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Malathion (Topical)


VA CLASSIFICATION
Primary: AP300

Commonly used brand name(s): Derbac-M; Ovide; Suleo-M.

Note: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).

Not commercially available in Canada.



Category:


Pediculicide—
Note: Malathion is an organophosphate cholinesterase inhibitor generally used as an insecticide.



Indications

Accepted

Pediculosis capitis (treatment)—Malathion is indicated for the treatment of infestation caused by Pediculus humanus var. capitis (head lice) and their ova. {14}


Pharmacology/Pharmacokinetics

Physicochemical characteristics:
Molecular weight—
    330.4 {03} {14}

Mechanism of action

Malathion acts via cholinesterase inhibition. It exerts both lousicidal and ovicidal actions in vitro .

Absorption:

Malathion in an acetone vehicle has been reported to be absorbed through normal human skin only to the extent of 8% of the applied dose. {14} Percutaneous absorption of malathion in alcohol has not been studied; {14} malathion lotion contains 78% isopropyl alcohol. {14} Absorption may be increased when malathion is applied to damaged skin.


Precautions to Consider

Note: Although topical malathion used in recommended dosage has not been reported to cause cholinesterase inhibition, the possibility exists.


Carcinogenicity

Carcinogenicity studies with topical malathion have not been done. However, studies in animals have not shown that malathion is carcinogenic in either male or female F344 rats fed for 2 years with up to 4000 ppm (0.4%) of malathion. Doses tested are approximately 4 to 40 times greater than those anticipated in humans (based on body surface area and assuming 100% bioavailability). {14}

Tumorigenicity

Studies in animals have not shown that malathion is tumorigenic in either Osborn-Mendel rats or B6C3F1 mice after feeding for 80 weeks with 8000 ppm (0.8%) and 16,000 ppm (1.6%) of malathion, respectively. Doses tested are approximately 4 to 40 times greater than those anticipated in humans (based on body surface area and assuming 100% bioavailability).{14}

Mutagenicity

Studies on the mutagenic effects of malathion have not been done. However, malathion has been shown to be genotoxic in several in vitro and in vivo mutation and clastogenicity assays.{14}

Pregnancy/Reproduction
Fertility—
Studies in humans have not been done.

Reproductive studies in rats at doses approximately 30 times greater than those anticipated in humans (based on body surface area and assuming 100% bioavailability) did not show impaired fertility.{14}

Pregnancy—
Studies in humans have not been done. However, malathion in an acetone vehicle has been shown to be systemically absorbed.{14}

Studies in rats and rabbits at doses approximately 2 to 10 times higher than anticipated human dose (based on body surface area and 100% bioavailability) have not shown that malathion causes adverse effects in the fetus. {14} {11}

FDA Pregnancy Category B. {14}

Breast-feeding

It is not known whether malathion is distributed into breast milk. Problems in humans have not been documented; however, malathion in an acetone vehicle has been shown to be systemically absorbed. {14}

Pediatrics

Malathion should not be used in neonates and infants because their scalps are more permeable and may have increased absorption.{14}

Children up to 6 years of age—Appropriate studies on the relationship of age to the effects of malathion have not been performed in children under 6 years of age. Safety and efficacy have not been established.{14}


Geriatrics


Appropriate studies on the relationship of age to the effects of malathion have not been performed in the geriatric population. However, no geriatrics-specific problems have been documented to date.

Drug interactions and/or related problems
The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):


Note: Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.

Aminoglycosides, parenteral    (if significant systemic absorption of topical malathion occurs, concurrent use may result in additive respiratory depression because of the neuromuscular blocking action of parenteral aminoglycosides)


Anesthetics, mucosal-local, ester-derivative, such as benzocaine, butacaine, butamben, and tetracaine    (if significant systemic absorption of topical malathion occurs, concurrent use may inhibit the metabolism of ester-derivative local anesthetics, including those topically applied and absorbed in significant amounts, leading to increased risk of systemic toxicity)


» Antimyasthenics or
» Cholinesterase inhibitors, other    (if significant systemic absorption of topical malathion occurs, concurrent use of antimyasthenics or other cholinesterase inhibitors [including ophthalmic cholinesterase inhibitors] with topical malathion may result in additive toxicity)


Carbamate- or organophosphate-type insecticides or pesticides    (if systemic absorption of topical malathion occurs, exposure to these preparations may increase the possibility of systemic effects due to absorption of the insecticide or pesticide through the respiratory tract or skin; patients should be advised to protect themselves from contact with such insecticides or pesticides during therapy with malathion)


Cocaine    (if significant systemic absorption of topical malathion occurs, the resulting inhibition of cholinesterase activity reduces or slows cocaine metabolism, thereby increasing and/or prolonging cocaine's effects and increasing the risk of toxicity {08})


Edrophonium    (since systemic absorption of topical malathion may occur, caution is recommended in administering edrophonium to patients with symptoms of myasthenic weakness who are also using topical malathion because symptoms of cholinergic crisis [overdosage] may be similar to symptoms occurring with myasthenic crisis [underdosage] and the patient's condition may be worsened by use of edrophonium)


» Succinylcholine    (if significant systemic absorption of topical malathion occurs, plasma concentrations or activity of pseudocholinesterase, the enzyme that metabolizes succinylcholine, may be decreased, thereby enhancing the neuromuscular blockade of succinylcholine when the two medications are used concurrently; increased or prolonged respiratory depression or paralysis [apnea] may occur but is of minor clinical significance while the patient is being mechanically ventilated; however, caution and careful monitoring of the patient are recommended following sequential use)


Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).


Risk-benefit should be considered when the following medical problems exist
Asthma, bronchial    (significant systemic absorption of malathion may precipitate an asthmatic attack)


Bradycardia and hypotension, pronounced or
Gastrointestinal disturbances, spastic or
Myocardial infarction, recent or
Parkinsonism or
Peptic ulcer or
Vagotonia, severe    (significant systemic absorption of malathion may exacerbate condition due to vagotonic effects of malathion)


Brain surgery, recent    (significant systemic absorption of malathion may cause central nervous system [CNS] toxicity, including seizures)


Conditions in which low concentrations of plasma cholinesterase may exist, such as:
Anemia, severe
Dehydration
Exposure to neurotoxic insecticides
Hepatic disease, severe or cirrhosis
Malnutrition
Recessive hereditary trait    (significant systemic absorption of malathion may result in additive respiratory depression)


Neuromuscular disease, such as myasthenia gravis    (significant systemic absorption of malathion may exacerbate condition)


Seizure disorders    (significant systemic absorption of malathion may precipitate seizures)


Sensitivity to malathion


Side/Adverse Effects

Note: Although topical malathion used in recommended dosage has not been reported to cause systemic toxicity, the possibility exists.
Malathion is considered to be one of the least toxic organophosphorus insecticides because it is hydrolyzed and detoxified much more rapidly in mammals than in insects. The estimated lethal dose of malathion in mammals is 1 gram per kg of body weight. Daily application of 10% malathion dust to adult human skin for 3 weeks has been shown to produce little or no inhibition of blood cholinesterase.

The following side/adverse effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Those indicating need for medical attention
Incidence rare
    
Allergic contact dermatitis (skin rash)

Symptoms of systemic toxicity
— may be delayed for up to 12 hours    
Abdominal cramps
    
anxiety or restlessness
    
clumsiness or unsteadiness
    
confusion or mental depression
    
diarrhea
    
dizziness
    
drowsiness
    
increased sweating
    
increased watering of mouth or eyes
    
loss of bowel or bladder control
    
muscle twitching of eyelids, face, and neck
    
pinpoint pupils
    
respiratory distress {09} ( difficult or labored breathing)
    
seizures
    
slow heartbeat
    
trembling
    
unusual weakness



Those indicating need for medical attention only if they continue or are bothersome
Incidence less frequent or rare
    
Conjunctivitis, mild (redness, pain, swelling of eye, eyelid, or inner lining of eyelid burning; dry or itching eyes; discharge; excessive tearing)—with accidental eye contact{14}
    
stinging or irritation of scalp {14}





Overdose
For specific information on the agents used in the management of malathion overdose, see:
   • Atropine in Anticholinergics/Antispasmodics (Systemic) monograph; and/or
   • Pralidoxime monograph.
For more information on the management of overdose or unintentional ingestion, contact a poison control center (see Poison Control Center Listing).

Clinical effects of overdose
The following effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Consideration should be given to the high concentration of isopropyl alcohol in the vehicle.{14}

Respiratory distress, severe (shortness of breath; troubled breathing)

Treatment of overdose
To decrease absorption—If accidentally swallowed, vomiting should be promptly induced or stomach lavaged with 5% sodium bicarbonate solution.{14}

Specific treatment—Atropine may be needed to counteract the symptoms of cholinesterase depletion.{14} The usual initial dose of atropine is 1 to 4 mg, with supplemental doses administered as needed. {09}Intravenous pralidoxime chloride may be used as an adjunct to atropine and supportive measures to reverse muscle paralysis. It appears to be most effective if administered within a few hours after poisoning occurs; it is usually not effective if initially administered after 48 hours have elapsed. A short-acting barbiturate may be given to control seizures.

Supportive care—Artificial respiration may be required for severe respiratory distress.{14}

Monitoring—Repeat analyses of serum and RBC cholinesterase may assist in establishing the diagnosis and formulating a long-range prognosis.{14}

Patients in whom intentional overdose is known or suspected should be referred for psychiatric consultation.


Patient Consultation
As an aid to patient consultation, refer to Advice for the Patient, Malathion (Topical).

In providing consultation, consider emphasizing the following selected information (» = major clinical significance):

Before using this medication
»   Conditions affecting use, especially:
Sensitivity to malathion
Other medications, especially antimyasthenics or other cholinesterase inhibitors

Proper use of this medication
» Not to be ingested; importance of keeping away from mouth and eyes

» Importance of not using more medication than the amount prescribed

Proper administration technique
Applying by sprinkling on dry hair; rubbing in until hair and scalp thoroughly moistened

Washing hands immediately after using medication

Allowing hair to dry naturally; using no heat and leaving hair uncovered

Leaving medication on hair and scalp for 8 to 12 hours

» Washing hair with nonmedicated shampoo and rinsing thoroughly

Using fine-toothed comb to remove dead lice and eggs from hair
» Avoiding contact with the eyes

Medication is flammable; not using near heat, near open flame, or while smoking

» Importance of household family members being examined for infestation, and treated if infested

» Proper dosing

» Proper storage

Precautions while using this medication

Using hygienic measures to control reinfestation or spread of infestation
Washing all clothing, bedding, towels, and washcloths in very hot water or dry-cleaning them

Washing hairbrushes and combs in very hot soapy water; not sharing them with other people

Cleaning house or room by thorough vacuuming
Caution in exposure to carbamate- or organophosphate-type insecticides or pesticides during therapy


Side/adverse effects
Signs of potential side effects, especially skin rash or symptoms of systemic toxicity such as abdominal cramps, anxiety or restlessness, clumsiness or unsteadiness, confusion or mental depression, diarrhea, dizziness, drowsiness, increased sweating, increased watering of mouth or eyes, loss of bowel or bladder control, muscle twitching of eyelids, face, and neck, pinpoint pupils, respiratory distress, seizures, slow heartbeat, or trembling, unusual weakness.


General Dosing Information
Malathion lotion contains 78% isopropyl alcohol. {14}

For treatment of adverse effects
If skin irritation occurs, wash scalp and hair immediately. If the irritation clears, malathion may be reapplied, otherwise consult a physician.{14}

If eye irritation occurs when contact with malathion, flush eyes immediately with water. If irritation persists or visual changes occur, consult a physician.{14}


Topical Dosage Forms

MALATHION LOTION USP

Usual adult and adolescent dose
Pediculosis capitis
Topical, to the hair and scalp, as a 0.5% lotion for one application, repeated after seven to nine days, if necessary. {14}


Usual pediatric dose
Infants and children up to 6 years of age—Safety and efficacy have not been established. {14}

Children 6 years of age and older—See Usual adult and adolescent dose. {14}

Strength(s) usually available
U.S.—


0.5% (Rx) [Ovide (isopropyl alcohol 78%) (pine needle oil)]

Canada—
Not commercially available.

Other countries—


0.5% [Derbac-M{12}] [Suleo-M{12}]

Packaging and storage:
Store below 40 °C (104 °F), preferably between 15 and 30 °C (59 and 86 °F), unless otherwise specified by manufacturer. Store in a tight container. Protect from freezing.

Auxiliary labeling:
   • For external use only.
   • Flammable



Revised: 06/10/2002



References
  1. Comment from manufacturer
  1. Hold
  1. Reynolds JEF, editor. Martindale, the extra pharmacopeia. 28th ed. London: The Pharmaceutical Press, 1982: 838-9.
  1. Hold
  1. Hold
  1. Hold
  1. Fleeger CA, editor. USAN 1988. USAN and the USP dictionary of drug names. Rockville, MD: The United States Pharmacopeial Convention, Inc., 1987: 393.
  1. Drug Information change sheet from EK re Cocaine, 12/87.
  1. Ovide package insert (GenDerm—US), Rev 89, Rec 2/90.
  1. Not used
  1. Prioderm product monograph (Block—Canada), Rev 1/89, Rec 5/90.
  1. Reynolds JEF, editor. Martindale, the extra pharmacopeia. 29th ed. London: The Pharmaceutical Press, 1989: 1351.
  1. Not used.
  1. Product Information: Ovide, malathion. Medicis, Phoenix, AZ, (PI revised 1999), reviewed 1/2000.
  1. Comment from Manufacturer (6/2002)
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