2. 2
Potassium
• Potassium has atomic number 19 and the chemical symbol K, which is derived
from its Latin name ‘kalium’.
Biological importance:
• Potassium ions are essential for the human body and are also present in plants,
• The so-called action potential occurs in a variety of excitable cells such as
neurons, muscle cells and endocrine cells
• The Na+/K+-based action potential is short-lived (only 1 ms) and therefore
mostly found in the brain and nerve cells
The major use of K+
• Fertilisers such as potassium chloride (KCl), potassium sulfate (K2SO4) and
potassium nitrate (KNO3).
• oxidizing agent such as potassium bromate (KBrO3)
• food preservative such as Potassium bisulfite (KHSO3) in wine and beer.
• In the human body, 95% of the K+ can be found inside the cells, with the
remaining 5% mainly circulating in the blood plasma
3. 3
• This balance is carefully maintained by the Na+/K+ pump, and imbalances, such as
seen in hypo or hyperkalaemia, can have serious consequences.
Hypokalemia. is a potentially serious condition where the patient has low levels of K+ in
his/her blood Plasma
Symptoms
• include weakness of the muscles or ECG (electrocardiogram) abnormalities
hypokalemia can be a result of
• reduced K+ intake caused by GI disturbance , such as diarrhea and vomiting
• increased excretion of K+ caused by diuresis is often found in patients treated with
diuretics such as thiazides
• Potassium ions are excreted via the kidneys. Within the kidneys, ∼150–180 of plasma
is filtered every day through the glomerulus, which is part of the nephron
• a variety of ions are secreted and re-absorbed in order to regulate plasma imbalances
and manage the urine volume
• K+ is passively secreted at the proximal tubule and also moves into the interstitial fluid
via a counter-flow process to Na+ mainly at the distal tubule (Figure 2.1).
5. 5
Oral supplementation
Oral supplementation in form of potassium salts is especially necessary in
patients
• patients who is take anti-arrhythmic drugs
• patients who is suffer from renal artery stenosis.
• patients who is suffer from severe heart failure.
• patients who is shown severe K+ losses due to
chronic diarrhea
abusive use of laxatives
• Regulation of the plasma K+ level may also be required in the care of
elderly patients when the K+ intake is reduced as a result of changing
dietary habits (special attention has to be given to patients with renal
insufficiency because K+ excretion might be reduced)
6. 6
Potassium salts and their clinical application:
•Potassium salts are preferably given as liquid preparations, and KCl is the preferred salt
used.
•Other potassium-based salts can be used if the patient is at risk of developing
hyperchloraemia – increased chloride plasma levels
•Typically potassium salts are dissolved in water, but the salty and bitter taste makes
them difficult to formulate
•Oral bicarbonate solutions such as potassium bicarbonate are typically given orally for
chronic acidosis states – low pH of the blood plasma
This can be again due to impaired kidney function. The use of potassium bicarbonate
for the treatment of acidosis has to be carefully evaluated
Potassium citrate is used in the United Kingdom as an over-the-counter drug for the
relief from discomfort experienced in mild urinary-tract infections by increasing the
urinary pH(It should be not given to men if they experience pain in the kidney area (risk
of kidney stones) or if blood or pus is present in the urine. Also, should avoid taking
potassium citrate without consultation with their general practitioner (GP). Caution is
generally advised to patients with renal impairment, cardiac problems and the elderly
7. 7
Adverse effects and toxicity: hyperkalaemia
• The therapeutic window for K+ in the blood plasma is very small (3.5–5.0 mmol), and
especially hyperkalemia, an increased level of K+ in the plasma, can lead to severe health
problems
• Potassium salts can cause nausea and vomiting and in extreme cases can lead to small
bowel ulcerations
• Acute severe hyperkalaemia is defined when the plasma potassium concentration
exceeds 6.5 mmol/l or if ECG changes are seen
• This can lead to cardiac arrest, which needs immediate treatment
Treatment options include
the use of calcium gluconate intravenous injections, which minimises the effects of
hyperkalaemia on the heart
The intravenous injection of soluble insulin promotes the shift of potassium ions into the
cells
Diuretics can also be used to increase the secretion of K+ in the kidneys
and dialysis can be a good option if urgent treatment is required
• Potassium salts are also available in the form of tablets or capsules for oral application
especially as nonprescription
• very high concentrations of K+ are known to be toxic to tissue cells and can cause injury to
the gastric mucosa. Therefore, nonprescription potassium supplement pills are usually
restricted to < 100 mg K+
8. 8
Magnesium
• The element magnesium (Mg) is a silvery-white and lightweight metal
• Mg2+ is an essential ion in the human body and the imbalance should be corrected
• Most magnesium salts are soluble in water, and given in large amounts they work as a
laxative in the human body
• Aqueous magnesium ions are sour in taste
• Magnesium hydroxide (MgOH2) has only limited solubility in water and the resulting
suspension is called milk of magnesia , which is commonly used as an antacid and is
known to be a mild base
•the most magnesium salts are water soluble and therefore processed vegetables,
mainly cooked in water, are low in magnesium ion content.
9. 9
Biological importance:
• Mg2+ is an essential ion in the human body
Mg2+ is a crucial constituent in numerous enzymatic processes
Mg2+ is essential to most living cells as a signaling molecule and is involved in nucleic
acid biochemistry dealing with the manipulation of ATP (adenosine triphosphate), DNA,
RNA and related processes. For example, ATP has to be coordinated to a magnesium ion
in order to become biologically active. Mg2+ also stabilizes DNA and RNA structures,
which can be seen in their increased melting points.
• Mg2+ ions form the redox-active center in chlorophyll
• In the human body, Mg2+ is the fourth most abundant cation and the second most
abundant ion in the interstitial fluid
• Mg2+ is an essential co-factor dealing with more than 300 cellular enzymatic processes
Clinical features
the human body contains about 24 g of magnesium ions, with half of it being incorporated
into bones and the other half being present in muscles and soft tissue
• The majority of Mg2+ is absorbed in the ilium and colon, and the kidneys are the major
excretory organ
• Mg2+ is filtered at the glomerulus
10. 10
• The kidneys regulate the magnesium ion levels in plasma.
• Magnesium ion imbalances can manifest in a variety of conditions such
as hypo- and hypermagnesaemia.
• Hypermagnesia
as a result high levels of Mg2+ are retained when the patient has renal
failure
hypermagnesia can cause muscle weakness and arrhythmia, but it is a
rare condition
• Hypomagnesia
defined as low magnesium levels in the blood plasma,
can be the result of losses in the GI tract, for example, excessive
diarrhea , alcoholism
Hypomagnesia is often followed by hypocalcaemia (low calcium ion
plasma levels) as well as hypokalaemia and hyponatraemia
11. 11
Oral supplementation and preparations
• Magnesium ion preparations are also used
antacids mostly in combination with aluminium-based salts aluminium hydroxide
[Al(OH)3] Magnesium hydroxide [Mg(OH)2] Magnesium trisilicate (Mg2Si3O8)
magnesium salts are involved in the treatment of arrhythmia
treatment of eclampsia (threatening hypertensive disorder in pregnant women)`
Laxative(stimulates intestinal movement, as the magnesium ions increases the water
content in the intestines through its osmotic effect and as a result softens any faeces
present.
threatening hypertensive disorder in pregnant women.
• Symptomatic hypomagnesaemia is associated with plasma serum Mg2+ levels of < 0.5-
1 mmol/ kg for a period of 5 days or more
• Mg2+ ions are initially given as intravenous (i.v.) or intramuscular (i.m) injection; the
latter is fairly painful and consisting of magnesium sulfate (MgSO4)
• MgSO4 can also be used as emergency treatment for very serious arrhythmias, a
disorder of the heart rate (pulse). In an emergency treatment, it is usually given
intravenously as one single dose or with one repeat
• orally taken magnesium salts can show interactions with other drugs taken
simultaneously.
Magnesium trisilicate reduces the absorption of iron products, certain antibiotics (such
as Nitrofurantoin) or antimalarial drugs (such as Proguanil)
12. 12
Calcium
Calcium (Ca) Calcium has the symbol Ca and atomic number 20 and is a soft grey
alkaline earth metal
Ca is the most abundant inorganic element in the human body
• Ca2+ has numerous intra and extracellular physiological roles
• Calcium carbonate CaCO3 can be found in clinical applications such as antacids
• Ca2+ play important roles in the human body
Biological importance
Calcium ions play important roles in the human body in a variety of neurological
and endocrinological processes
• Ca is known as a cellular messenger
• It has a large intra- versus extracellular gradient (1 : 10 000), which is highly
regulated by hormones
• This gradient is necessary to maintain the cellular responsiveness to diverse
extracellular stimuli
• Ca2+ are also involved in the formation of bones and teeth, which act also as a
reservoir for Ca2+
Magnesium salt preparations, which form part of antacids, are not recommended to be
taken at the same time as a variety of drugs such as ACE inhibitors, aspirin and
penicillamine.
13. 13
A normal adult body contains ~1000 g of Ca
•Most of which is stored in bones and teeth
•The remaining can be found in the extracellular space
•The intra and extracellular Ca2+ concentration is rigorously controlled
• Modified hydroxylapatite, also frequently called hydroxyapatite and better known
as bone mineral, makes up ~50% of our bones
• Hydroxylapatite is a natural form of the mineral calcium apatite, whose formula is
Ca10(PO4)6(OH)2
• Modifications of hydroxylapatite can also be found in the teeth A chemically
identical substance is often used as filler
• It is believed that an optimal dietary calcium intake can prevent chronic diseases In
the Stone Age, the average calcium intake was 2000-3000 mg Ca2+/day per adult
Now-a-days it has decreased to an average of 600 mg/day
• It is believed that there are linkages to various chronic diseases, such as bone
fragility, high blood pressure and colon cancer
Ca2+ is an essential nutrient
Three stages of life identified when the human body needs an increased level of
Ca2+:
• Childhood and adolescence
• Pregnancy and lactation
• Old age
14. 14
Osteoporosis is most commonly associated with Ca deficiency
• 99% of Ca2+ is found in the bones
• Ca uptake and plasma concentrations are closely regulated by hormones PTH
(parathyroid hormone)
• Studies support the hypothesis that Ca supplementation can reduce blood
pressure
• It has been hypothesised that there exists a link between dietary Ca and weight
management in humans
• Renal osteodystrophy, also called renal bone disease, is a bone mineralisation
deficiency seen in patients with chronic or end-stage renal failure
• Vitamin D is activated in the liver to calcidiol and then in the kidney to calcitriol •
In patients with renal failure, the activation to calcitriol is depressed
• Results in a decreased concentration of Ca2+ in the blood plasma, This reduces
the amount of free Ca2+ in the blood even more
• The pituitary gland senses the low levels of plasma Ca2+ and releases PTH
• This leads to a weakening of the bone structure
Around 20-40% of all kidney stones are associated with elevated Ca2+ level in the
urine, The conclusion is that kidney stone formation in healthy individuals is not
associated with Ca supplementation
15. 15
• Ca supplements are usually required only if the dietary Ca2+ intake is insufficient
A slow i.v. injection of a 10% calcium gluconate has been recommended In severe
acute hypocalcaemia,
Clinical application
• A variety of calcium salts are used for clinical application
Ca carbonate, Ca chloride, Ca phosphate , Ca lactate ,Ca aspartate, Ca gluconate
• Ca carbonate is the most common and least expensive calcium supplement
• Ca carbonate consists of 40% Ca2+
• Ca citrate is more easily absorbed (bioavailability is 2.5 times higher than Ca
carbonate)
• It is believed that it contributes less to the formation of kidney stones
• The properties of Ca lactate are similar to those of Ca carbonate
• Ca gluconate is prescribed as a Ca supplement
• It is also used in the urgent treatment of hyperkalaemia
• Side effects have been observed only at relatively high doses
•Manifested in GI disturbances such as constipation and bloating and, in extreme
cases, arrhythmia
• It is important to note that calcium ions can interfere with the absorption of
some drugs, such as antibiotics
16. 16
• It has been suggested that low dietary Ca intake would be the best method to
prevent the recurrence of kidney stones
• More recent studies showed that a low Ca diet did not prevent the formation
of kidney stones
• It was actually found that a higher Ca intake resulted in a significant reduction
of the recurrence of kidney stones by around 50%
• It is believed that the restriction of Ca leads to an increase in absorption and
excretion of oxalate in the urine.
