What are Class B and B* drugs?

Class B and B* Psychotropic Drugs: Cardiac Risk Classification

Class B and B drugs are psychotropic medications that require cardiac risk assessment before initiation due to their potential for QT prolongation and arrhythmias, unlike Class A drugs which can be started without additional cardiac evaluation.* 1

Definition and Clinical Significance

Class B and B psychotropic medications are those with documented or potential pro-arrhythmic effects that necessitate structured cardiac risk assessment prior to treatment initiation.* 1 This classification system was developed to stratify cardiac risk in psychiatric patients, particularly focusing on QT interval prolongation and risk of sudden cardiac death (SCD). 1

Key Distinction from Class A Drugs

• Class A drugs can be commenced without any cardiac risk assessment 1
• Class B and B drugs* require pre-treatment cardiac evaluation including medical history, ECG assessment, and medication review for drug interactions 1

Mandatory Pre-Treatment Assessment for Class B/B* Drugs

Before initiating any Class B or B* medication, the following structured evaluation is required: 1

• Medical history focusing on:

  • Known heart disease 1
  • Cardiac symptoms (chest pain, dyspnoea, palpitations, near-syncopes, syncopes) 1
  • Family history of sudden cardiac death 1

• Medication review to identify:

  • Other QT-prolonging drugs 1
  • Potassium-wasting medications 1
  • Potential drug interactions via cytochrome P450 system 1

• Baseline ECG to assess:

  • Signs of structural heart disease 1
  • Conduction disorders 1
  • QT interval prolongation 1

Follow-Up Monitoring Requirements

ECG re-evaluation must occur within 1-2 weeks (at steady-state, approximately 5 drug half-lives) after initiating Class B/B medications.* 1 This same monitoring protocol applies when significantly increasing the dose of these agents. 1

Critical QTc Thresholds

• QTc >500 ms or increment >60 ms from baseline: These values indicate definitively increased risk of Torsades de Pointes and should generally lead to drug discontinuation 1

High-Risk Populations Requiring Extra Caution

Elderly patients with ischemic heart disease represent the highest-risk group when exposed to Class B/B drugs, as they have the highest rate of sudden cardiac death.* 1 The annual incidence of SCD in 75-year-old men reaches 800 per 100,000. 1

Additional Risk Factors

• Structural heart disease 1
• Pre-existing QT prolongation 1
• Electrolyte disturbances 1
• Concomitant use of multiple QT-prolonging medications 2

Clinical Decision Algorithm

When cardiac risks are identified during assessment: 1

1. Optimize all reversible cardiac risk factors (correct electrolytes, review drug interactions) 1
2. Consider switching to a drug with more favorable risk profile if clinically appropriate 1
3. Refer to cardiology if structural heart disease, significant QT prolongation, electrolyte disturbances, or cardiac symptoms are present 1

Exception for Severe Psychiatric Illness

If the psychiatric condition is invalidating or life-threatening, a higher cardiac risk may be accepted, but this requires reduction of all reversible risk factors and close follow-up. 1

Common Pitfalls to Avoid

• Failing to recognize additive effects: Multiple QT-prolonging medications can have cumulative effects on cardiac conduction 2
• Assuming uniform risk: Not all psychiatric medications carry the same cardiac risk; quetiapine has moderate QT-prolonging effects (~6 ms average), while valproate is not classified as a QT-prolonging agent 2
• Inadequate follow-up timing: Waiting too long for repeat ECG misses the critical steady-state period when arrhythmia risk is highest 1