What are the causes and treatments of thrush?

Causes and Treatment of Thrush (Oral Candidiasis)

Causes of Thrush

Thrush is caused by overgrowth of Candida species, most commonly Candida albicans, a yeast fungus that normally exists as a commensal organism in the oral cavity. 1, 2

Predisposing Risk Factors

The following conditions promote fungal overgrowth and development of oral candidiasis:

• Immunocompromised states: HIV/AIDS, cancer, organ transplantation, and other conditions causing immune dysfunction 1, 3
• Medication use: Corticosteroids, broad-spectrum antibiotics, and antimicrobial therapy that disrupts normal oral flora 1, 4
• Diabetes mellitus: Uncontrolled blood glucose creates favorable conditions for fungal growth 1
• Denture use: Particularly ill-fitting dentures that create moist, macerated environments 1
• Poor oral hygiene: Inadequate cleaning allows fungal accumulation 3
• Radiation therapy: Damages oral mucosa and compromises local immunity 1
• Advanced age: Associated with waning immunity and increased denture use 1

Clinical Presentation

Thrush typically manifests as:

• Whitish patches or plaques on the buccal mucosa, tongue, palate, cheeks, and lips 2, 3
• Erythematous areas depending on the type of candidiasis 3
• Burning sensation and oral discomfort 3
• Loss of taste and aversion to food 5

Treatment of Thrush

Mild Disease (First-Line Options)

For mild oropharyngeal candidiasis, topical therapy is recommended:

• Clotrimazole troches 10 mg five times daily for 7-14 days 1
• Miconazole mucoadhesive buccal 50-mg tablet applied once daily to the mucosal surface over the canine fossa for 7-14 days 1
• Nystatin suspension (100,000 U/mL) 4-6 mL four times daily for 7-14 days 1
• Nystatin pastilles (200,000 U each) 1-2 pastilles four times daily for 7-14 days 1

Moderate to Severe Disease

For moderate to severe disease, oral fluconazole 100-200 mg daily for 7-14 days is the treatment of choice 1, 6. This systemic therapy is superior to topical agents in many studies and offers convenient once-daily dosing 1.

Fluconazole-Refractory Disease

When fluconazole fails (typically after prolonged azole exposure):

• Itraconazole solution 200 mg once daily for up to 28 days 1
• Posaconazole suspension 400 mg twice daily for 3 days, then 400 mg daily for up to 28 days 1
• Voriconazole 200 mg twice daily as an alternative 1
• Amphotericin B deoxycholate oral suspension 100 mg/mL four times daily 1
• Intravenous echinocandins (caspofungin, micafungin, or anidulafungin) or IV amphotericin B 0.3 mg/kg daily for truly refractory cases 1

Special Considerations

For denture-related candidiasis, disinfection of the denture in addition to antifungal therapy is mandatory 1. Without denture treatment, recurrence is inevitable.

For HIV-infected patients, antiretroviral therapy is strongly recommended to reduce recurrent infections 1. Prophylactic fluconazole 100 mg daily can prevent thrush in AIDS patients with negligible toxic effects 5.

Chronic suppressive therapy is usually unnecessary but if required for recurrent infection, fluconazole 100 mg three times weekly is recommended 1.

Important Caveats

• Oropharyngeal fungal cultures are of little benefit since many individuals have asymptomatic colonization, and treatment frequently does not achieve microbiological cure 1
• Repeated courses of azole therapy or chronic suppressive therapy increase the risk of developing azole-resistant Candida species, particularly C. glabrata 1
• Candida krusei is intrinsically fluconazole-resistant and requires alternative agents 1
• Treatment should focus on symptom relief rather than eradication of colonization 1