Bromelain
may enhane absorptionof amoxicillin, which is not necessarily a negative effect.

Calcium
may decrease absorption of the drug; avoid taking calcium within one to three hours of taking any of these antibiotics.

Iron
may make the antibiotic less effective; take iron supplements either two hours before or 2 hours after the drug.

Magnesium
may make the antibiotic less effective; take magnesium supplements one to  three hours before or after the drug.

Psyllium
may make the antibiotic less effective; consult your doctor.

Vitamin C
may enhance absorption of tetracycline. which is not necessarily a negative effect.

Zinc
may make the antibiotic less effective; take zinc supplements at least two hours after the drug.