www.klinickafarmakologie.cz / Klin Farmakol Farm. 2024;38(3):100-106 / KLINICKÁ FARMAKOLOGIE A FARMACIE 101 HLAVNÍ TÉMA Importance and safety of magnesium supplementation in pregnancy. To supplement or not? the years 2017 and 2018 found that US women had approximately 22% less dietary intake of magnesium than is the Recommended Dietary Allowance in relation to magnesium intake in pregnancy (10). The concentration of magnesium present in the umbilical cord blood is higher than maternal magnesium levels, the placenta is involved in the active transport of magnesium, and according to Jouanne et al. (2021), 50% of the dietary magnesium is absorbed (4). Recommended daily dietary allowance for pregnant women Magnesium is an important cation (11). Magnesium is also available as a supplement (12), while having significant importance as an electrolyte (13, 14) and also being an essential biogenic element (15). The recommended dietary allowance in pregnancy is 350 to 400 mg/day (2). It has been estimated that approximately 10% higher supply of magnesium is needed during pregnancy compared to non-pregnant women (2). Pregnant women can find magnesium-rich food in certain vegetables, fruits, (16) and in dairy or some fish products (17). Low levels of magnesium have been linked to various negative health consequences in the general population (18). Magnesium formulations, types of salts, and their absorption Magnesium can be present in different pharmaceutical dosage forms (19). There are different organic and inorganic forms of magnesium and their properties (15). Table 1 shows magnesium forms (20), their bioavailability, and absorption. Bioavailability is influenced by solubility. Convenient solubility at the point of absorption is crucial for good bioavailability (21). Magnesium as an electrolyte, mechanism and cellular physiology Electrolyte and fluid balance are of significant importance in preserving homeostasis (23). Electrolytes are necessary for keeping electrical neutrality in the cells (24). Magnesium is part of neurotransmitter activity and provides muscle and neurological functioning (24). Mg2+ is a versatile ion present in the main metabolic and biochemical pathways of the cell (25). Magnesium maintains normal cellular and organ functions (8). Magnesium pharmacokinetics in pregnancy Magnesium is primarily absorbed in the small intestine (14) and preserved as a bone mineral (5). Absorption can be decreased by nausea and vomiting (26, 27). During pregnancy, gastric pH is increased (26), intestinal motility is lowered, and blood flow in the intestinal area is increased (26). In terms of magnesium distribution, one-third of serum magnesium is bound to albumin in the general population (28), and it can be influenced by other distribution factors (29). Magnesium distribution is available and described in the case of parenterally administered magnesium sulphate in pregnancy (30). However, sufficient information about magnesium pharmacokinetics after oral administration has been available mainly in healthy male adults (31). Magnesium metabolism and balance are dependent on intestinal absorption, bone turnover, and renal excretion (5, 32); intestinal absorption is not dose-dependent, but it is dependent on magnesium status (5). Serum magnesium concentration is affected by renal magnesium reabsorption (32). Pregnancy leads to changes in the hepatic enzyme activities (33). Maternal endocrinological and nutritional status influence changes in bone mineral content (34). For magnesium elimination, the kidneys are the principal organ that influences magnesium homeostasis (35). Progesterone can produce an increase in renal plasma flow and glomerular filtration rate (36). In pregnancy, there is increased renal output of magnesium (37). Magnesium pharmacodynamics Magnesium plays a role in hundreds of reactions within the metabolism, as well as in the excitability of cardiac cells, neural activity, neurotransmitter release, muscle contractions, receptor binding, and others; furthermore, it has a role in bone mineralization, in mitochondrial function, and in ATP (adenosine triphosphate) creation (11, 38, 39). Aetiology of magnesium deficiency in pregnant women Various factors can contribute to the aetiology of magnesium deficiency besides pregnancy itself. For this purpose, Table 2 was created. The table does not summarise all possible aetiologies, and the information was derived from magnesium deficiency in the general population or from sources relevant to pregnancy data. Tab. 1. Overview of organic and inorganic magnesium salts with a focus on their solubility, bioavailability, and other-related information Magnesium salts Type of magnesium salt Absorption and bioavailability of magnesium salts magnesium citrate OS according to a small study, it is among the most bioavailable forms20 it is well soluble21 it is absorbed more completely, more bioavailable22 magnesium oxide IS it has lower solubility in GIT and lower bioavailability21 it is absorbed less completely and less bioavailable22 magnesium chloride IS well absorbed in GIT20 lower solubility in GIT21 absorbed more completely, more bioavailable22 magnesium lactate OS easily absorbed in GIT20 absorbed more completely, more bioavailable22 magnesium malate OS very well absorbed in GIT20 magnesium taurate OS insufficient data magnesium L-threonate OS easily absorbed20 magnesium sulfate IS absorbed less completely, less bioavailable22 magnesium glycinate OS easily absorbed20 good solubility and good bioavailability21 magnesium orotate OS easily absorbed20 good solubility and bioavailability21 dihydrate magnesium orotate showed the highest absorption in an in vitro simulated small intestinal environment and excellent in vitro dissolution parameters21 magnesium carbonate IS lower solubility in GIT and lower bioavailability21 magnesium aspartate OS good solubility and better bioavailability21 Note: Insufficient data: more detailed information that could provide a closer explanation in terms of solubility and bioavailability is not available. IS – inorganic salt, OS – organic salt, GIT – the gastrointestinal tract
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