NEET MDS Lessons
Pharmacology
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
Kinins
Peptide that are mediated in the inflammation.
Action of kinin:
On CVS: vasodilatation in the kidneys, heart, intestine, skin, and liver. It is 10 times active than histamine as vasodilator.
On exocrine and endocrine glands: kinin modulate the tone of pancreas and salivery glands and help regulate GIT motility, also affect the transport of water and electrolytes, glucose and amino acids through epithelial cell transport.
Class I Sodium Channel Blockers
• Block movement of sodium into cells of the cardiac conducting system
• Results in a stabilizing effect and decreased formation and conduction of electrical impulses
• Have a local anesthetic effect
• Are declining in use due to proarrhythmic effects and increased mortality rates
• Na channel blockers - Class 1 drugs are divided into 3 subgroups
• 1A. 1B, 1C based on subtle differences in their mechanism of action.
• Blockade of these channels will prevent depolarization.
• Spread of action potential across myocardium will slow and areas of pacemaker activity is suppressed.
Class IA Sodium Channel Blockers
• Treatment of: symptomatic premature ventricular contractions, supraventricular tachycardia, and ventricular tachycardia, prevention of ventricular fibrillation
– Quinidine (Cardioquin, Quinaglute)
– Procainamide (Pronestyl, Procanbid)
– Disopyramide (Norpace)
• Quinidine – prototype
• Low therapeutic index
• High incidence of adverse effects
Class IB Sodium Channel Blockers
• Treatment of: symptomatic premature ventricular contractions and ventricular tachycardia, prevention of ventricular fibrillation
– Lidocaine (Xylocaine)
– Mexiletine (Mexitil)
– Tocainide (Tonocard)
– Phenytoin (Dilantin)
Side Effects: Lidocaine
• Drowsiness • Paresthesias • Muscle twitching • Convulsions • Changes in mental status (disorientation, confusion) • Hypersensitivity reactions (edema, uticaria, anaphylaxis)
Side Effects: Phenytoin (Dilantin)
• Gingival hyperplasia
• Nystagmus
• Ataxia, slurring of speech
• Tremors
• Drowsiness
• Confusion
• Lidocaine – prototype
• Must be given by injection
• Used as a local anesthetic
• Drug of choice for treating serious ventricular arrhythmias associated with acute myocardial infarction, cardiac surgery, cardiac catheterization and electrical conversion
Class IC Sodium Channel Blockers
• Treatment of: life-threatening ventricular tachycardia or fibrillation and supraventricular tachycardia unresponsive to other drugs
– Flecainide
– Propafenone
Adverse Effects
• CNS - dizziness, drowsiness, fatigue, twitching, mouth numbness, slurred speech vision changes, and tremors that can progress to convulsions.
• GI - changes in taste, nausea, and vomiting. CV - arrhythmias including heart blocks, hypotension, vasodilation, and potential for cardiac arrest.
• Other Rash, hypersensitivity reactions loss of hair and potential bone marrow depression.
Drug-Drug Interactions
• Increased risk for arrhythmias if combined with other drugs that are know to cause arrhythmias- digoxin and beta blockers
• Increased risk of bleeding if combined with oral anticoagulants.
Drug Food Interactions
• Quinidine needs an acidic urine for excretion. Increased levels lead to toxicity
• Avoid foods that alkalinize the urine- citrus juices, vegetables, antacid, milk products
Gastric acid neutralizers (antacids)
Antacids act primarily in the stomach and are used to prevent and treat peptic ulcer. They are also used in the treatment of Reflux esophagitis and Gastritis.
Mechanism of action:
Antacids are alkaline substances (weak bases) that neutralize gastric acid (hydrochloric acid) they react with hydrochloric acid in the stomach to produce neutral or less acidic or poorly absorbed products and raise the pH of stomach secretion.
Antacids are divided into systemic and non-systemic.
• Systemic antacids (e.g. sodium bicarbonate) are highly absorbed into systemic circulation and enter body fluids. Therefore, they may alter acid–base balance. They can be used in the treatment of metabolic acidosis.
Non-systemic: they do not alter acid–base balance significantly, because they are not well-absorbed into the systemic circulation. They are used as gastric antacids; and include:
• Magnesium compounds such as magnesium hydroxide and magnesium sulphate MgS2O3. They have relatively high neutralizing capacity, rapid onset of action, however, they may cause diarrhoea and hypermagnesemia.
• Aluminium compounds such as aluminium hydroxide. Generally, these have low neutralizing capacity, slow onset of action but long duration of action. They may cause constipation.
• Calcium compounds such as. These are highly effective and have a rapid onset of action but may cause hypersecretion of acid (acid - rebound) and milk-alkali syndrome (hence rarely used in peptic ulcer disease).
Therefore, the most commonly used antacids are mixtures of aluminium hydroxide and magnesium hydroxide .
Adverse effects
Nitrates
– Headache, hypotension, dizziness, lightheadedness, tachycardia, palpitations
Beta-adrenergic blocking agents
– hypotension, bradycardia, bronchospasm, congestive heart failure
Calcium channel blockers
– hypotension, dizziness, lightheadedness, weakness, peripheral edema, headache, congestive heart failure, pulmonary edema, nausea, and constipation
Drugs that increase effects of Antianginal drugs
• Antihypertensive
• Diuretics
• Phenothiazine antipsychotic agents
• Cimetidine
• Digoxin
Drugs that decrease effects of Antianginal
• Adrenergic drugs - epinephrine
• Anticholinergic
• Calcium salts
• Phenobarbital, Phenytoin
Adjunctive Antianginal Drugs
In addition to antianginal drugs, several other drugs may be used to control risk factors and prevent progression of myocardial ischemia to myocardial infarction and sudden cardiac death.
These may include:
• Aspirin. This drug has become the standard of care because of its antiplatelet (ie, antithrombotic) effects. Recommended doses vary from 81 mg daily to 325 mg daily or every other day; apparently all doses are beneficial in reducing the possibility of myocardial reinfarction, stroke, and death. Clopidogrel 75 mg/day,
Is an acceptable alternative for individuals with aspirin allergy.
• Antilipemics. These drugs may be needed by clients who are unable to lower serum cholesterol levels sufficiently with a low-fat diet. Lovastatin or a related “statin” is often used. The goal is usually to reduce the serum cholesterol level below 200 mg/dL and lowdensitylipoprotein cholesterol to below
130 mg/dL.
• Antihypertensives. These drugs may be needed for clients with hypertension. Because beta blockers and calcium channel blockers are used to manage hypertension as well as angina, one of these drugs may be effective for both disorders.
Carbenicillin
Antibiotic that is chemically similar to ampicillin. Active against gram-negative germs. It is well soluble in water and acid-labile.
Neurolept Anesthesia
An antipsychotic agent such as droperidol plus an opiate analgesic agent such as fentanyl or sufentanil. This latter agent is approximately eight to ten times more potent than fentanyl.