Diethylcarbamazine Citrate
**Diethylcarbamazine citrate (DEC)** is a piperazine-derivative anthelmintic that was historically the hallmark agent for daily heartworm disease prophylaxis in dogs. * **Current Status**: Largely replaced by modern monthly macrocyclic lactones (e.g., ivermectin, milbemycin). It is no longer commercially available in veterinary oral dosage forms in the USA. * **Indications**: FDA-approved for the prophylaxis of heartworm disease (*D. immitis*) and the treatment of ascariasis in dogs. It has also been used in ferrets, zoo animals, and for parasitic bronchitis in cattle and sheep (in the UK). * **Clinical Pearl**: DEC must be administered *daily* for heartworm prevention, unlike newer monthly preventatives, which made owner compliance a historical challenge.
Mechanism: The exact mechanism of DEC is not completely understood, but it exhibits both direct paralytic and host-dependent immunomodulatory effects: * **Direct Paralysis**: DEC acts as an agonist at **nicotinic acetylcholine receptors (nAChRs)** on the nematode somatic muscle โ Depolarization of the muscle membrane โ **Spastic paralysis** of the parasite. * **Immunomodulation**: DEC alters the parasite's surface membrane (interfering with arachidonic acid metabolism) โ Exposes hidden antigens โ Enhances host immune system clearance of microfilariae.
Dosing by species
- Treatment of ascarids ยท 55-110 mg/kg PO ยท PO ยท Once ยท Single dose
- Heartworm prophylaxis ยท 5.5 mg/kg PO once a day ยท PO ยท q24h ยท Continuous
- Treatment of early stages of Dictyocaulus viviparous infestations ยท 22 mg/kg IM for 3 successive days; or 44 mg/kg IM once. ยท IM ยท q24h or Once ยท 3 days or Single dose ยท DEC is available in an injectable dosage form containing 400 mg/mL in the U.K., no FDA-approved injectable form is available in the U.S.A.
- Heartworm prophylaxis ยท 6.6 mg/kg PO once a day preceding infection and for 60 days following last exposure to mosquitoes. ยท PO ยท q24h ยท 60 days post-exposure ยท In dogs that become microfilaremic while on DEC, may continue, but do not interrupt daily DEC therapy.
- Heartworm prophylaxis ยท 6.6 mg/kg PO daily from beginning of mosquito season and for two months thereafter. ยท PO ยท q24h ยท Seasonal + 2 months ยท Should be given year-round in areas where mosquitoes are active throughout the year. Re-examine 3 months after starting therapy and at 6-month intervals for microfilaria.
- Heartworm prophylaxis ยท 2.5-3 mg/kg PO daily; begin prior to mosquito season ยท PO ยท q24h ยท Continuous
- Heartworm prophylaxis ยท 5-7 mg/kg PO daily. Begin before infection is likely and continue 60 days after mosquito season. ยท PO ยท q24h ยท Seasonal + 60 days ยท Some areas will require year-round treatment.
Routes of administration
Contraindications
- Dogs with circulating microfilaria (due to risk of severe shock-like reaction)
Adverse effects
- Vomiting
- Diarrhea
- Fixed drug eruptions (rare)
- Severe anaphylactoid reaction (in microfilaremic dogs)
- Hepatic injury (reported in cats)
Drug interactions
- Pyrantel ยท Theoretical enhancement of toxic effects due to shared nicotine-like mechanism of action; use with intensified monitoring.
- Morantel ยท Theoretical enhancement of toxic effects due to shared nicotine-like mechanism of action; use with intensified monitoring.
- Levamisole ยท Theoretical enhancement of toxic effects due to shared nicotine-like mechanism of action; use with intensified monitoring.
Monitoring
- Microfilaria status (prior to and during heartworm prophylaxis)
- Clinical efficacy (when used as an anthelmintic)
Overdose
DEC is considered a relatively non-toxic compound with a wide margin of safety. * **Clinical Signs**: Large overdoses generally result in self-limiting vomiting or CNS depression. * **Management**: For very large, recent ingestions, consider GI decontamination (inducement of vomiting, activated charcoal, cathartics). If clinical signs occur, provide supportive care (e.g., IV fluids).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.