Giardiasis Medication

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

Antibiotic therapy is standard in the treatment of giardiasis. [19, 50, 74] Antimicrobial resistance has been reported.

Metronidazole is the antimicrobial agent most commonly used in the treatment of giardiasis in the United States. It has a cure rate of 85-90%.

Tinidazole is also approved in the United States and considered a first-line agent outside the United States. It is given in a single dose, the efficacy is reported at 90%, and it is believed to have fewer side effects than metronidazole. A common adverse effect is GI upset. A meta-analysis of five trials comprising 403 children regarding the efficacy of tinidazole versus albendazole treatment for pediatric giardiasis showed that tinidazole significantly outperformed albendazole. [66]

Paromomycin has been recommended for use in pregnancy because systemic absorption is low, but the cure rate is lower than with other agents.

Some drugs not available in the United States are considered effective therapeutic alternatives. Quinacrine achieves a cure rate of 90-95% but is available as an orphan drug in the US. The most common adverse effects include nausea, vomiting, and abdominal cramping. Occasional yellow discoloration of the skin, urine, and sclerae may occur. This medication should not be used in patients with documented hypersensitivity to this medication or related products, those diagnosed with psoriasis, or those with a history of psychosis.



Class Summary

The therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting. [61] The two major classes of drugs that have proven benefit in the treatment of giardiasis are nitroimidazole derivatives and acridine dyes.

Although most experts recommend metronidazole and tinidazole as the drugs of choice because the brief treatment periods encourage good patient adherence, treatment failures occur in as many as 20% of cases, probably because of resistance. Therefore, treatment with a second-line drug (eg, mepacrine) may be necessary.

The effectiveness of quinacrine is similar to that of nitroimidazole derivatives; however, it is less tolerated because of its adverse effects. These include the following: mild and transient headache, dizziness, and GI complaints (diarrhea, anorexia, nausea, abdominal cramps, vomiting [rare]), pleomorphic skin eruptions, and neuropsychiatric disturbances (nervousness, vertigo, irritability, emotional change, nightmares, transient psychosis).

Nitazoxanide is approved by the US Food and Drug Administration for the treatment of children and adults for diarrhea from giardiasis.

Metronidazole (Flagyl)

Metronidazole is a nitroimidazole that, once concentrated within the organism, is reduced by intracellular electron transport proteins. The formation of free radicals causes disruption of cellular elements and subsequent death of the organism. It is the most commonly prescribed antibiotic for giardiasis. The recommended adult dose is 250 mg PO tid for 5-7 days.

Albendazole (Albenza)

This agent decreases adenosine triphosphate (ATP) production in worms, causing energy depletion, immobilization, and, finally, death. To avoid an inflammatory response in CNS, the patient also must be started on anticonvulsants and high-dose glucocorticoids.

Nitazoxanide (Alinia)

This agent inhibits growth of Cryptosporidium parvum sporozoites and oocysts and Giardia lamblia trophozoites. It elicits antiprotozoal activity by interfering with pyruvate-ferredoxin oxidoreductase (PFOR) enzyme-dependent electron transfer reaction, which is essential to anaerobic energy metabolism. It is available as a 20-mg/mL oral suspension.

Tinidazole (Tindamax)

Tinidazole is a nitroimidazole antiprotozoal agent. The mechanism by which tinidazole exhibits activity against Giardia and Entamoeba species is not known. The recommended adult dose is 2 g PO once; for children, the recommended dose is 50 mg/kg PO once.


Paromomycin is a poorly absorbed aminoglycoside that may be considered for use in severe infection in pregnant patients. The most common adverse effects include nausea, increased GI motility, abdominal pain, and diarrhea.


This agent, available as an orphan drug in the United States is indicated to treat giardiasis and cestodiasis. It is occasionally used to treat and suppress malaria. The recommended adult dose is 100 mg PO tid for 5-7 d; for children, the recommended dose is 2 mg/kg PO tid for 5-7 d.