Pharmacokinetic Profile of Oral Magnesium Hydroxide.

Despite the presumption of a beneficial effect of magnesium (Mg) supplementation on various diseases, little is known concerning the pharmacokinetics of Mg hydroxide. This study was designed to provide a pharmacokinetic profile of Mg hydroxide after a single oral dose. Ten healthy male adults participated in this cross-over study with three 24-hr study days. Interventions were (i) none (baseline), (ii) oral intake of three (3 × 360 mg) tablets of Mg hydroxide (Mablet® ) and (iii) IV bolus infusion of 2 g Mg sulphate (index drug). Blood samples were collected before the single dose, after (i.e. after treatment administration) 15, 30, 60, 90 and 120 min. and after 3, 4, 6, 8, 12 and 24 hr. Urine was collected in four 6-hr periods per study day. Blood (N = 10) and urine (N = 6) Mg were analysed by descriptive statistics. Bioavailability was 14.9% (CI: 8.3; 26.8), blood clearance was 5.1 L/hr (CI: 2.1; 17.0), apparent volume of distribution was 60.2 L (CI: 35.6; 102.0), elimination constant was 0.08 per hour (CI: 0.05; 0.14), half-life was 8.3 hr (CI: 4.8; 14.1), Cmax was 0.11 mmol/L (CI: 0.07; 0.14), and AUC[0-24] was 92.3 mmol/L × min. (CI: 45.5; 139.1). Urine Mg excretion augmented by 17.7% (CI: 8.9; 35.0) from baseline. No severe side effects were observed. The bioavailability of Mg hydroxide was 15%, and it constitutes a clinically relevant option for oral Mg supplementation. No severe side effects were seen.

Effect of routine doses of antacid on renal acidification.

Ten healthy volunteers took a magnesium and aluminium hydroxide antacid for 4 days, and their urinary acid excretion was measured. During antacid ingestion, blood bicarbonate levels did not change significantly, but there were highly significant rises in urine pH and bicarbonate excretion and falls in the 24 h excretion of titratable acid, ammonium, and net acid; the average change in net acid excretion was 41 +/- 4 mmol (72 +/- 9%) per 24 h. This large reduction in net acid excretion appears to result from neutralisation of more hydrochloric acid than sodium bicarbonate in the gastrointestinal tract rather than from absorption of exogenous alkali. Although metabolic alkalosis does not occur with their use in normal individuals, these antacids should not be termed "non-systemic". They might cause important changes in renal drug handling, solubility of excreted substances, or acid-base status in patients at risk.