What are days of therapy (DOTs) and how are they calculated in antibiotic treatment?

Days of Therapy (DOTs): Definition and Calculation

Days of therapy (DOTs) is a standardized metric that counts each calendar day a patient receives any amount of a specific antibiotic, regardless of dose or frequency, making it the preferred method for measuring antibiotic consumption in both adult and pediatric populations. 1

How DOTs Are Calculated

DOTs count each individual antibiotic administered on each calendar day as one day of therapy:

• If a patient receives one antibiotic on a given day = 1 DOT 1
• If a patient receives two different antibiotics on the same day = 2 DOTs 1
• If a patient receives three antibiotics on the same day = 3 DOTs 1

The calculation is independent of:

• The actual dose administered 1
• The number of doses given per day (once daily vs. multiple times daily) 1
• Whether the dose was adjusted for renal function 2
• The route of administration (oral, intravenous, intramuscular) 1

Practical Clinical Examples

Example 1: Simple Single-Agent Therapy

A patient with community-acquired pneumonia receives ceftriaxone for 5 consecutive days:

• Total DOTs = 5 (one antibiotic × 5 days) 1

Example 2: Combination Therapy

A patient with intra-abdominal infection receives piperacillin-tazobactam and vancomycin together for 7 days:

• Total DOTs = 14 (two antibiotics × 7 days) 1

Example 3: Sequential Therapy

A patient receives meropenem for 3 days, then switches to oral ciprofloxacin for 4 days:

• Total DOTs = 7 (3 days meropenem + 4 days ciprofloxacin) 1

Example 4: Tuberculosis Treatment

For a 6-month daily tuberculosis regimen given 7 days/week, the treatment consists of at least 182 doses of isoniazid and rifampin, and 56 doses of pyrazinamide, which translates to specific DOT counts for each agent over the treatment period 1

When tuberculosis treatment is given 5 days/week by directly observed therapy (DOT), the required number of doses is adjusted to 130 doses for the 6-month regimen 1

Why DOTs Are Preferred Over DDDs

The Infectious Diseases Society of America and Society for Healthcare Epidemiology of America recommend DOTs over defined daily doses (DDDs) because: 1

• DOTs are not affected by dose adjustments for renal or hepatic impairment, whereas DDDs can misrepresent actual use when doses are modified 1
• DOTs work equally well in pediatric and adult populations, while DDDs have limited utility in children due to weight-based dosing 1
• The CDC's National Healthcare Safety Network requires DOT reporting, making it the national standard 1
• DOTs require patient-level data, which provides more granular information for stewardship interventions 1

Reporting DOTs for Benchmarking

DOTs are typically normalized and reported as "DOTs per 1000 patient-days" or "DOTs per 1000 days present" to allow meaningful comparisons between facilities of different sizes and patient populations 1, 3

Calculation formula:

• (Total DOTs / Total patient-days) × 1000 = DOTs per 1000 patient-days 1

Important Caveats

DOTs measure quantity but not quality of antibiotic use - a hospital with lower DOTs is not necessarily using antibiotics more appropriately or using narrower-spectrum agents 1, 3

DOTs should be stratified by individual antibiotic to identify specific patterns of use and target stewardship interventions 1

Compliance with treatment guidelines is a separate measure that should be assessed alongside DOTs to evaluate appropriateness of prescribing 1

DOTs do not capture spectrum of coverage - newer metrics like days of antibiotic spectrum coverage (DASC) have been proposed to address this limitation by incorporating both consumption and spectrum breadth 3