Scabies Treatment–Challenging the Status Quo

Since 1989, more than 895+ new molecular entities have been approved by the FDA,1,2 but not one for scabies. Despite its prevalence and burden on public health, this “neglected, intensely pruritic” parasitic skin infection is long overdue for critical evaluation.

Perspective on Scabies: Pediatrics

Anthony J. Mancini, MD
Chief of Dermatology in the Department of Pediatrics Northwestern University Feinberg School of Medicine

Perspective on Scabies: Adults

Philip R. Cohen, MD
San Diego Family Dermatology, Adjunct Professor of Dermatology, Touro University California College of Osteopathic Medicine

Current Diagnostics Undermine Outcomes

Despite consensus criteria, accurately diagnosing scabies remains elusive, given the difficulty in differentiating infestations from generalized rashes3. As a result, we continue to see low rates of correct clinical diagnosis.

Diagnosing Scabies: Pediatrics

Diagnosing Scabies: Adults

To further complicate diagnosis, no standardized laboratory test methods or exam procedures are available for different practice specialties—and often, access to confirmatory diagnostic techniques is limited.3

  • Burrow ink test
  • Topical tetracycline
  • Light microscopy
  • Dermoscopy

An accurate scabies diagnosis is of real value only if safe and effective treatment options become readily available.

The FDA Redefines “Effective” Scabies Treatment

The FDA determined that a scabies patient was “cured” if all original lesions were either healed or improving, and there were no new lesions or signs of excoriation. Adverse events were left to the investigators’ discretion and graded on a scale of 0-3 to determine severity4.

The FDA defines a “complete cure” as being clinical and confirmatory.

Practitioners must determine that all symptoms have completely resolved, including burrows, lesions, and pruritus, and conduct microscopic or dermatoscopic assessments to validate the absence of mites, eggs, scybala, and burrows20.

Treatment Effectiveness: Pediatrics

Treatment Effectiveness: Adults

Do Today’s Therapies Offer a Complete Cure?

In the absence of a standard of care that meets FDA criteria, practitioners must decide which drug to utilize based on limited and subjective clinical data for efficacy and safety.
See where current therapies fall short.

  • Widespread resistance to the molecule among other ectoparasites has been confirmed; scabies mites may be underreported5-8
  • Reporting of reduced clinical cure rates are on the rise; a recent single-center, controlled, randomized trial reported ~30%5
  • Not FDA-approved for use with scabies
  • Not recommended for infants <15kg, children <5 years of age, pregnant women or nursing mothers5
  • Kinetics are disconnected from its pharmacodynamics; antiparasitic events persist for over a month after a single dose9
  • Clinical resistance has been well documented in literature10,11
  • Less effective than other therapies, with treatment failure attributed largely to resistance12,13
  • Should not be used to treat persons who weigh less than 110 pounds14
  • Systemic absorption can lead to neurotoxicity, especially in pediatric and elderly populations15-17
The need for novel targeted topical therapies that improve safety, efficacy, and tolerability while avoiding resistance is critical.

Limitations with Current Treatments: Pediatrics

Limitations with Current Treatments: Adults

In Search of A Targeted Topical Therapy (TTT)

Given that TTT has revolutionized the treatment of skin cancer and many common malignancies18, 19, imagine what it could do for scabies.

Does it recognize a specific target, like scabies mites, eggs, and scybala?

Is it active at the target site—in this case, the stratum corneum?

Does it avoid AEs associated with systemic absorption?

Is it immune to pathogen resistance, given the decline in treatment effectiveness?

The Need for Selectivity in Pediatric Population

The Need for Selectivity in Adult Population

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References: 1. U.S. FDA. (2018). Summary of NDA Approvals & Receipts, 1938 to the present. Retrieved from https://www.fda.gov/about-fda/histories-product-regulation/summary-nda-approvals-receipts-1938-present. 2. LaMattina, J. (2019). Can The Record Breaking Number Of FDA New Drug Approvals Continue? Forbes. Retrieved from https://www.forbes.com/sites/johnlamattina/2019/01/09/can-the-record-breaking-number-of-fda-new-drug-approvals-continue/?sh=260bdf15aa83. 3. Leung V, Miller M. Can J Infect Dis Med Microbiol. 2011;22(4):143-146. 4. Elimite (permethrin) Cream, 5% (NDA 19-855) FDA Approval Letter [Letter written August 25, 1989 to Burroughs Wellcome Company]. (1989). U.S. Food and Drug Administration. Division of Anti-Infective Drug Products. 5. Cohen PR. Cureus. 2020;12(3):e7419. 6. Meyersburg D et al. J Dermatolog Treat. 2020 Jun 4 [epub]. 7. Khalil S et al. PLoS Negl Trop Dis. 2017;11(11):e0005920. 8. Mounsey KE et al. Future Microbiol. 2008;3(1):57-66. 9. González Canga, A., Sahagún Prieto, A.M., Diez Liébana, M.J. et al. The Pharmacokinetics and Interactions of Ivermectin in Humans—A Mini-review. AAPS J 10, 42–46 (2008). 10. Currie BJ et al. Clin Infect Dis. 2004;39(1):e8-12. 11. Thomas J et al. BMC Infect Dis. 2015;15:250. 12. Golant AK, Levitt JO. Pediatr Rev. 2012;33(1):e1-e12. 13. Khalil S et al. PLoS Negl Trop Dis. 2017;11(11):e0005920. 14. CDC website. https://www.cdc.gov/parasites/scabies/health_professionals/meds.html. Accessed October 16, 2020. 15. Chandler DJ, Fuller LC. Dermatology. 2019;235(2):79-90. 16. Fox SM. Pediatric EM Morsels website. https://pedemmorsels.com/scabies. Accessed October 13, 2020. 17. Wooltorton E. CMAJ. 2003;168(11):1447-1448. 18. Blume-Peytavi U et al. J Eur Acad Dermatol Venereol. 2019;33(suppl 1):3-36. 19. Gerber DE. Am Fam Physician. 2008;77(3):311-319. 20. ParaPRO, LLC & Concentrics Research (2018). A Phase 3, Randomized, Double Blind, Placebo-Controlled Study to Assess the Safety, Efficacy and Pharmacokinetics of ParaPRO’s Investigational Product for the Treatment of Scabies (Clinical Study Protocol, Amd. 6.0, pp. 1-66).

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