NEET MDS Lessons
Pharmacology
Macrolide
The macrolides are a group of drugs (typically antibiotics) whose activity stems from the presence of a macrolide ring, a large lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, are attached. The lactone ring can be either 14, 15 or 16-membered. Macrolides belong to the polyketide class of natural products.
The most commonly-prescribed macrolide antibiotics are:
Erythromycin, Clarithromycin, Azithromycin, roxithromycin,
Others are: spiramycin (used for treating toxoplasmosis), ansamycin, oleandomycin, carbomycin and tylocine.
There is also a new class of antibiotics called ketolides that is structurally related to the macrolides. Ketolides such as telithromycin are used to fight respiratory tract infections caused by macrolide-resistant bacteria.
Non-antibiotic macrolides :The drug Tacrolimus, which is used as an
immunosuppressant, is also a macrolide. It has similar activity to cyclosporine.
Uses : respiratory tract infections and soft tissue infections.
Beta-hemolytic streptococci, pneumococci, staphylococci and enterococci are usually susceptible to macrolides. Unlike penicillin, macrolides have shown effective against mycoplasma, mycobacteria, some rickettsia and chlamydia.
Mechanism of action: Inhibition of bacterial protein synthesis by binding reversibly to the subunit 50S of the bacterial ribosome, thereby inhibiting translocation of peptidyl-tRNA. This action is mainly bacteriostatic, but can also be bactericidal in high concentrations
Resistance : Bacterial resistance to macrolides occurs by alteration of the structure of the bacterial ribosome.
Propoxyphene
- A methadone analog.Used orally to relieve mild to moderate pain.
- A typical opiate, it does not possess anti-inflammatory or antipyretic actions, but has little or no antitussive activity.
- Cannot be used parenterally because of irritant properties.
- Has a low addiction potential primarily due to its lack of potency as an opiate.
- The most common adverse side effects are:• dizziness, drowsiness, and nausea and vomiting. • these effects are more prominent in ambulatory patients.
- Withdrawal symptoms have occurred in both adults and in neonates following use of the drug by the mother during pregnancy.
- CNS depression is additive with other CNS depressants.
Ciclopirox:Ciclopirox is a synthetic antifungal agent for topical dermatologic use.
Fifth Generation:
These are extended spectrum antibiotics.
Ceftaroline, Ceftobiprole
Inhalational Anesthetics
The depth of general anesthesia is directly proportional to the partial pressure of the anesthetic agent in the brain. These agents enter the body through the lungs, dissolve in alveolar blood and are transported to the brain and other tissues.
A. Rate of induction and rate of recovery from anesthesia:
1. The more soluble the agent is in blood, the more drug it takes to saturate the blood and the more time it takes to raise the partial pressure and the depth of anesthesia.
2. The less soluble the agent is in blood, the less drug it takes to saturate the blood and the less time it takes to raise the partial pressure and depth of anesthesia.
B. MAC (minimum alveolar concentration)
The MAC is the concentration of the anesthetic agent that represents the ED50 for these agents. It is the alveolar concentration in which 50% of the patients will respond to a surgical incision.
The lower the MAC the more potent the general anesthetic agent.
C. Inhalation Anesthetic Agents
- Nitrous Oxide
- Ether
- Halothane
- Enflurane
- Isoflurane
Antianginal Drugs
Organic Nitrates :
Short acting: Glyceryl trinitrate (Nitroglycerine, GTN), Amyl Nitrate
Long Acting: Isosrbide dinitrate (Short acting by sublingual route), Erythrityl tetranitrate, penta erythrityl tetranitrate
Beta-adrenergic blocking agents : Propanolol, Metoprolol
Calcium channel blockers Verapamil, Nifedipine, Dipyridamole
Mechanism of action
– Decrease myocardial demand
– increase blood supply to the myocardium
Ketamine
- Causes a dissociative anesthesia.
- Is similar to but less potent than phencyclidine.
- Induces amnesia, analgesia, catalepsy and anesthesia, but does not induce convulsions.
- The principal disadvantage of ketamine is its adverse psychic effects during emergence from anesthesia. These include: hallucinations, changes in mood and body image.
- During anesthesia, many of the protective reflexes are maintained, such as laryngeal, pharyngeal, eyelid and corneal reflexes.
- Muscle relaxation is poor.
- It is not indicated for intracranial operations because it increases cerebrospinal fluid pressure.
- Respiration is well maintained.
- Arterial blood pressure, cardiac output, and heart rate are all elevated.