Number needed to treat/harm — MCQs

A pharmaceutical company reports a new antihypertensive drug reduces cardiovascular events with an NNT of 50 over 5 years based on a trial of 10,000 patients. An independent analysis reveals the benefit was driven entirely by a subgroup with resistant hypertension (20% of participants, NNT=15), while the remaining 80% showed no benefit over standard therapy (NNT approaching infinity). Evaluate the ethical and regulatory implications of reporting the overall NNT.

A public health agency must allocate a fixed budget between two interventions for diabetes prevention. Program A (intensive lifestyle modification): NNT=7, cost $3,500/person. Program B (metformin): NNT=14, cost $1,000/person. Both prevent one case of diabetes over 3 years. The budget allows treating 1,000 people with Program A or 3,500 people with Program B. Evaluate the optimal allocation strategy to maximize population health impact.

A 45-year-old woman with a strong family history of breast cancer (lifetime risk 25%) is considering chemoprevention with tamoxifen. A trial shows tamoxifen reduces breast cancer incidence from 5% to 3% over 5 years in high-risk women, but increases endometrial cancer from 0.2% to 0.6% and thromboembolic events from 0.5% to 1.5%. Evaluate whether she should be recommended this therapy based on comprehensive risk-benefit analysis.

A meta-analysis of 5 trials examines aspirin for primary prevention of cardiovascular disease. Individual trials show NNTs ranging from 250 to 2000, with confidence intervals overlapping. Trial A (high-risk population, NNT=250) and Trial E (low-risk population, NNT=2000) contribute most to heterogeneity (I²=78%). Analyze the appropriate interpretation and application of these findings.

A hospital formulary committee is reviewing a new expensive biologic agent for ulcerative colitis. Trial data shows clinical remission in 45% of treated patients versus 15% with placebo at 1 year. However, serious infections occur in 8% versus 2%. The drug costs $50,000 per patient per year. Analyze the pharmacoeconomic implications using NNT and NNH.

A clinical researcher is analyzing data from a trial of a new antibiotic for community-acquired pneumonia. The cure rate was 88% (352/400) in the treatment group and 80% (320/400) in the standard therapy group. When stratified by age, patients >65 years showed cure rates of 82% versus 70%, while patients ≤65 years showed 92% versus 88%. Analyze how this stratification affects the interpretation of NNT.

A 72-year-old woman with rheumatoid arthritis is prescribed a COX-2 inhibitor. A study shows the drug reduces joint pain requiring rescue analgesia in 60% of treated patients versus 40% with placebo over 3 months. However, cardiovascular events occur in 4% of treated patients versus 2% of placebo patients. Analyze the risk-benefit profile using NNT and NNH.

A 55-year-old man with hypertension is considering statin therapy for primary prevention of cardiovascular disease. A clinical trial reports that statin therapy reduced the 10-year risk of myocardial infarction from 8% to 5%. The patient asks how many people like him would need to take the medication for one person to benefit. Apply the trial data to provide this information.

A 68-year-old woman with atrial fibrillation is being counseled about anticoagulation therapy. A meta-analysis shows that warfarin reduces the risk of ischemic stroke from 6% to 2% per year, but increases major bleeding from 1% to 3% per year. Apply these data to calculate both the NNT for stroke prevention and the number needed to harm (NNH) for major bleeding.

A pharmaceutical company conducts a randomized controlled trial of a new antiplatelet drug for secondary stroke prevention. In the treatment group (n=1000), 80 patients experienced a recurrent stroke over 5 years. In the placebo group (n=1000), 120 patients experienced a recurrent stroke. Calculate the number needed to treat (NNT) to prevent one stroke over 5 years.