Respiratory Drugs Pharmacology

Front 1

Beta-2 agonist: mechanism

Back 1

Agonist of beta-2 adrenergic receptors > increasing cAMP level > relax bronchial smooth muscles and stabilise mast cells

Selective blockade of beta-2 adrenergic receptors reduce cardiovascular side effects

Front 2

Beta-2 agonist: clinical indications

Back 2

1. Asthma
2. COAD
- acute: by nebuliser
- chronic: maintenance therapy by inhaler or oral

Front 3

Beta-2 agonist: side effects

Back 3

1. Tremor
2. Tachycardia, hypokalemia: rare because of selective blockade/mode of administration/small dose

Front 4

Beta-2 agonist: examples

Back 4

1. Salbutamol
- best given as inhaler because of rapid and direct action, fewer systemic side effects, and relatively small dose is needed

2. Terbutaline
- available in oral/SC form

3. Salmeterol
- long acting b2>b1 agonist, for chronic treatment of asthma or broncho spasm in adults, usually in oral form

4. Epinephrine
- strong adrenergic agonist
- emergency usage for severe broncho constriction or anaphylaxis (vasodilation), short acting, not for maintenance.
- SE: tachycardia, CNS stimulation, metabolic and GI side effects

Front 5

Methylxanthines

Back 5

Theophylline:
1. Mechanism
- inhibit phosphodiesterase, the enzyme that breaks down cAMP; increased level of cAMP promotes broncho dilation and stabilise mast cells
2. Clinical indications
- slow inset limits usage in acute situation
- reserved for maintenance therapy for moderate to severe asthma
- in oral/PR form
3. Side effects:
- tachycardia, dizziness, nausea and vomiting, convulsion in high dose
- side effects are dose related; drug level can be monitored
- metabolised near exclusively in liver, cautious when used with cimetidine, oral contraceptives, and several antibiotics; don't use with other sympathomimetics as it will increase risk of heart and CNS toxicity

Aminophylline

- mechanism/side effects similar to theophylline
- available in IV form, so as to control acute severe bronchi constriction

Front 6

Mast cells stabilisers

Back 6

Cromolyn

1. Mechanism:
- prevents release of pro inflammatory mediators such as histamine from mast cells, neutrophils and macrophages

2. Clinical indications:
Prophylaxis against allergic asthma in children and young adults, in inhaled form

3. Minimal side effects

4. Used in conjunction to reduce dose of bronchodilator or corticosteroids

Front 7

Corticosteroids

Back 7

Beclomethasone

1. Mechanism
- decrease inflammation and oedema in respiratory tract
- enhance activity of sympathomimetics in hypoxia or acidotic states

2. Clinical indications:
Asthma that cannot be controlled by beta agonist alone

3. Inhaled beclomethasone does not induce systemic toxicity like systemic steroids ; however increases risk of oral Candida infection


Systemic steroids

- in Po/Iv/Im form
- systemic side effects of steroids: sodium/water retention, cardiovascular SEs, osteoporosis, peptic ulcers, weakness

Front 8

Leukotriene receptor antagonists

Back 8

Zafirlukast/Montelukast

- competitive antagonists of leukotriene D4/E4 receptors; inhibits broncho constriction and inflammation
- for prophylaxis and chronic asthma treatment, in oral form
- SE: GI side effects, headache
- efficacy similar to cromolyn