Chrysanthème Insecticide, Chrysanthemum cinerariifolium, Dalmation Insect Flowers, Dalmation Pellitory, Pelitre, Piretro, Pyrèthre, Pyrèthre de Dalmatie, Pyrethrum cinerariifolium, Tanacetum cinerariifolium.
Pyrethrum is a plant (Chrysanthemum cinerariifolium). Pyrethrum is also the name of the crude extract obtained from flowers of this plant.
Be careful not to confuse pyrethrum with pyrethrin. Pyrethrin refers to a more refined extract of pyrethrum. Pyrethrin is in body lice medicines such as A-200 Pyrinate, Barc, Lice-Enz, Licetrol, Pronto, R and C, RID, Tisit, Tisit Blue, and Triple X.
How does it work?
The active chemicals, the pyrethrins, are toxic to insect nervous systems.
- Head lice and crab lice. Applying pyrethrins to the skin in concentrations of 0.17% to 0.33% for 12-24 hours is effective for treating head lice and crab lice. Pyrethrins are usually combined with piperonyl butoxide (2% to 4%) to increase effectiveness.
- Scabies (mites).
Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).
The commercially available combination of pyrethrins (0.17-0.33%) and piperonyl butoxide (2-4%) seems to be safe when applied to the skin in a nonaerosol product.
Pyrethrum is POSSIBLY SAFE when used on the skin in amounts less than 2 grams. While pyrethrum has limited toxicity at low doses, it can cause some side effects such as headache, ringing of the ears, nausea, tingling of fingers and toes, breathing problems, and other nervous system problems.
Children: It's UNSAFE to put pyrethrum on children less than two years old.
Allergy to ragweed and related plants: The pyrethrum flower or pyrethrin extracted from it may cause an allergic reaction in people who are sensitive to the Asteraceae/Compositae family. Members of this family include ragweed, chrysanthemums, marigolds, daisies, and many others. If you have allergies, be sure to check with your healthcare provider before using pyrethrum.
The following doses have been studied in scientific research:
APPLIED TO THE SKIN:
- For treating head lice and crab lice: An over-the-counter (OTC) product that combines pyrethrins (0.17% to 0.33%) and piperonyl butoxide (2% to 4%) is applied to the affected area and allowed to remain for at least 10 minutes. The product is then thoroughly washed off with warm water. Pyrethrins are extracted from pyrethrum, and kill lice by harming their nervous systems.
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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Covington TR, et al. Handbook of Nonprescription Drugs. 11th ed. Washington, DC: American Pharmaceutical Association, 1996.
Drugs in Pregnancy and Lactation. 4th ed. Baltimore, MD: Williams & Wilkins, 1994.
Hardman JG, Limbird LL, Molinoff PB, eds. Goodman and Gillman's The Pharmacological Basis of Therapeutics, 9th ed. New York, NY: McGraw-Hill, 1996.
Wagner SL. Fatal asthma in a child after use of an animal shampoo containing pyrethrin. West J Med 2000;173:86-7. View abstract.