What are the general causes of rhinitis and rhinorrhoea?

Allergy, cold, chemical or drug damage, cold air or physical damage.

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

Decongestants

 Alpha1-agonists – phenylephrine

    Antihistaminic and antimuscarinic drugs - Brompheniramine

    Corticosteroids – Betamethasone

Anti-infective drugs

    Anti-allergy drugs – Sodium cromoglycate

    Mucolytics – Mesna

   Diverse Drugs – Normal salt solutions and volatile oils

    Mast cell stabilisers- Ketotifen.

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

Oral decongestants – contracts nasal passages by activating post junctional alpha-adrenergic receptors

Topical decongestants - work by constricting the blood vessels within the nasal cavity.

Short acting drugs have a duration of 4 to 6 hours

intermediate acting drugs have a 8 to 10 hour duration

long acting drugs have a 12 hour duration.

What is rhinitis medicamentosa?  How is it treated?

Rhinitis medicamentosa (privinism) is a condition that may present following chronic treatment with decongestants, where the permanent vasoconstriction with poor local blood supply leads to damage of the mucous membranes of the nose with permanent inflammation and swelling, as well as deregulation of the α-adrenergic receptors on the blood vessels, rendering them unresponsive towards the α-agonists.

It is treated by stopping the previous treatment and receiving local corticosteroids therapy

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?

Effectiveness of the first generation of antihistamines is due to their actions on histaminic and muscarinic receptors in the medulla. Second generation antihistamines do not cross the blood-brain barrier. Advantages of the second generation of antihistamines is that they lack sedation and impairment of performance, have a longer duration of action and do not have anticholinergic side effects. They should not be used to relieve cold rhinitis because histamine levels are not elevated in nasal secretions of people with a cold.

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

Corticosteroid nasal sprays use with caution in infection-induced conditions, this is due to increased systemic uptake. It is administered via the nasal route.

Anti-allergic drugs are used in treatment of allergen-induced rhinitis or/and rhinorrhoea. It is administered via the oral or parenteral route.

Mesna is regarded as a chemoprotective and anti-neoplastic drug. It reduces toxicity in urinary passages. It is adverse reactions includes respiratory disorders such as nasal congestion, cough, dry mouth, bronchoconstriction, etc. It is administered parenterally (intravenous injection).

Normal salt solutions are used to dilute mucus and are administered nasally.