WBR0629

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/Epidemiology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A study addresses the secondary prevention of acute coronary syndrome (ACS) using a novel cholesterol-lowering agent. After 5 years, follow-up of 4400 ACS patients reveals recurrence of at least 1 ACS event among 200 out of 2000 subjects who were administered the novel agent vs. 540 out of 2400 subjects who were administered standard therapy. How many patients should be administered the novel agent to prevent at least 1 ACS event for 5 years?]]
Answer A	AnswerA::4
Answer A Explanation	AnswerAExp::This number is incorrect.
Answer B	AnswerB::8
Answer B Explanation	[[AnswerBExp::In this vignette, the novel agent reduces the risk of ACS recurrence from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. The NNT for a 5-year treatment with the novel agent is the inverse of the absolute risk reduction. NNT = 1/0.125 = 8 patients]]
Answer C	AnswerC::16
Answer C Explanation	AnswerCExp::This number is incorrect.
Answer D	AnswerD::32
Answer D Explanation	AnswerDExp::This number is incorrect.
Answer E	AnswerE::64
Answer E Explanation	AnswerEExp::This number is incorrect.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The number needed to treat (NNT) is an epidemiological measure that indicates how many patients would require treatment with a form of medication to reduce the expected number of cases of a defined endpoint by one. It is defined as the inverse of the absolute risk reduction. In this vignette, the drug reduces the risk of recurrence of ACS from 22.5% to 10%. Therefore the absolute risk reduction is 12.5%. The NNT for a 5-year treatment with the novel cholesterol-lowering agent is the inverse of the absolute risk reduction (ARR), where ARR is the absolute difference in the event rate between the treatment group (novel drug) and the control group (standard therapy). Shown below is a detailed explanation of the calculation of NNT: Rate of ACS recurrence in the drug group: (200/2000) x 100 = 10% Rate of ACS recurrence in the placebo group: (540/2400) x 100 = 22.5% Absolute risk reduction (ARR) = 22.5 - 10 = 12.5% = 0.125 NNT = 1/0.125 = 8 patients Educational Objective: The number need to treat (NNT) is defined as the number of patients who require treatment with a form of medication in order to reduce the expected number of cases of a defined endpoint by one. NNT is calculated as the inverse of the absolute risk reduction. NNT=1/ARR. ARR is the absolute difference in the event rate between the treatment group and the control group. References: First Aid 2014 page 53]]
Approved	Approved::Yes
Keyword	WBRKeyword::Number needed to treat, WBRKeyword::NNT, WBRKeyword::Absolute risk reduction, WBRKeyword::ARR, WBRKeyword::Endpoint, WBRKeyword::ACS, WBRKeyword::Acute coronary syndrome
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::