USMLE (Subject) / Pharmacology - CNS (Lesson)

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  • Benzodiazepines - Potentiate GABAA receptors - ↑ the frequency of Cl- channel opening - Have no GABA mimetic activity - sedation, antianxiety, impairment of cognitive functions Toxicity: Sedation, anterograde amnesia --> reverse with flumazenil
  • Barbiturates eg phenobarbital, thiopental - Prolongation of GABA activity - ↑ duration of Cl- channel opening - Have GABA mimetic activity at high doses - stimulate heme synthesis (contraindicated in porphyrias!)
  • Alprazolam Benodiazepine Indication:- Anxiety- Panic- Phobia
  • Diazepam Benzodiazepine Indication:- Anxiety- Preop sedation- Muscle relaxation- Withdrawal states
  • Lorazepam Benzodiazepine Indication:- Anxiety- Preop sedation- Status epilepticus (IV)
  • Midazolam Benzodiazepine Indication:- Preop sedation- Anesthesie IV
  • Temazepam Benzodiazepine Indication:- Sleep disorders
  • Oxazepam Benzodiazepine Indication:- Sleep disorders- Anxiety
  • Buspirone - non-benzodiazepine drug - no effect on GABA - 5HT1A partial agonist - used for generalized anxiety disorders - nonsedative - takes 1 to 2 weeks for effects
  • SSRIs fluoxetine, paroxetine, sertraline, citalopram, fluvoxamine - selective blockade of 5HT uptake Uses:- major depression- OCD- bulimia- anxiety disorders (chronic treatment/acute, benzodiazepines) Interactions: serotonin syndrome with MAO inhibitors, TCAs, meperidine--> sweating, rigidity, myoclonus, hyperthermia, seizures
  • TCAs amitriptyline, imipramine, clomipramine - nonspecific blockade of 5HT and NE reuptake Uses:- major depressions- phobic and panic anxiety states- OCDs- neuropathic pain- enuresis Toxicity: the "3 Cs": coma, convulsions, and cardiotoxicity
  • MAO inhibitors phenelzine, moboclemide - irreversible inhibition of MAOA and MAOB - Use: atypical depressions Drug interactions:- Serotonin syndrome- ↑ NE: hypertensive crisis (↑ BP, arrhythmias, excitation, hyperthermia)
  • Lithium - DOC for bipolar disorders - usually antidepressants/antipsychotics also required - prevents recycling of inositol (↓PIP2), ↓cAMP - narrow therapeutic index (requires therapeutic monitoring)- tremor, flu-like symptoms, life-threatening seizures- hypothyroidism with goiter (↓TSH effects)- nephrogenic diabetes insipidus (↓ ADH effects)- teratogenicity: Ebstein's anomaly (malformed tricuspid valve)
  • Levodopa - prodrug converted to dopamine by aromatic amino acid decorboxylase (AAAD) - given with carbidopa Side effects:- dysinesias- psychosis- hypotension- vomiting
  • Selegiline MAOB-selective inhibitor (no tyramine interactions) - initial treatment and adjunct to levadopa Side effects:- dyskinesias- psychosis- insomnia (metabolized to amphetamine)
  • Bromocriptine Deopamine-receptor agonist Use: hyperprolactemia and acromegaly
  • Chlorpromazin - typical antipsychotic - EPS ++- M Block ++- Sedation +++- Alpha Block +++
  • Thioridazine - Typical Antipsychotic - EPS +- M Block +++- Sedation +++- Alpha Block - Cariotoxicity- Retinal deposits
  • Fluphenazine Typical Antipsychotic - EPS +++- M Block +- Sedation +- Alpha Block +
  • Haloperidol Typical Antipsychotic - EPS +++- M Block +- Sedation +- Alpha Block + - most likely cause of neuroleptic malignant syndrome (NMS) and TD
  • Clozapine Atypical Antipsychotic - EPS -- M Block ++- Sedation +- Alpha Block +++ - Blocks D2C and 5HT2 receptors- no TD (tardive dyskinesia)- Agranulocytosis --> requirement for weekly blood test- weight gain- increased salivation ("wet pillow" syndrome)- seizures
  • Olanzapine Atypical Antipsychotic - EPS -- M Block +- Sedation +- Alpha Block + - blocks 5HT2 receptors, improves negative symptoms
  • Risperidone Atypical Antipsychotic - EPS +- M Block -- Sedation ++- Alpha Block ++ - Blocks 5HT2 receptors, improves negative symptoms
  • Aripiprazole Atypical Antipsychotic - EPS +- M Block -- Sedation -- Alpha Block - - Parital agonist of D2 receptor; blocks 5HT2 receptors
  • Phenytoin - Blocks axonal Na+ channes in their inactivated state- Prevents seizure propagation Uses: seizure states Side effects:- CNS depression- Hirsutism- Osteomalacia (vitamin D ↓)- Megaloblastic anemia (folate ↓)- teratogenic
  • Carbamazepine - Blocks axonal Na+ channels in their inactivated state (like phenytoin) Uses: seizure states Side effects:- CNS depression- Osteomalacia- Megaloblasstic anemia- teratogenic
  • Valproic acid - Blocks axonal Na+ channels (like phenytoin), inhibits GABA transaminase, blocks T-type Ca2+ channels Uses: seizure states Side effects:- hepatotoxicity- thrombocytopenia- pancreatitis- teratogenic (spina bifida)
  • Gabapentin Anticonvulsant Used in seizure states, neuropathic pain 
  • Felbamate Anticonvulsant - Blocks Na+ channels and glutamate receptors Uses: seizure states (often adjunct therapy) Side effects: aplastic anemia
  • Ethosuximide Blockade of T-type Ca2+ channels in thalamic neurons Use: absence seizures
  • Lamotrigine Blocks Na+ channels and glutamate receptors - used in various seizures Side effects: Stevens-Johnson syndrome
  • Topiramate Blocks Na+ cahnnels and glutamate receptors and enhances GABA activity - Used in focal seizures in adults and children > age 2 Side effects: weight loss
  • General features of anticonvulsant drug use - anticonvulsants are additive with other CNS depressants - avoid abrupt withdrawal (may precipitate seizures) - ↓ efficacy of oral contraceptives via induction of cytochrome 450
  • Propofol Intravenous anaesthetic - used for induction and maintenance of anaesthesia- CNS and caridiac depressant
  • Fentanyl - Opiate used for induction and maintenance of anaesthesia - depresses respiratory function
  • Ketamine - dissociative anesthetic - NMDA-receptor antagonist - induction of anesthesia - emergent delirium, hallucinations - cardiovascular stimulation
  • Atracurium Nondepolarizing skeletal muscle relaxant - nicotinic antagonist (no effects on cardiac and smooth muscle) - safe in hepatic or renal impairment - spontaneous inactivation to laudanosine
  • Succinylcholine - depolarizing skeletal muscle relaxant - nicotinic agonist - rapidly hydrolyzed by pseudocholinesterase: short duration Cautions:- malignant hyperthermia- hyperkalemia
  • Acute toxicity (opioids): Classic triad 1. Pinpoint pupils 2. Respiratory depression 3. Coma
  • Cocaine - blocks DA, NE and 5HT reuptake in CNS; local anesthetic action from Na+ channel blockade - increase NE: sympathomimetic effect- increase DA: psychotic episodes, paranoia, hallucinaions, dyskinesias, endocrine disturbances- increase 5HT: behavioral changes, aggressiveness, decreased appetite Toxicity- excess NE: arrhythmias- excess DA: major psychosis- excess 5HT: serotonin syndrome
  • Amphetamines - Blockade of reuptake of NE and DA, release amines from mobile pool, weak MAO inhibitors
  • Marijuana - interaction with CB1 and CB2 cannabinoid receptors in CNS and periphery - sedation, euphoria, ↑ HR, delusions, hallucinations, conjunctival irritation
  • Fluoxetine SSRI - selective blockade of 5HT reputake Uses:- major depression- OCD- bulimia- anxiety disorders Toxicity: serotonin syndrome 
  • Sertraline SSRI - selective blockade of 5HT reputake Uses:- major depression- OCD- bulimia- anxiety disorders Toxicity: serotonin syndrome 
  • Citalopram SSRI - selective blockade of 5HT reuptake Uses:- major depression- OCD- bulimia- anxiety disorders Toxicity: serotonin syndrome 
  • Fluvoxamine SSRI - selective blockade of 5HT reuptake Uses:- major depression- OCD- bulimia- anxiety disorders Toxicity: serotonin syndrome 
  • Paroxetine SSRI - selective blockade of 5HT reuptake Uses:- major depression- OCD- bulimia- anxiety disorders Toxicity: serotonin syndrome 
  • Amitriptyline TCA - nonspecific blockade of 5HT and NE reuptake Uses:- major depressions- phobic and panic anxiety states- OCDs- neuropathic pain Side effects: muscarinic and α blockade Toxicity: the 3 Cs: coma, convulsions, and cardiotoxicity
  • Imipramine TCA - nonspecific blockade of 5HT and NE reuptake Uses:- major depressions- phobic and panic anxiety states- OCDs- neuropathic pain Side effects: muscarinic and α blockade Toxicity: the 3 Cs: coma, convulsions, and cardiotoxicity
  • Clomipramine TCA - nonspecific blockade of 5HT and NE reuptake Uses:- major depressions- phobic and panic anxiety states- OCDs- neuropathic pain Side effects: muscarinic and α blockade Toxicity: the 3 Cs: coma, convulsions, and cardiotoxicity

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