Contraindications with Maalox and Reglan
There are no absolute contraindications to using Maalox (aluminum/magnesium hydroxide) and Reglan (metoclopramide) together, but their concurrent use requires careful attention to timing of administration and monitoring for specific drug interactions and adverse effects.
Key Interaction Concerns
Absorption and Timing Issues
Antacids like Maalox can reduce the bioavailability of metoclopramide by altering gastric pH and forming complexes with medications. While the evidence base primarily demonstrates this interaction with fluoroquinolones and other antibiotics, the same mechanism applies to metoclopramide 1, 2.
To minimize interaction risk, separate administration by at least 2 hours: give metoclopramide first, then Maalox 2 hours later, or give Maalox first and metoclopramide 4 hours later 2.
Cardiovascular Monitoring Requirements
Both medications can prolong the QT interval, creating additive cardiac risk. The American Heart Association recommends evaluating patients for baseline conduction abnormalities before starting metoclopramide 3.
Monitor ECG in patients with known cardiovascular disease, family history of QT prolongation, or those taking other QT-prolonging medications 3.
Renal Function Considerations
In patients with creatinine clearance below 40 mL/min, start metoclopramide at half the standard dose due to primarily renal excretion 3.
Maalox contains magnesium and aluminum, both of which accumulate in renal insufficiency. Serum magnesium and aluminum levels shift higher with therapeutic Maalox dosing, though typically remain within physiological limits in patients with normal renal function 4.
Avoid or use extreme caution in dialysis patients, as magnesium hydroxide can cause symptomatic hypermagnesemia and intolerable gastrointestinal side effects 5.
Specific Clinical Scenarios Requiring Caution
Diabetes Management
Metoclopramide accelerates gastric emptying, which can precipitate hypoglycemia in diabetic patients taking insulin or sulfonylureas 3.
The Endocrine Society recommends monitoring blood glucose closely and adjusting antidiabetic medication doses when starting metoclopramide 3.
Medication Absorption Effects
Metoclopramide may delay absorption of oral contraceptives due to its effects on gastric motility 3.
Maalox delays time to peak plasma concentration for many orally administered drugs (demonstrated with paracetamol, though peak levels remain unchanged) 6.
Common Pitfalls to Avoid
Do not administer simultaneously: This maximizes the risk of reduced metoclopramide absorption and efficacy.
Do not ignore gastrointestinal tolerability: Maalox frequently causes diarrhea (from magnesium) or constipation (from aluminum), which can be intolerable when combined with metoclopramide's prokinetic effects 4, 5.
Do not overlook electrolyte monitoring in chronic use: Both magnesium and aluminum can accumulate, and phosphate elimination decreases with Maalox use 4.
Do not combine with other serotonergic agents without extreme caution, as metoclopramide has dopamine antagonist properties that can interact with serotonergic medications 7.
Practical Administration Algorithm
Assess renal function: If CrCl <40 mL/min, reduce metoclopramide dose by 50% 3.
Check baseline ECG in patients with cardiac risk factors 3.
Separate administration timing: Give metoclopramide at least 2 hours before Maalox, or Maalox at least 4 hours before metoclopramide 2.
Monitor for hypoglycemia in diabetic patients and adjust insulin/sulfonylurea doses as needed 3.
Assess gastrointestinal tolerability within the first week, as the combination may cause unpredictable bowel effects 4, 5.