DOXYCYCLINE (Apo-Doxy, Doxycin)

Trade Names: Apo-Doxy, Doxycin, Doxytab, Teva-Doxycycline

Mechanism of Action:
Doxycycline is an antimicrobial that inhibits protein synthesis in parasites.

Indications and Efficacy:

• Effective for the prevention and treatment of chloroquine-resistant P. falciparum malaria.
• Comparable efficacy to atovaquone-proguanil and mefloquine for preventing chloroquine-resistant P. falciparum.
• Must be taken daily and continued for four weeks after leaving a malaria-endemic area.
• Noncompliance with the daily regimen is a major cause of treatment failure.
• Travellers taking minocycline should switch to doxycycline 100 mg daily for malaria prevention, then revert to minocycline after completing the prophylaxis.

Adverse Effects, Contraindications, and Precautions:

• Common side effects include gastrointestinal upset and nausea; less common are esophageal ulceration and photosensitivity.
• Taking doxycycline with food and fluids can reduce gastrointestinal side effects.
• Absorption may be reduced if taken with dairy products.
• Photosensitivity may cause skin burns; sunscreen is recommended.
• May increase the risk of vaginal candidiasis in women.
• Interactions with barbiturates, carbamazepine, and phenytoin can decrease doxycycline serum concentration by 50%.
• Doxycycline should not be used within 3 days of the oral typhoid vaccine.
• Benign intracranial hypertension is a rare side effect.

Contraindications:

• Pregnant women (especially after the 4th month) and breastfeeding women.
• Historically contraindicated in children under 8 years, but may be considered for short-term use in children when no other options are available.
• Safe for long-term use (up to 12 months) in prophylactic doses.

Recommendations:

• High efficacy (93%–100%) for preventing chloroquine-resistant and mefloquine-resistant P. falciparum.
• Inform travellers about risks of esophageal ulceration, vaginal candidiasis, and photosensitivity.
• Switch to doxycycline for those on minocycline for acne or rheumatoid arthritis when entering a malaria-endemic area, then switch back post-travel.

Dosage Forms and Strengths:

• Commonly used form: 100 mg tablets or capsules.
• Can be taken orally with adequate fluid and food.
• Intravenous (IV) formulation is available for patients unable to take oral medications; avoid rapid IV administration.

Adult Dosage:

• Prevention: 100 mg once daily, starting one day before entering a malaria-endemic area, during exposure, and for 4 weeks after leaving.
• Treatment: 100 mg orally or IV twice daily for 7 days.

Pediatric Dosage:

• Prevention: 2 mg base/kg once daily (max 100 mg daily) for children < 25 kg or < 8 years; specific doses provided for various weights.
• Treatment: 2 mg base/kg orally or IV twice daily (max 200 mg daily); specific doses provided for various weights.

Advantage:

• Protection against leptospirosis.

Disadvantage:

• Daily dosing required for chemoprophylaxis.