Drugs For Pediculosis And Scabies, Antihistamines

Front 1

Lindane---Mechanism of action

Back 1

a. Used as a commercial insecticide as well as a topical medication.
b. Following absorption through the chitinous exoskeleton of arthropods, lindane presumably stimulates the nervous system, resulting in seizures
and death.

Front 2

Lindane--Adverse Effects

Back 2

a. Lindane is absorbed through skin and mucous membranes and from the GI tract; Lindane toxicity has been reported when the topical drug was used excessively or for prolonged periods and following accidental or intentional ingestion.
b. Neurotoxicity (e.g., dizziness, seizures, death)

Front 3

Permethrin---Mechanism of action

Back 3

a. An insecticide
b. Acts as a neurotoxin by depolarizing nerve cell membranes of parasites. The drug disrupts the sodium channel current by which membrane repolarization is regulated. Delayed repolarization results in paralysis of the nerves in the exoskeletal respiratory muscles of the parasite leading to death.

Front 4

Permethrin--Adverse Effects

Back 4

Neurotoxicity is extremely rare because the drug is rapidly metabolized by ester hydrolysis to inactive metabolites, which are eliminated rapidly in the
urine

Front 5

Malathion--- Mechanism of action

Back 5

a. An organophosphate anticholinesterase insecticide
b. The drug is an irreversible cholinesterase inhibitor.
c. Organophosphates inactivate acetylcholinesterase by phosphorylating the enzyme, which results in inhibition of acetylcholine hydrolysis and an increased concentration of acetylcholine at cholinergic synapses. Nervous system stimulation develops, resulting in rapid and massive paralysis of locomotory muscles and death.

Front 6

Malathion--Adverse Effects

Back 6

-Cholinergic Intoxication (more in notes) Initial signs and symptoms of malathion poisoning may be due
to excessive muscarinic effects including nausea, vomiting, abdominal cramps, diarrhea, urinary and/or fecal incontinence, hyperhidrosis, sialorrhea, miosis (pinpoint pupils), bradycardia, lacrimation, and increased nasal, pharyngeal, and bronchial secretions
-Flammable

Front 7

Piperonyl butoxide & Pyrethrins--- Mechanism of action

Back 7

a. Following absorption through the chitinous exoskeleton of arthropods, pyrethrins stimulate the nervous system by competitively interfering with
cationic conductances in the lipid layer of nerve cells, thereby blocking nerve impulse transmissions. Paralysis and death follow.
b. Piperonyl butoxide has little or no insecticidal activity but potentiates that of pyrethrins by inhibiting the enzymes responsible for pyrethrins' metabolism in arthropods. The insecticidal activity of pyrethrins is increased up to 10 times by the combination.

Front 8

Piperonyl butoxide & Pyrethrins--Adverse Effects

Back 8

a. Local irritation including erythema, pruritus, urticaria, edema, and eczema
b. Corneal erosion and stromal edema may occur --> avoid contact with the face, eyes, mucous membranes, and urethral meatus

Front 9

Ivermectin---Mechanism of action

Back 9

a. An anthelmintic drug with an off-label treatment of pediculosis and scabies.
b. Ivermectin binds selectively and with high affinity to glutamate-gated chloride ion channels in parasitic nerve and muscle cells, leading to an increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the cell leading to paralysis and death of the
parasite.

Front 10

Ivermection--Adverse Effects

Back 10

a. Ivermectin is safe for use in pediculosis and scabies; no serious adverse effects were noted in a program of mass treatment with ivermectin for children with scabies
b. Does not cross the blood-brain barrier -->no major CNS toxicity

Front 11

Summary of Treatment

Back 11

H=head, B=body, P=pubic, S=scabies
Ivermectin--HPS
Lindane--HPS
Malathion--HBPS
Permethrin--HBPS
Piperonyl Butoxide--HBP

Front 12

Treatment of first choice (pediculosis)? alternatives

Back 12

Permethrin
alternatives: Malathion, pyrethrins

Lindane is second-line. Oral ivermectin for resistance to pyr and malathion, and in large breakouts

Front 13

Histamine effect on BVs

Back 13

Receptors: H1/2
Action: Relaxation of vascular smooth muscle:
vasodilation & capillary dilatation
MOA: Indirect: release of NO and prostacyclin
from endothelium
Direct: relaxation of smooth Muscle

Front 14

Histamine Effect on Capillary Permeability

Back 14

Receptors: H1
Action: incr Permeability--> edema
MOA: Contraction & separation of endothelial
cells

Front 15

Histamine Effect on Cutaneous sensory nerve endings

Back 15

Receptors: H1
Action: Pain and itching
MOA: Activation of H1 receptors on nerve
endings

Front 16

Diphenhydramine and hydroxyzine--Mechanism of action

Back 16

1. Competitively antagonize the actions of histamine ONLY at H1 receptors
2. Pharmacologic effects in the skin
a. Partially inhibit vasodilation caused by histamine; incomplete since H2 receptors also are involved
b. Block capillary permeability
c. Itch inhibited

Front 17

Diphenhydramine and hydroxyzine--Admin

Back 17

1. Diphenhydramine is available for oral administration as well as topical dosage forms including cream, gel, liquid (e.g, spray and stick)
2. Hydroxyzine is available for oral administration.

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Diphenhydramine and hydroxyzine--Adverse Effects

Back 18

1. Oral
a. CNS depression--Diminished alertness, slow reaction times, somnolence
b. Gastrointestinal side effects include: anorexia, nausea, vomiting,
diarrhea or constipation
c. Antimuscarinic side effects include: dry mouth, urinary retention
2. Topical--Allergic dermatitis

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Diphenhydramine and hydroxyzine--Clinical Uses

Back 19

Pruritus--

H1 antagonists have a place in the treatment of pruritus. Some relief may be obtained in many patients suffering atopic dermatitis and contact dermatitis
(although topical corticosteroids are more effective) and in such diverse conditions as insect bites and poison ivy.

Major beneficial effect may come from sedation. Hydroxyzine is the antihistamine of choice.