Treatment algorithm

Please note that formulations/routes and doses may differ between drug names and brands, drug formularies, or locations. Treatment recommendations are specific to patient groups: see disclaimer

ACUTE

nonpregnant adult or child

1st line – antiprotozoal therapy

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ACUTE
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nonpregnant adult or child
1st line – 

antiprotozoal therapy

First-line therapy is tinidazole, metronidazole, or nitazoxanide.[1]​[54][72]​​​​​​ Some guidelines recommend tinidazole or nitazoxanide as the preferred options.[53][66]​​ Metronidazole is associated with a higher incidence of gastrointestinal adverse effects, but it is commonly used and widely available, although its use for giardiasis is off-label in the US.[66] [ Cochrane Clinical Answers logo ]

Tinidazole can be offered as a single dose and has an efficacy of 90% to 98%.[66][73]​ Nitazoxanide requires multiple doses and is 85% to 91% effective.[74][75]​ Metronidazole is given for 7 days and has an efficacy of 80% to 95%.[76]

Albendazole may be used in patients intolerant to nitroimidazoles and nitazoxanide.[80][81]

Treatment should also include advice regarding hygiene and prevention measures, and correction of dehydration and electrolyte abnormalities as required. Rehydration is of increased importance among infants, as dehydration due to diarrhea can be life-threatening.[72]​

Primary options

tinidazole: children ≥3 years of age: 50 mg/kg orally as a single dose, maximum 2 g/dose; adults: 2 g orally as a single dose

OR

nitazoxanide: children 1-3 years of age: 100 mg orally twice daily for 3 days; children 4-11 years of age: 200 mg orally twice daily for 3 days; children ≥12 years of age and adults: 500 mg orally twice daily for 3 days

OR

metronidazole: children: 5 mg/kg orally three times daily for 5-7 days, maximum 750 mg/day; adults: 250 mg orally three times daily for 5-7 days

Secondary options

albendazole: adults: 400 mg orally once daily for 3 days

pregnant; first trimester

1st line – consider paromomycin

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ACUTE
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pregnant; first trimester
1st line – 

consider paromomycin

Nonabsorbable aminoglycoside with in vitro activity against Giardia duodenalis. Most of the drug is excreted in feces without being metabolized. Recommended treatment during pregnancy, but should only be given when adequate hydration and nutritional status cannot be maintained.

Treatment should also include advice regarding hygiene and prevention measures, and correction of dehydration and electrolyte abnormalities as required. Rehydration is of increased importance among pregnant women, as they may be at higher risk for dehydration due to diarrhea.[72]​

Primary options

paromomycin: adults: 30 mg/kg/day orally given in 3 divided doses for 5-10 days

pregnant; second or third trimester

1st line – antiprotozoal therapy

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ACUTE
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pregnant; second or third trimester
1st line – 

antiprotozoal therapy

Treatment should be with either paromomycin or metronidazole, though metronidazole is not approved for this indication.

Treatment should also include advice regarding hygiene and prevention measures (particularly if there have been previous episodes of infection earlier in the pregnancy), and correction of dehydration and electrolyte abnormalities as required. Rehydration is of increased importance among pregnant women, as they may be at higher risk for dehydration due to diarrhea.[72]​

Primary options

paromomycin: adults: 30 mg/kg/day orally given in 3 divided doses for 5-10 days

OR

metronidazole: adults: 250 mg orally three times daily for 5-7 days

ONGOING

treatment failure or resistance

1st line – antiprotozoal therapy

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ONGOING
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treatment failure or resistance
1st line – 

antiprotozoal therapy

It is important to differentiate true drug resistance from cure followed by reinfection, post-Giardia dietary/lactose intolerance, or irritable bowel symptoms after therapy. Ongoing infection should be confirmed.

True treatment failure could mean infection with a drug-resistant isolate of G lamblia. Clinically resistant strains have often been treated with longer repeat courses or higher doses of the original agent.​​[83]​​ However, data indicate that the most efficacious means of eradicating these infections is to use a different class of drug to avoid potential cross-resistance.[84]​ If resistance or relapse has occurred, treatment with a drug of a different class or combination therapy for at least 2 weeks should eradicate infection.

Treatment should, in addition to standard therapy, include advice regarding hygiene and prevention measures for the patient and all household members, and correction of dehydration and electrolyte abnormalities as required. Rehydration is of increased importance among infants (dehydration due to diarrhea can be life-threatening) and pregnant women (may be at higher risk for dehydration due to diarrhea).[72]​

Primary options

tinidazole: children ≥3 years of age: 50 mg/kg orally as a single dose, maximum 2 g/dose; adults: 2 g orally as a single dose

OR

nitazoxanide: children 1-3 years of age: 100 mg orally twice daily for 2 weeks; children 4-11 years of age: 200 mg orally twice daily for 2 weeks; children ≥12 years of age and adults: 500 mg orally twice daily for 2 weeks

OR

metronidazole: children: 5 mg/kg orally three times daily for 2 weeks, maximum 750 mg/day; adults: 250 mg orally three times daily for 2 weeks

Secondary options

albendazole: adults: 400 mg orally once daily for 2 weeks

2nd line – combination regimens

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ONGOING
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treatment failure or resistance
2nd line – 

combination regimens

Combination regimens using metronidazole plus albendazole, metronidazole plus quinacrine, or other active drugs, or giving a nitroimidazole plus quinacrine for courses of at least 2 weeks, have been shown to be highly successful against refractory infection.​​​​[84]​​ Quinacrine is not available in the US.

Sometimes, several different combinations or approaches will be necessary to produce a cure. Little data exist for comparative efficacy between different combination regimens, and the choice of treatment is often determined by medication availability.

Consult a specialist for recommended combinations and dosing information.

Treatment should include advice regarding hygiene and prevention measures for the patient and all household members.

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Please note that formulations/routes and doses may differ between drug names and brands, drug formularies, or locations. Treatment recommendations are specific to patient groups. See disclaimer

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