Magnesium antacids

ANTACIDS. When antacids are given, the nurse keeps a record of the patient s bowel movements because these drug may cause constipation or diarrhea. If the patient experiences diarrhea, the nurse keeps an accurate record of fluid intake and output along with a description of the diarrhea stool. Changing to a different antacid usually alleviates the problem. Diarrhea may be controlled by combining a magnesium antacid with an antacid containing aluminum or calcium. 

Drug therapy, if necessary, may be initiated with aluminum, calcium, or magnesium antacids sucralfate or cimetidine or ranitidine. Lansoprazole, omeprazole, and metoclopramide are also options if the patient does not respond to histamine-2 receptor blockers. 

In terms of pharmacokinetics, LVX has an excellent profile. With an oral dose of 500 mg, LVX has a bioavailability of >99%, an AUC range of 41.9-47.7 mgh/mL, Cmax of 4.5-6.2 mg/mL, a clearance of 10.5-11.9 L/h, and a volume of distribution (Vd) of 1.3 L/kg (Hurst et al., 2002). In terms of protein bound material, only 24-38% is affected (Fish, 2003). Like other fluoroquinolones, there is a 19-44% AUC reduction when co-administered with an aluminum or magnesium antacid or iron sulfate (Qaqish and Polk, 2003). The major metabolite of levofloxacin arises from glucuronidation (Brysk-ier, 2005). 

Azithromycin is rapidly absorbed and well tolerated orally. It should be administered 1 hour before or 2 hours after meals. Aluminum and magnesium antacids do not alter bioavailability but delay absorption and reduce peak serum concentrations. Because it has a 15-member (not 14-member) lactone ring, azithromycin does not inactivate cytochrome P450 enzymes and therefore is free of the drug interactions that occur with erythromycin and clarithromycin. 

Chronic (usually with administration of magnesium) Antacid Cathartic Enema Infusion Dialysis Acute... 

Aluminium and magnesium antacid salts are included in reflux-suppressant formulations because they help to neutralise stomach contents and any material that is refluxed through the LOS. Gastric alkalinisation is also thought... 

Phosphate-binding drugs Sucralfate Calcium carbonate Aluminum/magnesium antacids Sevelamer... 

Potency Aluminum antacids are the most potent, because they carry three negatively charged groups. Magnesium antacids are next in line, because they cany two groups, followed... 

Onset and duration of action Sodium bicarbonate acts very quickly, but its effects are short-lived. Aluminum antacids are the slowest in onset, but have a long duration. Calcium and magnesium antacids are intermediate, with magnesium antacids being somewhat longer in duration and slower in onset than calcium antacids. 

Although information is limited, no particular precautions would seem to be needed if aluminium or aluminium/magnesium antacids are given with any of these antacids. Note that antacids have been frequently given with NSAIDs to reduce their gastric irritant effects. Consider also coxibs , (p.l39), diclofenac , (p.l40), diflunisal ,(p.l40), ibuprofenand related drugs , (p.l40), indometacin , (p.l41), fenamates , (p.l40), and oxi-cams , (below) for information about the interaction of other NSAIDs with antacids. 

The serum levels of many of the quinolone antibacterials can be reduced by aluminium and magnesium antacids. Calcium compounds interact to a lesser extent, and bismuth compounds onfy minimal. Separating administration by 2 to 6 hours where significant interactions occur reduces admixture in the gut and can minimise the effects. 

Table 10.3 , (p.329) shows that the aluminium/magnesium antacids can greatly reduce the bioavailabilities of the quinolones. Separating their administration to reduce the admixture of the two drugs in the gut minimises the interaction, a very broad rule-of-thumb being that the quinolones should be taken at least 2 hours before and not less than 4 to 6 hours after the antacid.The only obvious exception is fleroxacin, which appears to interact minimally. 

Information about the interactions with calcium carbonate is more limited than with the aluminium/magnesium antacids, but Table 10.3 , (p.329) shows that the bioavailabilities of ciprofloxacin and norfloxacin, and to a lesser extent gemifloxacin, can be reduced. These reductions are less than those seen with the aluminium/magnesium antacids, but using ciprofloxacin as a guide a very broad rule-of-thumb would be to separate the drug administration by about 2 hours to minimise this interaction. This is clearly not necessary with levofloxacin, lomefloxacin, moxifloxacin or ofloxacin, nor probably with some of the other qui-... 

Nix DE, Watson WA, Lener ME, Erost RW, Krol G, Goldstein H, Lettieri J, Schentag JJ. Effects of aluminum and magnesium antacids and ranitidine on the absorption of... 

Antacids roughly halve the AUC of delavirdine, and the 112-receptor antagonists or proton pump inhibitors would be expected to interact similarly. Aluminium/magnesium antacids do not interact to a clinically relevant extent with efavirenz or nevirapine, and famotidine does not alter the absorption of efavirenz. 

Food, dairy products and calcium compounds markedly reduce the absorption of strontium ranelate, and administration should be separated by at least 2 hours. Aluminium and magnesium antacids only slightly reduce strontium ranelate absorption. Strontium ranelate is predicted to reduce the absorption of the quinolones and the tetracyclines, and strontium should be stopped during courses of these antibacterials. Vitamin D does not affect strontium ranelate bioavailability. 

Trientine can possibly chelate with iron thereby reducing its absorption. On theoretical grounds a similar chelation interaction may occur with calcium and magnesium antacids and mineral supplements. 

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