What are the general causes of rhinitis and rhinorrhoea?

Allergy, cold, chemical, drug or physical damage.

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

Anti-histamines – Diphenhydramine

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

Decongestants are nonselective adrenergic agonists (alfa and beta stimulation).  Decongestants to are administered topically are direct acting and decongestants that are administered orally is indirect acting.

What is rhinitis medicamentosa?  How is it treated?

It is also known as rebound rhinitis.  It can appear after chronic use of decongestants, because of the chronic vasoconstriction and the poor blood supply you have damage to the mucous membranes that cause permanent inflammation and swelling.  There is also the deregulation of alfa-adrenergic receptors in the blood vessels that makes them unresponsive to alfa-adrenergic agonists.

Rhinitis medicamentosa is treated by local corticoids treatment.

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?

1^st generation:  They are multipotent competitive antagonists and they also blocks muscarinic receptors.  Due to its anti-muscarinic action it is effective in the treatment of rhinorrhoea.

2^nd generation:  They are only multipotent competitive antagonists, they don’t block muscarinic receptors.  They are only used in the treatment of allergic rhinitis.

The advantages of 2^nd generation anti-histamines is that they do not have as much side-effects as 1^st generation anti-histamines.  They don’t have sedation as a side effect. 

As 2^nd generation anti-histamines have no anti-muscarinic effects they can only be used for allergic rhinitis as it only has effects on allergies (IgE mediated).  With no anti-muscarinic effects has no effect on cold rhinitis.

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

Coricosteroids:  Treatment of privinism, allergic rhinitis.  Administered topically.

Anti-allegic drugs:  Prophylaxis of allergic rhinitis.  Administered topically.

Mensa:  For the use when the nasal secretion is sticky.  Administered topically.

Salt solution:  Humidifies the dry inflamed mucous membranes of the nose during colds, allergies or dry weather.