Drug information of spinosad


Drug group:

Natroba (spinosad) is an anti-parasite medicine.
Natroba topical suspension is used to treat head lice in adults and children who are at least 6 months old.

Mechanism of effect

Spinosad causes neuronal excitation in insects. After periods of hyperexcitation, lice become paralyzed and die.


The pharmacodynamics of Natroba Topical Suspension has not been studied.


An open-label, single-center trial was conducted over a period of seven days to determine the pharmacokinetic profile of spinosad 1.8% in pediatric subjects with head lice infestation. Fourteen (14) subjects, 4 – 15 years of age, with head lice were enrolled into the trial. All subjects applied a single topical (scalp) treatment of spinosad 1.8% for 10 minutes, after which the test article was washed off, and subjects underwent plasma sampling. Results demonstrated that spinosad was below the limit of quantitation (3ng/mL) in all samples. Plasma concentration of benzyl alcohol was not determined in these subjects.
An open-label, two-center trial was conducted over a period of 23 days to determine the pharmacokinetic profile of spinosad 0.9% and the ingredient benzyl alcohol in pediatric subjects with a head lice infestation. Twenty-six (26) subjects between 6 months to 4 years of age were enrolled into the study per protocol. All subjects applied a single topical (scalp) treatment of spinosad 0.9% for 10 minutes, after which the test article was washed off, and subjects underwent plasma sampling over a 12 hour period. Plasma spinosad concentrations were below the limit of quantitation (3 ng/mL) in all samples.
Benzyl alcohol was quantifiable (above 1 µg/mL) in a total of 8 plasma samples in 6 out of 26 subjects (25%): four out of 12 subjects in the 6 months to <2 years age group and two out of 14 subjects in the 2 to 4 years age group. The highest observed concentration was 2.37 µg/mL. Benzyl alcohol concentrations at 12 hours post-treatment were below limit of quantification (1 µg/mL) for all subjects.

Drug indications

Natroba (spinosad) Topical Suspension is indicated for the topical treatment of head lice infestation in patients six (6) months of age and older.


Shake bottle well. Apply sufficient Natroba Topical Suspension to cover dry scalp, then apply to dry hair. Depending on hair length, apply up to 120 mL (one bottle) to adequately cover scalp and hair. Leave on for 10 minutes, then thoroughly rinse off Natroba Topical Suspension with warm water. If live lice are seen 7 days after the first treatment, a second treatment should be applied. Avoid contact with eyes.

Drug contraindications


Side effects

Less common


Itching, burning, flaking, or redness of the scalp

redness of the eye or skin



Dry skin

dryness of the scalp

hair loss

thinning of the hair




Benzyl Alcohol Toxicity
Natroba Topical Suspension contains benzyl alcohol and is not recommended for use in neonates and infants below the age of 6 months. Systemic exposure to benzyl alcohol has been associated with serious adverse reactions and death in neonates and low birth-weight infants

Points of recommendation

For topical use only. Natroba Topical Suspension is not for oral, ophthalmic, or intravaginal use

Pregnancy level

US FDA pregnancy category B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

Breast feeding warning

No information is available on the clinical use of spinosad during breastfeeding. Because it is not systemically absorbed after topical application, it should not be present in breastmilk. However, the topical suspension contains benzyl alcohol, which may be systemically absorbed through the skin. High doses of benzyl alcohol are potentially toxic to neonates, but it is unlikely that doses this high reach breastmilk. The manufacturer states that mothers concerned about benzyl alcohol could pump and discard breastmilk for 8 hours, but this is probably unnecessary. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.

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