# Dichlorvos (DDVP): veterinary dose and monograph

> Dichlorvos (DDVP) is a veterinary antiparasitic. An older ORGANOPHOSPHATE anthelmintic/insecticide formulated as resin-bound pellets that release slowly along the gut to kill GI nematodes (and bots in horses) — used historically in pigs and horses, and as an environmental insecticide. Indications include porcine GI nematodes (Ascaris, Oesophagostomum, whipworm) — historical; equine GI nematodes and bots (Gasterophilus) — historical; environmental insect control (premises). This monograph lists 4 reference doses for dogs, cats, horses and pigs, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/dichlorvos · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Antiparasitic
- **Also known as:** DDVP, Atgard, Task, Nuvan
- **Species with doses:** Dogs, Cats, Horses and Pigs
- **General dose range:** 10–40 mg/kg PO single dose (repeat per cycle) — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Porcine GI nematodes (Ascaris, Oesophagostomum, whipworm) — historical
- Equine GI nematodes and bots (Gasterophilus) — historical
- Environmental insect control (premises)

## Dichlorvos (DDVP) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Dichlorvos (DDVP) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI nematodes (organophosphate — obsolete) | 26.4–33 mg/kg | PO | single dose | — |

- GI nematodes (organophosphate — obsolete): Papich 5e: 26.4–33 mg/kg once PO. Largely obsolete. Narrow margin (cholinesterase inhibitor) — never combine with other organophosphates, carbamates or cholinesterase-inhibiting drugs.

### Cats

*Dichlorvos (DDVP) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI nematodes (organophosphate — obsolete) | 11 mg/kg | PO | single dose | — |

- GI nematodes (organophosphate — obsolete): Papich 5e: 11 mg/kg once PO. Cats are sensitive to organophosphates — largely obsolete; prefer modern anthelmintics.

### Horses

*Dichlorvos (DDVP) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| GI nematodes / bots | 31–41 mg/kg | PO | single dose | — |

- GI nematodes / bots: Papich 5e: 31–41 mg/kg once PO. Historical organophosphate; safer modern anthelmintics are preferred.

### Pigs

*Dichlorvos (DDVP) doses for pigs*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| GI nematodes | 11.2–21.6 mg/kg | PO | single dose | — | Withdrawal NOT established — treat as extra-label |

- GI nematodes: Papich 5e: 11.2–21.6 mg/kg once PO; sows — 1000 mg/head daily in gestation feed for the last 30 days (334–500 g/ton); other pigs 334 g/ton as sole ration for 2 days. Plumb’s p.388: Atgard feed dosing per label by pig weight. Follow the label withdrawal. Never combine with other cholinesterase inhibitors.

## Contraindications

Concurrent other organophosphates/carbamates, cholinesterase inhibitors, neuromuscular blockers, or recent anaesthesia (additive cholinergic toxicity). Debilitated/ill or very young animals. Cats (organophosphate sensitivity). Known hypersensitivity. Largely superseded — prefer safer anthelmintics.

## Species-specific warnings

> **Caution:** Cats: Cats are highly sensitive to organophosphate toxicity — avoid dichlorvos; use safer feline anthelmintics.

> **Caution:** Horses: Largely historical in horses; safer macrocyclic lactones/benzimidazoles (and praziquantel-bot combinations) are preferred.

## Adverse effects

- Cholinergic (SLUD) toxicity at overdose: salivation, lacrimation, diarrhoea, colic, muscle tremor, bradycardia, dyspnoea
- Narrow safety margin
- Reduced cholinesterase activity

## Drug interactions

- Other organophosphates/carbamates, cholinesterase inhibitors (e.g. neostigmine), succinylcholine: additive, potentially fatal cholinergic toxicity — avoid
- Phenothiazines, CNS depressants: caution
- Recent anaesthesia/muscle relaxants: prolonged effects

## Pregnancy and lactation

Avoid in pregnancy where safer anthelmintics exist.

## Monitoring

- Cholinergic signs (SLUD, tremor, respiration) — toxicity surveillance
- Cholinesterase activity if toxicity suspected
- Avoid concurrent cholinesterase-inhibiting drugs and recent anaesthesia
- Withdrawal compliance (pigs)

## Toxicity and overdose

Organophosphate cholinergic toxicosis is the hazard — muscarinic (SLUD: salivation, lacrimation, urination, defecation, bradycardia, bronchorrhoea) and nicotinic (muscle tremor, weakness, paralysis) signs, progressing to respiratory failure. Narrow margin; cats are especially sensitive. Cholinesterase activity is depressed.

Management: Antidotes: ATROPINE for muscarinic signs and PRALIDOXIME (2-PAM) to reactivate cholinesterase (give early, before "aging") — the standard organophosphate-toxicosis treatment. Decontaminate, support ventilation, IV fluids; avoid the drugs listed under interactions. Intensive supportive care.

## Clinical pearls

- A historical organophosphate "resin-pellet" wormer — largely replaced by safer anthelmintics; included mainly for toxicology awareness
- Never combine with other cholinesterase inhibitors / organophosphates / carbamates / succinylcholine — additive, potentially fatal cholinergic toxicity
- Treat overdose as organophosphate toxicosis: ATROPINE + PRALIDOXIME (early), decontamination and ventilatory support
- Avoid in cats (organophosphate sensitivity) and debilitated animals

## Mechanism of action

An organophosphate that inhibits acetylcholinesterase in the parasite (and, at overdose, the host), causing acetylcholine accumulation, sustained cholinergic stimulation, spastic paralysis and death of the worm/insect. The resin-bound formulation limits host absorption by releasing the drug gradually in the gut, but the same mechanism produces cholinergic toxicity if too much is absorbed.

## Formulations and products

- Feed premix / resin pellets (Atgard, swine)
- Resin-bound granules (slow-release in gut)
- Atgard / Task (Various) — Dichlorvos resin pellets / premix, Feed premix / pellets

## Storage

Premix/pellets: 15–30 °C, dry, in original packaging; store securely away from food/feed for other species and from people (organophosphate).

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of Dichlorvos (DDVP) for dogs?

Reference doses for Dichlorvos (DDVP) in dogs: 26.4–33 mg/kg PO single dose (GI nematodes (organophosphate — obsolete)). Confirm against the label and the patient before use.

### What is the dose of Dichlorvos (DDVP) for cats?

Reference doses for Dichlorvos (DDVP) in cats: 11 mg/kg PO single dose (GI nematodes (organophosphate — obsolete)). Confirm against the label and the patient before use.

### What is the dose of Dichlorvos (DDVP) for horses?

Reference doses for Dichlorvos (DDVP) in horses: 31–41 mg/kg PO single dose (GI nematodes / bots). Confirm against the label and the patient before use.

### What is the withdrawal period for Dichlorvos (DDVP)?

Pigs, PO (GI nematodes): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Dichlorvos (DDVP) not be used?

Concurrent other organophosphates/carbamates, cholinesterase inhibitors, neuromuscular blockers, or recent anaesthesia (additive cholinergic toxicity). Debilitated/ill or very young animals. Cats (organophosphate sensitivity). Known hypersensitivity. Largely superseded — prefer safer anthelmintics.

### What are the side effects of Dichlorvos (DDVP) in animals?

Cholinergic (SLUD) toxicity at overdose: salivation, lacrimation, diarrhoea, colic, muscle tremor, bradycardia, dyspnoea; Narrow safety margin; Reduced cholinesterase activity.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.