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
In the treatment of head lice, malathion 0.5% lotion is applied to dry hair and neck overnight for 8-12 hours and rinsing with shampoo in the morning
True (retreatment may be necessary in 1 week if there is clinical evidence of infestation)
Malathion is not associated with any/negligible percutaneous absorption
True (and any absorbed malathion is rapidly metabolised by tissue A-esterases and carboxylesterases to inactive metabolites which are excreted in the urine, thus no serious systemic adverse reactions have been reported) - for head lice
The malathion 0.5% lotion is odoriferous and flammable owing to its high alcohol content, so care should be taken to avoid any heat sources while using the lotion
True (contains 78% isopropyl alcohol) - for head lice
Systemic toxicity of malathion is only reported with oral ingestion, where symptoms are similar to those of organophosphate poisoning due to cholinesterase depletion
True (not with topical application as there is virtually no systemic absorption of topical malathion)
Malathion is classified as pregnancy category B
True (head lice)
Malathion 0.5% lotion is the most effective treatment for head lice with superior ovicidal and pediculicidal activity against permethrin-resistant lice
True (therefore malathion is considered the first line therapy for the treatment of head lice in children 6 years and older)
Topical malathion may cause skin irritation
True (head lice)
Spinosad is a novel treatment recently approved by the FDA for treatment of head lice
True (available as a 0.9% solution)
Spinosad excites the motor neurones of arthropods as well as causes disruption of the nicotinic acetylcholine receptors, resulting in muscle contractions, paralysis and death
True (head lice)
Spinosad has a rapid onset of action as compared to the other treatment for head lice (malathion, permethrin)
True (after application to dry hair, the solution can be rinsed out after 10 mins; if live lice are observed after 1 week, then a second treatment may be used)
Spinosad is classified as pregnancy category B
True
Spinosad may cause erythema and skin irritation
True
The topical antiparasitic agents used in the treatment of head lice include:
(1) permethrin
(2) pyrethrins with piperonyl butoxide
(3) malathion
(4) spinosad
(5) lindane (banned)
True
Crotamiton 10% cream/lotion is FDA approved for the treatment of scabies but should not be considered as first line therapy
True (total 30g should be applied to the neck down for 2 consecutive days) - minimally effective
Crotamiton 10% cream/lotion is minimally effective for scabies (though FDA approved) but is promoted for its antipruritic effects
True
There are no known significant adverse effects to crotamiton
True
Crotamiton is classified as pregnancy category C
True
Benzyl benzoate can be compounded in a 10-25% solution for the topical treatment of scabies
True (no commercially available preparation)
Benzyl benzoate is inexpensive and effective for scabies, usually used in combination with ivermectin
True
The adverse effects associated with topical benzyl benzoate is usually limited to skin irritation
True
Patients on topical benzyl benzoate are advised to avoid alcohol consumption for 48 hours after benzyl benzoate application due to the likelihood of a disulfiram-like reaction
True
Safety is pregnancy has not been established for topical benzyl benzoate
True
6% Precipitated sulphur is widely used for the treatment of scabies and can be compounded in a cream/ointment vehicle
True (no commercially available preparation) - the compound is applied for 24 hours, washed off and repeated daily for 5 days
Many authorities consider compounded 6% precipitated sulphur to be the drug of choice for scabies treatment during pregnancy even though there are no published studies to support this claim
True
Precipitated sulphur is well tolerated with no significant adverse effects except for mild skin irritancy
True
Precipitated sulphur has a noxious odour
True
Tea tree oil (Melaleuca alternifolia) is an Australian Aboriginal traditional medication that ha shown to have in vitro scabicidal activity in patients with recurrent crusted scabies, and application resulted in death of all scabies mites within 3 hours
True
Although tea tree oil is generally well tolerated (scabies), contact sensitisation has been occasionally reported
True
The topical antiparasitic agents used in the treatment of scabies include:
(1) Permethrin
(2) Crotamiton
(3) Benzyl benzoate
(4) Precipitated Sulfur
(5) Tea tree oil
(6) Lindane (banned)
True
Lindane is an organochlorine insecticide previously used for scabies and pediculoses that inhibits neurotransmission, including respiratory and muscular paralysis in parasitic arthropods
True
Toxicity is rare when lindane is used properly, although repeated exposure or ingestion adversely affects the CNS with multiple reports of seizures due to this drug due to its wide distribution throughout the body, slow metabolism and storage in fatty tissues as well as the brain
True (it is an organochlorine insecticide that inhibits neurotransmission, including respiratory and muscular paralysis in parasitic arthropods)
Numerous systemic toxic effects have been reported with lindane, including aplastic anaemia and leukaemia
True (due to its wide distribution throughout the body, slow metabolism and storage in fatty tissues as well as the brain)
Minute amounts of lindane can still be detected in the body for months after topical application, with levels higher in infants, young children, and those with reduced body fat levels such as premature infants
True (Limdane has a wide distribution throughout the body, slow metabolism and storage in fatty tissues as well as the brain)
Due to the availability of safer alternatives to Lindane for treatment of scabies and pediculoses, this drug has been banned in many countries due to the serious CNS (seizures) and Haematological (aplastic anaemia and leukaemia) adverse effects
True (Lindane has a wide distribution throughout the body, slow metabolism and storage in fatty tissues as well as the brain)
Many of the non-pharmacologic treatments recommended as adjuvant therapy for head lice include wet combing and using diluted vinegar or 8% formic acid
True (wet combing itself is minimally effective as it temporarily immobilises the lice, though using diluted vinegar/8% formic acid can increase the efficacy of wet combing by helping to loosen the nits from the hair during the combing process)
Compounded Topical Thiabendazole was successful in patients with larva migrans when used 3 X daily for 5 days, in contrast to the usual treatment modality using liquid nitrogen cryotherapy
True (no commercially available preparation) - liquid nitrogen cryotherapy is often unsuccessful as it requires an understanding of the direction in which the parasite is headed as the organised can be several mm to a few cm ahead of the visible inflammatory trail
Topical compounded preparations of thiabendazole have demonstrated 98-100% clearance of cutaneous larva migrans
True (thiabendazole 15% ointment can be compounded in a lipophilic bas fat cream and dimethyl sulfoxide gel and used daily for 3-5 days)
Clinical resolution of cutaneous larva migrans from topical compounded thiabendazole is typically seen within 48 hours
True
Topical compounded thiabendazole is is of limited value for multiple cutaneous larva migrans lesions or hookworm folliculitis
True (
When thiabendazole is used topically, the rare adverse effects are limited to photoaggravated contact dermatitis
True
There are no known drug reactions when thiabendazole is used topically
True (oral thiabendazole is a CYP1A2 inhibitor and may elevated levels of theophylline)
Thiabendazole (oral) is classified as pregnancy category C
True (when taken orally, 90% is excreted within 48 hours, after which breastfeeding can be resumed)
