Spinosad

Products

Spinosad has been commercially available in the United States since 2011 as a topical suspension (Natroba, 9 mg/g). As a veterinary drug, it is also used orally to prevent and treat flea infestation with in dogs (Comfortis). Spinosad is further widely used as an insecticide.

Structure and properties

Spinosad is obtained by fermentation from the actinomycete. The bacterium was originally discovered in soil samples taken by a scientist during a vacation in the Virgin Islands at an old rum distillery in 1982 (Mertz, Yao, 1990). Spinosad is a mixture of the spinosynes spinosyn A and spinosyn D in a ratio of approximately 5:1. The structures of the two components differ only in a single methyl group. They are non-antibacterial macrolides and lactones with two sugar units. Synthetic derivatives are called spinosides.

Indications

  • For the treatment of head lice.
  • As a veterinary medicine for the prevention and treatment of flea infestation with in dogs.

Effects

Spinosad (ATC P03AX, ATCvet QP53BX03) has insecticidal and additional ovicidal properties, meaning it kills louse eggs. It causes neuronal hyperexcitation of the insects, which are paralyzed and killed. The effects are due to activation of the insects’ nicotinic acetylcholine receptors nAChR. In a clinical trial, spinosad was far superior to the standard permethrin and generally required only a single application and no combing out (Stough et al., 2009).

Dosage

According to package insert. The suspension must be shaken well before each application. First apply the liquid on the dry scalp, then on the hair. After an exposure time of 10 minutes, rinse well with warm water. Wash hands well afterwards. Repeat the treatment after 7 days if live lice are detected.

Contraindications

Spinosad should not be used in case of hypersensitivity. The drug is for external use only and should not be ingested or brought into contact with the eyes or mucous membranes. For complete precautions, see the drug label.

Interactions

Drug-drug interactions are not known. Concomitant use of other drugs is not indicated.

Adverse effects

The most common adverse effects include redness and irritation of the skin and eyes. Dry skin, skin sloughing, and hair loss have rarely been reported. Spinosad is poorly absorbed through the skin into the blood and is considered atoxic.