Parasitic Gastrointestinal Infections

• Asymptomatic patients do not require treatment.

Pathogens

• Giardia lamblia, Cryptosporidium parvum, Blastocystis species, Dientamoeba fragilis

Drug Treatment

• Duration: See below.

Giardia lamblia

• Treatment failure needs confirmation by repeat stool specimen as persistent symptoms may be the result of transient lactase deficiency.
• Resistance to imidazoles is an increasing problem. If two initial courses of metronidazole fail (second course 10 days duration), consult with Infectious Diseases/Clinical Microbiology/Gastroenterology.

metronidazole HMLSchedNZFPMLnoids Metronidazole F: 1 Half life: 8 hours Elimination: oxidation, glucuronidation fe: 0.1

PO 400 mg three times a day for 5 to 7 days

• Metabolised by unknown pathways. (fe = 0.1).

OR

• Avoid in pregnancy.

Cryptosporidium parvum

• Self-limiting diarrhoea except in immunocompromised hosts. No antimicrobial agent is reliably curative.
• If the patient is immunocompromised and has persistent diarrhoea, consult with Infectious Diseases/Clinical Microbiology/Gastroenterology.

Blastocystis species

• Asymptomatic and self-limiting carriage is common.
• Questionable as a pathogen.
• Treat only if two out of three stool samples on three separate days are positive with continuing diarrhoea and absence of other bowel pathogens or diagnoses.
• If symptoms persist and the parasite continues to be found - consult with Infectious Diseases/Clinical Microbiology/Gastroenterology.

• Metabolised by unknown pathways. (fe = 0.1).

OR

trimethoprim+sulfamethoxazole HMLSchedNZFPMLnoids Trimethoprim+Sulfamethoxazole F: 0.8 Half life: 9 hours / 12 hours Elimination: CYP2C8/9 acetylated fe: 0.3 / 0.7 (co-trimoxazole)

PO 160 mg/800 mg twice a day for 7 days

• fe (trimethoprim) = 0.7, fe (sulfamethoxazole) = 0.3, consider adjusting dose if CrCl reduced.
• Sulfamethoxazole is metabolised by CYP2C8/9 and conjugation.

Dientamoeba fragilis

• Asymptomatic carriage is common.
• Treat only if two out of three stool samples on three separate days are positive with continuing diarrhoea and absence of other bowel pathogens or diagnoses.
• If treatment fails, consult Infectious Diseases/Clinical Microbiology/Gastroenterology.

• Metabolised by unknown pathways. (fe = 0.1).

Topic Code: 99232

must be prescribed or recommended by a consultant.