A Textbook of Clinical Pharmacology and Therapeutics

DRUGS THAT BLOCK THE EFFECTS OF

MEDIATORS OF ALLERGY

Therapeutic approaches to the management of allergic disease
produced by mediators include the following:

• inhibition of their biosynthesis;


• blockade of their release;


• antagonism of their effects.

INHIBITION OF BIOSYNTHESIS OF

PRO-INFLAMMATORY MEDIATORS

INTRANASAL AND TOPICAL
GLUCOCORTICOSTEROIDS

These are covered in Chapters 33 and 40.

Uses

These preparations are used in the therapy of allergic rhinitis and

they are very effective in reducing the symptoms of nasal itching,

sneezing, rhinorrhoea and nasal obstruction (they are more effec-

tive than cromoglicate). Common agents used to treat hay fever

includebeclometasone,budesonideandfluticasone.

Adverse effects

The adverse effects of all these preparations are similar,

namely sneezing, and dryness and irritation of the nose and

throat. Occasionally, epistaxis is a problem.

BLOCKADE OF RELEASE OF PRO-INFLAMMATORY

MEDIATORS

SODIUM CROMOGLICATE AND NEDOCROMIL

See also Chapter 33.

Uses

Sodium cromoglicateandnedocromilare effective in prevent-

ing exercise-induced and allergic asthma (but less effective

than inhaled glucocorticosteroids for the latter). They are

also effective in preventing hay fever and its symptoms.

Cromoglicateis used as nasal or eye drops for allergic rhinitis

and conjunctivitis. Local adverse effects include occasional

nasal irritation or transient stinging in the eye.

ANTAGONISM OF THE EFFECTS OF

PRO-INFLAMMATORY MEDIATORS

ANTIHISTAMINES

There are a large number of antihistamines (H 1 -receptor antago-

nists) available, several of which are available without prescrip-

tion. Some of those in common use are listed in Table 50.2. Their

CHEMICALMEDIATORS OF THEIMMUNERESPONSE ANDDRUGSTHATBLOCK THEIRACTIONS 405

Table 50.2:Properties of commonly used H 1 -antagonists

Drug Duration of Degree of Anti-emetic Risk of ventricular tachycardia

effect (h) sedation action when prescribed with other drugs

inhibiting their metabolism

First generation

Promethazine 20 Marked Some?

Diphenhydramine 6 Some Little?

Chlorphenamine 4–6 Moderate Little?

Cyclizine 6 Some Marked?

Triprolidine 24 Moderate Little?

(slow release)

Second generation

Acrivastine 6–8 Nil Little None

Fexofenadine 12 Nil Little None

Cetirizine 24 Nil Little None

Loratadine 24 Nil Little None

Key points

Treatment of anaphylactic shock

Anaphylactic shock is a medical emergency and its

treatment is as follows:

• Stop the offending drug or blood/blood product infusion.


• Check the patient’s blood pressure (lie them flat) and
  check for the presence of stridor/bronchospasm.


• Administer oxygen (FiO 2 40–60%).


• Administer adrenaline (epinephrine) 0.5–1 mg
  intramuscularly, and repeat after ten minutes if
  necessary.


• Give intravenous colloids (0.9% NaCl) for refractory
  hypotension.


• Administer hydrocortisone, 100–200mg i.v.


• Administer chlorpheniramine, 12.5 mg i.v.


• Give nebulized salbutamol, 2.5–5 mg for refractory
  bronchospasm.