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Sunday, August 10, 2025

Central nervous system agents


1. Introduction

  • CNS agents are drugs that act on the brain and spinal cord to alter nervous system activity.

  • They can stimulate, depress, modulate, or otherwise modify neuronal function.

  • Used to treat neurological disorders, psychiatric conditions, sleep disturbances, pain, and infections affecting the CNS.

  • Include both therapeutic medications and diagnostic agents.

2. General Mechanisms of Action

  • Alter neurotransmitter synthesis, release, reuptake, or degradation.

  • Bind to specific CNS receptors to enhance or inhibit neuronal signaling.

  • Modulate ion channel activity (e.g., sodium, potassium, calcium, chloride channels).

  • Influence intracellular signaling cascades affecting neuronal excitability and plasticity.

3. Classification of CNS Agents

1. Analgesics

  • Opioid analgesics: morphine, fentanyl, oxycodone.

  • Non-opioid analgesics: acetaminophen, NSAIDs.

  • Adjuvant analgesics: antidepressants (duloxetine), anticonvulsants (gabapentin) for neuropathic pain.

2. Anesthetics

  • General anesthetics: propofol, sevoflurane, ketamine.

  • Local anesthetics: lidocaine, bupivacaine.

  • Neuromuscular blockers: used adjunctively in surgical anesthesia.

3. Anticonvulsants / Antiepileptics

  • Sodium channel blockers: phenytoin, carbamazepine, lamotrigine.

  • GABA enhancers: benzodiazepines, barbiturates, vigabatrin.

  • Calcium channel blockers: ethosuximide.

  • Broad-spectrum agents: valproic acid, levetiracetam, topiramate.

4. Antidepressants

  • SSRIs: fluoxetine, sertraline, escitalopram.

  • SNRIs: venlafaxine, duloxetine.

  • Tricyclic antidepressants: amitriptyline, nortriptyline.

  • MAO inhibitors: phenelzine, tranylcypromine.

  • Atypical antidepressants: bupropion, mirtazapine.

5. Antipsychotics

  • Typical (first-generation): haloperidol, chlorpromazine.

  • Atypical (second-generation): risperidone, olanzapine, quetiapine, clozapine.

6. Anxiolytics and Sedative-Hypnotics

  • Benzodiazepines: diazepam, lorazepam.

  • Non-benzodiazepine hypnotics: zolpidem, zaleplon.

  • Barbiturates: phenobarbital, pentobarbital.

7. CNS Stimulants

  • Amphetamines: dextroamphetamine, lisdexamfetamine.

  • Methylphenidate.

  • Modafinil and armodafinil for wakefulness promotion.

8. Anti-Parkinson Agents

  • Dopamine precursors: levodopa/carbidopa.

  • Dopamine agonists: pramipexole, ropinirole.

  • MAO-B inhibitors: selegiline, rasagiline.

  • COMT inhibitors: entacapone, tolcapone.

  • Anticholinergics: benztropine, trihexyphenidyl.

9. Multiple Sclerosis Agents

  • Immunomodulators: interferon beta, glatiramer acetate.

  • Oral agents: fingolimod, dimethyl fumarate, teriflunomide.

  • Monoclonal antibodies: natalizumab, ocrelizumab.

10. Migraine Medications

  • Acute: triptans, ergot derivatives, NSAIDs.

  • Preventive: beta-blockers, calcium channel blockers, anticonvulsants, CGRP inhibitors.

11. CNS Anti-infectives

  • Antivirals: acyclovir (herpes encephalitis).

  • Antibacterials: ceftriaxone, vancomycin (meningitis).

  • Antifungals: amphotericin B, fluconazole (cryptococcal meningitis).

12. Neuroprotective Agents

  • Drugs designed to limit neuronal injury after stroke, trauma, or neurodegenerative disease.

4. Therapeutic Uses

  • Pain relief (acute, chronic, neuropathic).

  • Sedation and anesthesia for surgery.

  • Seizure control in epilepsy and other convulsive disorders.

  • Management of depression, anxiety, bipolar disorder, schizophrenia.

  • Symptom control in Parkinson’s disease and multiple sclerosis.

  • Prevention and acute treatment of migraines.

  • Treatment of CNS infections.

  • Cognitive enhancement in certain disorders (e.g., Alzheimer’s disease).

5. Pharmacokinetic Considerations

  • CNS penetration depends on lipid solubility, molecular size, and blood-brain barrier permeability.

  • Many CNS agents require high lipid solubility to cross the blood-brain barrier effectively.

  • Metabolism often occurs in the liver; elimination can be renal or hepatic.

  • Some agents require dosage adjustment in renal or hepatic impairment.

6. Adverse Effects (General Trends)

  • CNS depression: drowsiness, sedation, respiratory depression.

  • CNS stimulation: insomnia, agitation, anxiety.

  • Cognitive effects: confusion, memory impairment.

  • Motor effects: tremors, ataxia, extrapyramidal symptoms.

  • Psychiatric effects: mood changes, hallucinations, psychosis.

  • Dependence and withdrawal potential (notably with benzodiazepines, opioids, stimulants).

7. Contraindications and Precautions

  • History of hypersensitivity to the drug or its class.

  • Severe respiratory depression (for CNS depressants).

  • Uncontrolled narrow-angle glaucoma (for certain antidepressants).

  • Seizure disorders (for some stimulants).

  • Cardiovascular disease (for potent CNS stimulants).

  • Pregnancy and lactation considerations depending on drug category.

8. Drug Interactions

  • Additive sedative effects when combining CNS depressants (e.g., benzodiazepines with opioids).

  • Altered metabolism via cytochrome P450 interactions (inhibitors/inducers).

  • Increased serotonergic toxicity risk with multiple serotonergic drugs.

  • Reduced effectiveness of some CNS drugs with concurrent antacids or gastrointestinal motility agents.

9. Special Considerations

  • Dosage individualization is essential based on patient’s age, organ function, and comorbidities.

  • Many CNS drugs have abuse potential and are controlled substances.

  • Long-term therapy may require monitoring for metabolic, cardiovascular, or neurologic side effects.

  • Withdrawal syndromes can occur if abruptly discontinued.




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