. F saon flower is often used in combination with other herbs , such a valerian, chamomile, and hops, for promoting relaxation, rest and sleep. Although no adverse reactions have been reported, large doses may cause CNS depression. The use of passion flower is contraindicated in pregnancy and in patientstaking the monoamine oxidase inhibitors (MAOIs). Fission flower contains coumarin, and the risk of bleeding may be increased when used in patientstaking warfarin and pasaon flower. 

The skeletal muscle relaxants are contraindicated in patients with known hypersensitivity. Baclofen is contraindicated in skeletal muscle spasms caused by rheumatic disorders. Carisoprodol is contraindicated in patients with a known hypersensitivity to meprobamate. Cyclobenzaprine is contraindicated in patients with a recent myocardial infarction, cardiac conduction disorders, and hyperthyroidism, hi addition, cyclobenzaprine is contraindicated within 14 days of the administration of a monoamine oxidase inhibitor. Oral dantrolene is contraindicated in patients with active hepatic disease and muscle spasm caused by rheumatic disorders and during lactation. See Chapter 30 for information on diazepam. 

The amphetamines and the anorexiants should not be given during or within 14 days after administration of monoamine oxidase inhibitors (see Chap. 31) because the patient may experience hypertensive crisis and intracranial hemorrhage. When guanethidine is administered with the amphetamines or the anorexiants, the antihypertensive effect of guanethidine may decrease. Coadministration of the amphetamines or the anorexiants with the tricyclic antidepressants may decrease the effects of the amphetamines or the anorexiants. 

The dopaminergic drug are contraindicated in patients with known hypersensitivity to the drugs. Levodopa is contraindicated in patients with narrow-angle glaucoma, those receiving a monoamine oxidase inhibitor (see... 

Levodopa interacts with many different drugs. When levodopa is used with phenytoin, reserpine, and papaverine, there is a decrease in response to levodopa The risk of a hypertensive crisis increases when levodopa is used with the monoamine oxidase inhibitors (see Chap. 31). Foods high in pyridoxine (vitamin B6) or vitamin B6 preparations reverse the effect of levodopa However, when carbidopa is used with levodopa, pyridoxine has no effect on the action of levodopa hi fact, when levodopa and carbidopa are given together, pyridoxine may be prescribed to decrease the adverse effects associated with levodopa... 

There is an increase in anticholinergic effects when antihistamines are administered with the monamine oxidase inhibitors (MAOIs) and additive sedative effects if administered with central nervous system depressants (eg, narcotic analgesics or alcohol). When cimetidine and loratadine are administered together there is a risk for increased loratadine levels. 

The decongestants are contraindicated in patients with known hypersensitivity, hypertension, and severe coronary artery disease These drugs are also contraindicated in patients taking monoamine oxidase inhibitors (MAOIs). Naphazoline is contraindicated in patients with glaucoma. 

When dextromethorphan is administered with the monoamine oxidase inhibitors (see Chap. 31), patients may experience hypotension, fever, nausea, jerking motions to the leg, and coma... 

The hypotensive effects of most antihypertensive dru are increased when administered with diuretics and other antihypertensives. Many dnigp can interact with the antihypertensive drugs and decrease their effectiveness (eg, antidepressants, monoamine oxidase inhibitors, antihistamines, and sympathomimetic bronchodilators). When the ACE inhibitors are administered with the NSAIDs, their antihypertensive effect may be decreased. Absorption of the ACE inhibitors may be decreased when administered with the antacids. Administration of potassium-sparing diuretics or potassium supplements concurrently with the ACE inhibitors may cause hyperkalemia. When the angiotensin II receptor agonists are administered with... 

The antidiarrheal drugs cause an additive CNS depression when administered with alcohol, antihistamines, narcotics, and sedatives or hypnotics. There are additive cholinergic effects when administered with other drugp having anticholinergic activity, such as antidepressants or antihistamines. Concurrent use of the antidiarrheals witii a monoamine oxidase inhibitor increases the risk of a hypertensive crisis. 

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