Pharmacy & Therapeutics - December 2008 - (Page 710)

Interpreting Estimates of Treatment Effects continued from page 703 Table 1 Measures of Magnitude of Effect Effect Size Relative measures Relative risk for improvement (RR) Odds ratio (OR) 1: no difference Less than 1: placebo better than drug Greater than 1: drug better than placebo 1: no difference Less than 1: placebo better than drug Greater than 1: drug better than placebo The number of times more likely a patient is to improve with a drug compared with placebo The increase in the odds for improvement that can be attributed to the treatment Meaning of Values Interpretation Absolute measures Standardized mean difference 0: no difference (SMD) Negative: placebo better than drug Positive: drug better than placebo Gives the difference between drug and placebo outcomes adjusted for measurement scale and measurement imprecision; can be translated into the probability of treated patients improving more than the average placebo patient The probability that a randomly selected member of the drug group will have a better result than a randomly selected member of the placebo group The number of patients, on average, who need to be treated for one patient to benefit from treatment lower NNT than the antidepressant treatment of generalized anxiety disorder. The table also shows differences among medications for the same disorder. The nonstimulant treatment of ADHD has nearly twice the NNT as the stimulant therapy for this disorder.17–22 The magnitude of effect is important when we consider the costs of various treatment options. One approach is to consider the costs of failed treatments. Based on the NNT, we can compute the probability of a failed treatment as: NNT 1 NNT Probability of benefit 0.5: no difference 0–0.49: placebo better than drug 0.51–1.0: drug better than placebo Negative: placebo better than drug Positive: drug better than placebo Number needed to treat (NNT) By understanding the different measures and how they are computed, health care professionals can make sense of the literature that uses these terms; perhaps more importantly, they can compute some measures that they find particularly useful for decision-making. Thinking in terms of magnitude of effect becomes particularly useful when effect sizes for other treatments are understood. Table 2 presents examples of measures of effect magnitude from meta-analyses of the psychiatric literature. The measures clearly show that some disorders can be treated more effectively than others. For example, the stimulant therapy for attention-deficit/hyperactivity disorder (ADHD) has a much (8) Table 2 Magnitude-of-Effect Measures for Classes of Psychiatric Medications Relative Measures Relative Risk for Improvement 2.5 3.6 3.7 2.2 1.5 1.9 Absolute Measures Probability of Benefit .67 .74 .75 .64 .57 .61 Number Needed to Treat 7 4 4 9 20 12 Medication Class Nonstimulants for ADHD Immediate-release stimulants for ADHD Long-acting stimulants for ADHD SSRIs for obsessive-compulsive disorder or depression Atypical antipsychotic drugs* for schizophrenia Antidepressants for generalized anxiety disorder Odds Ratio 3.1 5 5.3 2.5 1.6 2.1 SMD .62 .91 .95 .5 .25 .39 ADHD = attention-deficit/hyperactivity disorder; SMD = standardized mean difference; SSRI = selective serotonin reuptake inhibitor. * Olanzapine, quetiapine, risperidone, and sertindole. Data from Gale C, Oakley-Browne M. Clin Evid 2002(7):883–895;17 Faraone SV, et al. Medscape General Medicine e Journal. 2006;8(4):4;18 Faraone SV. Medscape Psychiatry Mental Health 2003;8(2);19 Geddes J, et al. Clin Evid 2002(7):867–882;20 Soomro GM. Clin Evid 2002(7):896–905;21 and Leucht S, et al. Schizophr Res1999;35(1):51–68.22 710 P&T® • December 2008 • Vol. 33 No. 12

Table of Contents Feed for the Digital Edition of Pharmacy & Therapeutics - December 2008

Pharmacy & Therapeutics - December 2008 Contents Editorial Medication Errors Prescription: Washington New Drugs/Drug News/ New Medical Devices Drug Forecast Interpreting Estimates of Treatment Effects Chemotherapy Foundation Symposium XXVI: Innovative Cancer Therapy for Tomorrow Third Annual Onmark National Payor/Provider Forum Fourth Annual Ophthalmic Drug Development and Delivery Summit Classification and Pharmacological Management Of Obesity CE Test and Forms Season’s Greetings: Thanks to Our Readers and Reviewers

Pharmacy & Therapeutics - December 2008

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