Giardiasis Treatment

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Two therapies are approved by the FDA for the treatment of giardiasis:

  • Tinidazole (Tindamax®)
  • Nitazoxanide (Alinia®)

Metronidazole

Metronidazole is not indicated for use in giardiasis but is the drug most often used in the United States. Metronidazole and tinidazole belong to a class of drugs called the nitroimidazoles. Metronidazole is a first generation nitroimidazole, and tinidazole is a second generation nitroimidazole.

Disappearance of Giardia from Stool
at Post-Treatment Examination2

Bar graph comparing the giardiasis cure rates, 12 days post-treatment, of tinidazole and metronidazole. For patients whose stools contained Giardia cysts only pre-treatment, tinidazole cured 100 percent and metronidazole cured 25 percent. For patients with trophozoites only, tinidazole cured 92 percent and metronidazole cured 72 percent. For patients who had both cysts and trophozoites, tinidazole cured 100 percent and metronidazole cured 38 percent.

Graph 1

According to the 2007 Medical Letter, metronidazole is administered in doses of 250 mg 3 times a day for 5-7 days for adults, and 15 mg/kg 3 times a day for 5-7 days in children.1 Side effects associated with metronidazole include metallic taste, dark urine, and gastrointestinal symptoms. As previously mentioned, metronidazole is not approved by the FDA for the treatment of giardiasis.

Tinidazole

Tinidazole is indicated for the treatment of giardiasis in adults with a single 2 g dose and with 50 mg/kg single dose in children over 3 years of age. In eight randomized comparative studies totalling 299 adult and pediatric patients, the average cure rate for tinidazole in giardiasis was 90%.2-8

Tinidazole has also demonstrated activity against the cyst stage of giardiasis in clinical use. Krishnamurthy demonstrated the activity of tinidazole against the cyst stage of Giardia in a study of 60 children, randomized to treatment with either metronidazole or tinidazole as a single dose of 50 mg/kg body weight. Cure rates were 97% for tinidazole and 50% for metronidazole. When looking at patients who had only cysts in the stool pre-treatment, cysts were cleared in 10 of 10 patients 12 days following treatment with tinidazole, compared to clearance of cysts in only 2 of 8 patients treated with metronidazole.2 Graph 1 depicts the percent of patients cured from Giardia cysts, trophozoites, and trophozoites and cysts, 12 days following treatment with single dose tinidazole and metronidazole.

Nitazoxanide

Nitazoxanide is indicated for giardiasis in adults with 500 mg every 12 hours with food for 3 days, and in children with 100-200 mg every 12 hours with food for 3 days. Nitazoxanide resolved the symptoms of giardiasis in 85% of 110 Peruvian children in one study.9 Nitazoxanide has been shown to be more active in vitro against Giardia than metronidazole, and it is active against metronidazole-resistant Giardia.10

 

 

 

Treatments for Giardiasis
Drug Dose Cure Rate
Tinidazole Adults11 1–2 g single dose 86–100%
Children11 50 mg/kg single dose (max. 2 g) 80–96%
Nitazoxanide Adults 500 mg bid × 3 days  
Children9 100–200 mg q12h × 3 days 85%
Metronidazole* Adults11 2.0–2.4 g single dose 36–60%
2.0–2.4 g qd × 2 days 67–80%
0–2.4 g qd × 3 days 80–100%
Children11 15–22.5 mg/kg/day × 5 – 10 days 80–100%
* Metronidazole is not indicated for use in giardiasis.
  1. Drugs for parasitic infections. Treat Guidel Med Lett. 2007 Sep;5(Suppl):1-15.
  2. Krishnamurthy KA, Saradhambal V. Single dose therapy of giardiasis: a comparative study of tinidazole and metronidazole in pediatric patients. Indian Pediatr. 1978 Jan;15(1):51-6.
  3. Bakshi JS, Ghiara JM, Nanivadekar AS. How does tinidazole compare with metronidazole? A summary report of Indian trials in amoebiasis and giardiasis. Drugs. 1978;15 Suppl 1:33-42.
  4. Jokipii L, Jokipii AM. Single-dose metronidazole and tinidazole as therapy for giardiasis: success rates, side effects and drug absorption and elimination. J Infect Dis. 1979 Dec;140(6):984-8.
  5. Kyrönseppä H, Pettersson T. Treatment of giardiasis: relative efficacy of metronidazole as compared with tinidazole. Scand J Infect Dis. 1981;13(4):311-2.
  6. Gazder AJ, Banerjee M. Single-dose treatment of giardiasis in children: a comparison of tinidazole and metronidazole. Curr Med Res Opin. 1977;5(2):164-8.
  7. Nigam P, Kapoor KK, Kumar A, Sarkari NB, Gupta AK. Clinical profile of giardiasis and comparison of its therapeutic response to metronidazole and tinidazole. J Assoc Physicians India. 1991 Aug;39(8):613-5.
  8. Speelman P. Single-dose tinidazole for the treatment of giardiasis. Antimicrob Agents Chemother. 1985 Feb;27(2):227-9.
  9. Ortiz JJ, Ayoub A, Gargala G, Chegne NL, Favennec L. Randomized clinical study of nitazoxanide compared to metronidazole in the treatment of symptomatic giardiasis in children from Northern Peru. Aliment Pharmacol Ther. 2001 Sep;15(9):1409-15.
  10. Fox LM, Saravolatz LD. Nitazoxanide: a new thiazolide antiparasitic agent. Clin Infect Dis. 2005 Apr 15;40(8):1173-80. Epub 2005 Mar 14.
  11. Gardner TB, Hill DR. Treatment of giardiasis. Clin Microbiol Rev. 2001 Jan;14(1):114-28.