Magnesium hydroxide Famotidine

A 41-year-old woman, with liver lacerations, rib fractures, and pneumothorax after a motor vehicle accident, was given haloperidol for agitation on day 7. During the first 24 hours she received a cumulative intravenous dose of 15 mg, 70 mg on day 2, 190 mg on day 3,160 mg on days 4 and 5, and 320 mg on day 6. An hour after the first dose of 80 mg on day 7, she had ventricular extra beats followed by 5-beat and 22-beat runs of ventricular tachycardia. The rhythm strips were consistent with polymorphous ventricular tachycardia or torsade de pointes and the QTC interval was 610 ms (normally under 450 in women). She received intravenous magnesium sulfate 2 g. Concurrent medications included enoxaparin, famotidine, magnesium hydroxide, ampicillin/sulbactam, nystatin suspension, midazolam, and 0.45% saline with 20 mmol/1 of potassium chloride. She had no further dysrhythmias after haloperidol was withdrawn. Eight days after the episode of torsade de pointes she had a QTC interval of 426 ms. 

Tablets, chewable 10 mg famotidine, 800 mg calcium carbonate, 165 mg magnesium hydroxide (ofc)...

The manufacturer notes that neither aluminium/magnesium hydroxide antacids nor famotidine had any effect on the absorption of efavirenz. No efavirenz dosage adjustment is expected to be necessary with these drugs. Other drugs that reduce gastric acidity are not expected to affect efavirenz absorption. ... 

Mylanta 11 (aluminium/magnesium hydroxide mixture) 30 mL reduced the AUC and peak serum levels of famotidine by about a third when taken simultaneously, but no significant interaction occurred when the antacid was taken 2 hours after famotidine.Another study found that the peak serum levels of famotidine were reduced by about 25% by Mylanta II in 17 healthy subjects. ... 

---