Giardiasis Treatment & Management

Updated: Jan 30, 2023
  • Author: Hisham Nazer, MBBCh, FRCP, DTM&H; Chief Editor: Burt Cagir, MD, FACS  more...
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Approach Considerations

Standard treatment for giardiasis consists of antibiotic therapy. [63] Metronidazole is the most commonly prescribed antibiotic for this condition. [36, 64, 65] However, metronidazole use has been associated with significant failure rates in clearing parasites from the gut and with poor patient compliance. [66] In addition, an increasing incidence of nitroimidazole-refractory giardiasis has been reported, particularly in travelers from India [67] and other regions in Asia. [68] An optimal treatment strategy for refractory giardiasis remains to be determined, and no standard treatment regimen for nitroimidazole-refractory giardiasis exists yet. [68]

In a systematic review and meta-analysis of seven trials comprising 639 patients to evaluate the efficacy of mebendazole in children with giardiasis, investigators found no clinical difference in parasitologic cure between mebendazole and metronidazole, with a relative risk of 0.81 but high heterogeneity. [7] The researchers indicated clinicians should use caution in interpreting and using these results in clinical practice

Real-time polymerase chain reaction (PCR) may aid in the evaluation of treatment success. van den Bijllaardt et al showed it took about 1 week for samples to become negative after treatment of a G lamblia infection, indicating rapid clearance of the parasitic DNA following successful therapy. [69]

Appropriate fluid and electrolyte management is critical, particularly in patients with large-volume diarrheal losses. [9]

Treat children with acute or chronic diarrhea who manifest a failure to thrive, malabsorption, or other GI tract symptoms in whom Giardia organisms have been identified. [61]

Generally, do not treat asymptomatic persons who excrete the organism, except to prevent household transmission (eg, from toddlers to pregnant women or to patients with hypogammaglobulinemia or cystic fibrosis) and to permit adequate treatment in individuals with possible Giardia intestinalis–associated antibiotic malabsorption who require oral antibiotic treatment for other infections. [40, 70]

Routine treatment of infected persons in highly endemic areas where water supplies continue to be contaminated is of questionable value because reinfection may readily occur. [18, 71] Treat all infected persons who are in nonendemic areas. [72]

Ensure that close contacts of the patient are also examined for giardiasis and treated if infected.

Severely dehydrated or malnourished patients should be admitted for further care.

Diet and Activity

No special diet is required. A significant portion of patients have symptoms of lactose intolerance (cramping, bloating, diarrhea), and maintenance on a lactose-free diet for several months may be helpful. Acquired lactose intolerance occurs in as many as 20-40% of cases. [12]

Activity restrictions are not indicated. However, infected subjects who are at risk of spreading the infection should be isolated and treated.

Pregnant Patients

No consistent recommendations exist for the treatment of pregnant patients because of the potential adverse effects of anti-Giardia agents on the fetus. If possible, treatment should be avoided during the first trimester. Mildly symptomatic women should have treatment delayed until after delivery. If treatment is necessary, paromomycin can be used as systemic absorption is poor. [71] If the patient is left untreated, adequate nutrition and hydration maintenance are paramount.

Failed Treatment

Documenting the continued presence of Giardia in patients who appear unresponsive to treatment is important. A significant number of patients develop post-Giardia lactose intolerance and present with symptoms consistent with persistent infection. These patients usually improve with time and with the institution of a lactose-free diet.

If Giardia is found in the patient, a careful history should indicate whether this is a reinfection or a treatment failure. A second course of the same drug, for a longer period or a higher dose, should be effective in reinfections, whereas the use of an alternative drug should be effective in true treatment failures. A combination therapy may have to be implemented in certain cases of treatment failure.

Patients who fail repeated courses of treatment should be evaluated for hypogammaglobulinemia and may require combination therapy or chronic suppressive therapy.


Infected persons and persons at risk should carefully wash their hands after they have any contact with feces. Careful hand washing is important, especially for caregivers of diapered infants in daycare centers, where diarrhea is common and carriers of Giardia organisms are numerous.

Chlorination, sedimentation, and filtration methods should be implemented to adequately purify public water supplies. Effective chlorine inactivation of Giardia cysts in water requires an optimal chlorine concentration, water pH, turbidity, temperature, and contact time. These variables cannot be appropriately controlled in all municipalities, and they are particularly difficult to control in swimming pools.

Advise travelers to endemic areas to avoid eating uncooked foods that may have been grown, washed, or prepared with contaminated water.

Drinking water can be purified by using filtration (pore size, < 1 µm) or by briskly boiling water for at least 5 minutes. Chlorine or iodine water treatments are less effective than boiling or filtration, but they may be used as alternatives when other methods are not available.

Infected individuals should refrain from using recreational water venues (eg, swimming pools, lakes, rivers) until they are symptom-free for a few weeks.

Breastfeeding appears to protect infants from Giardia intestinalis infection. [12, 18, 21] Breast milk contains detectable titers of secretory IgA, which is protective for infants, especially in developing countries. A study from Egypt [73] showed breast-fed infants had a lower incidence of symptomatic and asymptomatic infection. Furthermore, infected infants who were exclusively breast-fed had fewer clinical manifestations than those who were not exclusively breast-fed.