NEET MDS Lessons
Pharmacology
Anti-Histamines:
The effect of histamine can be opposed in three ways:
1. Physiological antagonism: by using a drug to oppose the effect (e.g adrenaline). Histamine constricts bronchi,
causes vasodilatation which increases capillary permeability. Adrenaline opposes this effect by a mechanism unrelated to histamine.
2. By preventing histamine from reaching its site of action (receptors), By competition with H1-H2 receptors (Drug antagonisms).
3. By preventing the release of histamine. (adrenal steroids and sodium-cromoglycate can suppress the effect on the tissues)
Types of Anti-histamine drugs
Selected H1 antagonist drugs
First-generation H1 receptor antagonists:
Chlorpheniramine (Histadin) & Dexchlorpheniramine
Diphenhydramine (Allermine)
Promethazine (Phenergan) - strong CNS depressants
Cyproheptadine (Periactin)
ACTION
These drugs bind to both central and peripheral H1 receptors and can cause CNS depression or stimulation.
- They usually cause CNS depression (drowsiness,sedation) with usual therapeutic doses
- Cause CNS stimulation (anxiety, agitation)
with excessive doses, especially in children.
They also have Anticholinergic effects (e.g. dry mouth, urinary retention, constipation, blurred vision).
Second-generation H1 receptor antagonists (non-sedating) agents
Terfenadine
Fexofenadine
Loratadine
Acravistine and Cetirizine
Astemizol
Action
They cause less CNS epression because they are selective for peripheral H1 receptors and do not cross the blood brain barrier.
Indications for use
The drugs can relieve symptoms but don’t relieve hypersensitivity.
1) Allergic rhinitis. Some relief of sneezing, rhinorrhea, nasal airway obstruction and conjunctivitis are with the use of antihistamine.
2) Anaphylaxis. Antihistamine is helpful in treating urticaria and pruritus.
3) Allergic conjunctivitis. This condition, which is characterized by redness, itching and tearing of the eyes.
4) Drug allergies. Antihistamines may be given to prevent or treat reactions to drugs (e.g, before a dignostic test that
uses an iodine preparation).
5) Transfusions of blood and blood products.
6) Dermatologic conditions. Antihistamines are the drug of choice for treatment of allergic contact dermatitis and
acute Urticaria. Urticaria often occurs because the skin has many mast cells to release histamine.
7) Miscellaneous. Some antihistamines are commonly used for non-allergic disorder such as motion sickness, nausea, vomiting, sleep, cough or add to cough mixtures.
Contraindication
hypersensitivity to the drugs, narrow-angle glaucoma, prostatic hypertroph, stenosing peptic ulcer, bladder neck obstruction, during pregnancy and lactating women
Adverse effects:
Drowsiness and sedation
Anticholinergic
Some antihistamines may cause dizziness, fatigue, hypotention, headache, epigastric distress and photosensitivity
Serious adverse reaction including cardiac arrest & death, have been reported in patients receiving high dose astemizole
H2-receptor antagonists
Cimetidine (Tagamate), Ranitidine (Zantac), Fomatidine, Nizatidine.
Mechanism of action
Numerous factors influence acid secretion by the stomach, including food, physiological condition and drugs. H2 receptor blockers reduce basal acid-secretion by about 95% and food stimulated acid-secretion by about 70%. Both conc. and vol. of H ions will decrease.
Pharmacokinetics:
1) They are all well absorbed after oral dose.
2) Antacids decrease their absorption in about 10-20%
Uses
Cimetidine - reduction of gastric secretion is beneficial, these are in main duodenal ulcer, benign gastric ulcer, stomach ulcer and reflux eosophagitis.
Rantidine -used as alternative for duodenal ulcer
Adverse effects:
headache, dizziness, constipation, diarrhoea, tiredness and muscular pain.
Tetracycline
Tetracycline is an antibiotic produced by the streptomyces bacterium
Mechanism and Resistance Tetracycline inhibits cell growth by inhibiting translation. It binds to the 30S ribosomal subunit and prevents the amino-acyl tRNA from binding to the A site of the ribosome. This prevents the addition of amino acids to the elongating peptide chain, preventing synthesis of proteins. The binding is reversible in nature.
Example: Chlortetracycline, oxytetracycline, demethylchlortetracycline, rolitetracycline, limecycline, clomocycline, methacycline, doxycycline, minocycline
Source: Streptomyces spp.; some are also semi-synthetic
Spectrum of activity: Broad-spectrum. Exhibits activity against a wide range of Gram-positive, Gram-negative bacteria, atypical organisms such as chlamydiae, mycoplasmas, rickettsiae and protozoan parasites.
Effect on bacteria: Bacteriostatic
Cells become resistant to tetracyline by at least two mechanisms: efflux and ribosomal protection.
Contraindications Tetracycline use should be avoided during pregnancy and in the very young (less than 6 years) because it will result in permanent staining of teeth causing an unsightly cosmetic result.
Tetracyclines also become dangerous past their expiration dates. While most prescription drugs lose potency after their expiration dates, tetracyclines are known to become toxic over time; expired tetracyclines can cause serious damage to the kidneys.
Miscellaneous: Tetracyclines have also been used for non-antibacterial purposes, having shown properties such as anti-inflammatory activity, immunosuppresion, inhibition of lipase and collagenase activity, and wound healing.
Cells of the Nervous System
1-Neurons (Nerve Cells):function units of the nervous system by conducting nerve impulses, highly specialized and amitotic. Each has a cell body (soma), one or more dendrites, and a single axon.
• Cell Body: it has a nucleus with at least one nucleolus and many of the typical cytoplasmic organelles, but lacks centriolesfor cell division.
• Dendrites:Dendrites and axons are cytoplasmic extensions (or processes), that project from the cell body. They are sometimes referred to as fibers. Dendrites (afferent processes) increase their surface area to receive signals from other neurons, and transmit impulses to the neuron cell body.
• Axon: There is only one axon (efferent process) that projects from each cell body.
It carries impulses away from the cell body.
2-Glial cells: do not conduct nerve impulses, but support, nourish, and protect the neurons. They are mitotic, and far more numerous than neurons.
Astrocyte: A glialcell that provides support for neurons of the CNS, provides nutrients regulates the chemical composition of the extracellularfluid.
• Oligodendrocyte: A type of glialcell in the CNS that forms myelin sheaths.
• Microglia:The smallest glialcells; act as phagocytes (cleaning up debris) and protect the brain from invading microorganisms.
• Schwann cell:A cell in the PNS that is wrapped around a myelinatedaxon, providing one segment of its myelin sheath.
Levofloxacin
Levofloxacin is effective against a number of gram-positive and gram-negative bacteria. Because of its broad spectrum of action, levofloxacin is frequently prescribed in hospitals for pulmonary infections
Calcium Channel Blocking Agents
• Act on contractile and conductive tissues of the heart and on vascular smooth muscles
• Prevent movement of extracellular calcium into the cell
– Coronary and peripheral arteries dilate
– Myocardial contractility decreases
– Depress conduction system
Therapeutic Actions
• Inhibit movement of calcium ions across the membranes of myocardial and arterial muscle cells. Altering the action potential and blocking muscle cell contraction
• Depress myocardial contractility
• Slow cardiac impulse formation in the conductive tissues
• Cause a fall in BP
Oxycodone
About equal potency to morphine. Very effective orally.
It is combined with aspirin or acetaminophen for the treatment of moderate pain and is available orally
Oxycodone is a semisynthetic compound derived from thebaine, with agonist activity primarily at mu receptors.
Antihypertensives Drugs
CATEGORIES
I. Diuretics to reduce blood volume
Chlorothiazide (Diuril)
II. Drugs that interfere with the Renin-Angiotensin System
A. Converting enzyme inhibitors Captopril , enalapril, Lisinopril
B. Angiotensin receptor antagonists Saralasin Losartan
III. Decrease peripheral vascular resistance and/or cardiac output
A. Directly acting vasodilators
1. calcium channel blockers Nifedipine , Diltiazem, amlodipine
2. potassium channel activators Minoxidil
3. elevation of cGMP Nitroprusside
4. others Hydralazin e
B. Sympathetic nervous system depressants
1. α-blockers Prazosin, phentolamine, phenoxybenzamine
2. β-blockers Propranolol ,Metoprolol, atenolol
3. norepinephrine synthesis inhibitors Metyrosine
4. norepinephrine storage inhibitors Reserpine
5. transmitter release inhibitors Guanethidine
6. centrally acting: decrease
sympathetic outflow Clonidine , methyldopa