MAOIs Imipramine

Note. AMI = amitriptyline DMI = desipramine ECT = electroconvulsive therapy IMI = imipramine MAOI = monoamine oxidase inhibitor T3 = triiodothyronine ... 

In 1958, another agent, imipramine, was discovered by chance to have beneficial effects in depression. This compound is not a MAOI and its actions were first described as a complete riddle . Axelrod s group in Washington (Hertting, Axelrod and Whitby... 

There was a problem with this first version of the biochemical theory of depression. Iproniazid was not the only drug that had been reported to be effective as an antidepressant. Imipramine, the drug that had been tested by the Swiss psychiatrist Roland Kuhn, seemed to have similar effects. But imipramine is not an MAOI it does not inhibit the destruction of neurotransmitters in the synapse. So if antidepressants worked by inhibiting monoamine oxidase, why was imipramine effective How could its apparent effectiveness be reconciled with the chemical-imbalance theory ... 

The answer is that there are two ways in which neurotransmitter levels might be increased. One is to inhibit their destruction after they have been released into the synaptic gap. That is how MAOIs are supposed to work. Recall, however, that after a neurotransmitter is released, some of its molecules are reabsorbed by the presynaptic neuron that released them in a process that is called reuptake . Blocking this reuptake process should also increase the level of neuro transmitters in the brain. In 1961, Julius Axelrod, who later received the Nobel Prize in Medicine for his work on the release and reuptake of neurotransmitters, reported that imipramine, as well as a few other drugs, inhibited the reuptake of norepinephrine in cats. Two years later he reported that these drugs also inhibited the reuptake of serotonin.13... 

Amitriptyline and imipramine, and the MAOI phenelzine, can be considered second- or third-line drugs for PTSD after SSRIs have failed. Mirtaza-pine and venlafaxine may also be effective. 

Unfortunately, some patients respond poorly to these first-line interventions. In particular, patients with a long duration of illness, extreme agoraphobic avoidance, and comorbid personality disorders are more likely to exhibit a poor treatment response. For such patients, TCAs such as imipramine or clomipramine and MAOIs such as phenelzine remain viable strategies. 

Iproniazid, an MAOI no longer available because of its hepatotoxicity, was the first effective antidepressant to be discovered it was introduced shortly before the discovery of imipramine. All MAOIs are presumed to have a similar mode of action, namely to inhibit the intra- and interneuronal metabolism of the biogenic amine neurotransmitters (noradrenaline, dopamine and serotonin). These amines are primarily metabolized by MAO-A (noradrenaline and serotonin) or MAO-B (dopamine). The irreversible MAOIs are inhibitors of MAO-A while selegiline (deprenyl), used as an adjunctive treatment for Parkinson s disease, is a selective, irreversible inhibitor of MAO-B. 

Imipramine (Tofranil) [Antidepressant/TCA] WARNING Close observation for suicidal thinking or unusual changes in behavior Uses Depres-sion, enuresis, panic attack, chronic pain Action TCA t CNS synaptic serotonin or norepinephrine Dose Adults. Hospitalized Initial 100 mg/24 h PO in doses T over several wk 300 mg/d max Output Maint 50-150 mg PO hs, 300 mg/24 h max Peds. Antidepressant 1.5-5 mg/kg/24 h daUy-qid Enuresis >6 y 10-25 mg PO qhs T by 10-25 mg at 1-2-wk int vals (max 50 mg for 6-12 y, 75 mg for >12 y) Rx for 2-3 mo, then tap Caution [D, /-] Contra Use w/ MAOIs, NAG, acute recovery from MI, PRG, CHF, angina, CVD, arrhythmias Disp Tabs, caps SE CV Sxs, dizziness, xerostomia, discolored urine Interactions t Effects W/ amiodarone, anticholinergics, BBs, cimetidine, diltiazem, Li, OCPs, quinidine, phenothiazines, ritonavir, verapamil, EtOH, evening primrose oil t effects OF CNS depressants, hypoglycemics, warfarin T risk of serotonin synd W/MAOIs 4-... 

Many antidepressant drugs have pronounced effects on sleep. Several tricyclic compounds (amitriptyline and others) have sedative actions while others (imipramine and others) are less sedative or even stimulant. Monoamine oxidase inhibitors (MAOIs) have central stimulant effects and may cause insomnia. Specific serotonin reuptake inhibitors (SSRls) and combined serotonin, noradrenaline reuptake inhibitors (SNRIs) can also cause insomnia. 

At about the same time that imipramine was being studied in the United States, investigators in England noted that some patients with hysteria responded positively to MAOIs. Subsequently, researchers in England and Canada showed MAOIs to be superior to placebo in hysteria with phobic symptoms, a subcategorization that may be similar to that described by Klein. 

Pheneizine The efficacy of both reversible and irreversible MAOIs for the treatment of PTSD has been studied in controlled trials. Phenelzine has been shown to be superior to placebo and imipramine in patients with chronic PTSD who had a very low placebo response ( 271, 283). Thus, we believe phenelzine is worth trying for patients who can adhere to dietary and medicinal restrictions. 

Panic disorder is one of the most prevalent psychiatric disorders in industrialized countries. It is often associated with agoraphobia and has an estimated prevalence of between 1% and 6%. The use of imipramine in the treatment of anxiety by Klein and Fink, and the discovery by William Sargant that monoamine oxidase inhibitors (MAOIs) were effective in the treatment of "atypical depression" over 30 years ago led to the investigation of the efficacy of such treatments in patients with panic disorder. Since that time, such drugs have been shown to attenuate the symptoms of panic in addition to those of phobic avoidance and anticipatory anxiety. As both the... 

Antidepressants were first introduced into the market in the 1950s with the serendipitous discovery of the antidepressant effect of two drugs initially evaluated for other medical uses Iproniazide, a monoamine oxidase inhibitor (MAOI), and Imipramine, a tricyclic antidepressant (TCA). Since then, a whole new generation of chemically and pharmacologically unrelated compounds have been introduced, which appear to be safer and better tolerated due to a more specific mechanism of action. These include selective serotonin reuptake inhibitors (SSRIs), serotonin and... 

Some antidepressants—specifically, tricyclics like imipramine (trade name Tofranil) and amitryptiline (trade name Elavil)—are thought to exert their antidepressant effect through inhibition of a reuptake mechanism that sucks back the neurotransmitters from the synapse into the neuron for storage and future use, a process mentioned in Chapter 1. The resulting net effect is an increase of these molecules at the synapse and thus a more robust neurotransmission. A different category of antidepressants—monoamine oxidase inhibitors (MAOIs)—display a different mechanism of action but with the same net effect of increasing norepinephrine and serotonin neurotransmission they inhibit the metabolism (breakdown) of the molecules stored in the neurons, thus creating more abundant supplies for neurotransmission. 

MAOIs TCAs-AMITRIPTYLINE CLOMIPRAMINE DESIPRAMINE IMIPRAMINE NORTRIPTYLINE t risk of stroke, hyperpyrexia and convulsions, t plasma concentrations of TCAs, with risk of toxic effects, t risk of serotonin syndrome and of adrenergic syndrome with older MAOIs. Clomipramine may trigger acute confusion in Parkinson s disease when used with selegiline TCAs are believed to also act by inhibiting the reuptake of serotonin and norepinephrine, increasing the risk of serotonin and adrenergic syndromes. The combination of TCAs and antidepressants can t risk of seizures Very hazardous interaction. Avoid concurrent use and consider the use of an alternative antidepressant. Be aware that seizures occur with overdose of TCAs just before cardiac arrest... 

LEVODOPA, SELEGILINE, POSSIBLY RASAGILINE, ENTACAPONE, TOLCAPONE MAOIs Risk of adrenergic syndrome -hypertension, hyperthermia, arrhythmias - and dopaminergic effects with selegiline Levodopa and related drugs are precursors of dopamine. Levodopa is predominantly metabolized to dopamine, and a smaller proportion is converted to epinephrine and norepinephrine. Effects are due to inhibition of MAOI, which breaks down dopamine and sympathomimetics Avoid concurrent use. Onset may be 6-24 hours after ingestion. Carbidopa and benserazide, which inhibit dopa decarboxylase that converts L-dopa to dopamine, is considered to minimize this interaction. However, MAOIs should not be used in patients with Parkinson s disease on treatment with levodopa. Imipramine and amitriptyline are considered safer by some clinicians... 

Generally, do nof use wifh MAO inhibifors, including f 4 days affer MAOIs are stopped do nof sfart an MAOl unfil 2 weeks affer disconfinuing imipramine, buf see Pearls... 

The first TCAs (imipramine and amitriptyline) and MAOIs appeared between 1957 and 1961 (Fig. 19.1). The MAOIs were developed from antituberculosis agents which had been noted to elevate mood. Independently, imipramine was synthesised from the antipsychotic drug chlorpro-mazine and found to have antidepressant rather than antipsychotic properties. Over the next 25... 

TCAs (especially imipramine and clomipramine)—contraindicated with MAOIs (trazodone may be used cautiously with MAOIs) Increased TCA levels s3mdrome of excitation, very high temperature, mania, seizures, coma, death... 

MAOIs phenelzine, tranylcypromine TCAs amitriptyline, imipramine, clomipramine... 

DA agonists levodopa, bromocriptine, ropinirole, pramipexole, selegiline AAAD inhibitor carbidopa M-blockers benztropine, trihexiphenidyl MAOIs phenelzine, tranylcypromine TCAs amitriptyline, imipramine, clomipramine SSRIs fluoxetine, paroxetine, sertraline Others bupropion, mirtazapine, nefazodone, trazodone... 

The TCAs arrived on the scene in the same period as the MAOIs. Imipramine (Table 12-17), which is a dibenzazepine, was synthesized as a logical isosteric extension of the phenothiazines. The antidepressant properties were subsequently discovered and the drug was clinically introduced in 1957. Furthermore, isosterically replacing the N with an sp3... 

---