3.18 - Pharmacology for Lice and Scabies

Question 1

Scabies: Primary Regimen

• Immunocompetent
• Norwegian Scabies, Immunocompromised, HIV/AIDS

Answer 1

Immunocompromised = Permethrin 5% cream

Norwegian Scabies, Immunocompromised, HIV/AIDS = Ivermectin + Permethrin

Question 2

Head Lice: Treatment strategy
- 2 tx uses Permethrin 1% (note that scabies requires 5%)

Note: Permethrin only kills living lice, not eggs

Answer 2

o Day 0 + Day 7 + Days 13-15
o Day 0 + Day 9 (to get lice that have hatched before reach sexual maturity & lay eggs)

• Egg takes 7 DAYS to hatch
• Bug molt 3 times (occurs 10 DAYS after hatching) to sexually mature and lay more eggs)

Question 3

two head lice treatments that do not require nit removal

• Non-ovicidal
• Ovidal

Note: nit comb is not essential but is recommended!

Answer 3

• Nonovicidal = topical ivermectin lotion. The mortality of the hatches larvae may be due to contact with residue ivermectin.
• Ovicidal (only one I think) = Spinosad

Question 4

MOA of Permethrin and Pyrethrins + Piperonyl Butoxide + the difference

Answer 4

Premethrin is synthetic while Pyrethrin + Piperonyl Butoxide is a natural extract from Chysanthemum flower.

Both Premethrin and Pyrethrin affects voltage gated sodium channel, therefore paralyzing the louse and preventing it from feeding.

Question 5

Contraindication of Pyrethrins + Piperonyl Butoxide

Answer 5

Should not be given to persons who are allergic to chrysanthemums or ragweed.

Also, Piperonyl butoxide is only an additive that works synergistically by inhibiting microsomal enzymes in the louse which prevent pyrethrin catabolism

Question 6

Special Note about Pyrethroid resistance that involves a mutation of the neuronal voltage gated sodium channel.

Answer 6

Permethrin 5% would be no more efficacious than permethrin 1% in these patients. It indirectly renders piperonyl butoxide ineffective

Question 7

Adverse Effect of Lindane Shampoo 1%

Answer 7

Overuse, misuse, or accidentally swallowing lindane can be toxic to the brain and other parts of the nervous system;

Therefore not used!