General Practice

Scombroid Poisoning

When there is too much histamine in fish, people should beware.

The Scombroid family of fish includes tuna and mackerel. When stored improperly, there can be too much histamine, which is not degraded by cooking. This causes symptoms of histamine excess, such as urticaria and all the usual culprits of unwellness.

The clinical diagnosis is based on history of multiple people being affected, rather than a single person with an allergy, as well as the redness of the presentation. Theoretically, the fish’s histamine can be measured. Histamine metabolites should show in the urine.

An antihistamine medication is the answer to this issue, such as the H1 antagonist diphenhydramine.

References

  1. Sicari V, Patel P, Zabbo CP. Diphenhydramine. [Updated 2025 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526010/.
  2. Liddiard, S., Nickson, C. and Nickson, S.L. (2024). Scombroid Poisoning. [online] Life in the Fast Lane • LITFL. Available at: https://litfl.com/scombroid-poisoning/.

ACE Inhibitors

Let’s learn about a good friend: ACE inhibitors!

Pertinent Facts

  • class of medication
  • used to treat hypertension
  • end in -pril
  • stop ACE from working its magic on the angiotensin I –> angiotensin II conversion
  • side effects: dry cough (due to bradykinin), hyperkalaemia (because of less aldosterone), angioedema (rare and life-threatening)
  • ARBs are an alternative

Further Details

Renin-Angiotensin-Aldosterone System

Renin (from those pesky organs called kidneys) turns angiotensinogen (also known as renin substrate) into angiotensin I.

ACE (whose full title is angiotensin-converting enzyme) turns angiotensin I into angiotensin II.

Angiotensin II has numerous magical properties: vasoconstriction, stimulating aldosterone release and more…so magical!

Dry Cough, Courtesy Of Bradykinin

Angiotensin II normally clears bradykinin. When ACE inhibitors block that, bradykinin builds up and makes the person cough.

Hyperkalaemia, Due To Vicious Subjugation Of Aldosterone

Aldosterone retains sodium and kicks out potassium. Take that, distal kidney parts! That’s where it acts.

Spironolactone, a medication well-known for its alluring gynaecomastia properties, is an aldosterone antagonist. It’s a potassium-sparing diuretic, which means it helps pass more urine without destroying the person’s blood potassium level to low, low amounts.

Let’s return to aldosterone itself, however. Aldosterone is like a vindictive, electrolyte-discriminating landlord that takes in sodium but evicts potassium from the rental property. It’s the excessively muscly security guard who stops that drunken, disorderly potassium from trying to enter the blood club.

Given the above, inhibition of aldosterone causes the opposite of its normal effects: not ejecting as much potassium from the system. Too much potassium is in the nightclub of your blood! That means hyperkalaemia!

Therefore, anything that stops the triggering of aldosterone creates a risk of hyperkalaemia.

But an ACE inhibitor stops angiotensin II from being formed! And that indirectly reduces the triggering of aldosterone that otherwise would have occurred! Hyperkalaemia might ensue! Chaos everywhere!

That explains one of the potential side effects of ACE inhibitors.

Angioedema Is Serious And Bad

If an ACE inhibitor triggers this, the patient can be switched to an ARB, which is an angiotensin II receptor blocker. It achieves a similar effect without as much risk of the side effects of ACE inhibitors.

Well, well, well, ACE inhibitors. We’ve figured you out now!

References

  1. CV Pharmacology. (2017). CV Pharmacology | Angiotensin Converting Enzyme (ACE) Inhibitors. [online] Available at: http://cvpharmacology.com/vasodilator/ACE [Accessed 30 Jul. 2017].
  2. Howarth, D. A. (2017). RACGP – ACE inhibitor angioedema: a very late presentation. [online] racgp.org.au. Available at: http://www.racgp.org.au/afp/2013/december/ace-inhibitor-angioedema/ [Accessed 30 Jul. 2017].
  3. Uptodate.com. (2017). Medline ® Abstract for Reference 63 of ‘ACE inhibitor-induced angioedema’. [online] Available at: https://www.uptodate.com/contents/ace-inhibitor-induced-angioedema/abstract/63?utdPopup=true [Accessed 30 Jul. 2017].