Dicloxacillin Drug Interactions: What to Avoid and What to Tell Your Doctor

Before starting Dicloxacillin, it's important to tell your doctor and pharmacist about all medications you're taking — including prescription drugs, over-the-counter medicines, vitamins, and supplements. Dicloxacillin has several known interactions that can either reduce the antibiotic's effectiveness or increase the risk of side effects.

Interactions to Avoid (Most Serious)

Tetracycline Antibiotics

Taking Dicloxacillin with tetracycline-class antibiotics — including doxycycline, minocycline, tetracycline, demeclocycline, sarecycline, and omadacycline — can significantly reduce Dicloxacillin's effectiveness. Tetracyclines slow bacterial growth (bacteriostatic), while Dicloxacillin works by killing actively dividing bacteria (bactericidal). If bacteria stop dividing due to tetracycline, Dicloxacillin loses much of its killing power.

What to do: If you are being prescribed both, discuss this with your doctor. Using them together is generally avoided unless specifically directed by a specialist.

Live Bacterial Vaccines (BCG, Cholera)

Dicloxacillin can kill the live bacteria in certain vaccines, potentially rendering them ineffective. Live bacterial vaccines affected include the BCG vaccine (used in some countries for tuberculosis) and the oral cholera vaccine.

What to do: Do not receive live bacterial vaccines while taking Dicloxacillin, and wait until your antibiotic course is complete (typically 14 days after finishing) before receiving these vaccines.

Interactions Requiring Close Monitoring

Warfarin (Blood Thinners)

Dicloxacillin may enhance the effects of warfarin (Coumadin), increasing the risk of bleeding. This happens through multiple mechanisms, including changes in gut flora that affect vitamin K absorption, and potential competition for protein-binding sites.

What to do: If you take warfarin, your INR should be monitored more frequently while on Dicloxacillin. Report any unusual bruising or bleeding to your doctor promptly.

Hormonal Contraceptives (Birth Control Pills, Patches, Rings, Injections)

Dicloxacillin may reduce the effectiveness of hormonal contraceptives by affecting CYP3A4 liver enzymes and altering intestinal flora. While the clinical significance of this interaction is considered low for most antibiotic-contraceptive pairs, it is mentioned in Dicloxacillin prescribing information.

What to do: Use a backup contraceptive method (condoms) during Dicloxacillin treatment and for at least one full cycle afterward. Discuss the specific risk with your provider.

Probenecid (Gout Medication)

Probenecid (used to treat gout and some other conditions) slows the kidney's ability to excrete Dicloxacillin. This increases Dicloxacillin blood levels — which could be beneficial in some contexts (it's sometimes used intentionally to boost antibiotic levels) but can also increase the risk of side effects.

What to do: Let your doctor know if you're taking probenecid so they can adjust the Dicloxacillin dose if needed.

Pacritinib and Other CYP3A4-Metabolized Drugs

Dicloxacillin can induce (speed up) the CYP3A4 liver enzyme, which is responsible for metabolizing many drugs. This means it can reduce blood levels of drugs metabolized by CYP3A4. Pacritinib (a cancer treatment) is specifically flagged in prescribing information as a drug to avoid combining with Dicloxacillin for this reason.

What to do: If you take any cancer therapies, immunosuppressants, or other specialty drugs, have your pharmacist run a comprehensive drug interaction check before starting Dicloxacillin.

Colestipol (Cholesterol Medication)

Colestipol, a bile acid sequestrant used to lower cholesterol, can bind to Dicloxacillin in the gut and reduce its absorption — meaning less of the antibiotic enters your bloodstream.

What to do: Take Dicloxacillin at least 1-2 hours before or 4-6 hours after colestipol to minimize the interaction. Ask your pharmacist for specific timing guidance.

What to Tell Your Doctor Before Taking Dicloxacillin

Make sure your doctor knows about:

All prescription medications you currently take

Any over-the-counter drugs (including NSAIDs like aspirin or ibuprofen)

Vitamins, minerals, and herbal supplements

Any history of penicillin or antibiotic allergy

Any liver or kidney disease

Whether you are pregnant, planning to become pregnant, or breastfeeding

For more on Dicloxacillin safety, see our guides to Dicloxacillin side effects and what Dicloxacillin is used for.