Pharmacology of drugs used to treat asthma

This chapter is related to the aims of Section F11(i) from the 2017 CICM Primary Syllabus, which expects the exam-going trainees to be able to "describe the pharmacology of anti-asthma drugs".  Unfortunately, though the examiners seem to love asthma, their love is expressed in the form of vague and haphazard gestures. Often, the questions will refer loosely to "drug groups commonly used to treat acute severe asthma", without specific boundaries, as if to test the candidates' capacity for self-control. Come on, we dare you: describe all the mechanisms.  This sort of stem is highly unhelpful, as asthma is a complex disease and drugs which are used to treat it come from a whole variety of classes. Taken completely literally, this syllabus item would also cover steroids, magnesium sulphate, ketamine, helium-oxygen mixtures and the halogenated anaesthetic ethers. 

Of course, a normal person would conclude that this would be insane, and that surely the college examiners expect a narrow focus; i.e. the question really asks "discuss the pharmacodynamics of bronchodilators". But in fact that is not the case. From the fragmented debris of past papers, one is able to reconstruct the incomplete skeletons of marking criteria, and this reveals that the examiners expected everything:

• β-agonists and their secondary messenger pathways
• Antimuscarinic agents
• Corticosteroids
• Methylxanthines
• Magnesium sulphate
• Ketamine
• Volatile anaesthetics
• Helium-oxygen mixtures
• Phosphodiesterase inhibitors

Desirable elements in the answers included:

• "A discussion of efficacy versus toxicity"
• "more comprehensive answers"  including esoterica such as Heliox
• A tabulated or "structured" approach was apparently favoured, at minimum featuring "details about drug class, mechanism of action and example(s)". 

We also know they did not want:

• long term inhaled steroids
• leukotriene antagonists
• anything relevant to the chronic management of asthma

Anyway. Given the vagueness and breadth of the SAQ, it is remarkable that in most cases the trainees do very well in answering it. Historically, the pass rates are in the order of 70%. Past paper questions which involved this subject were:

• Question 4 from the second paper of 2016 ("categorise the drugs")
• Question 11 from the second paper of 2014 ("mechanisms of action")
• Question 9 from the first paper of 2010 ("mechanisms of action")
• Question 11(p.2) from the second paper of 2007 ("mechanism of action")

In the interest of preserving some attachment to reality (i.e. what can be reasonably expected from a ten minute answer) the table offered here produces a minimalist entry for each class of drug, as well as a couple of examples, rather than a full-scale pharmacological breakdown (absorption, distribution., elimination, etcetera). Where possible, a faint trail of  references is left for the trainee to follow, in case they need more details from peer-reviewed publications.