Blog #3.4
What are the general causes of rhinitis and rhinorrhoea?
Usually caused by: Allergy, cold, chemicals, drugs or physical damage.

Which drug groups can be used for the treatment of rhinorrhoea? Name examples from each group.

α1 agonists (decongestants) :phenylephrine
Antihistamines: diphenhydramine
Corticosteroids: Betamethasone
Mast cell stabilisers: Ketotifen
Mucolytics: Mesna
Diverse drugs: Saline
Antibiotic: Neomycin

How do the decongestants differ with respect to the mechanism of action and duration of action?  How are they administered typically?

These are sympathomimetic agents which work by agonism on α1 receptors, causing vasoconstriction of the mucosal blood vessels (decrease in oedema of the nasal mucosa) . 
They can be short acting (4 hours), intermediate acting: (8-10 hours) and long acting (12 hours)

They are typically administered :topical decongestants: Nasal sprays, gels and nasal drops. Inhalation of volatile compounds to achieve decongestion of the mucous membranes of the nose

What is rhinitis medicamentosa?  How is it treated?
Rhinitis medicamentosa (RM) is a condition due overuse of nasal decongestants. This  can cause prolonged vasoconstriction of the nasal blood vessels leading to the continuing of poor blood supply to the nasal mucosa. Treatment includes cortisone nasal sprays such as beclomethasone.

How does the first and second generations of antihistamines differ with respect to the mechanisms according to which rhinitis and rhinorrhoea are relieved?  What are the advantages of the second generation of antihistamines?  Why should they not be used to relieve cold rhinitis?
First generation antihistamines have multipotent effects and not only blocks H1 receptors, but also muscarinic receptors. This antagonism can cause reduction of mucus secretion in the airways so they are usually used in cold preparations in rhinohorrea. They are sedative and can thus decrease concentration.

Second gen  only antagonise H1 receptors hence mucus production will not be decreased. They are, however, useful in long-term or short-term treatment of allergic rhinitis and  they do not possess sedative effects. Because histamine plays no part in cold rhinitis (but bradykinin does) these drugs do not help to clear up cold rhinitis.

When are corticosteroids, anti-allergic drugs, mesna and normal salt solution valid and how are they administered? 

Corticosteroids (nasal sprays) for clinical use for allergic rhinitis can be administered topically (nasal spray) or systemically (orally)

Anti-allergic drugs: nasal spray is very effective for the prophylactic treatment of allergic rhinitis, but the regular dosage makes it less popular

Mesna: Topical mesna (nasal spray) is especially meaningful to use when the nasal secretion is sticky.  The mesna helps to make the mucus more liquid.

Normal salt solution: It humidifies the dry, inflamed mucous membranes of the nose during colds, dry weather, allergy (hay fever), nose bleeding, overuse of decongestants and other irritations. It is administered  as nose drops.