Paracetamol

Paracetamol or acetaminophen is analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains.

paracetamol acts by reducing production of prostaglandins, which are involved in the pain and fever processes, by inhibiting the cyclooxygenase (COX)  enzyme.

Metabolism Paracetamol is metabolized primarily in the liver. At usual doses, it is quickly detoxified by combining irreversibly with the sulfhydryl group of glutathione to produce a non-toxic conjugate that is eventually excreted by the kidneys.

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.

Valdecoxib

used in the treatment of osteoarthritis, acute pain conditions, and dysmenorrhoea

Etoricoxib new  COX-2 selective inhibitor

ANTICHOLINERGIC DRUGS
Blocks the action of Ach on autonomic effectors.

Classification
Natural Alkaloids - Atropine. Hyoscine

Semi-synthetic deriuvatives:- Homatropine, Homatropine methylbromide, Atropine methonitrate.

Synthetic compounds 

(a) Mydriatics - Cyclopentolate. Tropicamide.
(b) Antisecretory - Antispasmodics - Propantha1ine. Oxy-phenonium, Pirenzipine.
c) Antiparkinsonism- Benzotopine, Ethopropazine, Trihexyphenidyl, Procyclidine, Biperiden 
Other drugs with anticholinergic properties • Tricyclic Antidepressants • Phenothiazines • Antihistaminics • Disopyramide

MUSCARINIC RECEPTORS SUBTYPES & ANTAGONISTS 
• M 1 Antagonists – Pirenzepine, Telenzepine, dicyclomine, trihexyphenidyl 
• M 2 Antagonists – Gallamine, methoctramine 
• M 3 Antagonists – Darifenacin, solifenacin, oxybutynin, tolterodine

Pharmacological Actions
CNS - stimulation of medullary centres like vagal. respiratory. vasomotor and inhibition of vestibular excitation and has anti-motion sickness properties.
CVS - tachycardia.
Eye - mydriasis
Smooth muscles - relaxation of the muscles receiving parnsympathetic motor innervation.
Glands - decreased secretion of sweat and salivary glands
Body Temperature - is increased as there is stimulation of  temperature regulating centre.
Respiratory System- Bronchodilatation & decrease in secretions. For COPD or Asthma - antimuscarinic drugs are effective
GIT - Pirenzepine & Telenzepine - decrease gastric secretion with lesser side effects.

EPHEDRINE

It act indirectly and directly on α and β receptors. It increases blood pressure both by peripheral vasoconstriction and by increasing the cardiac output. Ephedrine also relaxes the bronchial smooth muscles.

Ephedrine stimulates CNS and produces restlessness, insomnia, anxiety and tremors.
Ephedrine produces mydriasis on local as well as systemic administration.
Ephedrine is useful for the treatment of chronic and moderate type of bronchial asthma, used as nasal decongestant and as a mydriatic without cycloplegia. It is also useful in preventing ventricular asystole in Stokes Adams syndrome.

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