Unit-5 Parkinson’s, Alzheimer’s & Opioid Drugs Notes

Fig 1: Neurodegenerative Diseases & CNS Drugs Overview

Welcome to DrX Whiz Niraj. In this post, we provide comprehensive notes for B.Pharm 4th Semester, Pharmacology I (Unit 5). This unit covers Parkinson’s Disease, Alzheimer’s Disease, CNS Stimulants, Opioids, Drug Addiction, Tolerance, and Dependence.

Parkinson’s Disease

Definition: Parkinson's disease is a progressive neurodegenerative disorder characterized by the degeneration of dopaminergic neurons in the substantia nigra of the brain.

Pathophysiology: The loss of dopamine causes an imbalance between Dopamine (inhibitory) and Acetylcholine (excitatory) in the striatum.

↓ Dopamine + ↑ Acetylcholine → Impaired Motor Control

Symptoms of Parkinson's

Motor Symptoms: Tremors (resting), Rigidity, Bradykinesia (slowness of movement), Postural instability.
Non-Motor Symptoms: Depression, Sleep disturbance, Cognitive impairment.

Parkinson's Disease Substantia Nigra Diagram

Fig 2: Degeneration of Dopaminergic Neurons in Parkinson's Disease

Drugs Used in Parkinson’s Disease

1. Levodopa + Carbidopa

Levodopa crosses the blood-brain barrier and converts into dopamine.
Carbidopa inhibits the peripheral metabolism of Levodopa, allowing more drug to reach the brain.
Adverse Effects: Nausea, Dyskinesia, Hypotension.

2. Dopamine Agonists

Directly stimulate dopamine receptors in the brain.
Ex: Bromocriptine, Pramipexole, Ropinirole.

3. MAO-B & COMT Inhibitors

MAO-B Inhibitors: Prevent dopamine breakdown (Selegiline).
COMT Inhibitors: Increase Levodopa duration (Entacapone).

4. Anticholinergic Drugs

Reduce the overactivity of Acetylcholine, helping mainly with tremors and rigidity.
Ex: Trihexyphenidyl, Benztropine.

Alzheimer’s Disease

Definition: Alzheimer's disease is a chronic neurodegenerative disorder causing progressive loss of memory and cognition. It is mainly caused by the degeneration of cholinergic neurons and the formation of beta-amyloid plaques.

↓ Acetylcholine → Memory Impairment & Cognitive Decline

Drugs Used in Alzheimer’s Disease

Cholinesterase Inhibitors: Increase acetylcholine concentration in the brain by preventing its breakdown. (Ex: Donepezil, Rivastigmine, Galantamine)
NMDA Receptor Antagonist: Blocks glutamate excitotoxicity, preventing further neuronal damage. (Ex: Memantine)

CNS Stimulants & Nootropics

1. CNS Stimulants

Drugs that increase mental alertness, elevate mood, and increase motor activity by increasing the release of dopamine and noradrenaline.

Psychomotor Stimulants: Amphetamine, Methylphenidate (Used for ADHD, Narcolepsy).
Methylxanthines: Caffeine, Theophylline.
Respiratory Stimulants: Doxapram.

2. Nootropics (Cognitive Enhancers)

Drugs that improve memory and cognition by improving cerebral metabolism and blood flow. Used in Dementia and Brain injury.

Examples: Piracetam, Citicoline.

Opioid Analgesics & Antagonists

Definition: Opioid analgesics are strong pain-relieving drugs that act on specific opioid receptors in the CNS to block pain pathways.

Fig 3: Activation of Mu (μ) Opioid Receptors

Opioid Receptors:

Mu (μ), Kappa (κ), Delta (δ)

Classification

Natural: Morphine, Codeine.
Semi-Synthetic: Heroin, Oxycodone.
Synthetic: Fentanyl, Methadone.

Pharmacological Effects

Analgesia (pain relief), Sedation, Euphoria, Respiratory depression (major side effect), Constipation, Miosis (pinpoint pupil).

Opioid Antagonists

Drugs that block opioid receptors and reverse the effects of opioids. Used primarily in Opioid Overdose and addiction therapy.
Examples: Naloxone, Naltrexone.

Drug Addiction, Tolerance & Dependence

Fig 4: Brain Reward Pathway & Addiction

Drug Addiction: A chronic, relapsing disorder characterized by compulsive drug seeking and use despite harmful consequences (Craving & Loss of control).
Drug Abuse: Improper or excessive use of drugs for non-medical purposes (e.g., Heroin, Alcohol, Cocaine, Cannabis).
Tolerance: Decreased response to a drug after repeated administration. A higher dose is required to produce the same effect (Mechanism: Enzyme induction or Receptor down-regulation).
Dependence: Physical or psychological need for continuous drug use.
- Physical Dependence: Withdrawal symptoms (anxiety, tremors, sweating) appear if the drug is stopped.
- Psychological Dependence: Strong emotional desire or craving for the drug.

VVI Exam Questions

2 Marks Questions (Short Answers)

What is the difference between Drug Tolerance and Drug Dependence?
Name two Nootropic agents and mention their use.
What are Opioid Antagonists? Give two examples.
Name the opioid receptors.
Why is Carbidopa given along with Levodopa?

5 Marks Questions (Short Essays)

Explain the pathophysiology and clinical symptoms of Parkinson’s disease.
Write a short note on CNS Stimulants and classify them with examples.
Differentiate between Drug Addiction and Drug Abuse. Mention common withdrawal symptoms.
Briefly explain the pharmacological management of Alzheimer’s disease.

10 Marks Questions (Long Essays)

Classify anti-Parkinsonian drugs. Discuss the mechanism of action, therapeutic uses, and adverse effects of Levodopa.
Define Opioid Analgesics. Classify them and describe the pharmacological actions, mechanism of action, and adverse effects of Morphine in detail.

Unit-5 Parkinson’s, Alzheimer’s & Opioid Drugs Notes | CNS Pharmacology