NEET MDS Lessons
Pharmacology
Dextromethorphan
O-methylated dextrorphan, Excellent oral antitussive, No analgesic effect, No GI effects, No respiratory depression
Valdecoxib
used in the treatment of osteoarthritis, acute pain conditions, and dysmenorrhoea
Etoricoxib new COX-2 selective inhibitor
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.
Metabolism
Hepatic Drug-Metabolizing Enzymes: most drug metabolism in the liverperformed by the hepatic microsomal enzyme system.
Therapeutic Consequences of Drug Metabolism
- Accelerated Renal Drug Excretion: The most important consequence of drug metabolism is the promotion of renal drug excretion. Metabolism makes it possible for the kidney to excrete many drugs that it otherwise could not.
- Drug Inactivation
- Increased Therapeutic Action: Metabolism may increase the effectiveness of some drugs.
- Activation of Prodrugs: A prodrug is a compound that is inactive when administered and made active by conversion in the body.
- Increased or Decreased Toxicity
Factors that influence rate of metabolism:
- Age: Hepatic maturation doesn't occur until about a year old.
- Induction of Drug-Metabolizing Enzymes: Some drugs can cause the rate of metabolism to increase, leading to the need for an increased dosage. May also influence the rate of metabolism for other drugs taken at the same time, leading to a need for increased dosages of those drugs as well.
- First-Pass Effect: Hepatic inactivation of certain oral drugs. Avoided by parentaral administration of drugs that undergo rapid hepatic metabolism.
- Nutritional Status
- Competition between Drugs
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.
Warfarin (Coumadin):
- The most common oral anticoagulant.
- It is only active in vivo.
- Warfarin is almost completely bound to plasma proteins. -96% to 98% bound.
- Warfarin is metabolized by the liver and excreted in the urine.
- Coumarin anticoagulants pass the placental barrier and are secreted into the maternal milk.
- Newborn infants are more sensitive to oral anticoagulants than are adults because of lower vitamin K levels and lower rates of metabolism.
- Bleeding is the most common side effect and occurs most often from the mucous membranes of the gastrointestinal tract and the genitourinary tract.
Oral anticoagulants are contraindicated in:
• Conditions where active bleeding must be avoided, Vitamin K deficiency and severe
hepatic or renal disease, and where intensive salicylate therapy is required.
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