Psychopharmacology and Biological Treatments
This domain tests mechanisms, indications, adverse effects, interactions, monitoring, and non-drug biological treatments. Questions often ask what to check, switch, or avoid rather than simply naming a drug.
Core rules
- Antipsychotics act mainly at D2 receptors; high potency increases EPS risk, while low potency increases anticholinergic and sedative burden.
- Clozapine is for treatment-resistant psychosis but requires regular white-cell monitoring and vigilance for myocarditis, seizures, constipation, and metabolic effects.
- SSRIs can cause hyponatremia, bleeding risk, and serotonin syndrome; combination serotonergic drugs increase risk.
- Lithium requires renal, thyroid, calcium, and level monitoring; dehydration, NSAIDs, ACE inhibitors, and thiazides can raise levels.
- ECT is effective for severe depression, catatonia, and treatment-resistant mania; consent and cognitive effects must be addressed.
Worked example
An older adult on an SSRI develops confusion and a sodium of 124 mmol/L. Reasoning: SIADH is likely after other causes are excluded. The safest step is to review fluids and medicines, consider stopping or switching the SSRI, and monitor sodium closely rather than adding another serotonergic agent.
Traps
Do not confuse neuroleptic malignant syndrome with serotonin syndrome. Do not forget renal dosing and drug interactions. Do not attribute all agitation to psychiatry before checking delirium, pain, or withdrawal.