Pharmacology Cheat Sheet
Cns Therapeutics and Dependence
CNS pharmacology for NEET-PG: benzodiazepine vs barbiturate action, antiepileptic drugs of choice, lithium toxicity levels, and overdose antidotes.
MedNext Academy | 3 min read
Cns Therapeutics and Dependence
CNS pharmacology for NEET-PG: benzodiazepine vs barbiturate action, antiepileptic drugs of choice, lithium toxicity levels, and overdose antidotes.
Central nervous system pharmacology covering sedatives, antiepileptics, antipsychotics, antidepressants, opioids, and management of poisoning and dependence.
High-yield lines
- Benzodiazepines increase the frequency of chloride channel opening, while barbiturates increase the duration and can open channels even without GABA.
- Carbamazepine is the drug of choice for trigeminal neuralgia and focal seizures, undergoes autoinduction, and causes SIADH with hyponatraemia.
- Ethosuximide is the drug of choice for pure absence seizures but has no efficacy against tonic-clonic seizures.
- Valproate covers both absence and tonic-clonic seizures, making it preferred when a child has both.
- Clozapine is the only proven drug for treatment-resistant schizophrenia but causes agranulocytosis in about 1%, requiring regular white cell monitoring.
- Lithium toxicity begins with coarse tremor and ataxia above 1.5 mEq/L and progresses to seizures and coma above 2.5 mEq/L.
- Opioid tolerance develops to analgesia, euphoria, and respiratory depression but not to miosis or constipation.
- Naloxone is the opioid antidote, flumazenil reverses benzodiazepines, and both are short-acting requiring repeat dosing.
- Methanol poisoning causes optic nerve damage and high-anion-gap metabolic acidosis, treated with fomepizole or ethanol plus bicarbonate.
- Fomepizole and ethanol both inhibit alcohol dehydrogenase to block conversion of methanol to toxic formate.
- Sodium bicarbonate is the antidote for tricyclic antidepressant overdose.
- Disulfiram inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation with flushing and vomiting on alcohol ingestion.
- In status epilepticus, first-line treatment is IV lorazepam, followed by a second-line antiepileptic if seizures continue.
- Donepezil is used from mild Alzheimer's disease and memantine is added from the moderate stage.
Mapped competency codes
- PH1.19
- PH1.20
- PH1.21
- PH1.22
- PH1.23
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This summary maps to PH5-cns-pharmacology.
Frequently Asked Questions
How do benzodiazepines and barbiturates differ at the GABA channel?
Benzodiazepines increase the frequency of chloride channel opening, while barbiturates increase the duration and can open the channel without GABA at high doses.
What is the antidote for methanol poisoning?
Fomepizole (preferred) or ethanol, which block alcohol dehydrogenase, plus sodium bicarbonate, folinic acid, and dialysis in severe cases.
Why does clozapine require blood monitoring?
It carries an approximately 1% risk of agranulocytosis, so regular white cell and neutrophil counts are mandatory.
Which opioid effects do not develop tolerance?
Miosis and constipation persist, while tolerance develops to analgesia, euphoria, sedation, and respiratory depression.
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