CNS Medications and Neurotransmitters

Central Nervous System Medications

• Medications for the central nervous system (CNS) are discussed in chapters 12 & 14.
• The nervous system comprises the central nervous system (CNS), peripheral nervous system (PNS), autonomic nervous system (ANS), and somatic nervous system.
• The CNS includes the brain and spinal cord.
• The PNS consists of cranial nerves and spinal nerves.
• The ANS controls involuntary actions like heart rate and digestion. It is further divided into parasympathetic (rest-and-digest) and sympathetic (fight-or-flight) divisions.
• The somatic nervous system controls voluntary movements.

CNS Neurotransmitters

• Acetylcholine is involved in memory and learning.
• Dopamine is associated with pleasure and motor control.
• Glutamate is essential for memory.
• GABA (gamma-aminobutyric acid) plays a role in memory and movement.

Parkinson's Disease Treatments

• Parkinson's Disease is characterized by too little dopamine and too much acetylcholine.
• Treatments include dopaminergic agents (directly/indirectly activating dopamine receptors – more commonly used) and anticholinergic agents (blocking acetylcholine receptors).

Levodopa: Dopamine Replacement

• Levodopa is a prodrug that increases dopamine levels.
• Only about 2% of levodopa reaches the brain.
• Food, especially high-protein meals, can delay absorption.
• Levodopa has a short half-life (1-2 hours).
• "Loss of effect" is a common problem as the drug metabolizes and loses effectiveness over time.

Carbidopa/Levodopa (Sinemet)

• Carbidopa prevents levodopa breakdown before reaching the brain.
• Allows for a lower dose of levodopa, thus reducing side effects.
• Available only as a combination pill.

Levodopa Adverse Effects

• Common side effects include nausea, vomiting (N/V), involuntary movements (dyskinesias), cardiovascular issues (orthostatic hypotension, dysrhythmias), and psychiatric symptoms (hallucinations, vivid dreams, paranoia).
• Medications that block dopamine receptors can worsen Parkinson's symptoms.
• Medications that block acetylcholine receptors can help reduce acetylcholine side effects.

Nursing Considerations for Levodopa

• Patients should take levodopa without food, especially high-protein meals.
• Patients should be monitored for "loss of effect".
• Patients should be warned about postural changes.
• Patients should report any new tremors or twitching, palpitations, racing hearts, hallucinations, or paranoia.

Pramipexole: Dopamine Receptor Agonist

• Pramipexole directly activates dopamine receptors in the brain.
• Often used as a first-line treatment in early stages of Parkinson's.
• Can be used alone in early stages or with levodopa/carbidopa in advanced stages.

Pramipexole Adverse Effects

• Common side effects include nausea, dizziness, weakness, and sleep disturbances.
• Combining pramipexole with levodopa/carbidopa can lead to orthostatic hypotension, dyskinesias, or hallucinations.
• Patients taking pramipexole should be monitored for sleep attacks and impulse control disorders/compulsive behaviors.

Nursing Considerations for Pramipexole

• Patients should take pramipexole with meals.
• Patients should be advised to rise slowly from supine or sitting positions.
• Patients should report any sleep attacks or impulse control concerns.

Drugs for Seizures (AEDs)

• Antiepileptic drugs (AEDs) aim to reduce neuronal activity and prevent seizure spread.
• Four primary ways AEDs work:
  1. Suppressing sodium influx in cell membranes.
  2. Suppressing calcium influx in axon terminals.
  3. Antagonizing glutamate (a neurotransmitter).
  4. Potentiating GABA (a neurotransmitter).

Traditional vs Newer Anti-Epileptic Drugs

• Traditional AEDs (e.g., phenytoin, phenobarbital, valproic acid) are typically less expensive and may carry more side effects and drug interactions.
• Newer AEDs (e.g., oxcarbazepine) are typically more expensive and may have fewer side effects and interactions but can still have serious ones. They are often safer for pregnancy.

Phenytoin (Prototype)

• Phenytoin blocks sodium channels in hyperactive neurons.
• Therapeutic levels are 10-20 mcg/mL.
• Highly protein-bound.
• Liver metabolism can be overwhelmed by high doses.
• Half-life varies with dose.
• A CYP enzyme inducer.

Phenytoin Adverse Effects

• Adverse effects at therapeutic levels can include mild effects like headaches or drowsiness. At higher levels (> 20 mcg/mL), more serious effects may occur including nystagmus, increased sedation, ataxia, or diplopia.
• Other adverse effects include gingival hyperplasia, rashes, and teratogenic potential.
• Drug interactions are common.

Valproic Acid

• Blocks sodium and calcium channels and may potentiate GABA.
• Used for diverse seizure types and bipolar disorder.
• Common side effects include GI issues and rare but severe hepatotoxicity (liver damage).

Oxcarbazepine (Newer Prototype)

• Blocks overactive sodium channels.
• No drug level monitoring is required in most cases.
• Serious side effects like skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), or CNS issues (dizziness, drowsiness, double vision, nystagmus, headache, ataxia) are rare but possible.
• Can cause hyponatremia (low sodium levels).

Status Epilepticus

• A prolonged period of continuous seizure activity.
• A medical emergency.
• Treatment targets securing the airway, administering intravenous (IV) or oral benzodiazepines, and following-up with antiepileptics.

Drugs for Alzheimer's Disease

• Alzheimer's Disease is characterized by a lack of acetylcholine and unknown pathophysiology.
• Key treatments include cholinesterase inhibitors (e.g., donepezil, rivastigmine) and N-methyl-D-aspartate (NMDA) antagonists (e.g., memantine).

Donepezil (Cholinesterase Inhibitor)

• MOA: inhibits breakdown of acetylcholine.
• Benefits: improved quality of life, memory, and reasoning.
• Does not delay disease progression.
• Available as oral disintegrating tablets (ODTs).

Rivastigmine (Cholinesterase Inhibitor)

• MOA: inhibits breakdown of acetylcholine.
• Benefits: improved quality of life, memory, and reasoning.
• Does not delay disease progression.
• Available as a transdermal patch.

Memantine (NMDA Antagonist)

• MOA: blocks NMDA receptors, preventing excessive calcium accumulation.
• Benefits: slows disease decline and possibly improves symptoms.
• Does not modify the underlying disease process.
• Generally has fewer side effects compared to other Alzheimer's medications.

Spasm and Spasticity

• Spasm: involuntary muscle contraction.
• Spasticity: prolonged muscle tightness.

Medications for Spasm and Spasticity

• Cyclobenzaprine (centrally acting muscle relaxant) – used for spasm.
• Baclofen (centrally acting muscle relaxant) – used for spasticity.
• Dantrolene (direct-acting muscle relaxant) – used for spasticity.
• Diazepam (benzodiazepine) used for spasticity.

Medications for Muscle Spasms

• Acetaminophen
• Ibuprofen
• Cyclobenzaprine

Cyclobenzaprine

• Therapeutic use for acute muscle spasms.
• Not effective for spasticity.
• Adverse effects: CNS effects (drowsiness, dizziness), and anticholinergic effects (dry mouth, blurred vision, urinary retention, constipation).
• Drug interactions include alcohol and other CNS depressants.
• Tolerance and dependence can occur.

Baclofen

• Acts within the spinal cord to suppress hyperactive reflexes.
• Main adverse effect is sedation.
• Dosing may be oral or IV for malignant hyperthermia.

Dantrolene

• Acts directly on skeletal muscle.
• PO dosing used for spasticity.
• Serious adverse effect of hepatotoxicity.

This quiz covers essential information about medications affecting the central nervous system and their roles in various neurological functions. It includes discussions on neurotransmitters, their effects, and treatment options for conditions like Parkinson's Disease. Test your understanding of CNS components and pharmacology.