Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as ''
effectiveness'', and it has often been used synonymously, although in
pharmacology
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...
a
distinction is now often made between efficacy and effectiveness.
The word ''efficacy'' is used in
pharmacology
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...
and
medicine to refer both to the maximum response achievable from a
pharmaceutical drug in research settings,
[ and to the capacity for sufficient therapeutic effect or beneficial change in clinical settings.
]
Pharmacology
In pharmacology, efficacy () is the maximum response achievable from an applied or dosed agent, for instance, a small molecule drug. Intrinsic activity is a relative term for a drug's efficacy relative to a drug with the highest observed efficacy. It is a purely descriptive term that has little or no mechanistic interpretation.
In order for a drug to have an effect, it needs to bind to its target, and then to affect the function of this target. The target of a drug is commonly referred to as a receptor, but can in general be any chemically sensitive site on any molecule found in the body. The nature of such binding can be quantified by characterising how tightly these molecules, the drug and its receptor, interact: this is known as the affinity. Efficacy, on the other hand, is a measure of the action of a drug once binding has occurred. The maximum response, , will be reduced if efficacy is sufficiently low.
The definition of efficacy has been object for discussion. The only way in which absolute measures of efficacy have been obtained is by single ion channel analysis of ligand gated ion channels. It is still not possible to do this for G protein-linked receptors.
In the case of the glycine receptor and the nicotinic acetylcholine receptor (muscle type), it has been proposed by Sivilotti ''et al''. that opening of the ion channel involves two steps after agonist is bound. Firstly a conformation change to a higher affinity (but still shut) form, followed by the conformation change from shut to open. It was found that partial agonism results from deficiency in the first step, and that the opening and shutting steps are essentially the same for both full and partial agonists. This has been confirmed and extended by Sine and colleagues (2009). The implication of this work is that efficacy has to be defined by at least two equilibrium constants (or, more generally, by four rate constants).
The combined influences of affinity and efficacy determine how effectively a drug will produce a biological effect, a property known as potency.
Medicine
In medicine, efficacy is the capacity for beneficial change (or therapeutic effect) of a given intervention (for example a drug, medical device, surgical procedure
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...
, or a public health intervention). Establishment of the efficacy of an intervention is often done relative to other available interventions, with which it will be compared. Specifically, efficacy refers to "whether a drug demonstrates a health benefit over a placebo or other intervention when tested in an ideal situation, such as a tightly controlled clinical trial." These studies focus on a primary parameter to be shown statistically different between placebo and intervention groups. Comparisons of this type are called 'explanatory' randomized controlled trials, whereas 'pragmatic' trials are used to establish the ''effectiveness'' of an intervention regarding also non-specific parameters.
Effectiveness refers to "how the drug works in a real-world situation", and is "often lower than efficacy because of interactions with other medications or health conditions of the patient, sufficient dose or duration of use not prescribed by the physician or followed by the patient, or use for an off-label condition that had not been tested."[
]
Theology
Scripture
In Protestant Theology (esp. in Lutheran but also in Calvinist doctrine) ''efficacy'' is an attribute of Scripture. The efficacy of Scripture means that it is united with the power of the Holy Spirit and with it, not only demands, but also creates the acceptance of its teaching and that this teaching produces faith and obedience
Obedience, in human behavior, is a form of " social influence in which a person yields to explicit instructions or orders from an authority figure". Obedience is generally distinguished from compliance, which is behavior influenced by peers, and ...
. Efficacy further means that Holy Scripture is not a dead letter, but rather, the power of the Holy Spirit is inherent in it and that Scripture does not compel a mere intellectual assent to its doctrine, resting on logical argumentation, but rather it creates the living agreement of faith. The Smalcald Articles affirm, "in those things which concern the spoken, outward Word, we must firmly hold that God grants His Spirit or grace to no one, except through or with the preceding outward Word." The Formula of Concord teaches that when humans reject the calling of the Holy Spirit, it is not a result of the Word being less efficacious. Instead, contempt for the means of grace is the result of "the perverse will of man, which rejects or perverts the means and instrument of the Holy Ghost, which God offers him through the call, and resists the Holy Ghost, who wishes to be efficacious, and works through the Word..."Solid Declaration, article xii, "Election", par. 41
/ref>
Prayer
See also
* Average treatment effect
* Efficiency (disambiguation)
* Placebo (origins of technical term)
A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures.
In general, placebos can aff ...
* Potency (pharmacology)
* Pragmatic clinical trial
A pragmatic clinical trial (PCT), sometimes called a practical clinical trial (PCT), is a clinical trial that focuses on correlation between treatments and outcomes in real-world health system practice rather than focusing on proving causative e ...
* Self-efficacy
In psychology, self-efficacy is an individual's belief in their capacity to act in the ways necessary to reach specific goals. The concept was originally proposed by the psychologist Albert Bandura.
Self-efficacy affects every area of human endea ...
* Vaccine efficacy
References
{{Pharmacology
Medical terminology
Pharmacodynamics