I was trying to track down a reference on the NNH (number needed to harm)
for antibiotic use, but noticed instead the large number of good examples of
NNH calculations in journal articles with full text on the web.
The adverse neuro-developmental effects of postnatal steroids in the
preterm infant: a systematic review of RCTs. K. J. Barrington. BMC
Pediatr 2001: 1(1); 1.
[Medline]
[Abstract] [Full
text]
[PDF]
Postnatal steroid treatment is a bad idea because it increases the chances
of cerebral palsy and neuro-developmental impairment. The numbers needed to
harm are 7 and 11, respectively.
Systematic review and meta-analysis of early postnatal dexamethasone for
prevention of chronic lung disease. T. Bhuta, A. Ohlsson. Arch Dis Child
Fetal Neonatal Ed 1998: 79(1); F26-33.
[Medline]
[Abstract]
[Full text]
[PDF]
Dexamethasone is a treatment for chronic lung disease in very low
birthweight infants. Three different timings of medication were studied, and
the one that showed the greatest effect was when dexamethasone was started
within 7 to 14 days of birth. The NNT is 8 for mortality, meaning that you
would have to treat 8 infants on average with dexamethasone to prevent one
death. The NNT for prevention of chronic lung disease (CLD) at 28 days was 6,
meaning that you would have to treat 6 infants on average to prevent one case
of CLD. There was a significant increase in the risk of hypertension in this
group, with an NNH of 65. You would have to treat 65 patients, on average, in
order to see one additional case of hypertension. The authors mention that
this hypertension was temporary, so this seems like a side effect well worth
tolerating.
Finasteride in the treatment of clinical benign prostatic hyperplasia: a
systematic review of randomised trials. J. E. Edwards, R. A. Moore. BMC
Urol 2002: 2(1); 14.
[Medline]
[Abstract] [Full
text]
[PDF]
Finasteride has a significant effect on prostate volume, maximum urinary
flow rate, and symptom scores. These are continuous measures and thus are
presented as changes in mean scores rather than as NNTs. The prostate volume
decrease from 43.7 cubic cm to 32.7 in the finasteride group, but only from
44.8 to 43.0 in the control group. The urinary flow rates increased from
11.2mL/s to 12.5 after 24 months in the finasteride group, while they
increased only from 10.5 to 11.3 in the placebo group. Thus the finasteride
group had a 0.5 mL/s better improvement, on average. At 12 months, the
average symptom score was 3.7 points lower in the finasteride group compared
to a 2.3 point decline with placebo. The symptom score, developed by the
American Urological Association ranges between 0 and 35.
I'm not a urologist, but other than prostate volume, these changes look
small and of questionable clinical relevance.
The authors did show an NNT of 49 and 26 for avoiding acute urinary
retention at 24 months and at 48 months. The NNTs for avoiding prostate
surgeries were 31 and 18 for 24 and 48 months, respectively. Both acute
urinary retention and prostate surgery seem like rather extreme events, so
these NNTs would still be attractive.
There were several NNH calculations, as finasteride had an increased risk
for various side effects. The NNHs were 14 (sexual dysfunction), 47 (decrease
libido), 24 (impotence), and 55 (ejaculation disorder).
Here's where some value judgments come into play. How important is it to
decrease prostate volume and to avoid acute urinary retention and surgery? Is
the risk of various types of sexual dysfunction worth the benefits? The
benefits do seem to outweigh the risks to me, but different people may come
to different conclusions.
As a side note, this study avoided heterogeneity tests and funnel plots
because "they lack the power to reliably detect statistical heterogeneity or
publication bias" and use sensitivity analyses instead. I will try to write
up something about this issue soon.
Sildenafil (Viagra) for male erectile dysfunction: a meta-analysis of
clinical trial reports. R. A. Moore, J. E. Edwards, H. J. McQuay. BMC
Urol 2002: 2(1); 6.
[Medline]
[Abstract] [Full
text]
[PDF]
Sildenafil seems to work well. In the sildenafil group, 49% of the men has
a good outcome (meaning at least 60% of the attempts at sexual intercourse
were successful). In the placebo group only 11% had good outcomes. This leads
to an NNT of 2.7.
Inhaled corticosteroid doses in asthma: an evidence-based approach.
H. Powell, P. G. Gibson. Med J Aust 2003: 178(5); 223-5.
[Medline]
[Full text]
[PDF]
Single-dose ketorolac and pethidine in acute postoperative pain:
systematic review with meta-analysis. L. A. Smith, D. Carroll, J. E.
Edwards, R. A. Moore, H. J. McQuay. Br J Anaesth 2000: 84(1); 48-58.
[Medline]
[Abstract]
[PDF]
There were also two interesting methodology articles which are worth
looking at.
Linking evidence-based medicine therapeutic summary measures to clinical
decision analysis. B. Djulbegovic, I. Hozo, G. H. Lyman. MedGenMed 2000:
2(1); E6.
[Medline]
[Full text]
Reporting risks and benefits of therapy by use of the concepts of
unqualified success and unmitigated failure: applications to highly cited
trials in cardiovascular medicine. G. B. Mancini, M. Schulzer.
Circulation 1999: 99(3); 377-83.
[Medline]
[Abstract]
[Full text]
[PDF]
