NEET MDS Lessons
Pharmacology
Sympathomimetics
Beta-Adrenergic Agonists
Beta1-adrenergic agonists (dopamine, dobutamine, prenalterol, xamoterol) have been used to treat acute and chronic heart failure, but have limited usefulness in chronic CHF because of their arrhythmogenic effects, short duration of action, the development of tolerance, and necessity of parenteral administration
Dopamine (i.v.) is used in acute heart failure (cardiogenic shock) to increase blood pressure and increase cardiac output
- It has a short half-life (1 min)
- At high doses dopamine has potent peripheral vasoconstrictor effects (alpha-receptor stimulation), in addition to its inotropic effects
- Low dose dopamine has a renal artery dilating effect and may improve sodium and water excretion in patients refractory to loop diuretics
- When systolic pressure is greater than 90 mm Hg, nitroprusside can be added to reduce ventricular filling pressure and reduce afterload
- i.v. furosemide should also be administered to reduce edema
Levodopa and ibopamine, analogs of dopamine that can be administered orally, have been shown to improve symptoms in some patients, but can exhibit arrhythmogenic side-effects and tachyphylaxis
Dobutamine is a somewhat selective beta1-adrenergic agonist that lacks vasoconstrictor activity and causes minimal changes in heart rate
- It is frequently added to nitroprusside when blood pressure is adequate to increase cardiac output
- It is administered as an i.v. infusion to treat acute severe heart failure
- It has a short half-life (2.4 min) and is only used on a short-term basis, although long-term beneficial effects on cardiac function have been noted
- After 72 hours of therapy, tolerance can develop to dobutamine necessitating switch to other inotropic support (e.g. milrinone)
- Dobutamine can enhance AV conduction and worsen atrial tachycardia
Prenalterol and xamoterol are partial beta1-adrenergic agonists that may simultaneously stimulate beta1-receptors and block the receptors from stimulation by endogenous catecholamines, thereby protecting against beta1-receptor down-regulation
Classification Based on
a. Chemical structure
I. Sulphonamidcs.and others - c.g.. sulphadiazine. etc.
2. Beta-lactum ring - e.g.. penicillin
3. Tetracycline - e.g.. Oxytetracycline,.doxycycline.etc.
b. Mechanism of action
1. Inhibits cell-wall synthesis - penicillin. cephalosporin..cycloserine. etc.
2. Cause leakage from cell-membrane – polypeptides (polymyxin, Bacitracin), polyenes (Nystatin)
3. Inhibit protein synthesis - tetracyclines. chloramphenicols. erythromycin.
4. Cause mis-reading of mRNA code - aminoglycosides
5. Interfere with DNA function - refampicin.. metronidazole
6. Interfere with intermediary metabolism - sulphonamides. ethambutole
c. Type of organism against which it is primarily activate
I. Antibacterial - penicillin.
2. Antifungal - nystatin.
d. Spectrum of activity
1. Broad spectrum - tetracylines .
2. Narrow spectrum - penicillin G (penG). streptomycin.erythromycin
e. Type of action
I. Bacteriostatic - sulphonamides, erythromycin.tertracyclines
2. Bacteriocidal - penicillin. aminoglycoside
f. Source
I. Fungi - penicillin. cephalosporins
2. Bacteria - Polymyxin B
Types of Neurons (Function)
•There are 3 general types of neurons (nerve cells):
1-Sensory (Afferent ) neuron:A neuron that detects changes in the external or internal environment and sends information about these changes to the CNS. (e.g: rods and cones, touch receptors). They usually have long dendrites and relatively short axons.
2-Motor (Efferent) neuron:A neuron located within the CNS that controls the contraction of a muscle or the secretion of a gland. They usually have short dendrites and long axons.
2-Interneuron or association neurons: A neuron located entirely within the CNS in which they form the connecting link between the afferent and efferent neurons. They have short dendrites and may have either a short or long axon.
Anesthesia agents
1. Inhalation anesthetics (volatile anesthetics)
- gases : N2O, xenon
- Fluids (vaporisers)
2. Intravenous anesthetics
- Barbiturans : thiopental
- Others : propofol, etomidat
3. Pain killers
- Opioids: fentanyl, sufentanil, alfentanil, remifentanil, morphine
- Non Steroid Anti Inflamatory Drugs: ketonal, paracetamol
4. Relaxants
- Depolarising : succinilcholine
- Non depolarising : atracurium, cisatracurium, vecuronium, rocuronium
5. adiuvants
-benzodiazepins: midasolam, diazepam
Properties of inhalation anesthetics
The lower the solubility, the faster the onset and the faster the recoverability.
All general anesthetics:
1. inhibit the brain from responding to sensory stimulation.
2. block the sensory impulses from being recorded in memory.
3. prevent the sensory impulses from evoking “affect”.
Most general anesthetic agents act in part by interacting with the neuronal membranes to affect ion channels and membrane excitability.
· If the concentration given is too low:
1. Movement may occur
2. Reflex activity present (laryngeal spasm)
3. Hypertension
4. Awareness
Premedication of analgesic drugs and muscle relaxants are designed to minimise these effects
· If the concentration given is too high:
1. Myocardial depression
2. Respiratory depression
3. Delayed recovery
Clavulanic acid is often combined with amoxicillin to treat certain infections caused by bacteria, including infections of the ears, lungs, sinus, skin, and urinary tract. It works by preventing bacterium that release beta-lactamases from destroying amoxicillin.
Aspirin
Mechanism of Action
ASA covalently and irreversibly modifies both COX-1 and COX-2 by acetylating serine-530 in the active site Acetylation results in a steric block, preventing arachidonic acid from binding
Uses of Aspirin
Dose-Dependent Effects:
Low: < 300mg blocks platelet aggregation
Intermediate: 300-2400mg/day antipyretic and analgesic effects
High: 2400-4000mg/day anti-inflammatory effects
Often used as an analgesic (against minor pains and aches), antipyretic (against fever), and anti-inflammatory. It has also an anticoagulant (blood thinning) effect and is used in long-term low-doses to prevent heart attacks
Low-dose long-term aspirin irreversibly blocks formation of thromboxane A2 in platelets, producing an inhibitory affect on platelet aggregation, and this blood thinning property makes it useful for reducing the incidence of heart attacks
Its primary undesirable side effects, especially in stronger doses, are gastrointestinal distress (including ulcers and stomach bleeding) and tinnitus. Another side effect, due to its anticoagulant properties, is increased bleeding in menstruating women.