Giardia duodenalis infection (giardiasis)
Giardia duodenalis (formerly known as Giardia lamblia or Giardia intestinalis) is the most common protozoal cause of chronic diarrhoea.
Most G. duodenalis infections are acquired overseas. In Australia, exposure to animals is associated with increased risk of acquiring G. duodenalisZajaczkowski, 2018.
The mainstay of therapy for symptomatic patients with G. duodenalis is rehydration in combination with antimicrobial therapy.
Antimicrobial treatment for asymptomatic G. duodenalis carriage is usually not necessary. It can be considered if there is a risk of transmission to vulnerable individuals; for example, children attending daycare settings, childcare workers, food handlers, household contacts of people with immune compromise and household contacts of pregnant people.
Although tinidazole is only available in Australia via the Special Access Scheme, it has a higher rate of cure compared to metronidazoleOrdonez-Mena, 2018. If treatment for G. duodenalis infection is indicated, useOrdonez-Mena, 2018:
1metronidazole 2 g (child: 30 mg/kg up to 2 g) orally, daily for 3 days metronidazole metronidazole metronidazole
OR
1metronidazole 400 mg (child: 10 mg/kg up to 400 mg) orally, 8-hourly for 5 days metronidazole metronidazole metronidazole
OR
1tinidazole 2 g (child: 50 mg/kg up to 2 g) orally, as a single dose12. For dosage adjustment in adults with kidney impairment, see tinidazole dosage adjustment. tinidazole tinidazole tinidazole
There are data showing albendazole is effective for the treatment of G. duodenalis infection; it can be considered if metronidazole and tinidazole are unavailable or cannot be toleratedSolaymani-Mohammadi, 2010. Use:
albendazole orally, daily for 5 days albendazole albendazole albendazole
adult: 400 mg. For dosage adjustment in adults with kidney impairment, see albendazole dosage adjustment
child 6 months or older and 10 kg or more: 400 mg
child 6 months or older and less than 10 kg: 200 mg.
In pregnant patients, discuss the harms and benefits of therapy. If treatment is necessary, metronidazole or paromomycin can be used. While paromomycin has traditionally been preferred in pregnancy, especially in the first trimester, there is evidence and clinical experience to support the use of metronidazole throughout pregnancySheehy, 2015. If metronidazole is used, prescribe the 8-hourly regimen above.
Symptom recurrence after treatment may be caused by postinfection lactose intolerance (see Transient lactose intolerance after gastroenteritis), reinfection or drug resistance.
Metronidazole-resistant G. duodenalis is cross-resistant to tinidazole, but nitazoxanide3 is likely to remain effective. Alternative drugs for resistant G. duodenalis include mebendazole and paromomycin4 – seek expert advice from an infectious diseases physician.