What is the diagnosis and treatment for Giardiasis (infection caused by Giardia lamblia)?

From the Guidelines

Giardiasis is an intestinal infection caused by the parasite Giardia lamblia that requires prompt treatment with antiparasitic medications, with tinidazole being the first-line treatment, as recommended by the 2017 Infectious Diseases Society of America clinical practice guidelines 1. The diagnosis of giardiasis can be made through various tests, including stool ova and parasite tests, fecal immunoassays, and novel polymerase chain reaction tests, with fecal immunoassays being the most sensitive and specific, as reported in a 2019 technical review on the evaluation of functional diarrhea and diarrhea-predominant irritable bowel syndrome in adults 1.

Treatment Options

• Tinidazole is the first-line treatment for giardiasis, with a single 2-gram dose for adults or 50 mg/kg single dose for children, as recommended by the 2017 Infectious Diseases Society of America clinical practice guidelines 1.
• Metronidazole is an alternative treatment, with a dose of 250 mg three times daily for 5-7 days for adults, or 15 mg/kg/day divided into three doses for children.
• Nitazoxanide can also be used, with adults taking 500 mg twice daily for 3 days and children receiving weight-based dosing.

Prevention and Management

• Patients should stay well-hydrated during treatment and avoid alcohol while taking metronidazole or tinidazole due to disulfiram-like reactions.
• Family members or close contacts may need to be treated to prevent reinfection.
• Preventive measures include proper handwashing, drinking treated water, and avoiding swallowing water while swimming in potentially contaminated sources.

Symptoms and Prognosis

• Symptoms of giardiasis typically include diarrhea, abdominal cramps, bloating, nausea, and fatigue.
• Most patients improve within a week of starting treatment, as reported in various studies 1.

From the FDA Drug Label

1. 2 Giardiasis Tinidazole (2 g single dose) use in giardiasis has been documented in 19 published reports from the world literature involving over 1,600 patients (adults and pediatric patients) In eight controlled studies involving a total of 619 subjects of whom 299 were given the 2 g × 1 day (50 mg/kg × 1 day in pediatric patients) oral dose of tinidazole, reported cure rates ranged from 80% (40/50) to 100% (15/15). 1.2 Giardiasis Tinidazole is indicated for the treatment of giardiasis caused by Giardia duodenalis (also termed G. lamblia) in both adults and pediatric patients older than three years of age [see Clinical Studies ( 14.2)] .

Tinidazole is indicated for the treatment of giardiasis caused by Giardia duodenalis in both adults and pediatric patients older than three years of age. The cure rates for tinidazole in the treatment of giardiasis range from 80% to 100% 2.

From the Research

Treatment Options for Giardiasis

• The first-line drug treatment for giardiasis is tinidazole, which requires only a single dose to cure infection in most individuals 3.
• Metronidazole is also effective, but it requires 5 to 7 days of three times a day therapy 3.
• Nitazoxanide appears to be as effective as tinidazole or metronidazole, and it does not have the bitter taste of nitroimidazoles 3.
• Albendazole has been found to be equally as effective as metronidazole in the treatment of giardiasis in humans, with a lower risk of adverse effects 4.
• A study comparing the effectiveness of albendazole with metronidazole found that albendazole was probably equivalent to metronidazole at achieving parasitological cure and improving symptoms, but with fewer side effects 5.

Comparison of Treatment Efficacy

• A network meta-analysis of randomized clinical trials found that tinidazole was associated with higher parasitological cure than metronidazole and albendazole 6.
• Tinidazole was found to be the most effective drug for treating giardiasis, considering clinical efficacy, side effects, and amount of evidence 6.
• Nitazoxanide is effective against giardiasis, but requires multiple doses, and is also licensed for the treatment of cryptosporidiosis in non-immunodeficient children and adults 7.

Side Effects and Safety

• Albendazole has been found to have a lower risk of adverse effects compared to metronidazole, including gastrointestinal and neurological side effects 4, 5.
• Tinidazole has been found to have a higher efficacy and lower risk of side effects compared to metronidazole and albendazole 6.
• Nitazoxanide does not have the bitter taste of nitroimidazoles, making it a potentially more tolerable option for patients 3.