Magnesium plasma concentrations

Magnesium. In the adult human, 50—70% of the magnesium is in the bones associated with calcium and phosphoms. The rest is widely distributed in the soft tissues and body duids. Most of the nonbone Mg ", like K", is located in the intracellular duid where it is the most abundant divalent cation. Magnesium ion is efftcientiy retained by the kidney when the plasma concentration of Mg fads in this respect it resembles Na". The functions of Na", K", Mg ", and Ca " are interrelated so that a deficiencv of Mg " affects the metaboHsm of the other three ions (26). Foods rich in magnesium are listed in Table 9. 

Pharmacokinetics IM injection results in therapeutic plasma levels within 60 minutes and persists for 3 to 4 hours. IV doses provide immediate effects that last for 30 minutes. Effective anticonvulsant serum levels range from 2.5 to 7.5 mEq/L. Magnesium is excreted by the kidneys at a rate proportional to the plasma concentration and glomerular filtration. 

Magnesium sulfate, applied intravenously is often used as tocolytic. The mechanism of action is not completely clear but might involve a competition with calcium on the cellular level. Precautions in the sense of magnesium plasma level monitoring must be taken in patients with renal insufficiency since this divalent kation is eliminated by the kidneys. Relatively high plasma concentrations are necessary to achieve a sufficient tocolysis. The relatively frequent side effects are respiratory depression, depressed reflexes, headaches, palpitation and skin flushing in the mother and muscle relaxation and, rarely, CNS depression in the fetus. 

Drugs that have been associated with elevations in quinidine concentrations include acetazolamide, the antacids magnesium hydroxide and calcium carbonate, and the H2-receptor antagonist cimetidine. Cimetidine inhibits the hepatic metabolism of quinidine. Phenytoin, rifampin, and barbiturates increase the hepatic metabolism of quinidine and reduce its plasma concentrations. 

Q13 Magnesium is a major intracellular cation which acts as a co-factor in many intracellular enzyme reactions. Plasma concentration is normally 2 mg dl-1. This ion is abundant in the diet, and hypomagnesaemia is relatively uncommon, unless there is malabsorption or excessive loss via the kidney. However, when present, hypomagnesaemia can lead to hypoparathyroidism. Adjustment to the levels of magnesium can shift the function of the parathyroid glands back to normal. Chronic alcoholism, malnutrition, malabsorption, renal tubular dysfunction and excessive use of diuretics, such as loop and thiazide diuretics, may lead to hypomagnesaemia. Symptoms of magnesium deficiency include depression, confusion, muscle weakness and sometimes convulsions. 

A patient was found unconscious with plasma concentrations of bromazepam 277 pg/ml and methadone 3500 pg/ml, both of which were above the toxic threshold. The QTC interval was 688 ms. After initial improvement, torsade de pointes occurred and the patient was treated with DC shock 200 J, isoprenaline, magnesium, and potassium. The QTC interval improved to 440 ms after 3 days. 

The second patient was admitted to the hospital in a comatose state. Sinus bradycardia was present with a QTC interval of 736 ms. The plasma concentration of methadone was 1740 pg/ml. Ventricular bigeminy was followed by torsade de pointes. The patient was treated with DC shock 200 J, lidocaine, and magnesium. By the fifth day after the episode, the QTC interval had improved to 502 ms. 

ACE INHIBITORS TETRACYCLINES 1 plasma concentrations and efficacy of tetracyclines with quinapril. The absorption of tetracyclines may be reduced when taken concurrently with quinapril, due to the presence of magnesium carbonate as an excipient in quinapril s pharmaceutical formulation Magnesium carbonate (found in a formulation of quinapril) chelates with tetracyclines in the gut to form a less soluble substance that 1 absorption of tetracycline For short-term antibiotic use, consider stopping quinapril for duration of the course. For longterm use, consider an alternative ACE inhibitor... 

VITAMIN D MAGNESIUM t plasma concentrations of magnesium Due to T absorption Be aware... 

PREDNISONE, CORTISONE ZINC, CALCIUM, CHROMIUM, MAGNESIUM, SELENIUM 1 plasma/body concentrations of these minerals Attributed to t loss and/or 1 absorption Be aware and monitor plasma concentrations of these minerals provide supplements... 

Noormohamed FEI, Youle MS, Tang B, Martin-Munley S, Gazzard BG, Lant AF. Foscarnet-induced changes in plasma concentrations of total and ionized calcium and magnesium in EllV-positive patients. AntivirTher 1996 1 172-179. 

Figure 10.3 Mean plasma concentrations ( [ g cm of naproxen in 14 male volunteers with and without intake of sodium bicarbonate, magnesium oxide or aluminium hydroxide.

With the onset of starvation, aldosterone secretion increases with the results of increased urinary excretion and decreased plasma concentration of potassium. Magnesium, calcium, and phosphate are affected similarly, although the urinary excretion of phosphate gradually declines. The absolute urinary excretion of ammonia and creatinine increases with prolonged starvation but that of urea decreases. 

Enzyme activators are substances, often inorganic ions, that are required for certain enzymes to become active as catalysts. Activators can be determined by their effect on the rates of enzyme-catalyzed reactions. For example, it has been reported that magnesium at concentrations as low as 10 ppb can be determined in blood plasma based on activation by this ion of the enzyme isocitric dehydrogenase. 

Bradley JE, Baumgartner RJ Subsequent mental development of children with lead encephalopathy, as related to type of treatment. J Pediatr 53 311-315,1958 Bruhl HH, Foni J, Lee YH, et al Plasma concentrations of magnesium, lead, lithium, copper, and zinc in mentally retarded persons. American Journal of Mental Deficiency 92 103-111, 1987... 

Sotalol, Procainamide, Disopyramide, Dofetilide, Ibutilide, N oncardioacti ve , drugs (see text) Amiodarone (rare) interval (torsades de pointes) Isoproterenol Magnesium frequent Related to T plasma concentrations, except for quinidine... 

Mg + is eliminated solely by renal excretion and plasma concentration is directly proportional to glomerular filtration rate. Thus, in patients with renal dysfunction caution is advised. Unintentional high levels of serum magnesium may be obtained. 

In a landmark study of the effect of boron on steroid hormone metabolism (Nielsen et al., 1987), postmenopausal women lived in a metabolic ward under controlled conditions for 167 days. For the first 119 days, the participants were fed basal diets, which provided 0.25 mg boron/day. The interventions also included dietary periods of magnesium and aluminum suppl entation. In two additional dietary periods, a subsample of the women was provided with a boron supplanent of 3 mg/ day. The study demonstrated, for the first time, that supplementation of postmenopausal women with a low dose (3 mg/day) of boron increases significantly the plasma concentrations of 17b-estradiol and testosterone. The study showed also that boron suppl entation decreases significantly the urinary excretion of calcium and magnesium. 

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

The application of the Spectroscan DC plasma emission spectrometer confirmed that for the determination of cadmium, chromium, copper, lead, nickel, and zinc in seawater the method was not sufficiently sensitive, as its detection limits just approach the levels found in seawater [731]. High concentrations of calcium and magnesium increased both the background and elemental line emission intensities. 

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