NEET MDS Lessons
Pharmacology
Antiarrhythmic Drugs
Cardiac Arrhythmias
Can originate in any part of the conduction system or from atrial or ventricular muscle.
Result from
– Disturbances in electrical impulse formation (automaticity)
– Conduction (conductivity)
– Both
MECHANISMS OF ARRHYTHMIA
ARRHYTHMIA – absence of rhythm
DYSRRHYTHMIA – abnormal rhythm
ARRHYTHMIAS result from:
1. Disturbance in Impulse Formation
2. Disturbance in Impulse Conduction
- Block results from severely depressed conduction
- Re-entry or circus movement / daughter impulse
Types of Arrhythmias
• Sinus arrhythmias
– Usually significant only
– if they are severe or prolonged
• Atrial arrhythmias
– Most significant in the presence of underlying heart disease
– Serious: atrial fibrillation can lead to the formation of clots in the heart
• Nodal arrhythmias
– May involve tachycardia and increased workload of the heart or bradycardia from heart block
• Ventricular arrhythmias
– Include premature ventricular contractions (PVCs), ventricular tachycardia, and ventricular fibrillation
Class |
Action |
Drugs |
I |
Sodium Channel Blockade |
|
IA |
Prolong repolarization |
Quinidine, procainamide, disopyramide |
IB |
Shorten repolarization |
Lidocaine, mexiletine, tocainide, phenytoin |
IC |
Little effect on repolarization |
Encainide, flecainide, propafenone |
II |
Beta-Adrenergic Blockade |
Propanolol, esmolol, acebutolol, l-sotalol |
III |
Prolong Repolarization (Potassium Channel Blockade; Other) |
Ibutilide, dofetilide, sotalol (d,l), amiodarone, bretylium |
IV |
Calcium Channel Blockade |
Verapamil, diltiazem, bepridil |
Miscellaneous |
Miscellaneous Actions |
Adenosine, digitalis, magnesium |
Indications
• To convert atrial fibrillation (AF) or flutter to normal sinus rhythm (NSR)
• To maintain NSR after conversion from AF or flutter
• When the ventricular rate is so fast or irregular that cardiac output is impaired
– Decreased cardiac output leads to symptoms of decreased systemic, cerebral, and coronary circulation
• When dangerous arrhythmias occur and may be fatal if not quickly terminated
– For example: ventricular tachycardia may cause cardiac arrest
Mechanism of Action
• Reduce automaticity (spontaneous depolarization of myocardial cells, including ectopic pacemakers)
• Slow conduction of electrical impulses through the heart
• Prolong the refractory period of myocardial cells (so they are less likely to be prematurely activated by adjacent cells
Cough is a protective reflex which helps in expulsion of respiratory secretion or foreign particles which are irritant to respiratory
tract. Irritation to any part of respiratory tract starting from pharynx to lungs carried impulses by afferent fibres in vagus and
sympathetic nerve to the cough centre in the medulla oblongata. \
Cough may be dry (without sputum or unproductive) or productive (with sputum production).
Classification for drugs used in cough.
I. Pharyngeal demulcents
Certain lozenges, linctus and cough drops containing glycerine, liquorice and syrups.
II. Expectorants
Sodium and potassium citrate
Sodium and potassium acetate
Potassium iodide
Ammonium chloride & carbonate
Acetylcysteine
Bromhexine
Guaiphenesin
III. Antitussive
i. Opioids
Codeine (as linctus) Pholcodeine
ii. Non-opioids
Noscapine
Dextromethorphan
Pipazethate
iii. Antihistaminics
Chlorpheniramine
Diphenhydramine
Promethazine
Erdosteine is recently introduced mucolytic with unique protective functions for the respiratory tract. It is indicated in the treatment of acute and chronic airway diseases such as bronchitis, rhinitis, sinusitis, laryngopharyngitis and exacerbations of chronic bronchitis.
Ketorolac
Mechanism of action
primary action responsible for its anti-inflammatory/antipyretic/analgesic effects is inhibition of prostaglandin synthesis through inhibition of the enzyme cyclooxygenase (COX). Ketorolac is not a selective inhibitor of COX enzymes
Indications: short-term management of pain
Contraindications
hypersensitivity to ketorolac, and against patients with the complete or partial syndrome of nasal polyps, angioedema, bronchospastic reactivity or other allergic manifestations to aspirin or other non-steroidal anti-inflammatory drugs (due to possibility of severe anaphylaxis).
Sufentanil
- A synthetic opioid related to fentanyl.
- About 7 times more potent than fentanyl.
- Has a slightly more rapid onset of action than fentanyl.
Oxyphenbutazone: one of the metabolites of phenylbutazone. Apazone. Similar to phenylbutazone, but less likely to cause agranulocytosis
Clarithromycin Used to treat pharyngitis, tonsillitis, acute maxillary
sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia (especially atypical pneumonias associated with Chlamydia pneumoniae or TWAR), skin and skin structure infections, and, in HIV and AIDS patients to prevent, and to treat, disseminated Mycobacterium avium complex or MAC.
Unlike erythromycin, clarithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes.
Clarithromycin has a fairly rapid first-pass hepatic metabolism, i.e it is metabolised by the liver. However, this metabolite, 14-hydroxy clarithromycin is almost twice as active as clarithromycin.
Contraindications Clarithromycin should be used with caution if the patient has liver or kidney disease, certain heart problems (e.g., QTc prolongation or bradycardia), or a mineral imbalance (e.g., low potassium or magnesium levels).
Clotrimazole: Clotrimazole is a potent, specific inhibitor of p450 enzymes.
It is used in some antifungal medications, and in the treatment of yeast infections.