Dichlorvos
Dichlorvos (often abbreviated as DDVP) is a highly volatile **organophosphate** compound historically used as a broad-spectrum anthelmintic and ectoparasiticide. * **Veterinary Use**: Primarily utilized as an oral dewormer in swine (targeting roundworms, whipworms, and nodular worms) and as an environmental ectoparasiticide (e.g., 'No Pest Strips') for small mammals and premise fly control. * **Historical Context**: While it was once available for internal use in dogs, cats, and horses, it has been entirely replaced in these species by newer, safer, and more effective anthelmintics (such as macrocyclic lactones and benzimidazoles). > **Clinical Pearl**: Because dichlorvos is highly volatile, it is uniquely suited for use in resin strips that slowly release the chemical into the air to control flying insects and ectoparasites in enclosed spaces.
Mechanism: Dichlorvos acts by phosphorylating and inhibiting the enzyme **acetylcholinesterase (AChE)**. * **AChE Inhibition** → Prevents the breakdown of the neurotransmitter **acetylcholine (ACh)**. * **ACh Accumulation** → Continuous overstimulation of **nicotinic** and **muscarinic** receptors at the neuromuscular junction and autonomic synapses. * In susceptible parasites, this sustained depolarization leads to spastic paralysis and subsequent death. > **Pharmacological Note**: Organophosphate binding to AChE can become irreversible over time through a process called "aging." Prompt treatment of toxicity is required before aging occurs.
Dosing by species
- Internal parasites (Ascaris, Trichuris, Ascarops strongylina, Oesophagostomum spp.) · Specific amounts of feed per packet are dependent on pig weight. See the label for specific recommendations. · PO · Once · Single treatment · Administered by adding to feed (crumble-type or dry meal).
- Ectoparasite control · Hang 5 cm of a dichlorvos strip (e.g., Vapona No Pest Strip) 6 inches above cage for 24 hours, twice weekly for 3 weeks; OR hang in room for 24 hours once a week for 6 weeks; OR a 1 inch square laid on cage for 24 hours once a week for 6 weeks · Environmental · Twice weekly or once weekly · 3 to 6 weeks · For Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Concurrent use of other cholinesterase-inhibiting drugs, pesticides, or chemicals
- Allowing fowl access to medicated feed or manure from treated animals
Adverse effects
- Vomiting
- Tremors
- Bradycardia
- Respiratory distress
- Hyperexcitability
- Salivation
- Diarrhea
Drug interactions
- Acepromazine (and other phenothiazines) · May potentiate organophosphate toxicity; should not be given within one month of worming with an organophosphate.
- Anticholinesterase drugs (e.g., neostigmine, physostigmine, pyridostigmine) · Additive cholinesterase inhibition; avoid concurrent use.
- DMSO (Dimethyl sulfoxide) · Has anticholinesterase activity; avoid concurrent use with organophosphates.
- Morphine · Can inhibit cholinesterase; avoid concurrent use.
- Pyrantel pamoate or tartrate · Adverse effects could be intensified if used concomitantly.
- Succinylcholine · Prolonged neuromuscular blockade; do not use depolarizing muscle relaxants for at least 48 hours after organophosphate administration.
Monitoring
- Efficacy (resolution of parasite burden)
- Signs of organophosphate toxicity (SLUDDE signs, tremors, respiratory distress)
Overdose
> **Toxicity Warning**: Organophosphate overdosage causes severe cholinergic crisis, classically remembered by the acronym **SLUDDE** (Salivation, Lacrimation, Urination, Defecation, Dyspnea, Emesis). **Clinical Signs of Toxicity**: * Vomiting, diarrhea, and hypersalivation. * Muscle tremors, hyperexcitability, and seizures. * Bradycardia and severe respiratory distress (bronchoconstriction and increased secretions). **Treatment & Antidotes**: * **Atropine**: Acts as a muscarinic receptor antagonist to control life-threatening bradycardia, bronchoconstriction, and excessive secretions. * **Pralidoxime (2-PAM)**: An AChE reactivator that can reverse neuromuscular blockade (tremors/weakness) if administered before the enzyme-toxin complex "ages." * **Avoid**: Succinylcholine, theophylline, aminophylline, reserpine, or respiratory depressant drugs (e.g., narcotics, phenothiazines). * **Human Exposure**: If ingested by a human, immediately contact a poison control center, physician, or hospital emergency room.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.