Psychopharmacology and Biological Treatments
This domain tests applied psychopharmacology: mechanism, dose, monitoring, interactions, and the management of adverse effects. Questions usually present a patient on treatment who develops a problem; the mark goes to the drug that caused it, the monitoring that should have caught it, and the correct next step.
Core monitoring rules
- Clozapine: reserved for treatment-resistant schizophrenia after two adequate antipsychotic trials. Risk of agranulocytosis (roughly 1%) mandates regular full blood counts, weekly for the first 18 weeks, then less frequently, with immediate cessation and urgent FBC if fever or sore throat develops. Also watch for myocarditis in the first two months, seizures at higher doses, hypersalivation, constipation and ileus. Smoking induces CYP1A2, so stopping smoking raises plasma levels.
- Lithium: narrow therapeutic index. Typical maintenance targets are 0.6-0.8 mmol/L and 0.8-1.0 mmol/L in acute treatment. Check renal function, thyroid function and calcium at baseline and periodically. Toxicity presents with coarse tremor, vomiting, ataxia, dysarthria and confusion. Thiazides, NSAIDs and ACE inhibitors raise levels.
- Valproate: highly teratogenic with neurodevelopmental harm; avoid in women of childbearing potential unless a pregnancy prevention programme is in place. Lamotrigine must be titrated slowly because of Stevens-Johnson syndrome.
Adverse effect syndromes
Acute dystonia appears within hours to days, akathisia within days, parkinsonism over weeks, and tardive dyskinesia after months to years. Neuroleptic malignant syndrome is characterised by lead-pipe rigidity, hyperthermia, autonomic instability, raised creatine kinase and leucocytosis; management is stopping the drug, cooling, hydration, and dantrolene or bromocriptine. Serotonin syndrome instead shows clonus, hyperreflexia, agitation and diarrhoea.
Worked example
A 34-year-old on lithium for bipolar disorder develops vomiting and a coarse tremor after starting a thiazide for hypertension. Reasoning: the thiazide reduces renal lithium clearance, so this is early lithium toxicity; hold lithium, check the level and renal function, rehydrate, and restart at a lower dose with an alternative antihypertensive. Reassuring the patient and continuing the same dose would be the common wrong answer.
Traps that cost marks
Confusing serotonin syndrome with neuroleptic malignant syndrome. Forgetting that steady state is reached after four to five half-lives. Prescribing antidepressants alone in bipolar depression. Missing that ECT remains first-line in life-threatening depression with food refusal, in catatonia, and in severe depression in pregnancy when drugs fail.