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.

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

TRIMETHOPRIM

It is a diaminopyrimidine. It inhibits bacterial dihydrofolate reductase( DHFRase).

In combination with sulphamethoxzole it is called Co-trimoxazole.

Spectrum of action

 S. Typhi. Serratia. Klebsiela and many sulphonamide resistant strains of Staph.aureus. Strep pyogens

Adverse effects

Megaloblastic anemia. i.e.. due to folate defeciency.

Contraindicated in pregnancy.

Diuretics if given with co-trimoxazole cause thrombocytopenia.

Uses

I. UTI. 2. RTI. 3. Typhoid. 5. Septicemias. 5. Whooping cough

Ketamine 
- Causes a dissociative anesthesia.
- Is similar to but less potent than phencyclidine.
- Induces amnesia, analgesia, catalepsy and anesthesia, but does not induce convulsions.
- The principal disadvantage of ketamine is its adverse psychic effects during emergence from anesthesia. These include: hallucinations, changes in mood and body image.
- During anesthesia, many of the protective reflexes are maintained, such as laryngeal, pharyngeal, eyelid and corneal reflexes.
- Muscle relaxation is poor.
- It is not indicated for intracranial operations because it increases cerebrospinal fluid pressure.
- Respiration is well maintained.
- Arterial blood pressure, cardiac output, and heart rate are all elevated.

Pharmacodynamics

Pharmacodynamics is the study of what drugs do to the body and how they do it.

Dose-Response Relationships

- Basic Features of the Dose-Response Relationship:  The dose-response relationship is graded instead of all-or-nothing (as dose increases, response becomes progressively larger).

- Maximal Efficacy and Relative Potency

- Maximal Efficacy: the largest effects that a drug can produce

- Relative Potency:  Potency refers to the amount of drug that must be given to elicit an effect.

- Potency is rarely an important characteristic of a drug.

- Potency of a drug implies nothing about its maximal efficacy.
 

Roxithromycin

It is used to treat respiratory tract, urinary and soft tissue infections. Roxithromycin is derived from erythromycin, containing the same 14-membered lactone ring. However, an N-oxime side chain is attached to the lactone ring.

Roxithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Legionella pneumophilae.

When taken before a meal, roxithromycin is very rapidly absorbed, and diffused into most tissues and Phagocytes Only a small portion of roxithromycin is metabolised. Most of roxithromycin is secreted unchanged into the bile and some in expired air