Fosfomycin

What is fosfomycin?

Fosfomycin is an antimicrobial used to treat multi-drug resistant bacterial urinary tract infections (UTIs) in dogs.

It is used off label (extra label) in veterinary medicine and should never be used in cats, as it causes kidney damage in this species. Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet fosfomycin?

Fosfomycin comes in granule and compounded liquid suspension forms. 

• All forms are given orally (by mouth).
• Give this medication with food. 
• Measure liquid medications carefully. Contact your veterinarian if you have trouble measuring or giving the medication.
• Give this medication to your pet for the entire time prescribed by your veterinarian, even if it appears that your pet is feeling better.

This medication should start to take effect within a few hours, though outward effects may not be noticeable.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then wait the recommended time as prescribed by your veterinarian for the next dose. Do not give the pet two doses at once.

Are there any potential side effects from fosfomycin?

Fosfomycin may cause the following side effects:

• diarrhea
• inappetence

The following reactions are rare, but if they occur, contact your veterinarian immediately:

• an allergic reaction such as irregular breathing, rash, fever, puffiness and swelling around the face

Drug sensitivities can develop over time with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This medication is short-acting, meaning that effects will last less than 24 hours, though effects may last longer in pets with kidney or liver disease.

Are there any risk factors for this medication?

Fosfomycin should NOT BE USED in:

• cats, as it is nephrotoxic (toxic to the kidneys) in this species
• animals who are allergic to any component of the medication

Fosfomycin should be USED WITH CAUTION in pets who:

• are pregnant or nursing

Are there any drug interactions I should be aware of?

Certain medications should be USED WITH CAUTION when given with fosfomycin, including: 

• prokinetic gastrointestinal motility agents (e.g., metoclopramide)
• drugs that affect gastrointestinal motility (e.g., cisapride, bethanecol, laxatives)

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will assess a baseline urinalysis before starting this medication and recheck the urinalysis and urine culture after the medication course is complete.
• Your veterinarian will schedule follow-up visits for monitoring. In this case, follow your veterinarian’s directions.
• At home, monitor for any abnormal changes. If these occur, discontinue the medication and contact your veterinarian.

How do I store fosfomycin?

• Store at room temperature of 25°C (77°F), with excursions permitted to 15°C-30°C (59°F-86°F).
• Keep medication out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Adverse effects should be reported to the FDA or Health Canada.