Cardiotoxic effects of Mellaril: conduction disturbances and supraventricular arrhythmias

Interactions of CNS Drugs: Psychotherapeutic Agents—The Antipsychotic Drugs

Aspects of the pharmacology of the phenothiazine antipsychotic agents pertinent to possible interactions are reviewed. Pharmacokinetic interactions of possible clinical importance are the interference with the absorption of the phenothiazines by antacids, reversal of the hypotensive effect of guanethidine by psychotropic drugs, blockade of the effects of levodopa in Parkinson's disease, and stimulation of phenothiazine-metabolizing enzymes by phenobarbital. Pharmacologically, phenothiazines may potentiate certain depressant effects of other CNS depressants or add to the anticholinergic side effects of a number of other drugs. The phenothiazines appear to antagonize both the CNS stimulant and the anorexic effects of amphetamines and related substances. Other reactions of possible concern are the phenothiazine-induced hypoglycemia, the relationship of lithium toxicity to sodium intake, and the number of false positive pregnancy tests in patients on phenothiazine therapy.

Outcome of patients after market withdrawal of thioridazine: a retrospective analysis in a nationwide cohort

OBJECTIVE

Thioridazine is a first-generation antipsychotic drug that was withdrawn from the market worldwide in 2005. The outcome of clinically stable schizophrenia patients who used thioridazine before market withdrawal was evaluated.

METHODS

Nationwide registers in Finland were utilized to study thioridazine use, hospitalization rate and length of hospital stay.

RESULTS

Although thioridazine use continued to diminish year after year, the hospitalization rate remained constant until the withdrawal year of 2005, when the percentage of patients hospitalized for schizophrenia doubled.

CONCLUSION

The market withdrawal of thioridazine predisposed many stable patients towards psychotic relapses. In order to minimize this kind of risk, an overall risk-benefit assessment and a clear-cut plan for the replacement of an antipsychotic should be established before market withdrawal.

Torsade de pointes induced by psychotropic drugs and the prevalence of its risk factors

OBJECTIVE

To investigate all published case reports of torsade de pointes (TdP) induced by psychotropic drugs (PDs) in order to examine the prevalence of risk factors for TdP prior to the drug initiation.

METHOD

We found 45 reports on 70 patients with TdP induced by PDs. Each report was analyzed for the presence of risk factors for TdP: female gender, heart disease, hypokalemia, high doses of offending agent, concomitant use of a QT interval prolonging agent, and a history of long-QT syndrome.

RESULTS

Female gender was the most common risk factor for TdP (71.4%). The other studied risk factors were also frequently present (34.2-14.2%). Nearly all patients had at least one and 51 (73%) patients had >2 risk factors for TdP prior to PD initiation.

CONCLUSION

We wish to raise the level of awareness of risk factors for TdP in the psychiatric community.

Torsade de pointes due to noncardiac drugs: most patients have easily identifiable risk factors

Numerous medications, including drugs prescribed for noncardiac indications, can lead to QT prolongation and trigger torsade de pointes. Although this complication occurs only rarely, it may have lethal consequences. It is therefore important to know if patients with torsade de pointes associated with noncardiac drugs have risk factors that are easy to identify. We reviewed reports of drug-induced torsade de pointes and analyzed each case of torsade de pointes associated with a noncardiac drug for the presence of risk factors for the long QT syndrome that can be easily identified from the medical history or clinical evaluation (female gender, heart disease, electrolyte disturbances, excessive dosing, drug interactions, and history of familial long QT syndrome). We identified 249 patients with torsade de pointes caused by noncardiac drugs. The most commonly identified risk factor was female gender (71%). Other risk factors were frequently present (18%-41%). Virtually all patients had at least 1 of these risk factors, and 71% of patients had 2 or more risk factors. Our study suggests that almost all patients with torsade de pointes secondary to noncardiac drugs have risk factors that can be easily identified from the medical history before the initiation of therapy with the culprit drug.

Cardiotoxicity and prescription of thioridazine in New Zealand

OBJECTIVE

To review the production of cardiac arrhythmia by thioridazine, and consider the role of government regulation in light of antipsychotic prescribing trends in New Zealand.

METHODS

We conducted a focused literature review on psychotropic-induced cardiotoxicity, including mechanisms and incidence. In addition, we considered trends in antipsychotic prescription in New Zealand and decisions made by regulatory bodies in Australia, North America and the United Kingdom regarding restrictions on the prescription of thioridazine.

RESULTS

In general, the cardiotoxicity of antipsychotics, including thioridazine, relates to the ability of these drugs to antagonize voltage-sensitive potassium channels, and thereby prolong the QT interval. This action can lead to malignant arrhythmias in a very small proportion (< < 1%) of patients; the risk may be increased by other drugs or factors which prolong QT or inhibit the metabolism of thioridazine. A review of prescription doses and volumes in New Zealand indicates that thioridazine is prescribed mainly in low doses by non-specialists, and its use has been waning significantly over the past 2 years. These trends predate recent publicity regarding cardiotoxicity.

CONCLUSION

Recommendations regarding thioridazine use are presented. Although new patients should not receive this drug, existing patients benefiting from modest doses should not be denied access unless clear-cut risk factors for cardiotoxicity are evident.

Concentration-related pharmacodynamic effects of thioridazine and its metabolites in humans

OBJECTIVE

To measure cardiac and other effects of thioridazine and relate these to the plasma concentration of the parent drug and its principal metabolites.

METHODS

A double-blind, randomized-order crossover study involving nine healthy male subjects compared the effects of single doses of thioridazine (10 mg and 50 mg) with placebo. Plasma concentrations of thioridazine and its ring sulfoxide, side-chain sulfoxide, and side-chain sulfone metabolites were measured, together with effects on the ECG, blood pressure, salivary flow, and a batch of psychomotor tests for 72 hours after administration.

RESULTS

Thioridazine, 50 mg, reduced standing systolic blood pressure (mean peak changes from baseline [95% CI] -32 mm Hg [-55, 10 mm Hg]; p < 0.01 versus placebo) and diastolic blood pressure (-14 mm Hg [-26, -2 mm Hg]; p < 0.05), increased standing heart rate (7 beats/min [-1, 16 beats/min]; p < 0.05), impaired psychomotor function, and prolonged the JT (20 ms1/2 [7, 34 ms1/2]; p < 0.05), QTa (22 ms1/2 [8, 36 ms1/2]; p < 0.05), and QTc (22 ms1/2 [11, 33 ms1/2]; p < 0.01) intervals, but had no effect on QT dispersion (-12 ms1/2 [-31, 6 ms1/2]). Thioridazine, 1.0 mg, also significantly increased QTc, but the effect was less marked (9 ms1/2 [-1, 19 ms1/2]; p < 0.05). Plasma thioridazine and metabolite concentrations did not correlate significantly with these effects. Maximum effects on QTc occurred after peak concentrations of thioridazine but before peak concentrations of the ring sulfoxide and side-chain sulfone metabolites.

CONCLUSIONS

These data suggest that thioridazine has dose-related effects on ventricular repolarization and that the parent drug causes an important proportion of these effects, although its metabolites may also contribute.

Hyperthermia, hypertension, hypertonia, and coma in a massive thioridazine overdose

This report characterizes an atypical presentation of a thioridazine overdose. Clinical manifestations included wide Q.R.S. complex, hyperthermia, hypertension, hypertonia, and coma. Plasma catecholamine levels were markedly elevated. The patient was treated with dantrolene sodium and supportive care. The patient's condition improved over time, with questionable response to dantrolene sodium. Supportive care was the mainstay of treatment.

Cardiorespiratory depression and haemolysis due to thioridazine overdose in the rat

The cardiovascular and respiratory effects of an intravenous overdose of thioridazine (125 mg kg-1 h-1) were examined in either spontaneously breathing or artificially ventilated urethane-anaesthetized rats. In both groups PO2, heart rate and mean arterial pressure decreased and atrioventricular and intraventricular conduction time, as well as QT time, increased similarly. PCO2 and pH did not differ significantly except in spontaneously breathing rats where a severe acidosis occurred at the end of the experiments. Haemolysis was suspected. The same dose was administered intravenously to artificially ventilated rats. Plasma concentrations of the drug and its main metabolites, haematocrit and free plasma Hb were determined in separate groups. A severe haemolysis was observed. Thioridazine administered in the same doses intragastrically, intraduodenally or intraperitoneally resulted in lower plasma values than after intravenous administration and there was no haemolysis. Much higher oral doses produced haemolysis at 36 h, at which time plasma concentrations were not higher than those recorded after administration via the other non-intravenous routes. It is probable that the observed changes in cardiovascular and respiratory parameters are partly the result of haemolysis following thioridazine administration.

Diltiazem-like effect of thioridazine on the dihydropyridine binding site of the calcium channel of rat myocardial membranes

The phenothiazine thioridazine enhances the binding of [3H]-nitrendipine to cardiac membranes and antagonizes the inhibition of [3H]-nitrendipine binding by other classes of calcium channel blockers. These effects are similar to those of diltiazem. The increased binding of [3H]-nitrendipine in the presence of thioridazine or diltiazem is due to increased binding affinity rather than an increased number of binding sites. Increased affinity is due in part to a decrease in the dissociation rate of nitrendipine in the presence of either thioridazine or diltiazem. Thioridazine also reverses the blocking effect of tiapamil (a phenylalkylamine) on [3H]-nitrendipine binding to rat heart membranes, as does diltiazem, suggesting that thioridazine binds to the same site as diltiazem. Thioridazine may have calcium channel blocking effects in the high therapeutic and toxic dose ranges that could be responsible for some of its adverse cardiovascular effects.

Study of thioridazine cardiotoxic effects by means of His bundle activity recording

The effect of thioridazine on sinusal automaticity, myocardial excitability and auriculoventricular conduction have been studied in dogs by measuring the spontaneous heart rate, the effective refractory period of the atrial contractile tissue, the time of auriculonodal and infrahisian conduction. Chloralose anaesthetized dogs were administered 10 mg/kg thioridazine hydrochloride via intravenous route. While sinusal automaticity was not altered, conduction times were prolonged in the suprahisian and mainly the infrahisian part and the atrial refractory period increased. These effects are related to quinidine-like properties and consistent with cardiotoxic effects previously reported in clinical practice.