Psychopharmacology and psychotropic medicines in children and adolescents — branching viva

Stem

The examiner will test whether you can reason about developmental pharmacokinetics, choose first-line psychotropics by indication with evidence, reproduce dose and onset frameworks, justify the suicidality and metabolic monitoring obligations, counsel on valproate teratogenicity, and manage a psychotropic emergency. [1] [13]

Branch 1 — Developmental pharmacokinetics

Examiner: Why is a child not a small adult when you prescribe a psychotropic? [13]

Strong answer: Three developmental pharmacokinetic differences matter. Children have a larger liver mass per kilogram and higher glomerular filtration, so they often clear drugs faster per kilogram and need weight-based dosing; CYP enzyme ontogeny — particularly CYP2D6 and CYP2C19, which mature across childhood — changes exposure to atomoxetine, fluoxetine and many antipsychotics; and smaller fat stores shorten the half-life of lipophilic drugs. The practical consequence is dosing must be weight-based and titrated, never copied from an adult dose. [13] [14]

Examiner: Give me a clinical example where this changes your review timing. [14]

Strong answer: Stimulant core-symptom benefit is often evident the same day at an adequate dose, because methylphenidate blocks catecholamine reuptake directly; so I judge a stimulant at the next visit. Atomoxetine, a noradrenaline reuptake inhibitor, builds over 4 to 6 weeks, as does an SSRI. If I judged an atomoxetine or SSRI trial at three days, I would wrongly abandon an effective drug. The review rhythm is matched to the mechanism. [14] [13]

Branch 2 — Drug-class choice and monitoring

Examiner: A 10-year-old with moderate-to-severe ADHD. Walk me through first-line pharmacotherapy and its evidence. [12]

Strong answer: First-line is a long-acting methylphenidate product, started low in the morning and titrated weekly, alongside classroom supports and parent behavioural training. The Cortese network meta-analysis showed stimulants — particularly methylphenidate — had the largest effect on core ADHD symptoms in children at around 12 weeks, and the Storebø Cochrane review confirms efficacy while flagging study-quality limits. I confirm the exact dose against the local paediatric formulary, and monitor height and weight, blood pressure and heart rate, appetite, sleep, mood and tics. If a stimulant is unsuitable or diversion risk is high, atomoxetine (over weeks) or guanfacine XR are alternatives. [12] [13]

Examiner: What about an 8-year-old with autism and severe irritability not responding to behavioural intervention? [21]

Strong answer: After behavioural and educational intervention has genuinely failed, risperidone (RUPP trial) or aripiprazole (Marcus and Owen fixed-dose trials) have randomised controlled evidence for autistic irritability. The trade is metabolic, so behavioural failure is the threshold and not parental preference. I record baseline weight, height, BMI, waist, blood pressure, fasting glucose and lipids; repeat weight and BMI at least quarterly and glucose and lipids at around 12 weeks and then at least annually. Correll showed substantial metabolic change in the first 11 weeks of first-time paediatric use, with olanzapine highest; Ray linked antipsychotic treatment to higher unexpected-death risk in youth — both sharpen the need for clear indication, monitoring and a plan to trial off. [21] [22]

Branch 3 — The suicidality warning and valproate

Examiner: An adolescent starting fluoxetine for depression. How do you handle the black-box warning? [8]

Strong answer: The FDA black-box warning covers all antidepressants in people under 25. The Bridge meta-analysis found an increased rate of reported suicidal ideation and attempts in paediatric trials, while the Gibbons reanalysis argued the absolute risk is low and effective treatment itself protects against suicide. I counsel the family openly that fluoxetine takes 4 to 6 weeks to work, that early agitation or worsening must prompt immediate contact, and that combination with CBT lowers suicidality versus fluoxetine alone in TADS. I review at 1 week, 2 weeks and 4 weeks and at every dose change, assess suicidality explicitly, institute a safety plan and remove access to means — but I do not let the warning cause undertreatment of real depression. [8] [9] [1]

Examiner: A 15-year-old girl of childbearing potential with bipolar mania. What must you avoid? [21]

Strong answer: Valproate. It is highly teratogenic — neural tube defects — and associated with neurodevelopmental disorders in exposed children. It must not be used in a girl of childbearing potential without contraception and a pregnancy-prevention programme (PPP), and a safer alternative is sought wherever possible. A second-generation antipsychotic is often first-line for acute mania, with lithium for prophylaxis and lamotrigine for bipolar depression; lithium needs renal and thyroid monitoring and drug-level monitoring. [21]

Branch 4 — A psychotropic emergency

Examiner: An adolescent on an SSRI plus a newly added tramadol presents agitated, tremulous, hyperreflexic with clonus and fever. What is this and what do you do? [22]

Strong answer: This is serotonin syndrome, precipitated by the additive serotonergic load. I stop all serotonergic agents immediately, give benzodiazepines for agitation and rigidity, cool actively, hydrate, and escalate; cyproheptadine is used in severe cases. I distinguish it from neuroleptic malignant syndrome by the pattern: serotonin syndrome shows neuromuscular hyperactivity — hyperreflexia, clonus, myoclonus — while NMS shows lead-pipe rigidity and bradyreflexia, though both have fever and autonomic instability. If any rigidity raises NMS, I also stop any antipsychotic, cool, hydrate, and consider dantrolene in severe cases. This is the reason I check interactions before adding a serotonergic agent like tramadol to an SSRI. [22]

Examiner extras

• A child is not a small adult: weight-based dosing, CYP ontogeny, and shorter half-lives for lipophilic drugs. [13]
• Match your review rhythm to the drug: stimulant next day, SSRI and atomoxetine at 4 to 6 weeks. [14]
• TADS: fluoxetine plus CBT is safer and better than fluoxetine alone — combination lowers suicidality. [1]
• Every paediatric antipsychotic needs baseline and ongoing metabolic monitoring; olanzapine carries the highest metabolic risk. [21]
• Valproate is teratogenic: avoid in girls of childbearing potential without a PPP. [21]
• Serotonin syndrome shows hyperreflexia and clonus; NMS shows lead-pipe rigidity — both are emergencies. [22]