Viva A(ii)

This viva refers to  Section A(ii) of the 2017 CICM Primary Syllabus. Section A(ii)  mentions that the exam candidates are expected to "describe the pharmaceutics and formulation of drugs",  which includes drug excipients. 

What is an "excipient"?

An excipient is "A relatively inert substance which functions to ensure the dosage, stability and bioavailability of the active agent"

What sorts of excipients are you aware of?

• Lubricants
• Antioxidants
• Binders
• Buffers
• Carriers
• Chelators
• Coatings
• Colouring
• Flavours
• Disintegrants
• Emulsifiers
• Preservatives

What are the possible pharmacological effects of excipients?

• Degradation of the active ingredient
• Decreased bioavailability of the active ingredient
• Creation of toxic byproducts
• Toxicity of the actual excipient:
  • The excipient is relatively safe but is inadvertantly given in a relatively high dose to a susceptible population. eg. low birth weight neonates or people with impaired clearance mechanisms
  • The patient has an idiosyncratic or allergic reaction to the excipient
  • The drug is accidentally given using a route of administration which it is not meant for (eg. when you idiotically crush a tablet up and inject the contents)

Examples of adverse effects associated with specific classes include the following examples:

• Fluorinated hydrocarbon propellants, which cause arrhythmias similar to the toxicity of inhaling solvent fumes
• Preservatives such as chlorbutol, which can cause hypotension, and sodium benzoate which displaces bilirubin from albumin and which can cause kernicterus in the jaundiced neonate
• Colouring agents, such as tartrazine which can cause urticaria anaphylaxis and exacerbations of asthma in the group of aspirin-sensitive asthmatics
• Emulsifying agents, such as α-tocopherol which can cause renal and hepatic failure in infants
• Perfumes, which can cause contact dermatitis 
• Paraffin wax, which can burst into flames when the ointment is used prior to diathermy (this was reported from experiences of ophthalmic surgeons)
• Solvents such as ethanol, which can cause - wait for it - intoxication