DIP Episode 68 - Psych Pharm Part 2 (Final Part)

Source / episode info

• Episode: 68
• Title: Divine Intervention Episode 68 – Psych Pharm Part 2 (Final Part)
• Published: 2019-01-07
• Source: Episode page

One-liner

This episode provides an exhaustive review of psychopharmacology, detailing the pathophysiology of schizophrenia via dopamine pathways (mesolimbic/mesocortical), comparing typical and atypical antipsychotics based on D2/5-HT2 A receptor ratios, outlining management for bipolar disorder and lithium toxicity, and reviewing various drugs of abuse.

High-yield summary

• Schizophrenia Pathophysiology: Positive symptoms are linked to excess dopamine in the mesolimbic pathway; negative symptoms are linked to low dopamine in the mesocortical pathway.
• Antipsychotic Receptor Logic: Atypical antipsychotics (e.g., clozapine, risperidone) block 5-HT2 A receptors, which increases dopamine release in the mesocortical and tuberoinfundibular pathways, thereby improving negative symptoms and reducing hyperprolactinemia.
• Typical vs. Atypical: High-potency typical agents (e.g., haloperidol) are excellent for positive symptoms but carry a high risk of extrapyramidal symptoms (EPS).
• Lithium Toxicity: Lithium is nephrotoxic; toxicity can be exacerbated by any agent that increases the activity of the Renin-Angiotensin-Aldosterone System (RAAS), such as thiazide diuretics or NSAI Ds. Treatment involves ADH receptor antagonists like amiloride or triamterene.
• EPS Management: Acute dystonia is treated with anticholinergics (e.g., benztropine); Akathisia with alpha-2 adrenergic blockers (e.g., propranolol); Parkinsonism with dopamine agonists (e.g., benztropine).

Learning objectives

• Differentiate the pathophysiology of positive vs. negative symptoms in schizophrenia using dopamine pathway models.
• Compare and contrast the side effect profiles and receptor mechanisms of typical versus atypical antipsychotics.
• Identify appropriate pharmacological treatments for specific extrapyramidal symptoms (EPS).
• Recognize the mechanism, risks, and management of lithium toxicity, particularly concerning RAAS activation.
• Understand the unique metabolic and behavioral effects associated with various drugs of abuse (e.g., marijuana, PCP).

Board exam buzzwords

Rapid review table

Board-speak -> diagnosis

Differential diagnosis / distinguishing features

Antipsychotic Side Effects Comparison

Management pearls

• For acute dystonia, the first-line treatment is an anticholinergic agent like benztropine.
• Akathisia should be treated with a non-sedating alpha-2 adrenergic blocker such as propranolol; if unavailable, use benzodiazepines.
• In cases of suspected lithium toxicity, administer EDTA (if severe) and manage volume status aggressively.
• When treating bipolar disorder in pregnancy, haloperidol is preferred over lithium due to the risk of fetal cardiac malformations associated with lithium.

Don't miss

Integration & clinical reasoning

• Pharmacology & Metabolism: The use of tricyclic antidepressants (TC As) and low-potency typical antipsychotics shares side effects due to their non-selective blockade of muscarinic receptors (anti-histamine/anticholinergic effects).
• Endocrine & Psychiatry: Lithium's effect on the V2 receptor signaling cascade in the collecting duct is analogous to its ability to interfere with ADH action, leading to NDI.
• Neuroscience: The dopamine hypothesis of schizophrenia requires understanding that positive symptoms are linked to mesolimbic excess and negative symptoms to mesocortical deficiency.

OMM / COMLEX integration

• Acute Psychosis: In an unstable patient presenting with acute psychosis, standard emergency management (e.g., benzodiazepines for agitation) takes priority over specific psychotropic drug selection. Antipsychotics are used adjunctively after stabilization.
• Electrolyte Imbalance/Renal Failure: Any decision regarding lithium dosing or administration must first account for the patient's renal function and hydration status, as these factors drastically alter clearance and toxicity risk.

Concept connections / cross-references

• For detailed review of neurotransmitter systems and their clinical implications: [Episode 37] (If this episode covered general neuro/neurotransmitters).
• For comprehensive coverage of psychopharmacology side effects and drug interactions: [A hypothetical future Psych Pharm Review Episode].

High-yield association table

Key terms glossary

Study optimization

Question pattern recognition

• Mechanism of Action: Understanding how drugs interact with multiple receptors (e.g., low-potency antipsychotics blocking H1, \alpha_1, and muscarinic).
• Differential Diagnosis: Differentiating between various types of psychosis or metabolic derangements (e.g., NDI vs primary DI).
• Toxicity/Contraindications: Identifying which drugs exacerbate a specific condition (e.g., thiazides worsening lithium toxicity).

Test yourself

Common mistakes to avoid

Common traps