Learn a Drug a Day - Malathion

Today's drug is malathion.
What is malathion indicated for?
INDICATIONS : 

• It is indicated for patients infected with Pediculus humanus capitis (head lice and their ova) of the scalp hair.
• It is also indicated for patient infected with crab lice (the lice which are typically seen attached to hair in pubic areas, but may sometimes appear in other areas of the body where coarse hair is present such as beard, chest, armpits, etc.) or scabies (easily spread skin disease caused by a very small species of mite.). 

How does malathion work?
MECHANISMS OF ACTION : 

• Malathion is an organophosphate which binds irreversible to anticholinesterase. 
• It is an insecticide with both pediculicidal and ovicidal activity. 
• Malathion is active against Pediculus humanus var. capitalis and its nits (eggs) and Phlthirus pubis as shown in in vitro and in vivo studies.

How is malathion being used?
ROUTE OF ADMINISTRATION : 
(i) For Head Lice : 

• Apply malathion lotion on DRY hair in amount just sufficient to thoroughly wet the hair and scalp. 
• Pay particular attention to the back of the head and neck while applying malathion lotion. Wash
• hands after applying to scalp.

• Allow hair to dry naturally  -  use no electric heat source, and allow hair to remain uncovered.

• After 8 to 12 hours, the hair should be shampooed with non-medicated shampoo.

• Rinse and use a fine - toothed (nit) comb to remove dead lice and eggs.

• If lice are still present after 7 - 9 days, repeat with a second application of malathion lotion

• Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment .

(ii) For Crab Lice : 

• Apply over whole body (including the scalp, neck, face and ears). 
• Allow to dry naturally without the use of electric heat source. 
• Wash off after 12 hr or overnight. 
• Second application may be repeated after 7 days.

(iii) For Scabies : 

• Apply over whole body (including the scalp, neck, face and ears) and wash off after 24 hr. 
• Reapply if hands are washed with soap within 24 hr. 
• Repeat application after 7 days.

Are there any possible side effects?

SIDE EFFECTS :

• Skin and scalp irritation.
• Hair dryness. 
• Slight stinging or burning sensation.
• Accidental contact with the eyes can result in mild conjunctivitis. 

What precautions are necessary?

PRECAUTIONS :  

• Malathion lotion is flammable. The lotion and hair wet with lotion should not be exposed to open flames or electric heat sources, including hair dryers and electric curlers. Do not smoke while applying lotion or while hair is wet. The person applying malathion lotion should wash hands after application. Allow hair to dry naturally and to remain uncovered after application of malathion lotion.

• It should not be used on broken skin or secondarily infected skin. 

• It should only be used on children under the direct supervision of an adult. Children should be warned to stay away from lighted cigarettes, open flames, and electric heat sources while the hair is wet.

• In case of accidental ingestion of lotion by mouth, seek medical attention immediately.

• If malathion lotion comes into contact with the eyes, flush immediately with water. Consult a physician if eye irritation persists or if visual changes occur.

• If skin irritation occurs, wash scalp and hair immediately. If the irritation clears, malathion lotion may be reapplied. If irritation reoccurs, consult a physician.

• Slight stinging sensations may be produced when using malathion lotion. 

Pregnancy and breastfeeding:  

• This drug should be used (or handled) during pregnancy only if clearly needed.
• It is not known whether malathion is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when malathion lotion is administered to (or handled by) a nursing mother.

References : 

1. Malathion by MEDICIS.

2. Malathion by MIMS Malaysia.