2 - Topical Antiparasitic Agents Flashcards
The 3 major types of parasitic infection encountered in dermatology are:
(1) scabies
(2) pediculoses (head lice)
(3) larva migrans
True
Pyrethrins are organic compounds originally derived from a flower species of the genus Compositae, which is related to the chrysanthemum
True (permethrin is a synthetic pyrethroid)
Inspired by the pyrethrins (organic compounds), the chemically stable and more efficacious synthetic pyrethroids such as permethrin with a wider range of activity against scabies, lice, ticks and other arthropods were developed
True
Permethrin is a synthetic pyrethroid
True
Permethrin 5% cream is used for the topical treatment of scabies
True
Permethrin 1% cream rinse is for the treatment of head lice
True (pyrethrins with piperonyl butoxide also can be used)
After application of permethrin 5% cream, the mean systemic absorption is <1-2% owing to its minimal percutaneous absorption
True
Permethrin is metabolised through ester cleavages
True
Virtually all the percutaneously absorbed permethrin is excreted in the urine within 1 week
True
Permethrin acts on the cell membrane of arthropods by disabling the sodium transport mechanism which is responsible for maintenance of polarisation of arthropod neuromembranes, thus causing the scabies mite to be paralysed
True
Permethrin 5% cream is the treatment of choice for scabies
True (the cream should be applied to all body surfaces from neck down, particular care paid to the hands and fingernail areas because these sites harbour the greatest concentration of mites, intertriginous sites need careful application)
It is generally accepted that scabies infested patients should be treated with 2 overnight (8 hours) permethrin applications 1 week apart
True (even though there is a 97.8% cure rate with 1 topical permethrin dose)
Permethrin is approved for use in patients 2 months of age and older
True
Because scabies can affect the scalp and face of infants and young children, permethrin cream should be applied to these areas as well
True
Pruritus can often persist for up to 1 month after permethrin treatment
True (In severe cases, topical or systemic corticosteroids are prescribed to control the persistent itch)
All close contacts of patients with scabies should be treated with 1 overnight application of permethrin 5% cream
True
In contrast to pediculosis (head lice), the scabies mite cannot survive off the body for extended periods and so it is unnecessary to constantly wash bed linens and clothing when beginning scabies treatment
True (reasonable to machine wash any clothes and bed linen used in the previous 24 hours in hot water)
Even though permethrin 1% cream and pyrethroid are marketed as a single application treatment for head lice, they should be reapplied in 7-10 days as neither are reliably ovicidal
True
Prior to application of permethrin 1% cream rinse for head lice, hair should be washed with shampoo alone because conditioners impair permethrin’s adherence to the hair shaft, resulting in decreased efficacy
True (once the hair is towel dried, the entire scalp, hair and retroauricular areas should be saturated for 10 mins with the medication and subsequently rinsed with warm water)
Permethrin 5% cream is only used in the treatment of head and pubic lice when there is resistance to the 1% cream rinse
True (2 overnight applications to the scalp and neck 1 week apart is recommended)
There have been no reported adverse reactions to permethrin other than local irritation such as pruritus, and mild and transient burning and stinging which is common to all topical applications on inflamed skin
True
Persons with sensitivity to Compositae should not use pyrethrins because of the potential for cross-reactions
True
Permethrin is classified as pregnancy category B
True
It is not known whether permethrin is secreted in human milk, though it has been recommended that nursing should be discontinued if the drug will be used while the patient is nursing
True
Permethrin has been used for Demodex folliculitis
True
Malathion is a weak organophosphate that is converted to malaoxon, and FDA approved for treatment of head lice
True (malathion 0.5% lotion is the most effective agent for treating head lice)
Malathion irreversibly inhibits acetylcholinesterase, resulting in neuromuscular paralysis in arthropods
True (used in treatment of head lice)
The isopropyl alcohol and terpineol which is compounded with malathion also appear to have ovicidal and pediculicidal properties for head lice that work synergistically to increase the efficacy of malathion
True