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Medicines Q&As
Q&A 441.1
How should crusted and other forms of difficult-to-treat scabies be
managed?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
Before using this Q&A, read the disclaimer at www.ukmi.nhs.uk/activities/medicinesQAs/default.asp
Date prepared: 19th April 2016
Background
Crusted (Norwegian) scabies is a hyperinfestation with the Sarcoptes scabiei mite (1). Presentation
varies, but crusted plaques, papules and nodules have been described, and the palms of the hands,
soles of the feet, scalp, buttocks, and axillae are frequently affected (2). The crusted areas seen in
crusted scabies begin as erythematous patches that develop scales, finally becoming crusty with
fissures, through which bacteria can enter (3).
Crusted scabies occurs most often in people living in institutions, and in people with compromised
cellular immunity, e.g. those with HIV or on immunosuppressants (4). Affected individuals are unable
to control mite proliferation and large numbers of mites are present. As a result, crusted scabies is
highly infectious (4,5) and is resistant to topical treatment alone (6,7). Although itching tends to be
mild (8), possible complications include secondary bacterial infection which can lead to septicaemia
and, in some cases, death (4).
Forms of scabies other than crusted scabies that may be considered to be ‘difficult-to-treat’ are any in
which topical treatment has been ineffective or cannot be used (6).
Answer
Crusted scabies
The European guideline (currently being updated) for the management of scabies (2010)
recommends that crusted scabies be treated with either topical treatment or combined topical
treatment with oral ivermectin. Topical treatment comprises several applications of permethrin 5%
cream all over, including the head, which may be alternated with keratolytic therapy e.g. emollients or
bathing (2).
Combined oral and topical treatment is usually the favoured approach in treating crusted scabies
(4,9,10). In observational studies, ivermectin has shown efficacy in crusted scabies after the failure of
topical therapy (11).
The use of ivermectin in patients with scabies (both crusted and classical) has been reviewed in a
NICE Evidence summary on ‘Difficult-to-treat scabies: oral ivermectin’(6) and by NPS MedicineWise,
an independent, not-for-profit organisation, based in Australia, that provides evidence-based
information (11). According to the NPS review, the optimal dosing schedule for crusted scabies has
not been established (11). Neither review identified randomised controlled trials of ivermectin for
crusted scabies treatment (6,11), treatment failure rates have varied widely in published uncontrolled
trials and case series, (6,11) and more robust studies are needed to evaluate its safety and efficacy
for this indication.
Dosing guidance is provided by the European Summary of Product Characteristics (SPC) for
ivermectin 3mg tablets (Stromectol®) which states that the initial dose of ivermectin
200 micrograms/kg of body weight may need to be followed by a second dose within 8 to 15 days
and/or concomitant topical therapy for effective treatment of profuse and crusting scabies (12). The
possible requirement for a second dose is due to ivermectin being non-ovicidal (11).
However alternative treatment regimens have been suggested. The following treatment regimen,
which was originally published in a review on scabies in the New England Journal of Medicine (4), is
Available through NICE Evidence Search at www.evidence.nhs.uk
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Medicines Q&As
currently recommended by the US Centers for Disease Control and Prevention for crusted scabies
(5):
Topical permethrin 5% every 2-3 days for 1-2 weeks
and
Oral ivermectin (200 microgramskg/dose, with food)
as three doses (days 1, 2,and 8);
five doses (days 1, 2 , 8, 9, and 15);
or seven doses (days 1, 2, 8, 9, 15, 22, and 29), depending on the severity of infection.
In addition, keratolytic creams are recommended for skin crusts to aid breakdown of the skin
crusts and penetration of the topical therapy (4).
Ivermectin is not licensed in the UK but can be obtained on a named-patient basis from ‘special order’
manufacturers or specialist importing companies (6). As with any unlicensed drug, the responsibility
shouldered by the prescriber is greater than when a licensed medicine is prescribed within the terms
of its licence. For full details, see the GMC recommendations on prescribing unlicensed medicines:
http://www.gmc-uk.org/guidance/ethical_guidance/14327.asp (13).
Side effects reported in randomised controlled trials of ivermectin for classical/uncomplicated scabies
include itch aggravation, rash, headache, abdominal pain and mild diarrhoea (6).
Special patient groups: The safety of ivermectin in pregnant patients and children weighing less
than 15kg has not been established (12). Permethrin 5% (two applications) may be an appropriate
alternative treatment in these patient groups (14).
Severity of disease
For crusted scabies, there is no standard way of describing severity. However, a clinical grading scale
has been developed and used to guide treatment in a hospital in Australia (15). Using the scale to
determine the severity of the infestation, a patient is assigned a score between 4 and 12, which
corresponds with grade 1, 2, or 3. (15). Patients are then administered three, five, or seven doses of
ivermectin 200 micrograms/kg, depending on the grade assigned to them. The severity grading scale
for crusted scabies has been published by Davis et al (15) and is reproduced below:
Severity grading scale for crusted scabies (15)
A: Distribution and extent of crusting
1. Wrists, web spaces, feet only (<10% Total Body Surface Area (TBSA))
2. Above plus forearms, lower legs, buttocks, trunk or 10-30% TBSA
3. Above plus scalp or >30% TBSA
B: Crusting / Shedding
1. Mild crusting (<5mm depth of crust), minimal skin shedding
2. Moderate (5-10mm) crusting, moderate skin shedding
3. Severe (>10mm), profuse skin shedding
C: Past Episodes
1.
Never had it before
2.
One to three prior hospitalisations for crusted scabies or depigmentation of elbows, knees
3. Four or more prior hospitalisations for crusted scabies or depigmentation as above and
legs/back or residual skin thickening / ichthyosis
D: Skin Condition
1.
No cracking or pyoderma
2.
Multiple pustules and/or weeping sore and/or superficial skin cracking
3.
Deep skin cracking with bleeding, widespread purulent exudates
Available through NICE Evidence Search at www.evidence.nhs.uk
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Medicines Q&As
Grade 1: Total score 4-6
Grade 2: Total score 7-9
Grade 3: Total score 10-12
Treatment: Ivermectin 200 micrograms/kg rounded up to nearest 3mg.
Grade 1: 3 doses – Days 0, 1, 7
Grade 2: 5 doses – Days 0, 1, 7, 8, 14
Grade 3: 7 doses – Days 0, 1, 7, 8, 14, 21, 28
All patients also treated with benzyl benzoate and 5% tea tree oil alternating every other day with a
keratolytic cream.
Dealing with outbreaks
Patients with unrecognised crusted scabies are often the index patients at the heart of an outbreak of
classical scabies (5). Detailed suggestions for developing guidelines on the prevention, detection and
response to one or more cases of crusted scabies in an institution are published by the US Centers
for Disease Control and Prevention (5) on their website:
http://www.cdc.gov/parasites/scabies/health_professionals/crusted.html
The advice given includes the following:




Symptoms of scabies can take up to two months to appear, so it is essential to maintain
records of patient names, room numbers, roommates, and all attending staff.
To minimise the transmission of mites via objects such as furniture, clothing and carpets, use
protective garments such as gowns when caring for patients with crusted scabies.
Isolate patients with crusted scabies from other patients and clean and vacuum their rooms
thoroughly when they leave as well as during their stay. Collect bedding and clothing
belonging to these patients, transport it in a plastic bag directly to the washing machine and
wash it at temperatures higher than 50 degrees C for 10 minutes. Wear gloves and protective
garments if handling these items before they are washed
Identify and treat all patients, staff, and visitors who may have been exposed to a patient with
crusted scabies or to clothing, bedding, furniture, and other items used by the patient. Offer
treatment to household members of staff who are undergoing scabies treatment (5).
Difficult to treat classical scabies
The use of ivermectin in patients with classical scabies has been reviewed in a
NICE Evidence summary on ‘Difficult-to-treat scabies’ (6) and by NPS MedicineWise (11). In the UK,
ivermectin tends to be used in patients with classical scabies only when topical treatments (e.g.
permethrin or malathion) are inappropriate or have been ineffective. There is published evidence of
ivermectin having been used for scabies outbreaks in nursing homes and other similar institutions (6)
where topical therapy may be difficult to administer effectively.
The NICE Evidence summary mentioned above considers relevant results from a Cochrane review
(16) of 22 RCTs, and those of four additional RCTs (17-20). It concludes that oral ivermectin shows
efficacy in patients with classical or crusted scabies but notes that the differing treatment durations
and follow-up lengths of included studies makes comparison with topical treatments difficult (6).
Similarly, the NPS review (11) concludes that there is considerable heterogeneity in the methodology
of studies using ivermectin for classical scabies.
Ivermectin has proven efficacy in curing scabies (defined as no new lesions caused by the mite) after
two, separate doses (11). However, permethrin clears lesions more quickly. Also, ivermectin is nonovicidal so a single dose of 200 micrograms/kg body weight may not kill the mite in all its life stages.
To prevent mite resistance and increase the chances of treatment success, it is recommended that
ivermectin be reserved as second-line for typical scabies (after topical treatments) and that two doses
are used (11). No controlled clinical trials have been carried out to establish the most effective dosing
regimen for ivermectin in classical scabies, but Australian guidelines recommend that a second dose
is given after the first, with an interval of 8 to 15 days between doses (11).
Available through NICE Evidence Search at www.evidence.nhs.uk
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Medicines Q&As
The current European SPC for ivermectin 3mg tablets (Stromectol®) recommends a single dose of
ivermectin 200 microgramskg body weight for classical scabies, with a second dose of ivermectin not
being administered within two weeks of the initial dose unless the parasitologic examination is positive
at this time/new lesions have appeared (12).
The general management of classical scabies is covered thoroughly by the NICE Clinical Knowledge
Summary on scabies (21).
Summary
Crusted (Norwegian, hyperkeratotic) scabies is a severe form of scabies that occurs most often in
patients living in institutions, and in people with compromised cellular immunity, e.g. HIV or those on
immunosuppressants.
Combined oral and topical treatment is usually favoured for crusted scabies. The European SPC for
ivermectin 3mg tablets (Stromectol) recommends a dose of ivermectin 200 micrograms/kg of body
weight, followed by a second dose within 8 to 15 days and/or concomitant topical therapy. The US
Centers for Disease Control and Prevention currently recommend topical permethrin 5% every 2-3
days for 1-2 weeks and oral ivermectin (200 micrograms/kg/dose, with food) as three doses (days 1,
2, and 8), five doses (days 1, 2 , 8, 9, and 15), or seven doses (days 1, 2, 8, 9, 15, 22, and 29),
depending on the severity of infection. Although, for crusted scabies, there is currently no standard
way of describing severity, a clinical grading scale has been developed and used to guide treatment
in a hospital in Australia.
Patients with crusted scabies are often the index patients at the heart of an outbreak of classical
scabies.
In the UK, ivermectin tends to be used for classical scabies only when topical treatments are
inappropriate or have been ineffective. No controlled clinical trials have been carried out to establish
the most effective dosing regimen for ivermectin in classical scabies. The European SPC for
ivermectin 3mg tablets (Stromectol) recommends a single dose of ivermectin 200 micrograms/kg body
weight, with a second dose of ivermectin not being administered within two weeks of the initial dose
unless the parasitologic examination is positive at this time/new lesions have appeared. Australian
guidelines recommend that a second ivermectin dose is given after 8 to15 days.
Limitations
Ivermectin is not licensed in the UK for crusted or classical scabies. The most effective dosing
regimen for ivermectin in crusted/classical scabies has not been established. There is a lack of
consistent advice on use in pregnant women and children weighing less than 15kg.
References
1. Davis JS, McGloughlin S, Tong SYC, et al. A novel grading scale to guide the management of
crusted scabies. PLoS Negl Trop Dis 2013; 7(9): e2387.
2. Scott GR and Chosidow O. European guideline for the management of scabies. Int J STD
AIDS 2011;22:301-3.
3. Goldstein BG and Goldstein AO. Scabies. In: Post TW, editor. UpToDate. Waltham, MA:
Wolters Kluwer Health [cited 11 Jan 2016]. Available from: http://www.uptodate.com/home
4. Currie BJ and McCarthy JS. Permethrin and Ivermectin for scabies. N Engl J Med
2010;362(8):717-25.
5. Centers for Disease Control and Prevention (CDC). Parasites - Scabies [cited 11 Jan 2016].
Available from: http://www.cdc.gov/parasites/scabies/
6. National Institute for Health and Care Excellence (NICE) Evidence summary. ESUOM29:
Difficult-to-treat scabies: oral ivermectin. Published 18 March 2014 [cited 26 Nov 2015].
Available from: https://www.nice.org.uk/advice/esuom29/chapter/Key-points-from-theevidence
7. Ortega-Loayza AG, McCall CO, Nunley JR. Crusted scabies and multiple dosages of
ivermectin. J Drugs Dermatol 2013;12(5):584-5.
Available through NICE Evidence Search at www.evidence.nhs.uk
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8. Jungbauer FHW, Veenstra-Kyuchukova YK, Koeze J, et al. Management of nosocomial
scabies, an outbreak of occupational disease. Am J Ind Med 2015;58:577-82.
9. Hengge UR, Currie BJ, Jager G, et al. Scabies: a ubiquitous neglected skin disease. Lancet
Infect Dis 2006;6:769-79.
10. Alberici F, Pagani L, Ratti G, et al. Ivermectin alone or in combination with benzyl benzoate in
the treatment of human immunodeficiency virus-associated scabies. Br J Dermatol 2000;142:969-72.
11. NPS Medicinewise. Ivermectin (Stromectol) for typical and crusted scabies. NPS Radar.
Published 1 Aug 2014 [cited 19 Nov 2015]. Available from:
http://www.nps.org.au/publications/health-professional/nps-radar/2014/july-2014/ivermectin
12. European Summary of Product Characteristics – Stromectol 3mg tablets (ivermectin). Merck,
Sharp & Dohme BV. Obtained from MSD UK Medical Information [30 November 2015].
13. General Medical Council. Prescribing guidance: Prescribing unlicensed medicines [cited 1
Dec 2015]. Available from: http://www.gmc-uk.org/guidance/ethical_guidance/14327.asp
14. Vekic DA, Abbott L, Asher EM, Whitfield MJ. Treating scabies in immunodeficiency: New
evidence based care. ACD 47th Annual Scientific Meeting 2014. Australas J Dermatol
2014:15
15. Davis JS, McGloughlin S, Tong SYC, et al. A novel clinical grading scale to guide the
management of crusted scabies. PloS Negl Trop Dis 2013;7(9):e2387.
16. Strong M and Johnstone P. Interventions for treating scabies. Cochrane Database of
Systematic Reviews 2007, issue 3: CD000320.
17. Chhaiya SB, Patel VJ, Dave JN et al. (2012) Comparative efficacy and safety of topical
permethrin, topical ivermectin, and oral ivermectin in patients of uncomplicated scabies.
Indian Journal of Dermatology, Venereology and Leprology 78: 605–10
18. Goldust M, Rezaee E, Hemayat S (2012) Treatment of scabies: comparison of permethrin 5%
versus ivermectin. Journal of Dermatology 39: 545–7
19. Saqib M, Malik LM, Jahangir M (2012) A comparison of efficacy of single topical permethrin
and single oral ivermectin in the treatment of scabies. Journal of Pakistan Association of
Dermatologists 22: 45–9
20. Sharma R, Singal A (2011) Topical permethrin and oral ivermectin in the management of
scabies: a prospective, randomized, double blind, controlled study. Indian Journal of
Dermatology, Venereology and Leprology 77: 581–6.
21. Scabies. NICE Clinical Knowledge Summaries [cited 25 Feb 2016]. Available from:
http://cks.nice.org.uk/
Quality Assurance
Prepared by
Alex Bailey, Welsh Medicines Information Centre.
Date Prepared
19 April 2016
Checked by
Gail Woodland, Welsh Medicines Information Centre
Date of check
29 April 2016
Search strategy
Embase (*scabies/di, dm, dr, dt, ep, th [Diagnosis, Disease Management, Drug Resistance, Drug
Therapy, Epidemiology, Therapy] AND (crusted.m_titl. OR norwegian.m_titl. OR crusted.ab. OR
norwegian.ab)
Medline: (PubMed: "crusted scabies"[Title]) OR "norwegian scabies"[Title])
Medline-in-process: (crusted adj3 scabies).mp. OR (norwegian adj scabies).mp.)
In-house database/ resources: crusted/norwegian AND scabies
NHS Evidence (crusted AND scabies)
Available through NICE Evidence Search at www.evidence.nhs.uk
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