NEET MDS Lessons
Pharmacology
CHOLINERGIC DRUGS
Produce actions similar to Acetylcholine (Ach)
Cholinergic Agonists
1 Acetylcholine 2 Methacholine 3. Carbachol 4 Bethnechol
Alkaloids
1.Muscarine 2 Pilocarpine 3. Arecoline
MECHANISM OF ACTION
I Heart- hyperpolarizes the SA node and decreases the rate of diastolic depolarisation. thus the frequcncy of impulse generation is decreased. bradycardia.
2 Blood vessels- vasodilatation
3. Smooth muscles - increased contraction. increased tone. increased peristalsis.
4. Glands- increased sweating. increased lacrimation.
5 Eye- contraction of the circular muscle of iris (miosis).
Nicotinic action
Autonomic ganglia - stimu1ation of sympathetic and parasympathetic system.
Skeletalmuscles - contraction of fibres.
CNS..No effect as it does not penetrate the blood-brain barrier.
Toxic effects
Flushing. sweating.salivation. cramps. belching. involuntary mictuirition. defaccation.
Contraindication
1.. Anginapectoris- decreases the coronary flow.
2 Pepticulcer - increases the gastric secretion
3 Asthma- bronchoconstriction
4 Hyperthyroidisim
Cholinomimetic Alkaloids
Pilocarpine
Prominent muscarinic actions. causes marked sweating. salivation. Increase of secretions. small doses cause fall in BP but higher doses increase in BP. Applied to the eye cause miosis. fall in intraocular tension
Uses
I. .Open angle glaucoma
2. To counteract mydriasis
Anticholinesterase
They inhibit the enzyme cholinestrase and prolong the action of Ach
Reversible
Physostigamine, Ncostigamine, Pyridostigamine, Ambenonium, Edrophonium, Demecarium
Irreverible
Dyflos. Echothiphate.
Pharmacological Actions
I Ganglia - persistent depolarisation of ganglionic nicotinic receptors.
2 CVS - unprcdictable as Muscarinic-I receptor causes bradycardia but ganglionic stimulation
tachycardia.
3. Skeletal muscles - as Ach is not destroyed and rebinds to the same receptor or it diffuses on to the neighbouring receptors to cause repetitive firing. twitching and fasciculations.
Uses
I As miotic
a) Glaucoma : Acute congestive (narrow angle) glaucoma, Chronic simple (wide angle) glaucoma
b) Counter act atropine mydriasis.
2) Post operative paralytic ileus
3) Myasthenia gravis
4) Postoperativedecurarization
5) Cobra bite
6) Belladona poisoning
7) Other drug overdoses
Helicobacter Pylori Agents
Antimicrobial
• Amoxicillin,
• Clarithromycin,
• Metronidozole
• Tetracycline
Antisecreteory agents accelerates symptom relief and yield healing (omeprozole)
Bismuth subsalicylate
Therapy For H. Pylori
Original
• Tetracycline
• Metronidazole (Flagyl)
• Bismuth subsalicylate
• Given for 14 days
• >90% effective in eradicating microorganisms
New triple therapy
• Amoxicillin
• Clarithromycin
• Omeprazole (Prilosec)
• Given for 7 days
• >90% effective in eradicating microorganisms
Dual Therapy
Amoxicillin or clarithromycin
Omeprazole
Given for 14 days
60-80% effective in eradication of H. Pylori
Streptomycin
Streptomycin was the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus.
Streptomycin cannot be given orally, but must be administered by regular intramuscular injection.
Classification
I) Esters
1. Formed from an aromatic acid and an amino alcohol.
2. Examples of ester type local anesthetics:
Procaine
Chloroprocaine
Tetracaine
Cocaine
Benzocaine- topical applications only
2) Amides
1. Formed from an aromatic amine and an amino acid.
2. Examples of amide type local anesthetics:
Articaine
Mepivacaine
Bupivacaine
Prilocaine
Etidocaine
Ropivacaine
Lidocaine
Classification
1. Natural Alkaloids of Opium
Phenanthrenes -> morphine, codeine, thebaine
Benzylisoquinolines -> papaverine, noscapine
2. Semi-synthetic Derivatives
diacetylmorphine (heroin) hydromorphone, oxymorphone hydrocodone, oxycodone
3. Synthetic Derivatives
phenylpiperidines pethidine, fentanyl, alfentanyl, sufentnyl
benzmorphans pentazocine, phenazocine, cyclazocine
propionanilides methadone
morphinans levorphanol
Opiate Antagonists
Opiate antagonists have no agonist properties. They are utilized to reverse opiate induced respiratory depression and to prevent drug abuse.
A. Naloxone
Pure opiate antagonist , Short duration of action, Only 1/50th as potent orally as parenterally
B. Naltrexone
Pure opiate antagonist, Long duration of action, Better oral efficacy
Ethosuximide (Zarontin): use in absence seizures (may exacerbate tonic-clonic seizures)
Mechanism: ↓ T-type Ca currents in thalamic neurons, inhibits bursts of APs, ↓ synchronous neuronal firing
i. Thalamo-cortical reverberating circuits: during absence type seizures, have reverberating circuits between cerebral cortex and thalamus at 3 Hz maintained by T-type Ca channels (since blocking these channels blocks the reverberating circuit)
Side effects: quite non-toxic; common= N/V and anorexia; less common = headache, sedation, photophobia