Letters to the Editor

Spinosad: A Low-Risk, Effective Treatment for Lice


Am Fam Physician. 2019 Nov 15;100(10):601.

Original Article: Lice and Scabies: Treatment Update

Issue Date: May 15, 2019

Available online at: https://www.aafp.org/afp/2019/0515/p635.html

To the Editor: I enjoyed this article regarding treatment of lice, which is a common problem in young school-aged children and causes great stress for parents because of school policies and social stigma. The authors list permethrin 1% lotion (Nix) as first-line treatment based on its low cost and over-the-counter availability. However, resistance is a problem in some areas, as noted in the article. Many effective treatments are limited by high cost (spinosad [Natroba], malathion [Ovide]); limited effectiveness because of not being ovicidal (dimethicone [Nix Ultra, Lice MD], isopropyl myristate [Resultz], pyrethrins, permethrin); or toxicity/safety concerns, such as for pregnant women (oral ivermectin [Stromectol]).

Of these, spinosad has an extremely low risk of toxicity, is highly effective, and requires only a single treatment because it is ovicidal.1,2 In one trial, a single application of spinosad without the use of combing was more effective than permethrin.1 Unfortunately, it is limited by the high cost per treatment and the need for a prescription.

Yet spinosad is available without a prescription, and at 1/20th of the cost, if it is purchased at any gardening store. Permethrin has long been available as an organic pesticide at 0.5% concentration that has been deemed safe with low environmental and toxicity risks.3 This is compared with the 0.9% concentration of the prescription product. The additional product in the pesticide formulations tends to be propylene glycol, which is substantially less toxic (not known to be toxic at all, except in incredibly high exposures) than benzyl alcohol, which itself is known to be safe in terms of potential exposure to infants or mucosal linings.4,5

It remains to me a wonder why topical spinosad is not available inexpensively over the counter but instead is a very high-cost prescription drug, particularly when almost the exact same formulation is profitably sold at gardening centers around the world for a substantially lower price.

Editor's Note: In publishing Dr. Wright's letter, we wanted to clarify that AFP does not recommend that patients with lice self-treat with an unregulated product purchased at a garden store, regardless of cost savings. Rather, this scenario serves as an example of the disconnect between a pharmaceutical company's pricing of a drug for a common medical condition and the actual cost required to profit from its sale. Further information on what family physicians can do to help patients manage excessively high medication costs is available in a previous AFP editorial.1 —Kenny Lin, MD, MPH, deputy editor

1. Shaughnessy AF. Problematic jumps in drug prices and what you can do. Am Fam Physician. 2017;96(1):16–18. https://www.aafp.org/afp/2017/0701/p16.html

This letter was sent to the authors of “Lice and Scabies: Treatment Update” who declined to reply.

Author disclosure: No relevant financial affiliations.


show all references

1. Stough D, Shellabarger S, Quiring J, et al. Efficacy and safety of spinosad and permethrin creme rinses for pediculosis capitis (head lice). Pediatrics. 2009;124(3):e389–e395....

2. Yano BL, Bond DM, Novilla MN, et al. Spinosad insecticide: subchronic and chronic toxicity and lack of carcinogenicity in Fischer 344 rats. Toxicol Sci. 2002;65(2):288–298.

3. U.S. Environmental Protection Agency. EPA pesticide fact sheet: spinosad. Accessed May 22, 2019. https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-110003_19-Jul-99.pdf

4. Catanzaro JM, Smith JG Jr. Propylene glycol dermatitis. J Am Acad Dermatol. 1991;24(1):90–95.

5. Gershanik J, Boecler B, Ensley H, et al. The gasping syndrome and benzyl alcohol poisoning. N Engl J Med. 1982;307(22):1384–1388.

Send letters to afplet@aafp.org, or 11400 Tomahawk Creek Pkwy., Leawood, KS 66211-2680. Include your complete address, e-mail address, and telephone number. Letters should be fewer than 400 words and limited to six references, one table or figure, and three authors.

Letters submitted for publication in AFP must not be submitted to any other publication. Possible conflicts of interest must be disclosed at time of submission. Submission of a letter will be construed as granting the AAFP permission to publish the letter in any of its publications in any form. The editors may edit letters to meet style and space requirements.

This series is coordinated by Kenny Lin, MD, MPH, Associate Deputy Editor for AFP Online.



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