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PLANTS-USNIC ACID

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Classification   |    Detailed evidence-based information

Substances Included Synonyms

Therapeutic Toxic Class

    A) Usnic acid is a toxic principle found in a number of species of lichens. It is a phenol (resorcinol) with a dibenzofuran structure.

Specific Substances

    1) Usnein
    2) Usniacin
    3) Usninic Acid
    4) CAS 125-46-2

Available Forms Sources

    A) SOURCES
    1) Found naturally in various genera of lichens.
    2) Proprietary Preparations (JEF Reynolds , 2000).
    3) Omnigran A-(A German preparation of Usnea barbata for use in the cosmetic and pharmaceutical industry).
    4) Granobil (Available in Germany)
    5) Usnagren A and T: Lichen extracts available in Germany.
    6) "Oak Moss", a perfume constituent (Thune et al, 1982; Dahlquist & Fregert, 1981; Rademaker, 2000).
    B) USES
    1) Usnic acid has been marketed as an antibiotic ointment (Mitchell & Rook, 1979). Usnea barbata extract, usnic acid, and copper usnate have been produced as antimicrobial topical preparations (JEF Reynolds , 2000).
    2) In Italy, based on its antimicrobial effect, usnic acid has been found in various topical preparations, which have included: vaginal creams, foot creams and powders, and hair shampoo (Rafanelli et al, 1995).

Overview

Life Support

    A) This overview assumes that basic life support measures have been instituted.

Clinical Effects

    0.2.1) SUMMARY OF EXPOSURE
    A) Little data exists describing the toxic effects of usnic acid in humans. Allergic contact dermatitis has been reported, especially in foresters. Individuals may also be topically exposed to usnic acid by cosmetic or herbal products.
    B) Severe hepatotoxicity, resulting in liver transplantation in two patients, was reported following ingestion of dietary supplements containing usnic acid.
    0.2.4) HEENT
    A) Conjunctivitis has been associated with "wood cutters" eczema, which is considered to be partially due to usnic acid.
    0.2.7) NEUROLOGIC
    A) Ataxia leading to paralysis has been seen in animals.
    0.2.14) DERMATOLOGIC
    A) Dermatitis and skin eruptions can commonly occur from occupational exposure (forestry workers, repeated contact with wood or wood ash), and may also occur following contact with topical herbal products or fragrances that contain usnic acid.

Laboratory Monitoring

    A) Toxic serum or blood concentrations have not been established.

Treatment Overview

    0.4.2) ORAL/PARENTERAL EXPOSURE
    A) In the unlikely event that pure usnic acid has been ingested, dilute prior to giving charcoal.
    B) Systemic poisoning has not been reported in humans. Gastric decontamination is generally NOT necessary and should be considered only after large ingestions.
    C) DILUTION: If no respiratory compromise is present, administer milk or water as soon as possible after ingestion. Dilution may only be helpful if performed in the first seconds to minutes after ingestion. The ideal amount is unknown; no more than 8 ounces (240 mL) in adults and 4 ounces (120 mL) in children is recommended to minimize the risk of vomiting.
    D) ACTIVATED CHARCOAL: Administer charcoal as a slurry (240 mL water/30 g charcoal). Usual dose: 25 to 100 g in adults/adolescents, 25 to 50 g in children (1 to 12 years), and 1 g/kg in infants less than 1 year old.
    E) No specific treatment has been recommended. Treat as with any allergic contact dermatitis. No specific lesion has been found on autopsy of animals lethally exposed. Observe patients for neuromuscular symptoms.
    0.4.4) EYE EXPOSURE
    A) DECONTAMINATION: Remove contact lenses and irrigate exposed eyes with copious amounts of room temperature 0.9% saline or water for at least 15 minutes. If irritation, pain, swelling, lacrimation, or photophobia persist after 15 minutes of irrigation, the patient should be seen in a healthcare facility.
    0.4.5) DERMAL EXPOSURE
    A) OVERVIEW
    1) DECONTAMINATION: Remove contaminated clothing and jewelry and place them in plastic bags. Wash exposed areas with soap and water for 10 to 15 minutes with gentle sponging to avoid skin breakdown. A physician may need to examine the area if irritation or pain persists (Burgess et al, 1999).

Range Of Toxicity

    A) No human cases of toxic ingestion could be found. Dermatitis is not an uncommon symptom seen after exposure to usnic acid containing lichens or products that contain lichen.
    B) Animals who have ingested 1% of their body weight in usnic acid containing lichens for 5 days have had lethal outcomes.

Clinical Effects

Summary Of Exposure

    A) Little data exists describing the toxic effects of usnic acid in humans. Allergic contact dermatitis has been reported, especially in foresters. Individuals may also be topically exposed to usnic acid by cosmetic or herbal products.
    B) Severe hepatotoxicity, resulting in liver transplantation in two patients, was reported following ingestion of dietary supplements containing usnic acid.

Heent

    3.4.1) SUMMARY
    A) Conjunctivitis has been associated with "wood cutters" eczema, which is considered to be partially due to usnic acid.
    3.4.3) EYES
    A) CONJUNCTIVITIS was often seen in association with "woodcutter's eczema", which is due in part to the usnic acid contained in lichens (Mitchell & Rook, 1979).

Neurologic

    3.7.1) SUMMARY
    A) Ataxia leading to paralysis has been seen in animals.
    3.7.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) ATAXIA
    a) Sheep and cattle have developed ataxia, especially of the legs, in mild cases (Kingsbury, 1964).
    2) PARALYSIS
    a) Severe paralysis of the extremities has been seen in some animals (Kingsbury, 1964).

Hepatic

    3.9.2) CLINICAL EFFECTS
    A) INJURY OF LIVER
    1) WITH THERAPEUTIC USE
    a) CASE REPORTS - Severe hepatotoxicity was reported in two patients (husband and wife) after taking a multi-ingredient dietary supplement for 3 months. Each capsule of the supplement contained 150 mg of usnic acid, 525 mg of L-carnitine, and 1050 mg of calcium pyruvate. The dosage regimen for each patient was 3 capsules 3 times daily in 2-week cycles.
    1) The first patient (a 38-year-old woman) developed malaise, abdominal pain, and jaundice. Laboratory tests showed elevated liver enzyme levels. During hospitalization, the patient developed hepatic encephalopathy that worsened, necessitating emergency liver transplantation. Pathology of the explanted liver showed diffuse parenchymal necrosis. The patient gradually recovered and was discharged. One-year post-transplantation, the patient showed normal hepatic allograft function.
    2) The second patient (a 38-year-old man) presented with severe back pain with radicular symptoms approximately at the same time as his wife's liver transplantation. The back pain was due to a weight-lifiting injury and was exacerbated by a 16-hour airline flight. One week prior to presentation, the patient had taken acetaminophen/oxycodone (in recommended dosage) as well as consumed 120 grams of alcohol over a 16-hour period for relief of his back pain. Although the patient was asymptomatic for hepatotoxicity, laboratory studies, performed prior to neurosurgery for disk extrusion, revealed elevated liver enzyme levels. A liver biopsy showed severe acute hepatitis with periportal and lobular inflammation and bridging necrosis. The patient gradually recovered with supportive care (Sanchez et al, 2006).
    b) CASE REPORT - A 28-year-old woman presented with myalgias, arthralgias, vomiting, jaundice, and mild confusion. Over the next several days, she became obtunded, necessitating intubation for airway protection. Laboratory studies revealed elevated liver enzyme levels and negative viral serology results. A brain CT scan showed diffuse edema. The patient continued to deteriorate clinically, remaining unresponsive, and a liver transplantation was performed on hospital day 4. Following the transplantation, the patient completely recovered and was discharged without sequelae.
    1) Histologic examination of the explanted liver showed that there was extensive panlobular parenchymal collapse with the occasional occurrence of perivenular hepatocellular necrosis in the lobules. Further review of the patient's medication history revealed that, one month prior to presentation, she had been taking pure usnic acid, 500 mg daily, for weight loss. She had taken the herbal supplement for 2 weeks, had discontinued for 2 weeks, then had resumed taking the supplement for 4 days (Durazo et al, 2004).

Dermatologic

    3.14.1) SUMMARY
    A) Dermatitis and skin eruptions can commonly occur from occupational exposure (forestry workers, repeated contact with wood or wood ash), and may also occur following contact with topical herbal products or fragrances that contain usnic acid.
    3.14.2) CLINICAL EFFECTS
    A) ECZEMA
    1) WOODCUTTER'S ECZEMA - One of the primary causes of this illness is the usnic acid of lichens. Positive patch testing has been seen with usnic acid (Mitchell & Armitage, 1965; (Champion, 1965).
    B) CONTACT DERMATITIS
    1) SUMMARY - Dermatitis may occur from several sources: burning lichens covered logs, medications, wood cutting, model railroads, cloth dyes and funeral wreaths (Fisher, 1986). Other sources may also include fragrance products and topical herbal remedies (JEF Reynolds , 2000; Rafanelli et al, 1995).
    2) Usnic acid is found in oak moss, which is a lichen extract used in various cosmetics. Using these cosmetics may produce contact sensitivity reactions (Goncalo et al, 1988; Rademaker, 2000).
    3) CASE REPORTS
    a) A 48-year-old female tested positive to oak moss and usnic acid after developing facial dermatitis (Rademaker, 2000). Although conclusive evidence was not found, the elimination of a fragrance product (contained oak moss and usnic acid) resulted in no further symptoms and only reappeared when exposed to lichen in her garden several months later.
    b) Contact dermatitis was reported in a 37-year-old female after using vaginal ovules (commercially produced as an over-the-counter antibiotic cream in Italy) containing usnic acid (Rafanelli et al, 1995). Patch testing was positive for usnic acid.
    C) HYPERSENSITIVITY REACTION
    1) D-usnic acid has been shown to be allergenic, but L-usnic acid was inactive (Mitchell, 1966).
    2) However, Salo et al (1981) found the L-form to be active in a few patients. Some individuals who are sensitive to lichens show negative patch tests to usnic acid; therefore, they may be sensitive to other lichen chemicals such as atranorine, evernic and perlatolic acids (Mitchell & Shibata, 1969; Champion, 1971).
    D) LACK OF EFFECT
    1) PHOTOTOXICITY - Usnic acid was tested and found NOT to have phototoxicity (Mitchell, 1966a) Thune & Solberg, 1980; (Goncalo, 1987).

Laboratory Monitoring

Monitoring Parameters Levels

    4.1.1) SUMMARY
    A) Toxic serum or blood concentrations have not been established.
    4.1.2) SERUM/BLOOD
    A) TOXICITY
    1) Toxic serum or blood concentrations have not been established.

Treatment

Life Support

    A) Support respiratory and cardiovascular function.

Monitoring

    A) Toxic serum or blood concentrations have not been established.

Oral Exposure

    6.5.1) PREVENTION OF ABSORPTION/PREHOSPITAL
    A) SUMMARY
    1) Systemic poisoning has not been reported in humans. Gastric decontamination is generally NOT necessary and should be considered only after large ingestions.
    B) DILUTION
    1) In the unlikely event that pure usnic acid had been ingested, dilute prior to giving activated charcoal.
    2) DILUTION: If no respiratory compromise is present, administer milk or water as soon as possible after ingestion. Dilution may only be helpful if performed in the first seconds to minutes after ingestion. The ideal amount is unknown; no more than 8 ounces (240 mL) in adults and 4 ounces (120 mL) in children is recommended to minimize the risk of vomiting (Caravati, 2004).
    C) ACTIVATED CHARCOAL
    1) PREHOSPITAL ACTIVATED CHARCOAL ADMINISTRATION
    a) Consider prehospital administration of activated charcoal as an aqueous slurry in patients with a potentially toxic ingestion who are awake and able to protect their airway. Activated charcoal is most effective when administered within one hour of ingestion. Administration in the prehospital setting has the potential to significantly decrease the time from toxin ingestion to activated charcoal administration, although it has not been shown to affect outcome (Alaspaa et al, 2005; Thakore & Murphy, 2002; Spiller & Rogers, 2002).
    1) In patients who are at risk for the abrupt onset of seizures or mental status depression, activated charcoal should not be administered in the prehospital setting, due to the risk of aspiration in the event of spontaneous emesis.
    2) The addition of flavoring agents (cola drinks, chocolate milk, cherry syrup) to activated charcoal improves the palatability for children and may facilitate successful administration (Guenther Skokan et al, 2001; Dagnone et al, 2002).
    2) CHARCOAL DOSE
    a) Use a minimum of 240 milliliters of water per 30 grams charcoal (FDA, 1985). Optimum dose not established; usual dose is 25 to 100 grams in adults and adolescents; 25 to 50 grams in children aged 1 to 12 years (or 0.5 to 1 gram/kilogram body weight) ; and 0.5 to 1 gram/kilogram in infants up to 1 year old (Chyka et al, 2005).
    1) Routine use of a cathartic with activated charcoal is NOT recommended as there is no evidence that cathartics reduce drug absorption and cathartics are known to cause adverse effects such as nausea, vomiting, abdominal cramps, electrolyte imbalances and occasionally hypotension (None Listed, 2004).
    b) ADVERSE EFFECTS/CONTRAINDICATIONS
    1) Complications: emesis, aspiration (Chyka et al, 2005). Aspiration may be complicated by acute respiratory failure, ARDS, bronchiolitis obliterans or chronic lung disease (Golej et al, 2001; Graff et al, 2002; Pollack et al, 1981; Harris & Filandrinos, 1993; Elliot et al, 1989; Rau et al, 1988; Golej et al, 2001; Graff et al, 2002). Refer to the ACTIVATED CHARCOAL/TREATMENT management for further information.
    2) Contraindications: unprotected airway (increases risk/severity of aspiration) , nonfunctioning gastrointestinal tract, uncontrolled vomiting, and ingestion of most hydrocarbons (Chyka et al, 2005).
    6.5.2) PREVENTION OF ABSORPTION
    A) SUMMARY
    1) Systemic poisoning has not been reported in humans. Gastric decontamination is generally NOT necessary and should be considered only after large ingestions.
    B) DILUTION
    1) In the unlikely event that pure usnic acid had been ingested, dilute prior to giving charcoal.
    2) DILUTION: If no respiratory compromise is present, administer milk or water as soon as possible after ingestion. Dilution may only be helpful if performed in the first seconds to minutes after ingestion. The ideal amount is unknown; no more than 8 ounces (240 mL) in adults and 4 ounces (120 mL) in children is recommended to minimize the risk of vomiting (Caravati, 2004).
    C) ACTIVATED CHARCOAL
    1) CHARCOAL ADMINISTRATION
    a) Consider administration of activated charcoal after a potentially toxic ingestion (Chyka et al, 2005). Administer charcoal as an aqueous slurry; most effective when administered within one hour of ingestion.
    2) CHARCOAL DOSE
    a) Use a minimum of 240 milliliters of water per 30 grams charcoal (FDA, 1985). Optimum dose not established; usual dose is 25 to 100 grams in adults and adolescents; 25 to 50 grams in children aged 1 to 12 years (or 0.5 to 1 gram/kilogram body weight) ; and 0.5 to 1 gram/kilogram in infants up to 1 year old (Chyka et al, 2005).
    1) Routine use of a cathartic with activated charcoal is NOT recommended as there is no evidence that cathartics reduce drug absorption and cathartics are known to cause adverse effects such as nausea, vomiting, abdominal cramps, electrolyte imbalances and occasionally hypotension (None Listed, 2004).
    b) ADVERSE EFFECTS/CONTRAINDICATIONS
    1) Complications: emesis, aspiration (Chyka et al, 2005). Aspiration may be complicated by acute respiratory failure, ARDS, bronchiolitis obliterans or chronic lung disease (Golej et al, 2001; Graff et al, 2002; Pollack et al, 1981; Harris & Filandrinos, 1993; Elliot et al, 1989; Rau et al, 1988; Golej et al, 2001; Graff et al, 2002). Refer to the ACTIVATED CHARCOAL/TREATMENT management for further information.
    2) Contraindications: unprotected airway (increases risk/severity of aspiration) , nonfunctioning gastrointestinal tract, uncontrolled vomiting, and ingestion of most hydrocarbons (Chyka et al, 2005).
    6.5.3) TREATMENT
    A) SUPPORT
    1) No specific treatment has been recommended. No specific lesion has been found on autopsy of animals lethally exposed. Symptoms in animals have been neuromuscular. Observe for ataxia and gait abnormalities if large quantities have been ingested.

Eye Exposure

    6.8.1) DECONTAMINATION
    A) EYE IRRIGATION, ROUTINE: Remove contact lenses and irrigate exposed eyes with copious amounts of room temperature 0.9% saline or water for at least 15 minutes. If irritation, pain, swelling, lacrimation, or photophobia persist after 15 minutes of irrigation, an ophthalmologic examination should be performed (Peate, 2007; Naradzay & Barish, 2006).

Dermal Exposure

    6.9.1) DECONTAMINATION
    A) DERMAL DECONTAMINATION
    1) DECONTAMINATION: Remove contaminated clothing and wash exposed area thoroughly with soap and water for 10 to 15 minutes. A physician may need to examine the area if irritation or pain persists (Burgess et al, 1999).

Range Of Toxicity

Summary

    A) No human cases of toxic ingestion could be found. Dermatitis is not an uncommon symptom seen after exposure to usnic acid containing lichens or products that contain lichen.
    B) Animals who have ingested 1% of their body weight in usnic acid containing lichens for 5 days have had lethal outcomes.

Minimum Lethal Exposure

    A) ANIMAL DATA
    1) One percent of an animal's body weight of the usnic acid containing lichens (genus Parmelia) given for 5 days proved to be lethal. A single dose of 3.6% was also fatal. Both of these involved an amount in excess of what would be seen under natural feeding conditions (Kingsbury, 1964).

Maximum Tolerated Exposure

    A) GENERAL/SUMMARY
    1) No human cases of toxic ingestions could be found. Dermatitis is not an uncommon symptom seen after exposure to usnic acid containing lichens or products that contain lichen.

Toxicity Information

    7.7.1) TOXICITY VALUES
    A) LD50- (SUBCUTANEOUS)MOUSE:
    1) 75 mg/kg (RTECS, 2000)

Pharmacology Toxicology

Pharmacologic Mechanism

    A) Usnic acid has been reported to have antimicrobial activity (JEF Reynolds , 2000; Gonzalez et al, 1991), against Bacillus subtulis, Staphylococcus aureus, Streptococcus faecalis, Aspergillus niger and Penicillium chrysogenum, but not against Escherichia coli or Pseudomonas aeruginosa (Ahmadjian & Reynolds, 1961).
    B) Its mechanism as an antibiotic is apparently the uncoupling of the fixation of inorganic phosphate normally associated with oxidative reactions (Mitchell & Armitage, 1965).
    C) It is chemically related to the furocoumarins, but is NOT a photosensitizer (Fisher, 1973; (Goncalo, 1987).

Toxicologic Mechanism

    A) No specific target lesion or organ was found on autopsy of experimental animals exposed to lethal concentrations (Kingsbury, 1964).

Physicochemical

Physical Characteristics

    A) Usnic Acid: Yellow orthorhombic prisms.
    B) Sodium Dihydrate Salt: Pale yellow, silky, needles.

Molecular Weight

    A) 344.31 (Usnic Acid)

References

General Bibliography

    1) Ahmadjian V & Reynolds JT: Production of biologically active compounds by isolated lichenized fungi. Science 1961; 133:700-701.
    2) Alaspaa AO, Kuisma MJ, Hoppu K, et al: Out-of-hospital administration of activated charcoal by emergency medical services. Ann Emerg Med 2005; 45:207-12.
    3) Burgess JL, Kirk M, Borron SW, et al: Emergency department hazardous materials protocol for contaminated patients. Ann Emerg Med 1999; 34(2):205-212.
    4) Caravati EM: Alkali. In: Dart RC, ed. Medical Toxicology, Lippincott Williams & Wilkins, Philadelphia, PA, 2004.
    5) Champion RH: Atopic sensitivity to algae and lichens. Br J Dermatol 1971; 85:551-557.
    6) Champion RH: Wood-cutter's disease. Contact sensitivity to lichen. Br J Dermatol 1965; 77:285.
    7) Chyka PA, Seger D, Krenzelok EP, et al: Position paper: Single-dose activated charcoal. Clin Toxicol (Phila) 2005; 43(2):61-87.
    8) Dagnone D, Matsui D, & Rieder MJ: Assessment of the palatability of vehicles for activated charcoal in pediatric volunteers. Pediatr Emerg Care 2002; 18:19-21.
    9) Dahlquist I & Fregert S: Atranorin and oak moss contact allergy. Contact Derm 1981; 7:168-169.
    10) Durazo FA, Lassman C, Han SH, et al: Fulminant liver failure due to usnic acid for weight loss. Am J Gastroenterol 2004; 99(5):950-952.
    11) Elliot CG, Colby TV, & Kelly TM: Charcoal lung. Bronchiolitis obliterans after aspiration of activated charcoal. Chest 1989; 96:672-674.
    12) FDA: Poison treatment drug product for over-the-counter human use; tentative final monograph. FDA: Fed Register 1985; 50:2244-2262.
    13) Fisher AA: Contact Dermatitis, 3rd ed, Lea and Febiger, Philadelphia, 1986, pp 430-431-439.
    14) Golej J, Boigner H, Burda G, et al: Severe respiratory failure following charcoal application in a toddler. Resuscitation 2001; 49:315-318.
    15) Goncalo S, Cabral F, & Goncalo M: Contact sensitivity to oak moss. Contact Derm 1988; 19:355-357.
    16) Goncalo S: Contact sensitivity to lichens and compositae in Frullania dermatitis. Contact Derm 1987; 16:84-86.
    17) Gonzalez AG, Rodriquez-Perez EM, & Barrera JB: Biologically active compounds from the lichen Ramalina hierrensis. Planta Medica 1991; 57(Suppl):A2.
    18) Graff GR, Stark J, & Berkenbosch JW: Chronic lung disease after activated charcoal aspiration. Pediatrics 2002; 109:959-961.
    19) Guenther Skokan E, Junkins EP, & Corneli HM: Taste test: children rate flavoring agents used with activated charcoal. Arch Pediatr Adolesc Med 2001; 155:683-686.
    20) Harris CR & Filandrinos D: Accidental administration of activated charcoal into the lung: aspiration by proxy. Ann Emerg Med 1993; 22:1470-1473.
    21) JEF Reynolds : Martindale: The Extra Pharmacopoeia. The Pharmaceutical Press. London, UK (Internet Version). Edition expires 2000; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    22) Kingsbury JM: Poisonous Plants of the United States and Canada, Prentice-Hall, Inc, Englewood Cliffs, NJ, 1964, pp 86-87.
    23) Mitchell J & Rook A: Botanical Dermatology, Greengrass, Vancouver, BC, 1979, pp 434-436.
    24) Mitchell JC & Shibata S: Immunological activity of some substances derived from lichenized fungi. J Invest Dermatol 1969; 52:517-520.
    25) Mitchell JC: Absence of psoralen-type phototoxicity from usnic acid, some lichens and lichen substances. J Invest Dermatol 1966a; 47:61-62.
    26) Mitchell JC: Allergy to lichens. Arch Dermatol 1965; 92:142-146.
    27) Mitchell JC: Stereoisomeric specificity of usnic acid in delayed hypersensitivity. J Invest Dermatol 1966; 47:167-168.
    28) Naradzay J & Barish RA: Approach to ophthalmologic emergencies. Med Clin North Am 2006; 90(2):305-328.
    29) None Listed: Position paper: cathartics. J Toxicol Clin Toxicol 2004; 42(3):243-253.
    30) Peate WF: Work-related eye injuries and illnesses. Am Fam Physician 2007; 75(7):1017-1022.
    31) Pollack MM, Dunbar BS, & Holbrook PR: Aspiration of activated charcoal and gastric contents. Ann Emerg Med 1981; 10:528-529.
    32) Rademaker M: Allergy to lichen acids in a fragrance. Aust J Dermatol 2000; 41:50-51.
    33) Rafanelli S, Bacchilega R, & Stanganelli I: Contact dermatitis from usnic acid in vaginal ovules (letter). Contact Derm 1995; 33:271-272.
    34) Rau NR, Nagaraj MV, Prakash PS, et al: Fatal pulmonary aspiration of oral activated charcoal. Br Med J 1988; 297:918-919.
    35) Sanchez W, Maple JT, Burgart LJ, et al: Severe hepatotoxicity associated with use of a dietary supplement containing usnic acid. Mayo Clin Proc 2006; 81(4):541-544.
    36) Spiller HA & Rogers GC: Evaluation of administration of activated charcoal in the home. Pediatrics 2002; 108:E100.
    37) Thakore S & Murphy N: The potential role of prehospital administration of activated charcoal. Emerg Med J 2002; 19:63-65.
    38) Thune P, Solberg Y, & McFadden N: Perfume allergy due to oak moss and other lichens. Contact Derm 1982; 8:396-400.