Doxycycline

What is this medication for?

• Tick-borne disease (Ehrlichia, Anaplasma, Rickettsia, Lyme), Mycoplasma, Chlamydophila, Bordetella, Wolbachia adjunct (heartworm)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Always follow oral dosing in cats with food or ≥6 mL water — esophageal stricture from "dry pilling" is a well-documented, serious risk.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• stomach/intestinal (vomiting, diarrhea, loss of appetite) (Most common)
• Esophageal stricture/irritation (Documented risk, especially solid dosage forms)

Worth a phone call to your veterinarian

• ↑ Liver enzymes (ALT, ALP) (Up to 40% of treated dogs)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Fatal cardiac arrhythmia/collapse if given into a vein (Serious — horse-specific)

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Hypersensitivity; do not give into a vein to horses (fatal); do not give into a muscle/under the skin to any species
• has or has had: Significant hepatic dysfunction; young/pregnant animals (bone/teeth effects, though less than other tetracyclines)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Oral antacids/cations (Al, Ca, Mg, Zn, Bi, Fe)
  • Penicillins
  • Phenobarbital
  • Warfarin

Storage and handling

Room temperature, protect from light. Avoid mixing with cation-containing products. Compounded suspensions often unstable — watch for dark-brown color change indicating degradation.

Good to know

• Always follow oral dosing in cats with food or ≥6 mL water — esophageal stricture from "dry pilling" is a well-documented, serious risk.
• Unlike other tetracyclines, can be used in patients with renal insufficiency.
• MDR1 mutation does NOT require dose adjustment per WSU Clinical Pharmacology Lab, unlike many other P-glycoprotein substrates.