NEET MDS Lessons
Pharmacology
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
Mucosal protective agents.
These are locally active agents that help heal gastric and duodenal ulcers by forming a protective barrier between the ulcers and gastric acid, pepsin, and bile salts. They do not alter the secretion of gastric acid. These drugs include sucralfate and colloid bismuth compounds. (e.g. tripotassium, dicitratobismuthate). Colloidal bismuth compounds additionally exert bactericidal action against H.pylori. Also, Prostaglandins have both antisecretory and mucosal protective effects.
Example: Misoprostol- used for prevention of NSAID – induced ulcer.
- Drugs that exert antimicrobial action against H.pylori such as amoxicillin, metronidazole, clarithromycin and tetracycline are included in the anti-ulcer treatment regimens.
Ampicillin offered a broader spectrum of activity than either of the original penicillins and allowed doctors to treat a broader range of both Gram-positive and Gram-negative infections. Ampicillin is often used in molecular biology as a test for the uptake of genes (e.g., by plasmids) by bacteria (e.g., E. coli)
Aminoglycoside
Aminoglycosides are a group of antibiotics that are effective against certain types of bacteria. They include amikacin, gentamicin, kanamycin, neomycin, netilmicin, paromomycin, streptomycin, and tobramycin. Those which are derived from Streptomyces species
Aminoglycosides work by binding to the bacterial 30S ribosomal subunit, causing misreading of t-RNA, leaving the bacterium unable to synthesize proteins vital to its growth.
Aminoglycosides are useful primarily in infections involving aerobic, Gram-negative bacteria, such as Pseudomonas, Acinetobacter, and Enterobacter. In addition, some mycobacteria, including the bacteria that cause tuberculosis, are susceptible to aminoglycosides. Streptomycin was the first effective drug in the treatment of tuberculosis, though the role of aminoglycosides such as streptomycin and amikacin have been eclipsed (because of their toxicity and inconvenient route of administration) except for multiple drug resistant strains.
Infections caused by Gram-positive bacteria can also be treated with aminoglycosides, but other types of antibiotics are more potent and less damaging to the host. In the past the aminoglycosides have been used in conjunction with penicillin-related antibiotics in streptococcal infections for their synergistic effects, particularly in endocarditis.
Because of their potential for ototoxicity and renal toxicity, aminoglycosides are administered in doses based on body weight. Blood drug levels and creatinine are monitored during the course of therapy.
There is no oral form of these antibiotics: they are generally administered intravenously, though some are used in topical preparations used on wounds.
Aminoglycosides are mostly ineffective against anaerobic bacteria, fungi and viruses.
Pharmacodynamics
Pharmacodynamics is the study of what drugs do to the body and how they do it.
Dose-Response Relationships
- Basic Features of the Dose-Response Relationship: The dose-response relationship is graded instead of all-or-nothing (as dose increases, response becomes progressively larger).
- Maximal Efficacy and Relative Potency
- Maximal Efficacy: the largest effects that a drug can produce
- Relative Potency: Potency refers to the amount of drug that must be given to elicit an effect.
- Potency is rarely an important characteristic of a drug.
- Potency of a drug implies nothing about its maximal efficacy.
Lamotrigine (Lamictal): newer; broad spectrum (for most seizure types)
Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing)
Side effects: dizziness, ataxia, fatigue, nausea, no significant drug interactions
Patient positioning
The most common medical emergency encountered in the dental office setting is syncope. So patients in the supine or semi-supine position to improve venous return and cerebral blood flow provided that the position is tolerated by the patient and is appropriate for their medical condition.