Adverse drug events cause 5-15% of admissions to hospital and drug-drug interactions make up about a fifth of these. Most common are pharmacodynamic situations where two drugs have a similar outcome thereby overdoing the intended outcome. Pharmacokinetic interactions are more complicated to understand as they’re more indirect. For example, while medications are cleared by oxidative metabolism in the liver and gut, there are many drugs that interfere with the function of the cytochrome enzymes responsible. This can result in clearance of the first drug at too fast or too slow a rate.

Polypharmacy has become more frequent over the decades with more than half of people over the age of 75 on five or more prescriptions. This episode examines some of the systems that have led to current rates of polypharmacy, and strategies for deprescribing safely in a given patient. We're REWINDing it nine years after it was first published to celebrate the career of Professor Ric Day who has just retired after sixty years of service at St Vincent’s Hospital, Sydney. He has been a much-appreciated clinician and prolific research academic with several hundred published papers that have been cited more than forty thousand times.

Chapters
0:50 Prevalence of drug interactions
5:52 Pharmacodynamic vs pharmacokinetic interactions
9:25 Cytochrome enzymes
17:33 ACE inhibitors and more
26:48 Strategies for deprescribing

Guests
Professor Richard Day AM MBBS, FRACP (St Vincent’s Hospital; UNSW),
Professor Sarah Hilmer AM PhD FRACP FAAHMS (Royal North Shore Hospital; Kolling Institute/ USyd).
 
Production
Produced by Mic Cavazzini DPhil. Music courtesy of FreeMusicArchive includes ‘Flying Pea’ and ‘Cherry Blossom’ by Daddy Scrabble and “Manly Nunn Steps Out” by Doctor Turtle. Music licenced from Epidemic Sound includes ‘Train Ride’ (Instrumental) by Alex Kehm and ‘Yellow Leaf’ by Autohacker. Image adapted for RACP

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Key References
Life-threatening drug interactions: what the physician needs to know [Internal Medicine Journal]
Polypharmacy in older people: when should you deprescribe? [Medicine Today]