A clinical study investigates a newly developed oral medication aimed at reducing the inci… — USMLE Step 3

A clinical study investigates a newly developed oral medication aimed at reducing the incidence of recurrent urinary tract infections (UTIs) in postmenopausal women. The investigation includes $1,000$ participants who are randomly allocated in equal numbers to either the new medication or a placebo. Over a $12$ -month period, $150$ out of the $500$ participants taking the placebo develop a recurrent UTI. Meanwhile, $100$ out of the $500$ participants taking the new oral medication develop a recurrent UTI.

What is the number needed to treat (NNT) to prevent one recurrent UTI in this population?

Cevap: 10 patients

Cevap

The number needed to treat (NNT) represents how many patients must receive the intervention to prevent one additional adverse outcome. It is calculated by taking the reciprocal of the absolute risk reduction (ARR). First, calculate the event rates for the control group (

\frac{150}{500} = 0.30

) and the treatment group (

\frac{100}{500} = 0.20

). The ARR is the difference between these rates (

0.30 - 0.20 = 0.10

). Finally, NNT is

\frac{1}{\text{ARR}}

(

\frac{1}{0.10} = 10

Adım Adım Çözüm

Calculate the risk of the outcome in the control (placebo) group.

Control Event Rate (CER) =

\frac{150}{500} = 0.30

This establishes the baseline risk of developing a recurrent UTI without the active medication.

Calculate the risk of the outcome in the experimental (treatment) group.

Experimental Event Rate (EER) =

\frac{100}{500} = 0.20

This establishes the risk of the outcome when receiving the intervention.

Calculate the Absolute Risk Reduction (ARR).

\text{ARR} = 0.30 - 0.20 = 0.10

ARR measures the absolute difference in risk between the two groups.

Calculate the Number Needed to Treat (NNT).

\text{NNT} = \frac{1}{0.10} = 10

NNT is the reciprocal of the ARR and represents the number of patients who must be treated to prevent one adverse event.

Anahtar Kavram

The Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR), which is the absolute difference in event rates between the control and experimental groups.

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