pharma5 cns drugs

DRUGS AFFECTING THE AUTONOMIC & CENTRAL

NERVOUS SYSTEM

Merchie Lissa T. Alabat, RN

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The Nervous System

• Center of thinking, memory, judgement, sensation, movement, cognition, communication, behavior, and personality

• Innervates many other body systems and indirectly influences their actions

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Nervous system is divided into:

• Central Nervous System (CNS)– Brain– Spinal cord

• Peripheral Nervous System (PNS)– Cranial nerves– Spinal nerves– Autonomic NS

• Sympathetic• Parasympathetic NS

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Nervous System CellsThere are two main types of brain cells:

– Neurons– Neuroglial cells

- Provide protection, structure and nutrition to the neurons

4 types:

1. Astroglial

2. Ependymal

3. Oligodendrocytes

4. Microglial

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Neurons– Basic structural and functional units of the

nervous system– Cannot divide by mitosis– Respond to physical and chemical stimuli– Produce and conduct electrochemical impulses– Release chemical regulators

*The brain contains approximately more than 20 billion nerve cells, or Neurons

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Cell body (perikaryon)– “Nutrition center”– Cell bodies within CNS clustered into nuclei, and

in PNS in ganglia

Axons– Transmits impulses from its cell body to other

neurons

Dendrites– Provide receptive area– Transmit electrical impulses to cell body

Parts of a Neuron

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Synapses

• Impulses are transmitted to their final destination through synapses

• Types:– Neuron to neuron– Neuron to gland

Conduction of impulse across synapse: Pre-synaptic neuron

release neurotransmitter

synaptic cleft

neurotransmitter interacts with receptor

neurotransmitter-receptor complex initiates a sequence of events (open ion channel)

modulate the electrical activity of the postsynaptic neuron

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Neurotransmitters

• Chemical substances manufactured in the neuron that aid in the transmission of information throughout the body.

• Chemicals that take a nerve signal across the synaptic gap between a sending neuron, and a receiving one.

• Excitatory or inhibitory

Neurotransmitters

Dopamine(DA) Monoamines- Catecholamines

Norepinephrine (NE)

Serotonin (5HT) Monoamines- Indolamines

Acetylcholine (Ach) Cholinergics

Glutamate (Glu) Amino Acids

Gamma-Aminobutyric Acid (GABA)

Amino Acids

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Mechanism of Drugs on CNS(1)Axon: Slow/block axonal electrical conduction e.g. Antiepileptics Anaesthetics

(2)Synapse: most drugs

1. Affect transmitter: - synthesis, storage, release, reuptake. e.g. antidepressants

2. Affect receptor: activation/inhibition(block) e.g. benzodiazepines, antipsychotics3. Directly act on ion channels e.g. phenytoin

Blood Brain Barrier(1) Structure

3 parts:– barrier between blood and brain cell;– barrier between blood and cerebrospinal fluid– barrier between brain cell and cerebrospinal fluid.

(2) Function: restrict passage of polar compounds and macromolecules from blood into brain

(3) Pharmacological significance: prerequisite e.g. Penicillinmeningitis

AUTONOMIC NERVOUS SYSTEM DRUGS

CHOLINERGIC DRUGS• Promote the action of the neurotransmitter

acetylcholine• Called parasympathomimetic drugs

because they produce effects that imitate parasympathetic nerve stimulation

2 Major Classes• CHOLINERGIC AGONISTS- mimic the

action of neurotransmitter acetylcholine

• ANTICHOLINISTERASE DRUGS-work by inhibiting the destruction of acetylcholine at the cholinergic receptor sites

CHOLINERGIC AGONISTS• INCLUDE DRUGS SUCH AS:

– Bethanecol– Carbachol– Cevimiline– Pilocarpine

PHARMACOKINETICS– No IM or IV– Usually: orally, topically (eye drops), subQ

• METABOLISM/EXCRETION– Metabolized at muscarinic and nicotinic recepetor

sites– In the plasma portion of blood– In the liver– ALL DRUGS IN THIS CLASS ARE EXCRETED BY

THE KIDNEYS

PHARMACODYNAMICS• Work by mimicking the action of acetycholine on the

neurons in certain organs of the body called target organs. When they combine with receptors on the cell membranes of target organs, they stimulate the muscle and produce:– Salivation– Bradycardia– Dilation of blood vessels– Constriction of bronchioles– Increased activity of the GI tract– Increased tone and contraction of the bladder muscles– Constriction of the pupils

PHARMACOTHERAPEUTICS• Cholinergic drugs are used to:

– Treat atonic (weak) bladder conditions and post-op and post-partum urine retention

– Treat GI disorders, such as post-op abdominal distention and GI atony

– Reduce eye pressure in patients with glaucoma and during eye surgery

– Treat salivary gland hypofucntion caused by radiation therapy or Sjogren’s syndrome

ADVERSE EFFECTS• Side effects to

expect:– Nausea– Vomiting– Abdominal

cramping– Dizzines – Hypotension

• Side effects to report:– Bronchospasm– Wheezing– Bradycardia

NURSING RESPONSIBILITES• Take baseline VS of

HR and BP

ANTICHOLINISTERASE DRUGS

• Also known cholinergic-blocking agents• Block the action of the enzyme

acetylcholinisterase (which breaks down the neurotransmitter acetylcholine) at cholinergic receptor sites, preventing the breakdown of acetylcholine

• As acetylcholine builds up, it continues to stimulate the cholinergic receptors

2 CATEGORIES• REVERSIBLE

– Edrophonium– Neostigmine– Pyridostigmine

• IRREVERSIBLE

PHARMACOKINETICS• Generally absorbed by the GI tract, subQ

and mucous membranes• METABOLISM- by enzymes in the plasma• EXCRETED in the urine

PHARMACODYNAMICS• Promote the action of acetycholine at

receptor sites• Depending on the site and the drug’s dose

and duration of action, they can produce a stimulant or depressant effect on cholinergic receptors

PHARMACOTHERAPEUTICS- To reduce eye pressure in

patients with glaucoma during eye surgery

- To increase bladder tone- To improve tone and

peristalsis through the GI tract in patients with reduced motility or paralytic ileus

- To promote muscle contraction in patients with myasthenia gravis

• To diagnose myasthenia gravis (NEOSTIGMINE & EDROPHONIUM)

• As an antidote to cholinergic blocking agents, TCA, belladona and narcotics

• To treat mild to moderate dementia and enhance cognition in patients wih Alzheimer’s disease

ADVERSE EFFECTS • Side effects to expect:

– Blurred vision– Constipation– Urinary retention, – dryness of the mucosa

of the mouth, nose and throat

• Side effects to report:– Confusion– Depression– Nightmares– Hallucinations– Palpitations– Orthostatic

hypotension– Arrythmias– Glaucoma

NURSIING RESPONSIBILITIES

• All patients should be screened for the presence of closed-angle glaucoma

• Check for history of enlarged prostate

• Take baseline VS of HR and BP

• Sucking on candy or ice chips for dry mouth

• Give stool softeners as prescribed for constipation. Encourage adequate fluid intake and privde sufficient bulk

• Promote saferty for blurring of vision