Does Magnesium Decrease Gabapentin Absorption?
Yes, magnesium-containing antacids significantly reduce gabapentin absorption by approximately 20-43%, and this interaction is clinically important. 1, 2
Mechanism and Magnitude of Interaction
Antacids containing magnesium and aluminum hydroxides (such as Maalox®) reduce gabapentin bioavailability by approximately 20% when taken simultaneously. 1
When magnesium oxide (1 gram) is co-administered with gabapentin, the reduction is even more substantial: plasma concentrations (Cmax) decrease by 33%, AUC decreases by 43%, and oral bioavailability drops by 32%. 2
This interaction occurs through reduced intestinal absorption extent and rate, and is independent of gastric pH changes. The mechanism does not involve suppression of gastrointestinal acidification, as demonstrated by the lack of interaction with omeprazole (a proton pump inhibitor). 2
Clinical Management Strategy
To minimize this interaction, separate gabapentin administration from magnesium-containing products by at least 2 hours. 1
When gabapentin is administered 2 hours after antacid use, the reduction in bioavailability decreases to approximately 10%, which is less clinically significant. 1
This timing strategy is critical because gabapentin already has nonlinear, saturable absorption pharmacokinetics, making any further reduction in absorption potentially compromise therapeutic efficacy. 3, 4
Common Pitfalls to Avoid
Do not assume all acid-suppressing medications interact with gabapentin. Omeprazole (a proton pump inhibitor) does not affect gabapentin absorption, confirming the interaction is specific to magnesium-containing compounds rather than pH-mediated. 2
Do not overlook over-the-counter magnesium supplements or combination products. Many patients take magnesium supplements for various reasons (constipation, muscle cramps, general health) without considering drug interactions. 2
Remember that gabapentin requires therapeutic doses of 1800-3600 mg/day for neuropathic pain conditions, and any reduction in absorption can prevent patients from reaching effective plasma concentrations. 4
Practical Dosing Considerations
Given gabapentin's already complex dosing requirements (three-times-daily administration due to saturable absorption), adding a 2-hour separation from magnesium products creates additional complexity. 4
For patients requiring both gabapentin and magnesium-containing products, consider: administering gabapentin at standard meal times (breakfast, lunch, dinner) and scheduling magnesium products at bedtime or mid-morning/mid-afternoon to maintain the 2-hour separation. 4, 1
Alternative antacids without magnesium (such as calcium carbonate alone) may be considered if acid suppression is needed, though specific interaction data for these alternatives are limited. 1