This page from the British National Formulary briefly summarises the situation regarding potassium loss and the need for replacement therapy.
It provides the expected warnings about real insufficiency and potassium-sparing diuretics.
Liquid preparations, rather than tablets, are advised and a selection is listed, together with a modified-release preparation that is only recommended if oral liquids are inappropriate.
One paragraph in particular is worth reading and that is the note about how important it is not to confuse effervescent potassium tablets BPC 1968 with effervescent potassium chloride tablets. This is because the former do not contain chloride ions and their use should be restricted to hyperchloraemic states.
You have to register to gain access to the BNF online, but it is free and only takes a couple of minutes.
Why go there: the website provides sound and simple advice.
Information from: British National Formulary
Causes of hypokalaemia
As a contrast to the detail included on the Merck Manual site, visit this one and you get exactly what the title says - the causes of hypokalaemia on one page in a flow chart. Nothing more, nothing less.
It lists transient causes, what to exclude, what to test for, and gives causes of inadequate intake, extrarenal loss, and renal loss. Print off the page and you will never again be stuck when the electrolytes on that blood test suggest a low potassium.
Why go there: so simple.
Downside: no clinical data.
Information from: Sullivan Nicolaides Pathology, Australia.
Two interesting cases
I came across these case histories during my searches on this topic and was sufficiently intrigued to stop and read them, so you may find them interesting too. It relates two instances of liquorice causing hypertension and hypokalaemia.
The first concerns a 21-year-old woman, presenting with headache, whose blood pressure went up to 190/120mmHg with hypokalaemia. She was eating 100g of liquorice a day.
The other case is a 35-year-old woman who developed a hypokalaemia of 2.2mmol/l from using chewing gum that contained liquorice, even though she was not aware it contained any liquorice at all.
The culprit in both cases is glycyrrhizinic acid, found in liquorice products.
This article makes an educational read, just the thing to occupy you next time a patient doesn't turn up for an appointment. Who knows, you might make a star diagnosis next time a young person presents with a raised BP and a low potassium.
Why go there: pass the time while learning.
Information from: BMJ
Dr Barnard is a former GP in Fareham, Hampshire
Website of the week
I admit that this will make you blanch if you are looking for a quick update. There are several screens of text on these pages but it does cover pretty well everything.
It starts off by reminding us that potassium is the most abundant intracellular cation but only about 2 per cent of total body potassium is extracellular.
We are told that it is a major determinant of intracellular osmolality and that the ratio of intracellular and extracellular potassium concentrations strongly influences cell membrane polarisation, the conduction of nerve impulses and muscle (including myocardial) cell contraction. This is essential, because it explains why relatively small alterations in plasma concentration can have major clinical manifestations.
It covers pathophysiology, symptoms and signs, diagnosis and prevention of hypo- and hyperkalaemia. The ECG examples are particularly handy.
Why go there: thorough.
Downside: could be briefer.
Information from: Merck Manual.
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