The short answer
Calcium carbonate can change raltegravir exposure, but the practical advice differs by regimen. The U.S. instructions allow calcium carbonate antacid with Isentress 400 mg twice daily without separation. With Isentress HD 1,200 mg once daily, calcium carbonate antacid is not recommended.
What this answer covers
Adult oral raltegravir tablets with calcium carbonate antacid. Direct studies used an antacid amount of 3,000 mg calcium carbonate; supplement doses, combination products and pediatric formulations cannot be assumed to have the same measured effect.
- Supplement or preparation
- Calcium carbonate
- Medication ingredient
- raltegravir
What does calcium carbonate do to raltegravir?
Calcium carbonate supplies calcium ions that can interact with raltegravir in the digestive tract. Label studies recorded lower concentrations, but their clinical interpretation depends on the regimen. A reduction in a laboratory measure does not automatically mean every use of the two products requires avoidance. Current instructions distinguish the twice-daily 400 mg tablet from the once-daily 1,200 mg Isentress HD regimen.
What if I take Isentress 400 mg twice daily?
For this specific adult regimen, the U.S. label does not require a dose adjustment when calcium carbonate antacid is used. NIH guidance explicitly says no separation is necessary. This differs from aluminum/magnesium antacids, which are not recommended with raltegravir. Check that the product really contains calcium carbonate and that it does not also contain another antacid ingredient with a different instruction.
What if I take Isentress HD once daily?
Calcium carbonate antacid is not recommended with the 1,200 mg once-daily regimen. In a study, simultaneous use reduced overall raltegravir exposure to about 28% of reference. A twelve-hour gap improved total exposure but left the 24-hour concentration at about 43% of reference. Those results do not establish that taking the antacid later in the day solves the interaction with Isentress HD.
How should I review an antacid or calcium supplement?
Show your HIV pharmacist the exact tablet strength and calcium product. The direct study used an antacid amount, not every dose taken for bone health. Nutritional supplements and mixed-mineral products may need separate guidance. Do not change the raltegravir dose or switch formulations to accommodate calcium. If the combination is not recommended for your regimen, the pharmacist can help identify an appropriate alternative.
Evidence and practical considerations
Absorption & effectiveness
Calcium carbonate can change raltegravir exposure, but the practical advice differs by regimen. The U.S. instructions allow calcium carbonate antacid with Isentress 400 mg twice daily without separation. With Isentress HD 1,200 mg once daily, calcium carbonate antacid is not recommended.
- Exact scope
- Adult oral raltegravir tablets with calcium carbonate antacid. Direct studies used an antacid amount of 3,000 mg calcium carbonate; supplement doses, combination products and pediatric formulations cannot be assumed to have the same measured effect. with Adult oral raltegravir tablets: Isentress 400 mg twice daily versus Isentress HD 1,200 mg once daily
- Medication form and route
- Adult oral raltegravir tablets: Isentress 400 mg twice daily versus Isentress HD 1,200 mg once daily; oral mineral, supplement or antacid within stated preparation scope
- Timing or duration
- Short pharmacokinetic studies of calcium carbonate coadministration and twelve-hour separation; clinical virologic outcomes were not measured.
What remains uncertain
- Different adult tablet regimens yield different management recommendations. Reduced exposure does not directly quantify clinical failure, and antacid findings do not establish instructions for every nutritional dose.
Factors that may matter: Exact mineral ingredients, preparation and elemental amount; Isentress 400 mg twice daily versus Isentress HD 1,200 mg once daily; Food and direction of administration when applicable; Concurrent mineral products, adherence and viral-load monitoring.
Read the supporting source summaries
Source 1: current manufacturer U.S. regulatory prescribing information
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People using oral raltegravir; adult 400 mg twice-daily Isentress and 1,200 mg once-daily Isentress HD regimens are distinguished.
Aluminum/magnesium antacids are not recommended even with staggered dosing. Calcium carbonate antacid requires no adjustment with 400 mg twice daily but is not recommended with 1,200 mg once daily. With the once-daily regimen, a 12-hour gap still left markedly reduced trough levels.
How this applies: Explicit salt-to-active-moiety bridge for exact RxNorm raltegravir. Each article preserves the 400 mg twice-daily versus 1,200 mg once-daily distinction and does not extend these tablet data to pediatric chewable tablets or suspension. Exact article scope: Adult oral raltegravir tablets with calcium carbonate antacid. Direct studies used an antacid amount of 3,000 mg calcium carbonate; supplement doses, combination products and pediatric formulations cannot be assumed to have the same measured effect.
The adult tablet regimens are not interchangeable. These exact antacid studies do not establish effects of all dietary mineral salts, zinc, iron or vitamin-only products. Healthy and HIV-positive study conditions differ; reductions in drug concentrations do not directly quantify treatment failures.
Source 2: U.S. expert clinical treatment guideline
clinicalinfo.hiv.gov · Source check Sep 10, 2026
Population: Adults and adolescents receiving integrase inhibitor regimens for HIV.
Bictegravir mineral directions depend on cation and food. If raltegravir must be used with polyvalent mineral supplements, give it at least 2 hours before or 6 hours after and monitor virologic response. Multivitamin chelation magnitude is uncertain. Raltegravir antacid rules are separate: avoid Al/Mg, and distinguish calcium carbonate 400 mg twice daily from 1,200 mg once daily. Do not coadminister bictegravir with St. John’s wort.
How this applies: Exact-drug management guidance. Bictegravir sodium and raltegravir potassium are interpreted through their labels’ active-moiety equivalents. Calcium/iron food exceptions for bictegravir do not transfer to raltegravir. Exact article scope: Adult oral raltegravir tablets with calcium carbonate antacid. Direct studies used an antacid amount of 3,000 mg calcium carbonate; supplement doses, combination products and pediatric formulations cannot be assumed to have the same measured effect.
Expert recommendations include predicted interactions where exact-pair clinical studies are absent. A suggested supplement schedule does not supersede the distinct antacid avoidance instructions. No universal safe dose or virologic risk percentage is established.
Source 3: peer-reviewed prospective human pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 20 adults with HIV already receiving raltegravir in a fixed-sequence pharmacokinetic study; 19 evaluable for several comparisons.
Simultaneous calcium carbonate reduced exposure to 28% and 24-hour concentration to 52% of reference. Twelve-hour-separated calcium carbonate preserved overall exposure but reduced 24-hour concentration to 43%; separated Al/Mg reduced that concentration to 42%.
How this applies: Exact raltegravir with specified antacids under adult once-daily conditions. Combined Al/Mg cannot distinguish the individual ion’s contribution. Exact article scope: Adult oral raltegravir tablets with calcium carbonate antacid. Direct studies used an antacid amount of 3,000 mg calcium carbonate; supplement doses, combination products and pediatric formulations cannot be assumed to have the same measured effect.
Original abstract was read; full journal text was not retrieved. Drug concentration endpoints, not virologic failure rates. This 1,200 mg once-daily result cannot be directly assigned to the 400 mg twice-daily formulation or to every nutritional mineral product.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Current exact-drug labeling and guidance checked; original human studies and neutral findings assessed. Current statements adjudicated with formulation, food and directional timing corrections. Article written; clinical sign-off not recorded. | |
| Research summary published |
Article revision: 0c9b442d2f2e92c8
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.