Chemoprophylaxis

  • administration of a medication for the purpose of preventing disease or infection
  • The use of chemoprophylactic agents is based on knowledge of the epidemiology and clinical implications of the infectious diseases from which protection is sought.
  • Generally, chemoprophylaxis is taken for diseases that are common, or where the clinical impact of infection is high.
  • Drugs may be taken before exposure (pre-exposure prophylaxis) or
  • after potential exposure to an infectious agent (post-exposure prophylaxis).

Latent tubercular infection (Chemoprophylaxis)

indicated only in subjects at high risk of developing active TB, viz.:

  • Contacts of open cases who show recent Mantoux conversion.
  • Children with a sputum positive TB patient in the family.
  • Neonate of a tubercular mother.
  • Patients of leukemia, diabetes, silicosis or those receiving immunosuppressant medication or those on long-term corticosteroid therapy.
  • HIV infected contacts of sputum positive index cases.

The standard drug for chemoprophylaxis of TB is INH 300 mg (10 mg/kg in children) daily for 6 months.

Suppressive prophylaxis  – Malaria

Chloroquine sensitive Plasmodium falciparum (P.f):

Chloroquine (CQ) 300 mg or 5 mg/kg weekly.

In travelers. start one week before with a loading dose of 10 mg/kg and continue till one month after return from the endemic area.

Since CQ-resistant Pf is now widespread in Indiaà CQ is no longer employed as prophylactic in India.

  • Short-term chemoprophylaxis (less than 6 weeks)

Doxycycline: 100 mg daily in adults, 1.5 mg/kg body weight for children more than 8 years old.

The drug started 2 days before travel and continued for 4 weeks after leaving the malarious area.

  • It is contraindicated in pregnant women and children < 8 yr.
  • Long-term chemoprophylaxis (more than 6 weeks)

Mefloquine: 5 mg/kg body weight (up to 250 mg) weekly and should be administered 2 weeks before, during and 4 weeks after leaving the area.

  • In India, the use of mefloquine for prophylaxis is not allowed among residents but may be used by travelers for long term (6 weeks to I year) prophylaxis.

Chemoprophylaxis:

  • limited to short-term use in special risk groups, such as – nonimmune travelers,
  • nonimmune persons living in endemic areas for fixed periods (army units, labor forces), infants, children and pregnant women (falciparum malaria has serious consequences in the pregnant).

Traveler’s Diarrhea

  • Diarrhea is the most common affliction for travelers to tropical countries.
  • Between 20–60% of visitors to resource-poor countries are affected
  • Prevention is primarily through attention to food and hand hygiene.
  • Chemoprophylaxis, using rifaximin has been shown to be effective in reducing the incidence of traveler’s diarrhea
  • In a dose of 200 mg/day, it reduced traveler’s diarrhea by 72%
  • Quinolone antibiotics (ciprofloxacin and norfloxacin) are around 90% efficacious in preventing traveler’s diarrhea, but are associated with the development of resistant organisms, are not generally recommended as chemoprophylaxis

Scrub Typhus

  • Scrub typhus is caused by Orientia tsutsugamushi and transmitted to humans via the bite of the mite
  • These exposures can sometimes be predicted and use of doxycycline in a dose of 200 mg weekly has been shown to be effective

Leptospirosis

  • Leptospirosis is a zoonotic bacterial disease transmitted to humans who come in contact with water that has been contaminated with the urine of infected animals.
  • Certain groups of people, e.g., farmers, or participants in water sporting events, are at higher risk for  acquisition of this disease, and floods may be associated with large outbreaks
  • a weekly dose of 200 mg doxycycline

Schistosomiasis

  • a common problem in returned travelers, especially after exposure to freshwater in Africa
  • Artemether, a methyl ether derivative of qinghaosu, has anti-schistosomal properties, and because it affects the parasite at the larval stage was proposed as a chemoprophylactic agent for this disease
  • Chemoprophylaxis against schistosomiasis should only be considered for unavoidable exposure in high-risk settings.

Leprosy

  • skin and nerve disease caused by Mycobacterium leprae.
  • single doses of rifampicin are effective at a population level and amongst close contacts (post-exposure) in preventing leprosy
  • Chemoprophylaxis for leprosy would normally only be considered in special circumstances in travelers.

Exposure to HIV

The use of chemoprophylaxis is limited primarily by two factors: risk and financial costs.

Risk: All medications have the potential to cause side effects. In general, chemoprophylaxis should be initiated only when the benefits of treatment outweigh the risks.

Financial Cost: The cost associated with chemoprophylaxis may be prohibitive, particularly when the cost of treatment is high or the incidence of the target disease is low. Many forms of chemoprophylaxis are therefore not cost-effective.

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