Pharmacotherapy of scabies

Pathophysiology of scabies
Clinical presentation,
Principles of treatment.
Antiscabietic drugs: permethrin, benzyl benzoate, crotamiton,lindane and Ivermectin.
Instruction to patien,t
Clinical problem and
Causes of persistent itching

1. Pharmacotherapy of Scabies Dr.Uma Advani Assistant Professor Pharmacology, SMS,MC Jaipur

2. Learning objectives Pathophysiology of scabies Clinical presentation Principles of treatment Antiscabietic drugs: permethrin , benzyl benzoate, crotamiton,lindane and I vermectin Instruction to patient Clinical problem Causes of persistent itching

3. Scabies infection caused by arthropod Sarcoptes scabiei var. hominis. World wide prevalence around 300 million cases yearly. Symptoms: nocturnal itching, rash . Spreads among people by contact. Either direct(i.e.,skin to skin contact) or indirect (through infested bedding, clothing or other fomites). Affects families and institutional settings.

4. “ Sarcoptes scabiei is notorious for its lack of respect for person, age, sex or race. Whether it is in the epidermis of an emperor or a slave, a centenarian or a nursling, it makes itself perfectly at home with undiscriminating impudence and equal obnoxiousness”. – Friedman.

5. Clinical presentation Generalised and intense itching which spares the head and face. Lesions located mostly on the finger webs, on the flexor surface of the wrists, on the elbows, in the axillae, on the buttocks and genitalia and on the breasts of women. Burrows and nodules specific for scabies. Burrows occur as wavy, dirty appearing line in the interdigital web spaces.

6. Common sites

7. Principles of treatment Establish your diagnosis. Choose an appropriate medication. Treat the whole body from neck to toe in adults and head and face in babies. Treat all the contacts. Give a detailed verbal and written instruction.

8. Principles of treatment Treat secondary infection if present. Avoid over treatment. Have a follow up at one and four weeks after treatment. Launder clothing and bedding after completing treatment.

9. Antiscabietic drugs -Permethrin 5% cream -Lindane (gamma benzene hexachloride) 1% lotion or cream -Benzyl benzoate 10% and 25% lotion or emulsion. -Malathion 0.5% lotion -Monosulfiram 25% lotion -Crotamiton 10 % cream -Precipitated sulfur 2-10% ointment -Esdepallethrine -Ivermectin 0.8% lotion -oral ivermectin.

10. Permethrin Synthetic pyrethroid and potent insecticide. Drug of choice for all ages. More effective than lindane. Applied over night to the whole body once a week for two weeks including head in infants. No allergic effects. Safe and cosmetically acceptable. Most recent and effective treatment.

11. Benzyl benzoate Neurotoxic to mites Used as a 25% emulsion. Contact period is 24 hours. Should be applied three times within 24 hours. Not to be used in pregnant women, children less than 2 years. Especially used in Permethrin resistant scabies. Cheap .

12. Crotamiton Used as 10% cream or lotion. To be applied twice daily for 5 consecutive days after bathing and chaning. Not very effective. Often used in scabietic nodules in children.

13. Lindane Also known as gamma benzene hexa chloride. Acts on the CNS of insects and leads to increased excitability, convulsions and death. Single six hour application is effective in the treatment of scabies. Available as cream, shampoo or lotion. Disadvantage: CNS toxicity – especially in malnourished children and those with seizure disorder. Cheap alternative to permethrin.

14. Ivermectin Acts by suppressing conduction of nerve impulses in the nerve muscle synapses of insects by stimulation of GABA from pre synaptic nerve endings. Single dose effective – 0.2 mg/kg. Effective in clearing the lesions and also the pruritus. Used in crusted scabies with high mite burden. C/I in patients with CNS disorders.

15. Instructions to patients Start with a bath and dry thoroughly. The medication provided should be rubbed into the skin. All parts of the body from chin downwards, whether involved or uninvolved should be treated. Treatment is best done at night before going to bed. Avoid touching your mouth or eyes with your hands.

16. Instructions to patients (contd..) Change your underclothing and sheets the next day and launder them. You may itch for a few days but do not repeat the treatment. Everyone in the house should be treated at the same time Report to your doctor after one week

17. Ans : Precipitated sulfur 6 % ointment . Least effective of all treatments. Disadvantages : messy, malodorous, stains clothing, and can cause irritant dermatitis in humid weather. Safe in pregnancy, lactation and infants. Cheapest scabietic drug. Name the agent used for Scabies in pregnancy?

18. A 25 year old male was treated with lindane for scabies . After one week he comes back to you telling that his itching has not stopped. What will you do for him now ?

19. Possible causes of persistent itching Overtreatment – treat with emollients Severe eczematous scabies - emollients Contact dermatitis - topical steroids Poor compliance – supervised application Resistance – switch to alternative drug Reinfestation- simultaneous treatment Delusions of parasitoses – psychiatric referral

20. THANK TOU