NEET MDS Lessons
Pharmacology
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:
α-glucosidase inhibitors
acarbose
miglitol
Mechanism
inhibit α-glucosidases in intestinal brush border
delayed sugar hydrolysis
delayed glucose absorption
↓ postprandial hyperglycemia
↓ insulin demand
Clinical use
type II DM
as monotherapy or in combination with other agents
Dental implications of these drugs:
1. Adverse effects: gingival hyperplasia (phenytoin), osteomalacia (phenytoin, Phenobarbital), blood dyscrasias (all but rare)
2. Drug interactions: additive CNS depression (anesthetics, anxiolytics, opioid analgesics), induction of hepatic microsomal enzymes (phenytoin, Phenobarbital, carbamazepine), plasma protein binding (phenytoin and valproic acid)
3. Seizure susceptibility: stress can → seizures
Nalidixic acid:
Nalidixic acid is the basis for quinolone antibiotics. It acts bacteriostatically (that is, it inhibits growth and reproduction) or bactericidally (it kills them) on both Gram positive and Gram negative bacteria, depending on the concentration. It is especially used in treating urinary tract infections, caused for example by Escherichia coli, Proteus, Enterobacter and Klebsiella.
Heparin:
- Inhibits blood coagulation by forming complexes with an α2-globulin (Antithrombin III) and each of the activated proteases of the coagulation cascade (Kallikrein, XIIa, XIa, IXa, Xa, and Thrombin). After formation of the heparin-ATIII-coagulation factor, heparin is released and becomes available again to bind to free ATIII.
- Blocks conversion of Prothrombin to Thrombin and thus inhibits the synthesis of Fibrin from Fibrinogen.
- Inhibits platelet function and increases vascular permeability. May induce moderate to severe thrombocytopenia.
- Is prescribed on a “unit” basis.
- Heparin is not effective after oral administration and is generally administered by intravenous or subcutaneous injection. Intramuscular injections should be avoided.
- Heparin does not cross the placenta and does not pass into the maternal milk.
- is contraindicated in any situation where active bleeding must be avoided.
Ulcerative lesions, intracranial hemorrhage, etc.
Overdosage:
• Simple withdrawal.
• Protamine sulfate: Highly basic peptide that binds heparin and thus neutralizes its effects.
Topical Anesthetics
Benzocaine
Benzocaine is a derivative of procaine, an ester type local anesthetic, and is poorly soluble in water and is
available only as a topical anesthetic.
- Localized allergic reactions are sometimes encountered
- Overdosing is unlikely as benzocaine is poorly absorbed into the blood, which decreases the likelihood of systemic toxicity.
- The onset of surface anesthesia is rapid requiring less than one minute.
Tetracaine
- Tetracaine is an ester type local anesthetic
- Topically applied tetracaine as opposed to benzocaine has a prolonged duration of action.
Cocaine
- Cocaine is a ester type anesthetic that is used exclusively as a topical agent.
- Cocaine is unique among topical and injectable anesthetics in that it has vasoconstrictive as well as anesthetic properties. It is used sparingly because of its abuse potential but is still used when hemostasis of mucous membranes is essential.
- Cocaine is generally available in concentrations of 2-10 % solution.
Lidocaine
- Lidocaine is an amide local anesthetic that is available in injectable and topical formulations.
- It is available in gel, viscous solution, ointment and aerosol preparations in concentrations ranging from 2-10 %.
- The onset of anesthesia is slower relative to benzocaine but, the duration is about the same.
- Absorption into the bloodstream is greater than benzocaine providing a greater risk of systemic toxicity.
Nimesulide
analgesic and antipyretic properties
Nimesulide is a relatively COX-2 selective, non-steroidal anti-inflammatory drug (NSAID) with analgesic and antipyretic properties. Its approved indications are the treatment of acute pain, the symptomatic treatment of osteoarthritis and primary dysmenorrhoea in adolescents and adults above 12 years old.
Banned - not used