Usage
Permethrin topical is prescribed for the treatment of scabies and head lice infestations. It belongs to the pharmacological classification of pyrethrins, which are synthetic insecticides. Permethrin acts by disrupting the sodium ion channels in the nerve cell membranes of parasites, leading to paralysis and death.
Alternate Names
There are no widely recognized alternate names for permethrin, though some regional variations may exist. Brand names under which permethrin is marketed include Nix, Elimite, and Acticin.
How It Works
Pharmacodynamics: Permethrin exerts its insecticidal effect by targeting the parasite’s nerve cells. It binds to voltage-gated sodium channels, delaying their closure and causing prolonged depolarization. This disruption interferes with neuronal signaling, leading to paralysis and death of the parasite.
Pharmacokinetics: Permethrin is minimally absorbed through intact skin, with less than 2% systemic absorption after topical application. The absorbed drug is rapidly metabolized in the liver through hydrolysis and oxidation, and the metabolites are excreted primarily in the urine. CYP enzymes are not significantly involved in the metabolism of permethrin.
Mode of Action: Permethrin’s primary mode of action involves binding to and disrupting the function of voltage-gated sodium channels in the nerve cell membranes of parasites, which leads to their paralysis and death.
Dosage
Standard Dosage
Adults:
Apply a thin layer of 5% permethrin cream to the entire body from the neck down to the soles of the feet. Typically, 30g is sufficient for an average adult, but some may require up to 60g. Leave the cream on for 8-14 hours, then wash it off thoroughly. For head lice, apply the 1% lotion or cream rinse to washed hair, leave on for 10 minutes, then rinse and comb out nits.
Children:
- Scabies: 2 months to <1 year: Up to 3.75 g of 5% cream; 1-5 years: Up to 7.5 g of 5% cream; 6-12 years: Up to 15 g of 5% cream; >12 years: Same as adult dose. For 5% lotion, 2 months to 1 year: Up to 1/8 of a 50 mL bottle; 2-5 years: Up to 1/4 of a 50 mL bottle; 6-12 years: Up to 1/2 of a 50 mL bottle; >12 years: Same as adult dose.
- Head Lice: Use 1% lotion or cream rinse as directed for adults.
Special Cases:
- Elderly Patients: Same as adult dose for scabies. For head lice, apply as directed for adults.
- Patients with Renal Impairment: No dose adjustment is typically necessary due to minimal systemic absorption.
- Patients with Hepatic Dysfunction: No dose adjustment is typically necessary due to the metabolic pathway.
- Patients with Comorbid Conditions: No specific dose adjustments are usually required. However, caution should be exercised in patients with sensitive skin or pre-existing skin conditions.
Clinical Use Cases
Permethrin topical is not indicated for use in clinical settings like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. Its use is limited to topical treatment of scabies and head lice infestations.
Dosage Adjustments
Dosage adjustments may be needed for patients with extensive body surface area coverage requirements for scabies.
Side Effects
Common Side Effects
Pruritus, burning, stinging, tingling, or numbness of the treated area may occur.
Rare but Serious Side Effects
Severe allergic reactions (rash, hives, difficulty breathing, swelling of the face, lips, tongue, or throat).
Long-Term Effects
No significant long-term side effects are associated with permethrin topical use.
Adverse Drug Reactions (ADR)
Severe skin reactions and allergic manifestations constitute clinically significant ADRs and necessitate immediate intervention.
Contraindications
Hypersensitivity to pyrethrins or any component of the formulation.
Drug Interactions
No significant drug interactions are known for permethrin topical.
Pregnancy and Breastfeeding
Permethrin topical is generally considered safe to use during pregnancy and breastfeeding. It is minimally absorbed systemically, posing a low risk to the fetus or nursing infant. However, it’s always advisable to consult with a healthcare professional before using any medication during pregnancy or while breastfeeding.
Drug Profile Summary
- Mechanism of Action: Disrupts sodium channels in parasite nerve cells, leading to paralysis and death.
- Side Effects: Pruritus, burning, stinging. Rarely, allergic reactions.
- Contraindications: Hypersensitivity to pyrethrins.
- Drug Interactions: None significant.
- Pregnancy & Breastfeeding: Generally safe.
- Dosage: Varies by age and indication. See detailed dosage guidelines.
- Monitoring Parameters: Observe for treatment efficacy and any adverse reactions.
Popular Combinations
Permethrin topical is typically used as a single agent. No specific drug combinations are commonly recommended.
Precautions
- General Precautions: Avoid contact with eyes and mucous membranes. Wash hands thoroughly after application.
- Specific Populations: Use with caution in individuals with sensitive skin.
- Lifestyle Considerations: None specific.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Permethrin Topical?
A: See detailed dosage guidelines above, which vary based on age, indication (scabies or head lice), and formulation (cream or lotion).
Q2: How long should permethrin cream be left on the skin for scabies treatment?
A: Permethrin 5% cream should be left on the skin for 8-14 hours, then washed off thoroughly.
Q3: Can permethrin topical be used in pregnant or breastfeeding women?
A: Generally considered safe, but consult with a healthcare professional before use.
Q4: What are the common side effects of permethrin topical?
A: Common side effects include pruritus, burning, stinging, tingling, or numbness at the application site.
Q5: How often can permethrin be applied?
A: For scabies, a single application is usually sufficient. Reapplication may be considered after 7 days if live mites are still present. For head lice, repeat application after 7 days if lice or nits are still present.
Q6: What should be done if permethrin gets into the eyes?
A: Immediately flush the eyes with plenty of water.
Q7: Can permethrin topical be used to treat other types of insect infestations?
A: No, permethrin topical is specifically indicated for scabies and head lice.
Q8: What should I do if itching persists after scabies treatment with permethrin?
A: Persistent itching can occur for several weeks after treatment and does not necessarily indicate treatment failure. Consult a physician if itching is severe or worsening.
Q9: Are there any drug interactions I should be aware of with permethrin topical?
A: No significant drug interactions are known for permethrin topical.
