DRUGS ACTING ON NERVOUS SYSTEM
PREPARED BY MR. ABHIJIT DAS
ANAESTHETICS
Anaesthetics are substances used to induce a reversible loss of sensation, typically to prevent
pain during medical procedures. There are two main types:
1.
General Anaesthetics:
These induce a state of controlled unconsciousness and
a lack of sensation over the entire body.
2.
Local Anaesthetics:
These numb a specific part of the body,
allowing a patient to remain conscious.
GENERAL ANAESTHETICS
STAGES OF ANAESTHESIA:
1.
Stage 1: Analgesia
·
Onset:
Begins with the administration of the anaesthetic.
·
Symptoms:
The patient starts to feel drowsy, experiences a reduction
in pain perception, and may remain conscious.
2.
Stage 2: Excitement (Delirium)
·
Onset:
Starts with the loss of consciousness.
·
Symptoms:
The patient may exhibit irregular breathing,
increased heart rate and increased blood pressure. This stage can be marked
by agitation or delirium.
3.
Stage 3: Surgical Anaesthesia
·
Onset:
Begins as the patient stabilizes into a regular
pattern of breathing and relaxation.
·
Symptoms:
This stage is characterized by the absence of
reflexes, relaxed muscles, and
adequate depth of anaesthesia for surgical procedures.
Breathing is steady, and the patient's eyes may become fixed.
4.
Stage 4: Overdose
·
Onset:
Begins if the anaesthetic depth is too great.
·
Symptoms:
Characterized by severe depression of the central
nervous system, including the respiratory
and cardiovascular systems. This stage can lead to respiratory arrest, cardiovascular
collapse, and can be fatal if not
promptly corrected.
CLASSIFICATION OF GENERAL ANAESTHETICS:
§ Inhalational
Anaesthetics:
1.
Gas: Nitrous Oxide
2.
Volatile Liquid: Isoflurane,
Sevoflurane, Desflurane, Ether, Halothane
§ Intravenous
(IV) Anaesthetics: Propofol, Thiopental, Etomidate,
Ketamine, Midazolam
NITROUS OXIDE
MOA:
Nitrous oxide (N2O) works by entering the neuron and
causing disturbances within the cell
membrane. This process, known as membrane
fluidization, alters the physical properties of the lipid bilayer of the
neuron.
As a result, the ion channels embedded in the
membrane, particularly those for sodium ions (Na+), are affected. The
fluidization of the membrane prevents the normal influx
of Na+ ions into the neuron, thereby
inhibiting the generation and propagation of action potentials.
This disruption of neuronal signaling leads to a
lack of sensation and contributes to the anaesthetic and analgesic effects of
nitrous oxide.
ADVERSE EFFECTS:
1.
Respiratory depression
2.
Nausea and vomiting
3.
Hypotension
USES:
1.
Surgical procedures
2.
Sedation for medical procedures
3.
Management of acute pain
DOSE AND ROUTE:
Dose: For general anaesthesia: Usually administered
in concentrations ranging from 50% to 70%, mixed with oxygen.
Route of Administration: Inhalation
CONTRAINDICATIONS:
1.
Pneumothorax:
Nitrous oxide can expand trapped air, worsening the condition.
[NOTE: Pneumothorax
is a medical condition characterized by the presence of air or gas in the
pleural cavity, the space between the lung and the chest wall.]
2.
Middle ear blockage:
Nitrous oxide can cause further pressure build-up in these areas.
[NOTE:
Middle Ear Blockage occurs when the Eustachian tube, which connects the middle
ear to the back of the nose and throat, becomes blocked or swollen.]
3.
Pregnancy:
Nitrous oxide is contraindicated in the first trimester due to potential
teratogenic effects.
ROLE OF NURSE:
1.
Assessing patients for suitability.
2.
Educating patients about the procedure.
3.
Preparing equipment and monitoring
patients during administration.
4.
Assisting the healthcare team.
5.
Documenting the procedure and providing
post-procedure care.
TECHNIQUES OF INHALATION OF
ANAESTHETICS:
1.
Open Drop Method:
·
An older technique where the anaesthetic
liquid is dropped onto a gauze or mask.
·
The patient inhales the vapors directly.
2.
Through Anaesthetic Machines:
·
Modern technique using specialized
machines.
·
Machines precisely control and deliver a
mix of anaesthetic gas and oxygen to the patient.
PRE-ANAESTHETIC MEDICATION:
Medications given before administering anaesthesia
to enhance its effectiveness and manage potential side effects.
1.
Sedative/Antianxiety Drugs:
·
Examples: Diazepam, Midazolam
·
Purpose: Reduce anxiety and induce
calmness.
2.
Opioids:
·
Examples: Morphine, Fentanyl
·
Purpose: Provide pain relief and
sedation.
3.
Anticholinergics:
·
Examples: Atropine, Glycopyrrolate
·
Purpose: Reduce secretions and prevent
bradycardia.
4.
Antiemetics:
·
Examples: Ondansetron, Metoclopramide
·
Purpose: Prevent nausea and vomiting.
LOCAL ANAESTHETICS
CLASSIFICATION:
1.
Injectable:
·
Examples: Lidocaine, Bupivacaine,
Ropivacaine
2.
Surface:
·
Examples: Benzocaine, Lidocaine,
Tetracaine
COMMON MOA:
Local anaesthetics block sodium (Na+) channels in
the peripheral nervous system (PNS), preventing the transmission of nerve
signals and thus blocking sensation.
ADVERSE EFFECTS:
1.
Allergic reactions
2.
Localized swelling or redness
USES:
1.
Minor surgeries
2.
Localized pain relief
ROLE OF NURSE:
1.
Preparation:
Nurses ensure all necessary equipment and medications are available and
properly set up for the procedure.
2.
Assessment:
Nurses evaluate the patient's medical history, allergies, and current condition
to determine the suitability for local anaesthetic administration. They also
inspect the administration site for any signs of infection or
contraindications.
3.
Education:
Nurses provide clear and concise information to the patient about the
procedure, potential side effects, and post-procedure care instructions.
4.
Assistance:
Nurses aid the healthcare provider during local anaesthetic administration,
assisting with patient positioning and providing support as required.
5.
Monitoring:
Nurses closely monitor the patient's vital signs and response to the local
anaesthetic, promptly identifying any signs of allergic reactions or adverse
effects.
6.
Documentation:
Nurses maintain accurate records of the local anaesthetic administration,
documenting the type and dosage given, any adverse reactions observed, and the
patient's response to the medication.
STIMULANTS
Stimulants are a class of drugs that stimulates the central nervous system, leading to
heightened alertness, increased energy, and improved focus.
1. Psychomotor Stimulants
These drugs primarily increase motor activity,
enhance alertness, and reduce fatigue by stimulating the central nervous
system.
Classes of Psychoactive Drugs
1. Psychomotor Stimulants
These drugs primarily increase motor
activity, enhance alertness, and reduce fatigue by stimulating the central
nervous system.
a. Methylxanthines
- Examples
and Sources:
- Caffeine
- Source:
Found in coffee beans, tea leaves, and cacao beans.
- Description:
Caffeine is the most widely consumed stimulant. It works by blocking
adenosine receptors, preventing drowsiness, and increasing the release
of dopamine and norepinephrine.
- Theophylline
- Source:
Found in tea leaves (Camellia sinensis) and in small amounts in coffee.
- Description:
Theophylline is used medically to treat respiratory diseases such as
asthma and chronic obstructive pulmonary disease (COPD). It relaxes
bronchial smooth muscle and has a stimulating effect on the central
nervous system.
- Theobromine
- Source:
Found in cacao beans, making it a component of chocolate, as well as in
tea leaves.
- Description:
Theobromine has a milder stimulating effect compared to caffeine and
theophylline. It acts as a vasodilator, diuretic, and heart stimulant.
It is also used therapeutically for its smooth muscle relaxant
properties.
b. Nicotine
- Example:
Tobacco products (cigarettes, cigars, e-cigarettes)
- Description:
Nicotine stimulates nicotinic acetylcholine receptors, leading to
increased release of dopamine and norepinephrine. It has a stimulating
effect on the central nervous system and is highly addictive.
c. Cocaine
- Example:
Cocaine hydrochloride
- Description:
Cocaine inhibits the reuptake of dopamine, norepinephrine, and serotonin,
leading to increased levels of these neurotransmitters in the brain. It produces
intense euphoria, increased energy, and alertness but is highly addictive
and neurotoxic.
d. Amphetamine
- Example:
Adderall (mixed amphetamine salts)
- Description:
Amphetamines increase the release of dopamine and norepinephrine and
inhibit their reuptake, leading to heightened alertness, concentration,
and energy. Used medically for ADHD. They have a high potential for abuse.
e. Methylphenidate
- Example:
Ritalin
- Description:
Similar to amphetamines, methylphenidate blocks the reuptake of dopamine
and norepinephrine, enhancing focus and alertness. It is primarily used to
treat ADHD and narcolepsy.
2. Hallucinogens
These drugs primarily alter perception, mood, and a
variety of cognitive processes.
a. LSD (Lysergic Acid Diethylamide)
- Example:
LSD-25
- Description:
A potent hallucinogen that alters perception, thought, and mood. It acts
primarily on serotonin receptors in the brain, particularly the 5-HT2A
receptor, leading to profound changes in sensory perception and
consciousness.
b. Tetrahydrocannabinol (THC)
- Example:
Marijuana (Cannabis)
- Description:
The primary psychoactive component of cannabis. THC acts on cannabinoid
receptors in the brain, leading to altered sensory perceptions, mood
changes, and cognitive impairments. It can produce euphoria, relaxation,
and, in higher doses, hallucinations.
ETHYL ALCOHOL
PHARMACOLOGICAL ACTIONS
- CNS
Depressant: Ethanol depresses the central
nervous system, leading to sedation, relaxation, and, in higher doses,
anesthesia.
- GABA
Modulation: Enhances the inhibitory effects
of GABA (gamma-aminobutyric acid) in the brain.
- Dopamine
Release: Increases dopamine release,
contributing to its rewarding and reinforcing effects.
- Cardiovascular
Effects: Causes vasodilation, leading to a
feeling of warmth and, in higher doses, hypotension.
- Metabolic
Effects: Can lead to hypoglycemia and has
caloric content, providing a source of energy.
Adverse Effects
- Acute
Effects: Drowsiness, impaired
coordination, slurred speech, nausea, vomiting, and hangover.
- Chronic
Effects: Liver disease (cirrhosis),
cardiovascular disease, neuropathy, cognitive impairment, gastrointestinal
issues.
- Psychological
Effects: Dependence, withdrawal symptoms,
mood disorders, and increased risk of depression and anxiety.
METHYL ALCOHOL POISONING
DRUGS USED FOR METHANOL POISONING:
1. Fomepizole
- Mechanism
of Action: Fomepizole is an inhibitor of
alcohol dehydrogenase, the enzyme responsible for metabolizing methanol
into its toxic metabolites, formaldehyde and formic acid.
2. Ethanol