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 

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 
 

Carbapenems: Broadest spectrum of beta-lactam antibiotics.

imipenem with cilastatin

meropenem

ertapenem

Monobactams: Unlike other beta-lactams, there is no fused ring attached to beta-lactam nucleus. Thus, there is less probability of cross-sensitivity reactions.

aztreonam

Beta-lactamase Inhibitors No antimicrobial activity. Their sole purpose is to prevent the inactivation of beta-lactam antibiotics by beta-lactamases, and as such, they are co-administered with beta-lactam antibiotics.

clavulanic acid

tazobactam

sulbactam

Ofloxacin : It is a quinolone antibiotic and similar in structure to  levofloxacin. It is an alternative treatment to ciprofloxacin for anthrax.

PHARYNGEAL DEMULCENTS 
Administered in the form of lozenges, cough drops and cough linctus. 
Produce soothing action on throat directly and by increasing the flow of saliva and provide symptomatic relief from dry cough.

EXPECTORANT

Expectorants are the drugs which increase the production of bronchial secretion and reduce its viscosity to facilitate its removal by coughing. 

ANTITUSSIVES

They are central cough suppressants and act centrally to raise the threshold of cough centre and inhibit the cough reflex by suppressing the coordinating cough centre in the medulla oblongata. 

Codeine - it depresses cough centre but is less constipating and abuse liability is low.

Pholcodeine is similar to codeine in efficacy and is longer acting. It has no analgesic or addicting property.

Noscapine is another opium alkaloid of benzylisoquinoline group. It is used as antitussive with no analgesic and drug abuse or drug dependence property. 

Dextromethorphan is a synthetic compound and its dextroisomer is used as antitussive and is as effective as codeine

Pipazethate is another synthetic compound of phenothiazine category used as antitussive with little analgesic and sedative properties.

ANTIHISTAMINICS
They do not act on cough centre but provide relief due to their sedative and anticholinergic action.

BRONCHODILATORS
Bronchodilators are helpful in individuals with cough and bronchoconstriction due to bronchial hyperreactivity. They help by improving the effectiveness of cough in clearing secretions.

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.

On the basis of Receptors, drugs can be divided into four groups,

a. agonists

b. antagonists

c. agonist-antagonists

d. partial agonists

a. Agonist

morphine fentanyl pethidine

Action : activation of all receptor subclasses, though, with different affinities

b. Antagonist

Naloxone , Naltrexone

Action :  Devoid of activity at all receptor classes  

c. Partial Agonist: (Mixed Narcotic Agonists/Antagonists)

Pentazocine, Nalbuphine, Butorphanol , Buprenorphine

Action: activity at one or more, but not all receptor types

With regard to partial agonists, receptor theory states that drugs have two independent properties at receptor sites,

a. affinity

The ability, or avidity to bind to the receptor
Proportional to the association rate constant, Ka

b. efficacy

or, intrinsic activity, and is the ability of the D-R complex to initiate a pharmacological effect

Drugs that produce a less than maximal response and, therefore, have a low intrinsic activity are called partial agonists.

These drugs display certain pharmacological features,

a. the slope of the dose-response curve is less than that of a full agonist

b. the dose response curve exhibits a ceiling with the maximal response below that obtainable by a full agonist

c. partial agonists are able to antagonise the effects of large doses of full agonists