Rod: I agree with you point that when we make recommendations we should
define our perspective: is it from societal or a patient's point of view? I
would just add that we should make every effort to EXPLICITLY define
reasoning that goes into our recommendations (benefit vs harm vs cost vs
values).
ben
Benjamin Djulbegovic, MD
Associate Professor of Medicine
H. Lee Moffitt Cancer Center & Research Institute
at the University of South Florida
Division of Blood and Bone Marrow Transplant
12902 Magnolia Drive
Tampa, FL 33612
e-mail:[log in to unmask]
http://www.hsc.usf.edu/~bdjulbeg/
phone:(813)979-7202
fax:(813)979-3071
> -----Original Message-----
> From: Rod Jackson [SMTP:[log in to unmask]]
> Sent: Tuesday, March 09, 1999 5:59 AM
> To: Djulbegovic, Benjamin
> Cc: [log in to unmask]
> Subject: RE: What is a good number for NNT?
>
> Ben - while no one would argue that the treatment should be withheld if
> the
> risk of CVD is below AT using your terminology, the converse is not so
> clear cut. Evidence that a treatment results in more good than harm is a
> necessary but not sufficient reason for treatment. Alternative uses of
> scarce health resources need to be considered and this is very dependant
> on
> the wealth of the community in which you live. In New Zealand we suggest
> a
> 10-15% 5 year risk of CVD is a reasonable level at which to discuss
> pharmacological treatment of raised blood pressure with patients. As it
> happens in NZ if we only treated people with a 15% 5 yr CVD risk, this
> would lead to little net change in numbers treated (although many would
> stop and many others would start) and we would inccrease the number of
> events prevented over 5 yrs by about 30%. We have a different threshold
> for lipid lowering treatment because despite a similar effect on risk, the
> drugs cost alot more in NZ. In the ideal world we would estimate $/QALY
> for all interventions and use these to help prioritise who should be
> treated with what.
>
> Rod
>
>
> >As I argued it at this group before and as we described it elsewhere
> (for
> >details see Cancer Control 1998;5:394-405; also at
> >http://www.moffitt.usf.edu/pubs/ccj/v5n5/article2.html , Med Decision
> >Making 1998;18:464
> >; Comp Biomed Res; or, see
> >http://www.hsc.usf.edu/~bdjulbeg/Programs/BR/br-java.htm ), normatively
> >highest (maximum) NNT at which treatment is worth administering in
> >prophylactic setting is equal to:
> > NNT<NNH or NNT<1/ R
> >where R is risk of the treatment .
> >For example, for a toxicity of 2%, the treatment NNT has to be at most 50
> to
> >be worth administering the treatment, for a toxicity of 4%, the NNT has
> to
> >be at most 25, etc.
> >
> >If this condition is not satisfied, no NNT is "good NNT".
> >
> >In the setting of selection of Rx1 vs Rx2, in order to even consider the
> >treatment Rx1 as opposed to the alternative treatment Rx2, the following
> >inequality must be satisfied:
> >
> >NNT1 <= 1/(R1 - R2 + 1/NNT2)
> >
> >
> >This is not only normatively correct, but also makes sense intuitively:
> we
> >should not consider measures of treatment benefits without consideration
> of
> >other side of therapeutic coin (that is, treatment harm).Again, as I
> wrote
> >before, it is important to realize that same units of benefits and harms
> are
> >used when these calculations are performed.
> >
> >I am not aware of any normative model that successfully integrated
> patients
> >values with NNT, NNH or with any other EBM summary measures of
> therapeutic
> >effects (although, I should say that we are currently working on one such
> >model)
> >
> >Intertwined with this issue is the question of "action threshold". I will
> >try to illustrate it from perspective of ongoing discussion of CVD risk
> and
> >New Zealand tables for CVD. The tables use data from Framingham Heart
> study.
> >These tables suggest threshold for therapeutic action if risk of CVD is
> >10-15% at 5yrs (NNT=25 for 5 years) (see:
> >http://cebm.jr2.ox.ac.uk/docs/prognosis.html ) However, this treatment
> >threshold appears to be quite arbitrary. As I argued before, normatively
> >this action threshold (AT) is equal to
> >
> >AT= NNT/NNH or AT=risk of treatment*NNT=treatment
> >risk/(RRR*morbidity/mortality without Rx) (for details see references
> >provided above).
> >
> >We should treat if estimated risk of clinical event (in this case, CVD)
> is
> >above AT; conversely, we should withhold Rx if risk of CVD is below AT.
> For
> >example, package insert for pravastatin indicated that at median
> treatment
> >of 4.8 years, 0.10% of patients treated with pravastatin developed
> elevation
> >of AST as opposed to 0.03% of placebo treated patients. This would amount
> >roughly to NNH=1428. Using the action threshold equation this means that
> we
> >can consider treatment with statins if risk of CVD exceeds >1.7% at 5
> years
> >(AT=25/1428). Even when I vary risk in sensitivity analysis, I still
> obtain
> >threshold for action, which is below recommended 2% or 3% per year. It is
> >not clear to me how current recommendations (for treatment actions) have
> >been derived. Can somebody care to comment? (Cardiovascular medicine is
> not
> >my field, and I am perhaps missing something here).
> >
> > (Incidentally, I developed a simple BASIC program that integrates this
> >threshold model with Framingham risk equations. If anybody is interested
> in
> >the program, I will be happy to send it to him/her.)
> >
> >
> >
> >hope this clarifies this issue
> >
> >ben d
> >
> >Benjamin Djulbegovic, MD
> >Associate Professor of Medicine
> >H. Lee Moffitt Cancer Center & Research Institute
> >at the University of South Florida
> >Division of Blood and Bone Marrow Transplant
> >12902 Magnolia Drive
> >Tampa, FL 33612
> >
> >e-mail:[log in to unmask]
> >http://www.hsc.usf.edu/~bdjulbeg/
> >phone:(813)979-7202
> >fax:(813)979-3071
> >
> >> -----Original Message-----
> >> From: Takeo Saio [SMTP:[log in to unmask]]
> >> Sent: Friday, March 05, 1999 5:32 PM
> >> To: Amit Ghosh
> >> Cc: [log in to unmask]
> >> Subject: RE: What is a good number for NNT?
> >>
> >> Hello! That's very good question.
> >>
> >> I think the NNTs of 2-4 are for therapeutic usage of drugs,and the NNTs
> >> over 20 are for preventitive usage of drugs.
> >> i.e. for acute condition,NNTs of 2-4:for chronic condition,NNTs of over
> >> 20.
> >>
> >>
> >> > A question I have , is what is a good number for NNT? Bandolier 12
> >> >indicated that a NNT of 2-4 is suggestive of good NNT ( i.e., ARR of
> >> >0.25-0.50). However most the the RCT reported in journal s NEJM,
> Annals
> >> >etc have statistical significance however their NNT are usually over
> 20,
> >> >ie, finasteride for BPH( NNT= 30). I reckon one of the disadvantages
> of
> >> >NNT maybe that despite the NNT being over 20 , these patients may have
> >> >significant improvement in quality of life and other subjective
> issues.
> >> >Or is the fact that NNT of 2-4 an over enthusiastic expectation when
> it
> >> >comes to a clinical response.I guess in the case of chronic diseases
> >> >with outcomes occurring over decades a NNT of 50 would be acceptable,
> >> >however in other more acute conditions one would consider a smaller
> >> >number for NNT as desirable. Could the members throw some additional
> >> >light in the defining what is a good number for NNT.
> >> **********************************************
> >> Saio,Takeo
> >> ///////////////CHIAKI hospital,JAPAN/////////
> >> e-mail;[log in to unmask]
> >> **********************************************
> >>
> >>
> >>
>
>
> Dr Rodney Jackson MBChB PhD FAFPHM
> Associate Professor of Epidemiology
> Head of Department
> Dpt of Community Health, School of Medicine
> University of Auckland
> (Grafton Mews, 52-54 Grafton Rd)
> Private Bag 92019, Auckland, New Zealand
> Phone: +64 (0)9-3737599 ext 6343
> Fax: +64 (0)9-3737503
> e-mail: [log in to unmask]
>
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