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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Malathion
Generic Name
Malathion
Active Ingredient
MalathionCategory
Cholinesterase Inhibitor [EPC]
Variants
2
Different strengths and dosage forms
| Strength | Form | Route | NDC |
|---|---|---|---|
| .005 g/mL | LOTION | TOPICAL | 68022-0001 |
| .0005 g/mL | LOTION | TOPICAL | 51672-5294 |
References used for this content
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Malathion, you must consult a qualified healthcare professional.
Detailed information about Malathion
Malathion is a potent organophosphate pediculicide used for the topical treatment of head lice and their eggs. It acts as an irreversible cholinesterase inhibitor in insects, providing a high cure rate for infestations.
For the treatment of head lice in adults, the standard dosage is a single application of Malathion Lotion, 0.5%. The amount of lotion required depends on the length and thickness of the hair.
Malathion is approved for use in children aged 6 years and older.
Because systemic absorption of topical malathion is minimal (less than 10%), dosage adjustments are generally not required for patients with renal impairment. However, such patients should be monitored for any unusual systemic effects.
Similar to renal impairment, hepatic adjustments are typically unnecessary for topical use. The rapid hydrolysis of absorbed malathion by plasma carboxylesterases reduces the burden on the liver.
Clinical studies did not include sufficient numbers of subjects aged 65 and over to determine if they respond differently than younger subjects. In general, dose selection for an elderly patient should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function.
Malathion is for external topical use only. It should never be ingested or applied to mucous membranes.
Since malathion is typically a one-time application (or two applications spaced a week apart), a 'missed dose' usually refers to forgetting the second application if lice persist. If you forget to apply the second treatment on day 7 or 9, apply it as soon as you remember, provided live lice are still present.
Accidental ingestion of malathion can lead to severe organophosphate poisoning, characterized by a 'cholinergic crisis.' Symptoms include excessive salivation, lacrimation (tearing), urination, defecation, gastrointestinal distress, and emesis (vomiting)—often abbreviated as SLUDGE. More severe signs include muscle twitching, respiratory distress, and seizures.
In the event of ingestion, seek emergency medical attention immediately. Treatment typically involves the administration of atropine and pralidoxime (2-PAM) as antidotes.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or re-apply the medication more frequently than directed without medical guidance.
Most patients tolerate malathion well when it is used correctly. However, because the formulation contains high concentrations of alcohol and other volatile oils, local skin reactions are common.
The most critical safety warning regarding malathion is its extreme flammability. Because the lotion contains 78% isopropyl alcohol, it can easily ignite. Patients and caregivers must be strictly instructed to avoid smoking, open flames, and heat sources while the hair is wet with the lotion. This includes avoiding the use of hair dryers, curling irons, or flat irons. The hair should be allowed to air dry naturally and remain uncovered.
No FDA black box warnings for Malathion. However, the 'Flammable' warning is a primary safety consideration that must be communicated to every patient.
Patients with a known allergy to malathion or any of the inactive ingredients (such as terpineol or pine needle oil) should not use this product. Anaphylaxis is rare but possible. If a patient has a history of severe allergies to other pesticides or organophosphates, a patch test or alternative treatment may be warranted.
While topical malathion has low systemic absorption, certain combinations should be avoided to prevent cumulative toxicity:
Malathion must NEVER be used in the following circumstances:
Malathion is classified as FDA Pregnancy Category B. This means that animal reproduction studies have failed to demonstrate a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. Because animal studies are not always predictive of human response, malathion should be used during pregnancy only if clearly needed.
It is not known whether topical malathion is excreted in human milk. However, many drugs are excreted in human milk, and because of the potential for serious adverse reactions in nursing infants from malathion, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. If used, the mother should ensure the infant does not come into contact with the treated hair or scalp until it has been thoroughly washed.
Malathion is an organophosphate that acts as a potent, irreversible inhibitor of the enzyme acetylcholinesterase (AChE). In the target parasite (Pediculus humanus capitis), malathion is metabolically activated via oxidative desulfuration to its oxygen analog, malaoxon. This conversion is much more efficient in insects than in humans. Malaoxon binds to the active site of AChE, preventing the hydrolysis of the neurotransmitter acetylcholine. This results in permanent overstimulation of the insect's nervous system, leading to paralysis and death. Malathion also possesses ovicidal activity (killing the eggs), though the exact mechanism for its penetration through the nit shell is enhanced by the alcohol and terpene carriers in the formulation.
The pharmacodynamic effect of malathion is localized to the site of application (the scalp and hair). The onset of action against adult lice is rapid, with paralysis occurring shortly after contact. However, to ensure the death of all nits, a contact time of 8 to 12 hours is clinically required. There is no evidence of tolerance development in individual patients, although 'resistance' in the lice population (due to genetic mutations in their AChE enzymes) is a recognized public health concern.
Common questions about Malathion
Malathion is a prescription medication primarily used for the topical treatment of head lice (Pediculus humanus capitis) and their eggs, known as nits. It belongs to a class of drugs called organophosphates and acts as a potent insecticide that paralyzes and kills lice by inhibiting a key enzyme in their nervous system. Healthcare providers typically prescribe it for patients 6 years of age and older, often when other over-the-counter treatments have failed. It is formulated as a 0.5% lotion that must be applied to the scalp and hair according to specific safety protocols. Because it is a powerful medication, it should only be used under the guidance of a medical professional.
The most common side effects of Malathion lotion are localized to the area of application on the scalp. Patients frequently report skin irritation, itching, or a mild stinging and burning sensation, which is often due to the high alcohol content of the formulation. Some individuals may also experience temporary redness or dry skin on the scalp and neck. These effects are usually mild and resolve once the medication is washed out after the 8-12 hour treatment period. If you experience severe blistering, swelling, or signs of an allergic reaction, you should contact your healthcare provider immediately.
There is no known direct drug interaction between oral alcohol consumption and the topical use of Malathion. However, because Malathion lotion itself is highly flammable and contains 78% isopropyl alcohol, it is vital that patients and caregivers remain fully alert and cautious during the application process. Consuming alcohol could potentially impair your ability to follow the strict fire safety instructions required for this treatment. It is generally recommended to avoid alcohol until the treatment has been safely washed off and the hair is dry. Always discuss your lifestyle habits with your doctor when starting a new prescription.
Malathion is classified as FDA Pregnancy Category B, which indicates that while animal studies have not shown harm to the fetus, there are no comprehensive studies in pregnant women. Because systemic absorption through the skin is low (less than 10%), the risk to the developing fetus is generally considered to be minimal when the drug is used correctly. However, healthcare providers typically only prescribe Malathion during pregnancy if the benefits clearly outweigh the potential risks. If you are pregnant or planning to become pregnant, you must discuss the use of this medication with your obstetrician or primary care provider. They may suggest alternative treatments or provide specific instructions for safe use.
Malathion begins working to paralyze adult lice shortly after contact, but it requires a significant amount of time to effectively kill all the lice and their eggs (nits). The lotion must be left on the hair and scalp for a full 8 to 12 hours to ensure maximum efficacy. After this period, the hair is washed, and a nit comb is used to remove the dead parasites. While many infestations are cleared with a single application, your healthcare provider will likely ask you to check for live lice again in 7 to 9 days. If live lice are still present at that time, a second application may be necessary to complete the treatment.
Malathion is not a daily medication; it is a one-time or two-time topical treatment for an active lice infestation. Therefore, 'stopping' the medication suddenly is not applicable in the same way it would be for a chronic pill. However, if you develop a severe skin reaction or chemical burn while the lotion is on your head, you should wash it off immediately with non-medicated shampoo and contact your doctor. Do not complete the 8-12 hour treatment if you experience severe pain or blistering. Always follow the specific instructions provided by your healthcare professional regarding the duration of the application.
Because Malathion is usually applied only once or twice, a missed dose typically refers to forgetting the second application if it was recommended by your doctor. If you were told to re-apply the medication 7 to 9 days after the first treatment because live lice were still present, and you forgot to do so, apply it as soon as you remember. If you have already cleared the infestation and no live lice are found, a second dose may not be necessary. You should consult your healthcare provider if you are unsure about the timing of a repeat treatment. Never apply the lotion more than twice for a single infestation without medical advice.
No, Malathion does not cause weight gain. It is a topical treatment used for a very short duration (8-12 hours) and has very low systemic absorption into the bloodstream. Weight gain is typically a side effect associated with systemic medications like corticosteroids, certain antidepressants, or hormonal therapies that are taken over a long period. Since Malathion acts locally on the scalp to kill lice and is rapidly broken down by enzymes if any small amount enters the body, it does not affect the metabolic processes or appetite centers that lead to weight changes.
Malathion is applied topically, which reduces the risk of interactions with most oral medications. However, it can interact with other drugs that affect the cholinesterase enzyme, such as those used for Myasthenia Gravis or Alzheimer's disease. Additionally, if you are undergoing surgery, you must tell your doctor if you have recently used Malathion, as it can interact with certain muscle relaxants (like succinylcholine) used during anesthesia. You should also avoid using other topical scalp treatments or pesticides at the same time. Always provide your healthcare provider with a full list of your current medications and any recent chemical exposures.
Yes, Malathion is available as a generic 0.5% topical lotion. The generic version is bioequivalent to the brand-name product Ovide, meaning it contains the same active ingredient and works in the same way. Generic medications are typically more cost-effective for patients while maintaining the same FDA standards for safety and efficacy. When picking up your prescription, you can ask your pharmacist if a generic version is available and appropriate for you. Regardless of whether you use the brand-name or generic version, the safety precautions regarding flammability and application time remain exactly the same.
Other drugs with the same active ingredient (Malathion)
> Warning: Stop using Malathion and call your doctor or seek emergency care immediately if you experience any of the following:
Malathion is intended for short-term, episodic use. There are no documented long-term side effects associated with the correct use of one or two applications. However, repeated, chronic misuse could theoretically lead to skin sensitization or cumulative minor cholinesterase inhibition, though this is not observed in standard clinical practice.
There are currently no FDA Black Box Warnings for Malathion. However, the labeling carries a prominent 'Flammable' warning that is treated with similar clinical gravity. The product must be kept away from open flames and heat sources (including hair dryers) during and after application until the hair is washed.
Report any unusual or persistent symptoms to your healthcare provider. You may also report side effects to the FDA at 1-800-FDA-1088.
Malathion should not be applied to skin that is severely inflamed, raw, or bleeding. Broken skin significantly increases the risk of systemic absorption, which could lead to organophosphate toxicity. Healthcare providers should inspect the scalp for secondary bacterial infections (common in severe lice infestations) before prescribing malathion.
Malathion is a severe eye irritant. Care must be taken to prevent the lotion from running into the eyes during application. If contact occurs, immediate and prolonged irrigation with water is required. The medication is not for use inside the nose, mouth, or vagina.
While the risk is low, the vapors from the lotion can be irritating. Application should take place in a well-ventilated room. Patients with reactive airway diseases, such as asthma or COPD, should be monitored for bronchospasm if they are applying the medication or are in the vicinity of its use.
For standard topical use, routine laboratory monitoring (such as blood counts or liver function tests) is not required. The primary monitoring is clinical:
Topical use of malathion at the recommended dose does not typically affect the ability to drive or operate machinery. However, if systemic absorption occurs and causes blurred vision or dizziness, these activities should be avoided.
There are no known direct interactions between topical malathion and the consumption of oral alcohol. However, since the product itself is alcohol-based and flammable, patients should avoid consuming alcohol during application to ensure they remain alert and can follow all safety precautions regarding fire hazards.
There is no withdrawal syndrome associated with malathion, as it is used for short-term treatment. If a patient develops a severe skin reaction, the medication should be washed off immediately with non-medicated shampoo, and the treatment should be discontinued in favor of an alternative pediculicide.
> Important: Discuss all your medical conditions, especially skin sensitivities and respiratory issues, with your healthcare provider before starting Malathion.
There are no documented interactions between topical malathion and specific foods. Unlike many oral medications, malathion’s efficacy and safety are not affected by grapefruit juice, dairy, or high-fat meals.
There are no well-documented interactions between topical malathion and herbal supplements. However, patients using topical essential oils (like tea tree oil or eucalyptus oil) on the scalp should be cautious, as these may increase skin irritation when combined with the alcohol-based malathion lotion.
Malathion may interfere with the following laboratory tests:
The primary mechanism for these interactions is pharmacodynamic additive effect. Because malathion and other cholinesterase inhibitors target the same enzyme (acetylcholinesterase), their combined use can lead to an excessive accumulation of acetylcholine. The clinical consequence is an increased risk of 'cholinergic crisis' symptoms. Management involves avoiding concurrent use and ensuring a 'washout' period between treatments.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including any recent exposure to industrial or agricultural chemicals.
Conditions requiring a careful risk-benefit analysis by a healthcare provider include:
Patients who are sensitive to other organophosphate compounds (found in certain agricultural pesticides) may exhibit cross-sensitivity to malathion. Additionally, those with sensitivities to perfumes or essential oils (specifically pine or citrus oils) may be at higher risk for contact dermatitis due to the presence of pine needle oil and dipentene in the formulation.
> Important: Your healthcare provider will evaluate your complete medical history and the condition of your scalp before prescribing Malathion to ensure it is safe for you.
Clinical trials of Malathion Lotion did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. In general, skin in the elderly may be thinner or more prone to irritation. Healthcare providers should consider the overall skin integrity and the presence of comorbid conditions when prescribing for this population.
No specific dosage adjustments are provided in the manufacturer's labeling for patients with renal impairment. Given that topical absorption is minimal and the absorbed fraction is rapidly metabolized, renal dysfunction is unlikely to significantly impact the safety profile of a single topical application. However, patients with end-stage renal disease (ESRD) should be monitored for any signs of systemic cholinergic activity.
Because malathion is primarily detoxified by carboxylesterases found in the plasma as well as the liver, hepatic impairment does not typically necessitate a dose adjustment for topical use. However, in cases of severe liver failure where enzyme production might be compromised, caution is advised.
> Important: Special populations require individualized medical assessment. Always inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding before using this medication.
| Parameter | Value |
|---|---|
| Bioavailability | < 10% (Topical) |
| Protein Binding | Not clinically significant for topical use |
| Half-life | Short (Rapidly hydrolyzed in plasma) |
| Tmax | 2 to 4 hours (for minor systemic absorption) |
| Metabolism | Plasma/Hepatic Carboxylesterases |
| Excretion | Renal (as inactive metabolites) |
Malathion is a member of the organophosphate class of chemicals. Within the therapeutic area of dermatology, it is classified as a pediculicide. It is distinct from other lice treatments like permethrin (a pyrethroid) or ivermectin (an avermectin) because of its irreversible inhibition of cholinesterase, making it a powerful alternative for resistant infestations.