Definition of Antitubercular Drug Defaulter
A defaulter from antitubercular therapy is defined as a patient who interrupts treatment for 2 or more consecutive months.
Guideline-Based Definition
The standard definition used in tuberculosis treatment programs and clinical practice guidelines consistently defines a defaulter as:
- A patient who interrupts antituberculosis treatment for ≥2 consecutive months 1, 2, 3
- This definition applies to both new cases and retreatment cases 1
- The interruption period is measured from the time the patient misses scheduled appointments and fails to continue prescribed therapy 3
Clinical Context and Timing
When Default Typically Occurs
- Intensive phase: The majority of defaults occur during the intensive phase of treatment, with median duration of treatment prior to default being 81 days (approximately 2.7 months) 1
- Early hospitalization period: 61% of patients default while still hospitalized during intensive phase 4
- Transition period: 26% default just before starting the continuation phase 4
- Continuation phase: Additional defaults occur during continuation phase, with rates of 10.9% in new cases and 16.5% in retreatment cases 2
Distinction from Treatment Failure
It is important to distinguish defaulters from treatment failures:
- Treatment failure is defined as continuously or recurrently positive cultures after 4 months of appropriate chemotherapy 5
- Defaulters voluntarily interrupt treatment, whereas treatment failures continue therapy but do not respond microbiologically 5
Risk Factors for Default
Understanding who is at risk helps identify potential defaulters:
- Previous treatment history: Former defaulters have significantly higher risk (adjusted OR: 33.2) 6
- Socioeconomic factors: Low income (<$2,000/month), unemployment, being a pensioner 6, 4
- Social factors: Homelessness, alcoholism, living alone or with friends rather than family 4, 3
- Healthcare system factors: Treatment by non-pulmonologist (adjusted OR: 14.6), public health facility-based treatment observation 6
- Ethnic and cultural factors: Non-Chinese ethnicity in Singapore studies, lack of family support 3
Clinical Implications
Management of Defaulters
When patients default and later return:
- For patients who received DOT: Retreatment using standard intensive phase regimen until susceptibility results are available 5
- For patients without DOT or irregular treatment: Higher risk of acquired drug resistance; consider expanded empiric regimen with consultation from drug-resistant TB experts 5
- Expanded regimen components: Standard intensive phase (INH, RIF, PZA, EMB) plus later-generation fluoroquinolone, injectable agent, and potentially additional second-line drugs 5
Prevention Strategies
- Enhanced monitoring: Patients with absence of disease stigma, low income, previous default history, and those treated by non-specialists require careful monitoring 6
- Retrieval efforts: Current retrieval efforts after treatment interruption are often inadequate, with home visits failing to contact patients 41% of the time 1, 3
- Community-based treatment: May reduce default rates compared to facility-based observation 1