Drugs Affecting the Central Nervous...

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Chapter 22

Drugs Affecting the Central Nervous

System


Neurotransmitters

Cause electrical depolarization and passage

of signal to next neuron

Most are returned to releasing nerve terminal

and “recycled”


Neurotransmitters (cont’d)

Factors impacting effect:

Amount released

Type/quantity of transport proteins

Previous release

Modifiers present

Reuptake process

Modulating interneurons


Psychiatric Medications

Antidepressants

Selective serotonin reuptake inhibitors (SSRIs) are

first-line treatment

Newer: Serotonin norepinephrine reuptake

inhibitors

Depression


Psychiatric medications (cont’d)

Mood stabilizers

Used primarily for bipolar disorder

• Alternating depression/mania (or hypomania)

Drugs: lithium, valproic acid, carbamazepine,

gabapentin, lamotrigine, and antipsychotics

Main side effect is sedation



Antipsychotics

Increase dopamine levels in brain

Psychotic disorders

• Impaired reality

• Schizophrenia

• Psychosis associated with depression or mania



Antipsychotics (cont’d)

Newer agents more tolerable

• Risperidone

• Olanzapine

• Quetiapine



Drugs for Alzheimer’s dementia:

cholinesterase inhibitors

Increase acetylcholine levels in brain

Drugs:

• Donepezil

• Tacrine

• Galantamine

• Rivastigmine

May cause gastrointestinal (GI) side effects



Anxiolytics

Also used as amnesics

May augment opioid respiratory depression

Benzodiazepines

• Hyperpolarize neurons

• Good for anesthesia induction

• Prevent “unpleasant recall”

• Terminate seizures/increase threshold


Psychiatric Medications (cont’d)

Barbiturates

Toxic potential and rapid tolerance

• Depress neuron activity

• High risk of addiction and abuse

Used for

• Anesthesia induction

• Hypnotics

• seizures


Psychiatric Medications (cont’d)

Other hypnotics

Often used to induce sleep

Hypnotics to induce sleep are generally

recommended for 1 to 2 weeks

Eszopiclone

• New drug

• Approved for long-term use


Ethyl Alcohol

Socially acceptable nonprescription sedative-

hypnotic

Also has disinhibiting effect

In excess = general anesthetic

400 to 600 mg/dl = respiratory arrest

Delirium tremens

CNS hyperactivity on withdrawal


Pain Treatment

Pain is now the fifth vital sign

The pain experience

Pain

• Input from CNS pain receptors

Suffering

• Emotional response to pain experience


Pain Treatment (cont’d)

Nonsteroidal antiinflammatory drugs

(NSAIDs)

Affect hypothalamus and inhibit production of

inflammatory mediators at pain site

Some may cause gastric irritation/ulceration

Salicylates are oldest (aspirin)

Acetaminophen (Tylenol)



Opioid analgesics

Derivatives of naturally occurring opium

Used to treat moderate to severe pain

Exert effect by binding to receptors for

endogenous opioids (endorphins and enkephalins)

Popular drugs of abuse



Routes of opioid administration

As needed (by nurse)

Patient-controlled analgesia (PCA) pumps

• Better to keep control of pain than regain control

Opioid inhalation

• Decreases dyspnea in advanced respiratory failure

• Has shown good clinical effect on cancer patients without

lung disease



Local anesthetics

Interrupt nerve signals (pain) from damaged area

• Block Na channels along nerve cells

Also useful as analgesia and for terminating

cardiac conduction abnormalities

Can suppress irritant tracheal cough response



Epidural analgesia

Infusions of local anesthetics/opioids improve

postoperative pain therapy and outcome

Provides better pain control versus systemic

analgesics



Combinations of analgesic classes

Prescription combinations of NSAIDs and opioids

are widely available

Separate dosing may prove better with various

side effects, toxicities, and half-lives

• More troublesome for patients to take independently


Chronic Pain Syndromes

Central sensitization can occur secondary to

acute pain from surgery or trauma

Hyperesthesia, hyperpathia, and allodynia

Treatment during acute phase may reduce

likelihood of neuropathic problem later


Chronic Pain Syndromes (cont’d)

Characteristics of neuropathic pain

Evidence of primary injury

Pain involving body area with sensory loss

Pain characterized as burning, electric, or

shooting

Dysesthesias in the area

Sympathetic hyperactivity

Hyperalgesia, hyperpathia, and allodynia


Anesthesia

Drug-induced absence of perception

Usually inhaled or IV

Gases and volatile liquids

Depth is determined by response to painful

stimuli

Change in heart rate or blood pressure


Anesthesia (cont’d)

Conscious sedation

Patient remains conscious

• Able to communicate and protect airway

• Ability may be lost during procedure

Goal is improved patient comfort and outcome

Conscious sedation standards are required by

Joint Commission on Accreditation of Healthcare

Organizations (JCAHO)


Anesthesia (cont’d)

Standards for providing conscious sedation

Resuscitation equipment and trained personnel

immediately available

Conscious sedation requires >1 person

Deep sedation/general anesthesia require at least

3 people


CNS and Respiratory Stimulants

Analeptic drugs

Increase activity of brain

Treat: narcolepsy, attention-deficit

hyperactivity disorder (ADHD), obesity

No clinical role in treating respiratory

failure

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