Antidepressants cardiotoxicity

The excellent clinical efficacy of the TCAs has been well documented and the pharmacokinetic profiles are favourable. The most serious disadvantage of the TCAs lies in their cardiotoxicity. Thus, with the exception of lofepramine, all the tricyclic antidepressants, including maprotiline, block the fast sodium channels in the heart which can lead to heart block and death. Approximately 15% of all patients with major depression die by suicide and a high proportion of these (up to 25%) do so by taking an overdose of TCAs. Such a dose can be as low as 5-10 times the recommended daily dose. 

Mianserin was the first of the second-generation antidepressants to be developed. It lacked the amine reuptake inhibitory and MAOI actions of the first-generation drugs and also lacked the cardiotoxicity and anticholinergic activity of the TCAs. However, it was sedative (antihistaminic), caused postural hypotension (alpha-1 blockade) and also caused blood dyscrasias and agranulocytosis in a small number of patients. This has limited the use of mianserin in recent years. 

Selective serotonin re-uptake inhibitors (SSRIs) and tricyclic antidepressants are equally effective. Hov/ever, SSRIs tend to have fewer antimuscarinic side-effects and are less cardiotoxic in case of overdosage. SSRIs tend to cause gastrointestinal side-effects. Both SSRIs and tricylic antidepressants exhibit a time lag before the action of the antidepressants becomes effective. 

Fluoxetine, along with sertraline, fluvoxamine, and paroxetine, belongs to the more recently developed group of SSRI. The clinical efficacy of SSRI is considered comparable to that of established antidepressants. Added advantages include absence of cardiotoxicity, fewer autonomic nervous side effects, and relative safety with overdosage. Fluoxetine causes loss of appetite and weight reduction. Its main adverse effects include overarousal, insomnia, tremor, akathisia, anxiety, and disturbances of sexual function. 

Tricyclic antidepressants are cardiotoxic, inducing tachycardias and an increased tendency for ventricular arrhythmias with high doses. This dose dependent cardiotoxicity gives these agents a low therapeutic index. Overdoses are characterized by cardiac conduction disturbances, hyperpyrexia, hypertension, confusion, hallucinations, seizures and coma and there is a high mortality rate in suicide attempts. Depressed patients should therefore not be given more than one week supply of these drugs. 

Agents from this class of antidepressants are selective blockers of the re-uptake of serotonin at presynaptic neurones and have little if any effects on muscarinic, histaminergic, adrenergic or serotonergic receptors. They are as effective as the tricyclic antidepressants in the management of depressive disorders, but have less cardiovascular effects. They have less anticholinergic activity and because of their lower risk of cardiotoxicity in overdose they... 

Maprotiline and amoxapine are selective norepinephrine uptake inhibitors. They share most of the properties of the tricyclic antidepressants. Maprotiline has less sedating effect than mianserin and it is more epileptogenic than any other antidepressant. It shows considerable cardiotoxicity when taken in overdose. 

Trazodone appears to be iess cardiotoxic than tricyciic antidepressants, aithough arrhythmias may occur in patients with preexisting cardiac disease. 

Those who fail to respond to an SSRI may respond to a TCA, and vice versa. Thus, these two broad-spectrum classes can be used in a sequential strategy to adequately treat the majority of cases. However, many physicians try another newer antidepressant (e.g, venlafaxine, bupropion, nefazodone) in such patients because of the safety and tolerability problems associated with TCAs. Of note, the tolerability profile of secondary amine TCAs such as desipramine is as favorable as any of the newer antidepressants and probably better than nefazodone. Nevertheless, the secondary amine TCAs have a therapeutic index as narrow as tertiary amine TCAs (e.g., amitriptyline, imipramine) in terms of lethality in overdoses resulting from cardiotoxicity. 

Bicarbonate, sodium Membrane-depressant cardiotoxic drugs (tricyclic antidepressants, quinidine, etc) 1-2 mEq/kg IV bolus usually reverses cardiotoxic effects (wide QRS, hypotension). Give cautiously in heart failure (avoid sodium overload). 

Beta agonists. Beta adrenergic receptors can be rapidly down regulated by agonists and if this is desired for an antidepressant action, beta agonists may be useful. To date, it has not been possible to identify beta 1 or beta 2 agonists that successfully penetrate the brain and yet are not cardiotoxic. Pursuing safer beta 1 and beta 2... 

A few deaths have occurred during overdosage of SSRIs when other drugs were also being taken. The likelihood of fatalities from SSRI overdoses is extremely low. In case of overdose, only supportive treatment can be offered, since the high volume of distribution, as with other antidepressants, rules out removal of drug by dialysis. As much as 2.6 g of sertraline has been taken with survival. Overdoses of paroxetine are relatively benign Up to 850 mg has been taken with no evidence of cardiotoxicity. 

The side effects and cardiotoxicity of the tricyclic antidepressants have been discussed in detail elsewhere in this volume and, while there is ample evidence of their therapeutic efficacy, it seems difficult to justify their use, particularly in a group of patients who are most vulnerable to their detrimental side effects. Of the newer antidepressants, the reversible inhibitors of monoamine oxidase type A such as moclobemide may also be of value in the elderly depressed patient, particularly in those patients who fail to respond to the amine uptake inhibitor type of antidepressant. 

The selective serotonin-reuptake inhibitors (SSRI) are a new group of chemically unique antidepressant drugs that specifically inhibit serotonin reuptake (see Figure 12.3). This contrasts with the tricyclic antidepressants that nonselectively inhibit the uptake of norepinephrine, and serotonin, and block muscarinic, H histaminic and a -adrenergic receptors. Compared with tricyclic antidepressants, the SSRIs cause fewer anticholinergic effects and lower cardiotoxicity. However, the newer serotonin reuptake inhibitors should be used cautiously until their long-term effects have been evaluated. 

Q12 An SSRI, such as fluoxetine, can be started at a dose of 20 mg per day. Although similar in their efficacy and time course to the tricyclic drugs, the advantage of the SSRIs is their lack of serious side effects, such as cardiotoxicity, sedation, blurred vision, dry mouth and so on, which are associated with tricyclic antidepressants. 

Although pediatric psychopharmacology is much neglected, nocturnal enuresis is an area of extensive research. An earlier review catalogued almost 100 publications on the topic (13). The tricyclic antidepressants have been shown to be effective in well-controlled trials, and over 40 publications had appeared before 1970. At that time adverse effects in children appeared to be minimal and comparable to those in adults. Since then considerable concern has developed over cardiotoxic effects and the risks of accidental overdose in children. The earlier reports have been summarized (SEDA-1,10) managing overdose in children has been reviewed (SEDA-2,10) death in a 16-month-old infant has been reported (SEDA-3, 9). 

---