Nervous System Drugs — AI Study Guide

Mastering Nervous System Drugs

CNS pharmacology covers drugs that affect the brain and spinal cord: antidepressants, anxiolytics, antipsychotics, mood stabilizers, hypnotics, CNS stimulants, anticonvulsants, and analgesics. The common thread is the modulation of neurotransmitter systems — serotonin, dopamine, norepinephrine, GABA, glutamate — that underlie psychiatric and neurological disorders.

Antidepressants target monoamine systems. SSRIs (fluoxetine, sertraline, escitalopram) block serotonin reuptake, increasing synaptic serotonin — they are first-line for depression and anxiety. SNRIs (venlafaxine, duloxetine) block both serotonin and norepinephrine reuptake. TCAs (tricyclic antidepressants) block multiple receptors including muscarinic and histaminic, causing anticholinergic and sedating side effects. MAOIs inhibit monoamine oxidase, requiring dietary tyramine restriction to prevent hypertensive crisis.

Antipsychotics treat psychosis primarily through dopamine D2 receptor antagonism. Typical antipsychotics (haloperidol, chlorpromazine) potently block D2 receptors with high risk of extrapyramidal side effects (EPS: dystonia, akathisia, parkinsonism, tardive dyskinesia). Atypical antipsychotics (clozapine, quetiapine, olanzapine, risperidone) block D2 and 5-HT2A receptors with lower EPS risk but higher metabolic side effects (weight gain, diabetes, hyperlipidemia). Clozapine requires weekly WBC monitoring due to agranulocytosis risk.

Analgesics address pain through different mechanisms. NSAIDs (ibuprofen, naproxen) inhibit COX-1 and COX-2, reducing prostaglandin synthesis — anti-inflammatory, analgesic, and antipyretic. Opioids (morphine, oxycodone, fentanyl) activate mu-opioid receptors, reducing pain perception and producing euphoria — risk of dependence, respiratory depression, and constipation. Acetaminophen inhibits COX in the CNS, providing analgesia and antipyresis without anti-inflammatory effects or GI irritation.

Frequently Asked Questions: Nervous System Drugs

What are the extrapyramidal side effects of antipsychotics?

Extrapyramidal side effects (EPS) result from dopamine D2 blockade in the nigrostriatal pathway. Acute EPS: acute dystonia (sustained muscle contractions, occurs hours-days after starting; treat with anticholinergics or benzodiazepines), akathisia (inner restlessness, treat with beta-blockers or benzodiazepines), and drug-induced parkinsonism (tremor, rigidity, bradykinesia, treat by reducing dose or adding anticholinergics). Tardive dyskinesia (involuntary orofacial movements) occurs with long-term use and may be irreversible.

How do NSAIDs, opioids, and acetaminophen differ?

NSAIDs (ibuprofen, naproxen) inhibit COX enzymes, reducing prostaglandin synthesis. They are anti-inflammatory, analgesic, and antipyretic. Adverse effects: GI bleeding (COX-1 inhibition), renal toxicity, cardiovascular risk. Opioids (morphine, oxycodone) activate opioid receptors, reducing pain perception in the CNS. Adverse effects: respiratory depression, constipation, dependence. Acetaminophen inhibits COX centrally without significant peripheral anti-inflammatory effect. Adverse effects: hepatotoxicity in overdose. Best used in combination: different mechanisms provide additive analgesia with reduced individual drug doses.

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