ACEM Primary
Respiratory Pharmacology
Sympathomimetics
- Adrenoceptor agonists
- Bind beta R in airway smooth muscle-> increased adenylyl cyclase-> bronchodilation, inhibits release histamine from mast cells
- AE = tachycardia, tremor, hypokalaemia
- Best delivered by inhalation
| Drug | R | Dose/ AE |
| NON SELECTIVE | ||
| Epinephrine | B1, B2, alpha R | Dose: SC 0.4mL 1:1000 Inhaled 320mcg – maximal bronchodilation ~15 mins, lasts 60-90 mins AE: tachycardia, arrthythmia, worsening angina Helpful in treating acute vasodilation and shock (anaphylaxis) |
| Ephedrine | B1, B2 | Infrequently used |
| Isoproterenol | B1, B2 | Rarely used due to risk of cardiac arrhythmias |
| B2 SELECTIVE | ||
| Albuterol/ salbutamol Terbutaline Metaproterenol Pirbuterol | SABA | Bronchodilation maximal ~ 15 mins, persists 3-4 hours Can be given inhaled, nebulised |
| Salmeterol (partial agonist) Formoterol (full agonist) | LABA | Persist 12 hours due to high lipid solubility – can dissolve in smooth muscle membrane in high concentrations |
Muscarinic Antagonists
- Ipratropium (SAMA), tiotropium (LAMA)
- Inhibit action of Ach at muscarinic R-> block bronchoconstriction and increase mucous secretion
Corticosteroids
- Reduce bronchial hyperreactivity
- Reduce frequency of exacerbations if taken regularly
- MOA = inhibit lymphocytes, mast cells and eosinophils from infiltrating airways + contract engorged vessels in bronchial mucosa + potentiate B agonist effect
- Treatment of exacerbation = 30-60mg prednisolone daily 5-10 days
- Regular inhalational treatment = beclomethasone, budesonide, ciclesonide, flunisolide, fluticasone, mometasone, triamcinolone
- Eg. Inhaled beclomethasone 800mcg equivalent to 10-15mg/ daily oral prednisolone with fewer systemic effects
- AE = oral candidiasis
Methylxanthines
- 3 types:
- Theophylline (aminophylline preparation) = most effective bronchodilator
- Plasma conc 5-20 mg/L improve pulmonary function, require blood level monitoring
- AE: tachyarrhythmias, anorexia, NV, abdominal pain, headache, anxiety
- Clearance by liver
- PO 3-4mg/kg q6 hourly
- Rarely used as monotherapy, mainly as add on treatment
- Theobromine
- Caffeine
- Theophylline (aminophylline preparation) = most effective bronchodilator
- Increasing concentrations of intracellular cAMP-> relaxation of smooth muscle + reduction in histamine release
- Pharmacodynamics:
- CNS – Cortical arousal, alertness, deferral of fatigue
- CVS – positive inotropic and chronotropic effects
- GI – increased secretion of gastric acid and digestive enzymes
- Renal – increased GFR, reduced tubular sodium reabsorption = weak diuretics
- Smooth muscle – bronchodilation
- Skeletal muscle – improved contractility (reverse fatigue of diaphragm in COPD)
Disodium Cromoglycate
- Cromolyn and nedocromil
- Previously used for antigen and exercise induced asthma
- Nil effect of smooth muscle
- MOA = act on airway nerves mediating cough + inhibit mast cells and eosinophils
- Dose 2-4 puffs BD
Leukotriene antagonists
- Montelukast, zafirlukast
- Block leukotriene D4 R-> blocks airway response to exercise and antigen challenge
- Used in asthma prophylaxis, in children
IgE antibody
- Omalizumab
- Humanized IgE antibody reduces circulating IgE
- Reduces frequency of asthma exacerbations – for severe asthma, inadequately controlled on other agents
- Given IV, duration 2-4 weeks
Anti-tussive
- Opioid derivatives, at doses below those necessary to produce analgesia
- Dextromethorphan (15-30mg TDS), codeine (15mg)
- Caution in patients on MAO I
Last Updated on September 24, 2021 by Andrew Crofton
Andrew Crofton
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