NEET MDS Lessons
Pharmacology
Antiemetics
Antiemetic drugs are generally more effective in prophylaxis than treatment. Most antiemetic agents relieve nausea and vomiting by acting on the vomiting centre, dopamine receptors, chemoreceptors trigger zone (CTZ), cerebral cortex, vestibular apparatus, or a combination of these.
Drugs used in the treatment of nausea and vomiting belong to several different groups. These include:
1. Phenothiazines, such as chlorpromazine, act on CTZ and vomiting centre, block dopamine receptors, are effective in preventing or treating nausea and vomiting induced by drugs, radiation therapy, surgery and most other stimuli (e.g. pregnancy).
They are generally ineffective in motion sickness.
Droperidol had been used most often for sedation in endoscopy and surgery, usually in combination with opioids or benzodiazepines
2. Antihistamines such as promethazine and Dimenhyrinate are especially effective in prevention and treatment of motion.
3. Metoclopramide has both central and peripheral antiemetic effects. Centrally, it antagonizes the action of dopamine. Peripherally metoclopramide stimulates the release of acetylcholine, which in turn, increases the rate of gastric. It has similar indications to those of chlorpromazine.
4. Scopolamine, an anticholinergic drug, is very effective in reliving nausea & vomiting associated with motion sickness.
5. Ondansetron, a serotonin antagonist, is effective in controlling chemical-induced vomiting and nausea such those induced by anticancer drugs.
6. Benzodiazepines: The antiemetic potency of lorazepam and alprazolam is low. Their beneficial effects may be due to their sedative, anxiolytic, and amnesic properties
Doxycycline
Commonly prescribed for infections and to treat acne. treat urinary tract infections, gum disease, and other bacterial infections such as gonorrhea and chlamydia., as a prophylactic treatment for infection by Bacillus anthracis (anthrax). It is also effective against Yersinia pestis and malaria.
Pharmacokinetics
Pharmacokinetics is the way that the body deals with a drug - how that drug moves throughout the body, and how the body metabolizes and excretes it. The factors and processes involved in pharmacokinetics must be considered when choosing the most effective dose, route and schedule for a drug's use.
The four processes involved in pharmacokinetics are:
Absorption: The movement of a drug from its site of administration into the blood.
Several factors influence a drug's absorption:
- Rate of Dissolution: the faster a drug dissolves the faster it can be absorbed, and the faster the effects will begin.
- Surface Area: Larger surface area = faster absorption.
- Blood Flow: Greater blood flow at the site of drug administration = faster absorption.
- Lipid Solubility: High lipid solubility = faster absorption
- pH Partitioning: A drug that will ionize in the blood and not at the site of administration will absorb more quickly.
Distribution: The movement of drugs throughout the body.
Metabolism: (Biotransformation) The enzymatic alteration of drug structure.
Excretion: The removal of drugs from the body.
As a drug moves through the body, it must cross membranes. Some important factors to consider here then are:
Body's cells are surrounded by a bilayer of phospholipids (cell membrane).
There are three ways that a substance can cross cell membranes:
- Passing through channels and pores: only very small molecules can cross cell membranes this way.
- Transport Systems: Selective carriers that may or may not use ATP.
- Direct Penetration of the Cell Membrane:
ANTIDEPRESSANTS
Monoamine uptake inhibitors
1. Tricyclic antidepressants (TCAs)
2. Selective serotonin reuptake inhibitors (SSRIs)
3. Serotonin-norepinephrine reuptake inhibitors(SNRIs)
4. Norepinephrine reuptake inhibitor
Monoamine oxidase inhibitors (MAOIs)
Monoamine receptor antagonists
SYMPATHOMIMETICS
β2 -agonists are invariably used in the symptomatic treatment of asthma.
Epinephrine and ephedrine are structurally related to the catecholamine norepinephrine, a neurotransmitter of the adrenergic nervous system
Some of the important β 2 agonists like salmeterol, terbutaline and salbutamol are invariably used as bronchodilators both oral as well as
aerosol inhalants
SALBUTAMOL
It is highly selective β2 -adrenergic stimulant h-aving a prominent bronchodilator action.
It has poor cardiac action compared to isoprenaline.
TERBUTALINE
It is highly selective β2 agonist similar to salbutamol, useful by oral as well as inhalational route.
SALMETEROL
Salmeterol is long-acting analogue of salbutamol
BAMBUTEROL
It is a latest selective adrenergic β2 agonist with long plasma half life and given once daily in a dose of 10-20 mg orally.
METHYLXANTHINES (THEOPHYLLINE AND ITS DERIVATIVES)
THEOPHYLLINE
Theophylline has two distinct action:
smooth muscle relaxation (i.e. bronchodilatation) and suppression of the response of the airways to stimuli (i.e. non-bronchodilator prophylactic effects).
ANTICHOLINERGICS
Anticholinergics, like atropine and its derivative ipratropium bromide block cholinergic pathways that cause airway constriction.
MAST CELL STABILIZERS
SODIUM CROMOGLYCATE
It inhibits degranulation of mast cells by trigger stimuli.
It also inhibits the release of various asthma provoking mediators e.g. histamine, leukotrienes, platelet activating factor (PAF) and interleukins (IL’s) from mast cell
KETOTIFEN
It is a cromolyn analogue. It is an antihistaminic (H1 antagonist) and probably inhibits airway inflammation induced by platelet activating factor (PAF) in primate.
It is not a bronchodilator. It is used in asthma and symptomatic relief in atopic dermatitis, rhinitis, conjunctivitis and urticaria.
LEUKOTRIENE PATHWAY INHIBITORS
MONTELUKAST
It is a cysteinyl leukotriene receptor antagonist indicated for the management of persistent asthma.
Sulfonylureas
1st generation
tolbutamide
chlorpropamide
2nd generation
glyburide
glimepiride
glipizide
Mechanism
glucose normally triggers insulin release from pancreatic β cells by increasing intracellular ATP
→ closes K+ channels → depolarization → ↑ Ca2+ influx → insulin release
sulfonylureas mimic action of glucose by closing K+ channels in pancreatic β cells
→ depolarization → ↑ Ca2+ influx → insulin release
its use results in
↓ glucagon release
↑ insulin sensitivity in muscle and liver
Clinical use
type II DM
stimulates release of endogenous insulin
cannot be used in type I DM due to complete lack of islet function
Toxicity
first generation
disulfiram-like effects
especially chlorpropamide
second generation
hypoglycemia
weight gain
Different Systems of the CNS & their functions
These systems are pathways formed of specific parts of the brain and the neurons connecting them.
They include:
1.The pyramidal system
2.The extrapyramidal system
3.The limbic system
4.The reticular formation
5.The tuberohypophyseal system
The pyramidal system:
It originates from the motor area of the cerebral cortex and passes through the spinal cord, therefore it is also known as the “corticospinaltract”.
It is responsible for the regulation of the fine voluntary movements.
The extrapyramidal system:
It also controls the motor functionbut involves areas other than the corticospinal tract.
It is involved in the regulation of gross voluntary movements, thus it complements the function of the pyramidal system.
The “basal ganglia” constitute an essential part of this system.
Degenerative changes in the pathway running from the “substantianigra”to the “corpus striatum”(or nigrostriatal pathway) may cause tremors and muscle rigidity characteristic of “Parkinson’s disease”.
The limbic system:
The major parts of this system are: the hypothalamus, the basal ganglia, the hippocampus(responsible for short term memory), and some cortical areas.
The limbic system is involved in the control of “behavior”& “emotions”.
The reticular formation:
It is composed of interlacing fibers and nerve cells that run in all directions beginning from the upper part of the spinal cord and extending upwards.
It is important in the control of “consciousness” and “wakefulness”.
The tuberohypophyseal system:
It is a group of short neurons running from the hypothalamusto the hypophysis(pituitary gland) regulating its secretions.