Nitazoxanide

Introduction Overview

Generic Name

Nitazoxanide

Brand Name

Alinia

Dosage Form

Oral powder for reconstitution (100 mg/5 mL), Oral tablet (500 mg)

Drug Class

Amebicides

Pharmacokinetics

Absorption:
Nitazoxanide exhibits rapid absorption after oral administration, with its active metabolite tizoxanide reaching peak plasma concentrations generally within 1-4 hours. The bioavailability of nitazoxanide can be enhanced with food intake, as taking the drug with food increases systemic exposure significantly. This interaction is clinically relevant, necessitating administration with meals to ensure optimal efficacy. Studies indicate that the oral suspension form may have slightly different absorption kinetics compared to tablets, with the suspension facilitating quicker onset due to its formulation. The poor aqueous solubility of nitazoxanide is partly responsible for variable absorption; however, the prodrug nature allows conversion in the gastrointestinal tract to tizoxanide, the active moiety.

Distribution:
Following absorption, nitazoxanide is rapidly converted to tizoxanide, which binds extensively to plasma proteins (>99%). This high protein binding limits the free drug concentration but maintains a reservoir of active drug circulating in plasma. The apparent volume of distribution is comparatively low to moderate, reflecting its limited tissue penetration. Nonetheless, tizoxanide and its glucuronide metabolites have been detected in various tissues indicating some distributive capacity beyond plasma. Because of its high plasma protein binding, displacement interactions with other highly bound drugs may impact free concentrations and clinical response.

Metabolism:
Nitazoxanide undergoes extensive first-pass metabolism in the gastrointestinal wall and liver to its main active metabolite, tizoxanide. Tizoxanide is further conjugated primarily to tizoxanide glucuronide via phase II metabolism. This biotransformation occurs predominantly in the liver, catalyzed by UDP-glucuronosyltransferases. The metabolic profile contributes to the drug's antiparasitic activity and systemic exposure characteristics. The pharmacologically active metabolites contribute to the overall clinical efficacy and have been the key targets in pharmacokinetic studies, highlighting that the parent compound is essentially a prodrug.

Elimination:
Elimination of tizoxanide and its glucuronide conjugate occurs primarily via the biliary and renal pathways. Approximately 60%-80% of the administered dose is recovered in feces as metabolites, while 20%-25% is excreted in urine. The elimination half-life is about 1.3 hours for tizoxanide, allowing dosing twice daily to maintain effective plasma levels. The drug's clearance is affected in patients with severe hepatic dysfunction, but clinically relevant accumulation has not been conclusively demonstrated. Renal impairment appears to have minimal effect on elimination, supporting use without dose adjustment in mild to moderate renal disease. Overall, clearance mechanisms support the typical 3-day treatment course without significant risk of accumulation.

Dosage Forms

Available Dosage Forms:
- Oral tablet: 500 mg nitazoxanide
- Oral powder for reconstitution (oral suspension): 100 mg/5 mL nitazoxanide

Dosages for Adults and Adolescents:
- Cryptosporidiosis and Giardiasis: 500 mg orally every 12 hours for 3 days
- Adults and children 12 years and older generally receive the tablet form as above

Specific Patient Populations:
- Pediatric patients aged 1 to 3 years: 100 mg orally every 12 hours (oral suspension only)
- Pediatric patients aged 4 to 11 years: 200 mg orally every 12 hours (oral suspension)
- Pediatric patients 12 years and older: receive adult tablet dosing (500 mg every 12 hours)
- Tablets should not be administered to children under 12 years; oral suspension is preferred
- Renal and hepatic impairment: No dose adjustment is generally required in mild to moderate dysfunction; caution advised in severe liver disease
- Pregnancy: Nitazoxanide is not expected to be harmful, but use should be according to physician’s direction

General Guidance:
- The oral suspension should be shaken well before dosing
- Liquid formulation should be measured accurately using the dosing syringe or appropriate device
- Unused oral suspension should be discarded after 7 days
- Take all doses with food to improve absorption and reduce gastrointestinal side effects
- Therapy duration is typically 3 days for standard indications; dosing adjustments or prolonged therapy not routinely recommended

Mechanism Of Action

Nitazoxanide is a broad-spectrum antiprotozoal agent whose primary mechanism involves interference with the pyruvate:ferredoxin oxidoreductase (PFOR) enzyme-dependent electron transfer reaction essential to anaerobic energy metabolism in protozoa and some anaerobic bacteria. By inhibiting PFOR, nitazoxanide disrupts the anaerobic energy metabolism pathway critical to the survival of parasites such as Giardia lamblia and Cryptosporidium parvum.

At a molecular level, nitazoxanide is a prodrug, rapidly metabolized to tizoxanide, its active form, which selectively targets PFOR without affecting similar enzymes in mammalian cells, leading to selective toxicity against protozoa. The blockade of electron transfer from PFOR to ferredoxin results in impaired anaerobic metabolism, leading to a reduction in adenosine triphosphate (ATP) production and subsequent parasite death.

In addition to its PFOR inhibition, nitazoxanide induces alterations in the expression of viral proteins and interferes with viral maturation in certain viral infections, indicating immunomodulatory properties. Clinical studies demonstrated potential efficacy against a range of viruses including rotavirus, hepatitis B and C viruses, although these indications remain investigational.

Comparatively, nitazoxanide’s mechanism is unique among amebicides and antiparasitic agents, providing an alternative to nitroimidazoles like metronidazole that primarily inhibit DNA synthesis and cause strand breaks. This distinct mechanism minimizes cross-resistance and broadens therapeutic options. Its efficacy against both protozoal and helminthic parasites, combined with immunomodulatory potentials, underscores its value in treating parasitic infections and possibly expanding indications in infectious diseases.

Pharmacological Actions

Antiprotozoal activity targeting anaerobic protozoa such as Giardia lamblia and Cryptosporidium parvum
Inhibition of pyruvate:ferredoxin oxidoreductase (PFOR) enzyme-mediated electron transfer leading to impaired energy metabolism in parasites
Selective toxicity against protozoa with minimal impact on mammalian cells
Broad-spectrum antiparasitic properties with activity against some helminths and anaerobic bacteria
Demonstrates antiviral effects through interference with viral protein maturation and enhancement of host immune responses
Exhibits oral bioavailability suitable for systemic treatment of gastrointestinal parasitic infections
Rapid conversion to active metabolite tizoxanide which mediates the pharmacologic effect
Low potential for resistance development due to unique mechanism
Dual action as both direct antiparasitic agent and immune modulator
Effective in both adults and pediatric populations with age-appropriate formulations
Suitable for short-course oral therapy with favorable safety and tolerability
Extensively metabolized with active metabolites contributing to clinical efficacy
Minimal drug accumulation with standard dosing regimens
Compatibility with food enhances absorption and therapeutic outcomes
Demonstrated activity against multiple species causing traveler’s diarrhea and opportunistic infections

Therapeutic Or Clinical Uses

Treatment of diarrhea caused by Giardia lamblia infection (giardiasis)
Treatment of diarrhea caused by Cryptosporidium parvum infection (cryptosporidiosis)
Management of traveler’s diarrhea associated with protozoal infections
Therapeutic use in both adult and pediatric patients one year and older
Potential investigational use in viral infections including hepatitis B and C
Alternative therapy option for patients intolerant or unresponsive to nitroimidazole agents
Use in immunocompromised patients such as those with HIV/AIDS with parasitic diarrhea
Off-label treatment of other parasitic infections including amebiasis and helminthic infections
Adjunctive treatment in infections caused by protozoa resistant to standard therapies
Rapid symptom relief and resolution of parasitic diarrhea within standard 3-day regimens
Prevention and treatment of protozoal gastrointestinal infections in endemic areas
Facilitation of hydration and nutritional status improvement in affected individuals
Improved patient compliance due to favorable dosing frequency and tolerability
Reduces disease transmission by clearing protozoal organisms from the gastrointestinal tract
Supportive therapy in severe or persistent parasitic gastrointestinal disease

Side Or Adverse Effects

Nausea and gastrointestinal discomfort including mild stomach pain
Headache, which is typically transient and mild
Discolored urine, often greenish or yellowish tint, harmless and reversible
Rare allergic reactions presenting with hives, facial or throat swelling, and breathing difficulties requiring immediate medical attention
Possible mild diarrhea or altered bowel habits during treatment
Occasional dizziness or fatigue reported in some patients
Rare reports of elevated liver enzymes, warranting monitoring in patients with liver disease
No significant reports of hematologic toxicity or serious adverse reactions in standard therapy
Minimal reports of hypersensitivity or rash
Low incidence of drug-related systemic side effects due to localized activity in the gastrointestinal tract
No documented cases of nephrotoxicity in clinical use
Well tolerated in pediatric populations with appropriate formulations
Adverse effects are generally self-limiting and resolve upon discontinuation
No known long-term adverse effects from short-course therapy
No clinically relevant drug-induced QT prolongation or cardiac toxicity reported

Precautions

Do not use if allergic to nitazoxanide or any components of the formulation
Use cautiously in patients with liver disease; monitor liver function tests during therapy in hepatic impairment
Inform healthcare provider of any history of kidney disease prior to initiation
Exercise caution in patients with immunodeficiency including HIV/AIDS
Avoid tablet formulation in children under 12 years old; use oral suspension instead
Advise patients to take medication with food to improve absorption and reduce gastrointestinal upset
Avoid concurrent use with other drugs without consulting healthcare provider due to potential interaction
Pregnant women should use nitazoxanide only if clearly needed and after discussing risks with their doctor
Uncertain excretion into breast milk; breastfeeding mothers should discuss therapy risks and benefits with healthcare providers
Ensure accurate dosing, particularly with oral suspension to prevent under or overdosing in pediatric patients
Patients should be advised not to share medication with others to prevent inappropriate use
Monitor for signs of hypersensitivity reactions during treatment
Patients should report any unusual or severe side effects immediately
Adherence to full course of therapy is critical to prevent relapse or resistance
Keep medication out of reach of children to prevent accidental ingestion

Warnings

Potential for serious allergic reactions including anaphylaxis; seek immediate medical attention if symptoms such as hives, swelling, or breathing difficulty occur
Not recommended for children under 1 year of age due to insufficient safety data
Avoid use in pediatric patients under 12 years old in tablet form due to risk of choking and dosing inaccuracy
Use with caution in patients with known hepatic or renal impairment; monitor organ function
May cause discoloration of urine which is benign but may alarm patients; provide counseling
Do not exceed prescribed dosing interval to avoid toxicity
Missed doses should not be doubled to compensate; maintain regular schedule to preserve efficacy
Pregnancy category considered relatively safe but should be used only if clearly indicated by physician
Drug interactions can affect efficacy and safety; always inform healthcare providers about all medications being taken
Requires proper storage at room temperature, protecting from moisture and heat to maintain stability
Expired or unused liquid formulation should be discarded 7 days after opening to prevent microbial contamination
Patients with weakened immune systems may require careful monitoring during therapy
Not a substitute for proper hydration and supportive care in severe diarrheal illnesses
Resistance development is rare but possible; avoid indiscriminate use
Do not administer parenterally; intended for oral use only

Contraindication

Known hypersensitivity or allergy to nitazoxanide or any ingredient in the formulation
Children younger than 1 year old due to lack of established safety
Use of tablet form contraindicated in children younger than 12 years of age
Severe hepatic impairment where metabolism and clearance may be significantly altered
Patients with history of severe allergic reactions to other amebicides or antiprotozoals should exercise caution
Concurrent use with medications known to have severe interactions with nitazoxanide unless benefits outweigh risks
Not intended for treatment of bacterial infections where alternative antibiotics are indicated
Contraindicated in patients with established sensitivity to yellow dye (in some formulations) if applicable
Avoid use if history of severe skin reactions to nitazoxanide or related drugs
Contraindicated in patients unable to safely swallow tablets and if oral suspension is not available
Not recommended in neonates or infants under 1 year due to immature metabolic pathways
Patients with uncontrolled chronic gastrointestinal diseases where absorption may be compromised
Use with caution or avoid in patients with known QT prolongation or cardiac arrhythmias if other interacting drugs are present
Known intolerance to any excipients present in formulation
Use in critically ill patients only under strict medical supervision due to limited data

Drug Interactions

Concomitant use with drugs highly bound to plasma proteins may alter free drug concentrations due to nitazoxanide’s high protein binding
Potential interaction with warfarin and other anticoagulants necessitating monitoring of coagulation parameters
Possible reduced absorption or altered metabolism when administered with rifampin or other enzyme-inducing agents
Concomitant use with antiretroviral drugs requires clinical monitoring though no major interactions have been reported
Coadministration with proton pump inhibitors or antacids may affect gastric pH and alter absorption; clinical significance yet to be fully established
No significant interaction reported with most common antibiotics, but caution advised with multidrug regimens
Vitamins and herbal products should be disclosed to the healthcare provider as some may affect liver enzyme systems influencing nitazoxanide metabolism
Certain immunosuppressants could have altered pharmacodynamics when given with nitazoxanide
No major interactions reported with oral contraceptives or hormonal therapies to date
Methadone interaction data is limited; care in patients on opioid substitution therapy recommended
Concurrent use with nephrotoxic or hepatotoxic drugs necessitates close monitoring
Potential pharmacodynamic interaction when combined with other antidiarrheal agents
Interactions with medications metabolized by UDP-glucuronosyltransferases cannot be excluded
No contraindicated combinations definitively identified, but thorough review of patient medication list is essential
Drug Interaction Checker tools and consultation with pharmacists recommended prior to initiating therapy

Preparations Of The Drug

Oral tablets containing 500 mg nitazoxanide for systemic antiparasitic treatment
Oral powder for reconstitution to 100 mg/5 mL suspension suitable for pediatric dosing
Formulations designed to be taken with food to enhance bioavailability and reduce gastrointestinal side effects
Suspension packaged with dosing syringe or marked measuring devices for accurate administration
Tablets formulated for ease of swallowing in adult and adolescent patients
Non-intravenous formulations; not indicated for parenteral use
Storage instructions specify keep at room temperature, away from moisture and heat to preserve stability
Bottle dispensing with child-resistant caps to prevent accidental ingestion by children
Single-ingredient preparations without additional antimicrobial preservatives to reduce risk of hypersensitivity
Produced under Good Manufacturing Practice (GMP) compliant conditions ensuring quality and purity
Commercially available packaging supports short-course therapy protocols
Formulations intended for treatment of amebiasis, giardiasis, and cryptosporidiosis as per labeling
Accessible through prescription with brand name 'Alinia' and generic equivalents
Supplied with patient information leaflets detailing dosing, precautions, and storage
Liquid formulation shelf-life limited to 7 days after reconstitution to prevent microbial contamination