CNS DRUGS

Anatomy & Physiology (CNS)

• Pons & Medulla - controls breathing, regulates BP, vomiting & swallowing
• RAS (Reticular Activating System) - controls sleep, arousal and awareness of stimuli
• Cerebellum - controls motor activity
• Limbic System - controls emotions
• Hypothalamus - controls thermoregulation, fluid balance, appetite
• Thalamus - sends information to cerebrum
• 31 spinal nerve pairs, 2 roots
• dorsal root - transmits sensory information
• ventral root - transmits motor information

Opioids

• FOR MODERATE TO SEVERE PAIN
• S/E: abuse, dependence, opioid tolerance, histamine release, CNS depression
• Agonists
• Morphine
• For myocardial infarction, cancer, dyspnea from pulmonary edema
• Provide to patients with myocardial infarction if symptoms persist after nitroglycerin to relieve pain and reduce heart's workload
• ANTIDOTE: naloxone
• Crosses placenta and present in breastmilk
• Meperidine (Demerol)
• Drug of choice for pregnancy
• Agonist-Antagonist
• Nalbuphine (Nubain), Butorphanol, Buprenorphine, Pentazocine
• Binds to pain receptors but causes a weaker response; blocks other opioid receptors
• LESS ABUSE POTENTIAL
• MORE PSYCHOTIC-LIKE REACTIONS (e.g. delusions, hallucinations)
• May be used during labor & delivery
• Antagonists
• Naloxone (Narcan) - morphine antidote
• Nalmefone, naltrexone
• Binds to opioid receptors but doesn’t reduce pain
• Competes with & reverses effects of agonist & partial agonists
• Nursing Considerations
• Have antagonists (e.g. naloxone) on standby
• Assess pain intensity, type, & character especially for PRN pain meds
• Assess level of consciousness & respiratory depression (indicates overdose)
• Provide pain relief prior to onset of pain

Non-Opioids

• NOT ADDICTIVE, less potent than narcotics
• FOR MILD TO MODERATE PAIN
• Causes gastric irritation; thus, should be taken with meals
• Analgesic, antipyretic, anti-inflammatory & Anti-platelet effects
• Aspirin
• Oldest non-narcotic drug
• Causes REYE’S SYNDROME when given to children under 12 yrs
• Symptoms include brain swelling (which leads to confusion, fever, headaches, hyperreflexia, coma, seizures) and fatty liver (which leads to hyperammonemia, although no jaundice)
• Acetaminophen / Paracetamol (Biogesic, Tylenol)
• Appropriate substitute for aspirin
• Contraindicated in G6PD deficiency & severe liver disease
• ANTIDOTE: ACETYLCYSTEINE

Anesthetics

• Drugs that depress the CNS & PNS
• General Anesthetics
• Lipid solubility & drug potency go hand in hand (OVERTON-MEYER THEORY); meaning increased lipid solubility of a drug means increased potency
• FOR SURGICAL PROCEDURES
• Contraindicated in pregnancy and malignant hyperthermia
• S/E: myocardial & respiratory depression
• Expected Outcomes:
• Pain relief
• Loss of consciousness
• Deep muscle relaxation
• Reflex reduction
• Classifications:
• Inhaled
• Volatile (easily evaporates) liquids or gases that are vaporized with oxygen and inhaled to induce anesthesia
• Gas – nitrous oxide
• Liquid – desflurane, enflurane, sevoflurane, halothane
• Injectable
• For induction of anesthesia or amnesia
• For maintenance of general anesthesia
• etomidate and propofol
• Local Anesthesia
• EPINEPHRINE prevents rapid absorption and succeeding toxicity of drug
• Interferes with nerve transmission in a specific area
• Causes loss of consciousness, muscle relaxation, loss of responsiveness
• Lidocaine, Tetracaine, Benzocaine
• Neuromuscular Blocking Agents (NMBA)
• Prevent nerve transmission to certain muscles leading to their paralysis
• For the maintenance of controlled ventilations during surgery
• To facilitate intubation
• Polarizing NMBAs – potentiates effects of acetylcholine and binds to cholinergic receptors to cause muscle depolarization; e.g. SUCCINYLCHOLINE
• SUCCINYLCHOLINE
• Non-Depolarizing NMBAs – prevent acetylcholine from acting on a neuromuscular junction; e.g. PANCURONIUM

Types of Local Anesthesia Routes

• Central
• Spinal – injected into the area near the spinal cord
• Intrathecal – injected into the subarachnoid space
• Epidural – injected into the epidural space via a small catheter
• Peripheral
• Infiltration – injected in and around the operative site
• Nerve Block – injected at the site where a nerve innervates
• Topical Anesthesia – applied directly onto the skin surface, eyes, or other mucus membranes

Acronyms for Anesthesia Routes

• GETA - General Endotracheal Anesthesia
• OTT - Orotracheal Tube
• ETT - Endotracheal Tube
• SCCS - SuccinylCholine Chloride Sedation
• CSEA - Combined Spinal Epidural Anesthesia
• CLEA - Continuous Lumbar Epidural Anesthesia
• SAB - Sub-Arachnoid Block

CNS Stimulants

• ADHD Drugs
• Elevates mood, produces a sense of increased energy and alertness, decreased appetite, enhanced task performance
• METHYLPHENIDATE (Ritalin)
• S/E: dry mouth, GI upset, tremors, headaches, insomnia, anxiety, increased metabolic rate

CNS Depressants

• Barbiturates
• Acts on RAS, reducing impulses traveling to area of brain
• Potentiates GABA (gamma-aminobutyric acid, neurotransmitter for regulation of muscle tone)
• SUPPRESSES REM SLEEP
• INCREASES SEIZURE THRESHOLD (less likely to have seizures)
• STIMULATES LIVER ENZYMES
• Ultrashort Acting - methohexital, thiopental
• Short Acting - pentobarbital, secobarbital (Seconal) (relieves anxiety, seizures & status epilepticus)
• Intermediate Acting - butabarbital (used as a preOP sedative)
• Long Acting - phenobarbital (Luminal) (may cause NEONATAL HYPERBILIRUBINEMIA & tonic-clonic seizures)
• Benzodiazepines
• Depresses activity in CNS
• DOESN’T SUPPRESS REM SLEEP
• DOESN’T STIMULATE LIVER ENZYMES
• ANTIDOTE: flumazenil
• Estazolam, Flurazepam, Triazolam
• Muscle Relaxants
• Potentiates GABA
• FOR SPASTICITY (continued muscle spasm)
• Central-acting - acts on the CNS
• Baclofen, Cyclobenzaprine
• Direct-acting - acts directly on skeletal muscle
• Dantrolene

Epilepsy vs. Convulsions vs. Seizures

• (the disorder) Epilepsy is the recurrent episodes of convulsive seizures
• (the malfunction) Seizures are sudden bursts of abnormal neuronal activity
• (the manifestation) Convulsions are spasmodic contraction of voluntary muscles

Anti-Epileptic Drugs (AED)

• Hydantoins
• Phenytoin (Dilantin) (1^st Line AED, most prescribed), Fosphenytoin, Valproic Acid
• Management of tonic-clonic and partial seizures
• S/E: lethargy, abnormal movements, mental confusion, cognitive changes
• May cause DILANTIN FACIES or hypertrophy of subcutaneous facial tissue
• Inject phenytoin SLOWLY; very painful
• Iminostilbenes
• Carbamazepine
• Treatment for trigeminal neuralgia (manifests with severe facial pain)
• Undergoes AUTOINDUCTION, process wherein it increases its own metabolism overtime
• Oxcarbazepine
• Treatment for partial seizures

Parkinson's Disease

• Chronic, progressive, degenerative, disorder affecting the dopamine-producing neurons in the brain
• Dopamine deficit in the SUBSTANTIA NIGRA (part of the midbrain which produces dopamine)
• DECREASED DOPAMINE, INCREASED ACETYLCHOLINE

Anti-Parkinsonian Drugs

• Dopaminergic
• Releases dopamine from remaining functional dopamine vesicles in presynaptic fibers or inhibit dopamine-metabolizing enzymes; in short, releases dopamine from functional cells that can still release dopamine
• Increases brain levels of dopamine by providing exogenous sources of dopamine; in short, provides dopamine directly
• Dopaminergic agonists that act as substitutes and stimulate receptors in place of dopamine; in short, mimics the action of dopamine to produce its effect
• LEVODOPA-CARBIDOPA (carbidopa protects levodopa from being metabolized in the body; levodopa is processed in the brain to become dopamine)
• Anticholinergic
• Block the effects of acetylcholine
• Useful in treating muscle tremors and rigidity
• BENZTROPINE
• Nursing Considerations:
• Assist in walking
• Oral doses should be given with food
• Avoid pyridoxine (Vit B6)
• Doses should be given hours before bedtime

Anti-Migraine

• 5-HT (Serotonin) Receptor Agonists / Triptans
• Stimulate 5-HT receptors in cerebral arteries causing vasoconstriction and reducing/eliminating headaches
• Contraindicated in cardiovascular disease (worsens symptoms)
• Sumatriptan
• Ergot Derivatives
• Causes constriction of cranial blood vessels & decreases the pulsation of the cranial arteries
• Reduces hyperperfusion of basilar artery vascular bed
• Contraindicated in coronary artery disease & pregnancy
• Ergotamine & Methysergine