Jeffrey Aronson: When I Use a Word . . . Defining drug shortages

Over the last four weeks I have been discussing drug shortages, their history, causes, harms and errors that can result, and proposed solutions. But defining a drug shortage is not easy.

I have found two systematic reviews of definitions. The first listed 18 general definitions of a shortage plus eight definitions describing drugs for which shortages are reported; the second, a WHO review, listed 56 statements of various kinds described as definitions. However, many of the so-called definitions listed in these reviews are not definitions at all (see Box 1). The WHO reviewers recognized this: “Some papers described conditions or systems in which an action was required to address a shortage or stockout, in which case these descriptions were taken to be definitions.” Even though they are not.

Box 1. Principles underlying the formulation of a good definition

  • A good definition describes all the essential attributes of the definiendum, the thing being defined. To define something (Latin definire) is to determine its boundaries (Latin fines), to state exactly what the thing is, and hence to explain its essential nature; this is what Aristotle called τό τί ἦν εἶναι (literally, that which is). Thus, a definition is “a precise statement of the essential nature of a thing” (Oxford English Dictionary).
  • It must not be too wide or too narrow. As its etymology implies, a boundary must be drawn round a definition, so that it includes everything essential and excludes everything inessential.
  • It should avoid circularity. For example, to define a medication error as “any error occurring in the medication process” is circular, since what it unhelpfully says, in effect, is that a medication error is an error in medication. This implies that a word that is related to the definiendum should be avoided in the definition (e.g. defining a shortage as a shortcoming).
  • It must not be obscure. The words used in a definition must themselves be easily understood without further definition. When defining technical terms it may be hard to achieve this.
  • It should, if possible, be positive, not negative. One should not, for example, define “wisdom” as “the absence of folly”; after all, there are many other things one could put in place of “folly” here. Negative definition also encourages circular definition; having defined “wisdom” as “the absence of folly, one might, for example, define “folly” as “the absence of wisdom”.
  • A definition should not simply describe the circumstances in which the definiendum arises, which is not, properly speaking, a definition, although the terms in which it is couched can often be reworded so as to produce a satisfactory definition.

Combining the two lists and adding other definitions that I have found, I have compiled a list of 43 descriptions in all. There is no general agreement as to what constitutes a shortage. Furthermore, some terms need to be separately defined and others need careful consideration.

Supply Of the 43 descriptions, 22 include the word “supply”, in terms such as non-supply, supply disruption, supply chain, supply problems, [in]appropriate and [non]continued supply, inadequate supply, and supply issue (i.e. non-issue). You might think that inadequate supply of a medicine constitutes a shortage. However, an individual pharmacy may run out of a medicine which is generally available elsewhere.

Stock-out This term, which alludes to the absence of a medicine from the pharmacy shelves, appears in 13 of the 43 texts. It is variously defined as an inability of a pharmacy to deliver a drug to a patient, zero usable stock, complete absence of a medicine in stock, no medicine facility shelf, and absence of a medicine at a health facility level; in at least one specific case it is defined as either a complete absence or a certain minimum level of stock for a given duration. But again, a local absence of stock need not imply a general shortage.

Pharmacy Different terms are used to qualify the term “pharmacy” (e.g. community, hospital, dispensary, internal use, and health facility pharmacy).

Patients Only 18 of the 43 texts specifically mention patients, and none mentions effects on public health. Phrases used include: problems with continued treatment, detrimental consequences, affecting patients’ ability to access required treatment, compromising or influencing or impacting on patient care, [failure to] meet/comply with patients’ needs, [failure to] meet current projected demand at the patient/user level, and [failure to] meet expected patient volumes. In these paraphrases, I have added the bracketed word “failure”, since no definition mentions it, even though we are talking about a failure to meet patients’ therapeutic needs.

Duration Different definitions offer different time courses over which a medicine cannot be obtained in order to define a shortage: at least one day, three days, four days, 14 days, 20 days, or at least one month; some are more vague: “every delay in monthly supply” or “within a few days”. However, different delays affect different medicines differently. For example, even a delay of a day in supplying an oral contraceptive may be deleterious, while other medicines can be missed for longer periods. This concept has been referred to as “forgiveness”, a measure of the length of time a medicine can be omitted without loss of benefit.

Specificity Some definitions, particularly those included in legislation, refer to a specific country. Some refer to specific diseases. Only two take in a wider purview, referring to local, national, and international shortages, and both of those derive from the same original source.

In Box 2 I have listed some of the general problems with the definitions that have hitherto been suggested. The WHO reviewers proposed the following definition of a drug shortage: “The supply of medicines, health products, and vaccines identified as essential by the health system is considered to be insufficient to meet public health and patient needs.” This definition, probably deliberately, leaves some things unsaid. For example, it does not define “essential”. And there is also the lexicographical problem that this is not strictly speaking a definition, but a “when” description that omits the word “when” (Box 2).

I shall try to tackle these problems next week.

Box 2. Some general problems with published definitions of a drug shortage

  • Interchangeability of terms meaning different things: shortage, [un]availability, supply disruption/interruption/issue, stock-out
  • Varying definitions depending on different aspects of the supply chain being addressed—manufacture, distribution, dispensing
  • Varying specificity, e.g. in reference to locality, different types of pharmacy, or specific medicines
  • Varying time frames or durations specified or not specified at all
  • The contrast between definitions relating to supply and those relating to demand
  • Lexicographical problems; for example, many of the statements describe when a drug shortage occurs rather than defining a drug shortage itself; the word “when” used in this way appears in 14 of the 43 descriptions (e.g. “occurs when”, “happens when”, “is a situation when”)


Jeffrey Aronson is a clinical pharmacologist, working in the Centre for Evidence Based Medicine in Oxford’s Nuffield Department of Primary Care Health Sciences. He is also president emeritus of the British Pharmacological Society.

Competing interests: None declared.