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Diethylcarbamazine (Filaribits®)

By: Dr. Dawn Ruben

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Please note: Diethylcarbamazine was recently taken off the market by the manufacturer. If your pet has been receiving this drug and you have any questions, please contact your veterinarian.

  • There are a number of excellent drugs available to prevent the development of the canine heartworm, Dirofilaria immitis. The oldest of this still in use is diethylcarbamazine or DEC.
  • Diethylcarbamazine belongs to a class of drugs known as parasite control agents. It is thought that diethylcarbamazine affects the nervous system of the parasite, resulting in paralysis and death of the parasite.
  • DEC differs from other heartworm preventatives in terms of administration and timing of treatment. The drug must be given daily and if more than two days are missed the risk of heartworm infection is significant. In addition, the drug works in a 'contemporary' manner, meaning that it only works for one to two days following administration. For that reason, the drug must be given for 30 to 60 days after the last potential bite from a mosquito harboring heartworm larvae.
  • Diethylcarbamazine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

    Brand Names and Other Names

  • This drug is registered for use in humans and animals.
  • Human formulations: Hetrazan® (Lederle)
  • Veterinary formulations: Filaribits® (SmithKline Beecham), Filaribits Plus® (Pfizer)

    Uses of Diethylcarbamazine

  • Diethylcarbamazine is primarily used to prevent heartworm infections.
  • It also can be used to treat roundworm infections, but is infrequently employed for that purpose.

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, diethylcarbamazine can cause side effects in some animals.
  • Diethylcarbamazine should not be used in animals with known hypersensitivity or allergy to the drug.
  • Diethylcarbamazine should not be used in animals with heartworm infections. A negative heartworm test is crucial prior to beginning administration of diethylcarbamazine.
  • Diethylcarbamazine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with diethylcarbamazine.
  • Side effects are unlikely but vomiting and diarrhea has been reported.
  • Severe adverse effects such as drooling, vomiting, stumbling, lethargy, low blood pressure, rapid heart rate, breathing problems and death can occur if DEC is given to dogs with active heartworm infections and circulating microfilaria (the offspring of adult heartworms).
  • Overdoses rarely result in toxicity. Vomiting or diarrhea may occur.
  • DEC plus oxibendazole (Filarabits Plus®) has been associated with liver injury. This is considered a rare side effect.
  • There is a rare potential for DEC to reduce sperm count in breeding dogs.

    How Diethylcarbamazine Is Supplied

  • Diethylcarbamazine is available in 50 mg, 60 mg, 100 mg, 120 mg, 180 mg, 200 mg, 300 mg and 400 mg tablets. Some combination products include oxibendazole as a preventative against gastrointestinal parasites (worms).
  • Diethylcarbamazine is also available in a 60mg/ml syrup.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • A dose of 3 mg per pound once daily is recommended for heartworm prevention.
  • To treat roundworms, a dose of 25 to 50 mg per pound is recommended.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.

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