The short answer
Zinc sulfate can reduce oral cephalexin absorption. In the direct human study, taking cephalexin first and zinc three hours later avoided a significant change. Taking zinc three hours before cephalexin still reduced exposure, so a generic instruction to separate them by three hours is incomplete.
What this answer covers
Oral cephalexin capsules with immediate-release zinc sulfate. The trial used 56 mg elemental zinc; other salts, lower doses and repeated regimens are not equally studied.
- Supplement or preparation
- Zinc
- Medication ingredient
- cephalexin
What did the study measure?
Twelve healthy men received cephalexin 500 mg alone and with zinc sulfate 250 mg, equivalent to 56 mg elemental zinc. Taking both together lowered peak antibiotic concentration about 31% and overall exposure about 27%. The study also calculated time above a target concentration, but it did not measure infection cure or prove a specific probability of treatment failure.
Which product needs to come first?
In this experiment, cephalexin three hours before zinc did not significantly change antibiotic pharmacokinetics. Zinc three hours before cephalexin still lowered overall exposure about 18%. The authors therefore recommended antibiotic first, zinc later. Ask the pharmacist to fit this direction into your full prescription, especially when cephalexin has several daily doses.
Does this cover every zinc supplement?
Only one immediate-release zinc sulfate product and one elemental dose were tested. Zinc gluconate, citrate, lozenges and lower-dose multivitamins cannot automatically be assigned the same percentage effect. The investigators explicitly noted that other doses and schedules were untested. Keep the elemental amount, salt and frequency available when discussing the product.
What does the label add?
Current cephalexin capsule labeling confirms the oral formulation and the need to follow the prescribed schedule, including kidney-related adjustments, but it does not supply a zinc interval. The direction-specific advice comes from the original clinical study. It should not be replaced by mineral instructions for cefdinir or another cephalosporin merely because the drugs share a family.
Evidence and practical considerations
Absorption & effectiveness
Zinc sulfate can reduce oral cephalexin absorption. In the direct human study, taking cephalexin first and zinc three hours later avoided a significant change. Taking zinc three hours before cephalexin still reduced exposure, so a generic instruction to separate them by three hours is incomplete.
- Exact scope
- oral immediate-release zinc sulfate, with other zinc formulations requiring individual applicability with oral cephalexin capsules, with monohydrate strengths expressed as cephalexin
- Medication form and route
- oral
- Timing or duration
- Single-dose four-way crossover with seven-day washouts. No validated repeated-dose or other-interval schedule from this experiment.
What remains uncertain
- Twelve healthy men, one relatively high zinc dose, one preparation and no infection outcome. Direction-specific result cannot be treated as a symmetric three-hour rule.
Factors that may matter: exact formulation and dose; order and interval of doses; single versus repeated administration; patient population and product ingredients.
Read the supporting source summaries
Source 1: regulatory product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed oral cephalexin capsules.
Allows dosing without regard to meals, requires patient-specific prescription/renal dosing, and warns about antibiotic-associated diarrhea. Does not supply a zinc-specific or Lactobacillus-specific interval.
How this applies: Exact parent RxCUI 2231 with documented monohydrate-to-cephalexin equivalence. Does not establish interchangeability with cefdinir or another cephalosporin. Article-specific counterparty: oral immediate-release zinc sulfate, with other zinc formulations requiring individual applicability.
Absence of a supplement interaction from this label does not establish absence of risk; no probiotic benefit or universal dose interval provided.
Source 2: original human pharmacokinetic study
pmc.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 12 healthy adult men in randomized single-dose four-way crossover, seven-day washouts.
Concurrent zinc lowered cephalexin peak by 31.05% and AUC by 27.40%; zinc three hours before still lowered peak 11.48% and AUC18.12%. Zinc three hours after cephalexin did not significantly change pharmacokinetics.
How this applies: Direct exact cephalexin capsule/zinc sulfate study. The order is essential: antibiotic first, zinc three hours later. The reciprocal three-hour direction was not equally effective. Article-specific counterparty: oral immediate-release zinc sulfate, with other zinc formulations requiring individual applicability.
One high-dose zinc sulfate preparation, healthy men, single doses, no infection cure outcomes. Only two staggered schedules tested; significance testing does not prove all-salt or repeated-dose equivalence.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Exact-drug labels, original clinical research and formulation limits checked; complete private article and current-claim adjudications prepared. | |
| Research summary published |
Article revision: 3fb4aa01dbe622bb
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.
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.