MedDRA Rules and Conventions

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Chapter: Pharmacovigilance: Medical Dictionary for Regulatory Activities (MedDRA)

There are several MedDRA rules or conventions, some of which will be presented here.


There are several MedDRA rules or conventions, some of which will be presented here. First, there are some linguistic/lexical conventions. Thus, for example, abbreviations are permitted if these are in common usage and unambiguous. For example, ALT Increased is an abbreviation of Alanine aminotrans-ferase increased. These abbreviations are LLTs and are unpunctuated. Another convention concerns word order. This is generally as in normal language at the PT level, unless the terms constitute a list or index – thus, for example, Pneumonia salmonella; Pneumonia staphylococcal; Pneumonia streptococcal, and so on. A personally rather pleasing convention is that PTs in English use the British spelling (Oedema; Anaemia; Oesophagitis). American English is relegated to the LLT level. It is important to remember this, other-wise when looking at tables of data that are arranged alphabetically as PTs under SOC, for example, it is possible to miss terms due to the spelling convention.

Another convention concerns the anatomical loca-tion of terms under primary and secondary SOC. The convention is that the pathological process takes precedence over the anatomical location. Thus, congenital conditions have their primary location in the Congenital, familial and genetic disorders SOC. Hence, for example, the PT Heart disease congenital has its primary location there, with a secondary loca-tion under the Cardiac disorders SOC. In the same way, Pharyngitis streptococcal has its primary loca-tion in the Infections and infestations SOC, with a secondary location under Respiratory, thoracic and mediastinal disorders SOC. The convention applies equally to neoplasms.

An important convention is that a distinction is made in MedDRA between reports of an investi-gational finding and reports of an apparent medical condition. Thus, a report of hyponatraemia would be coded with the LLT Hyponatraemia, for which the corresponding PT is in the Metabolism and nutri-tion disorders SOC. However, a report of low serum sodium would be coded with the LLT Serum sodium decreased, for which the PT is present in the Investi-gations SOC. This is particularly important, because terms in the Investigations SOC, like those in the Social circumstances SOC and the Surgical and medical procedures SOC, have no secondary loca-tions. Hence, similar cases might be represented in two separate locations in a table – some under the Investigations SOC, others under the SOC for the respective body system or disease process. Another example: Atrioventricular block first degree is in the Cardiac disorders SOC, whereas Electrocardiogram PR prolongation – the manifestation of this condition as an investigation finding – is in the Investiga-tions SOC.

A rule regarding the structure of MedDRA is worthy of mention here. Whilst a term may be represented in more than one SOC – multiaxiality – it cannot be present under more than one grouping term within a SOC. Thus, a PT is only associated with one HLT and one HLGT within its primary SOC. It may be associated with a different (single) HLT and (single) HLGT in each of its secondary SOCs. Hence, for example, the PT Peptic ulcer haemorrhage is associ-ated with the HLT Gastrointestinal haemorrhages in the Gastrointestinal disorders SOC. It cannot there-fore also be associated with the HLT Peptic ulcers and perforation in the same SOC. This has impor-tant implications for database searches (Brown, 2003; Bousquet et al., 2005) that will be referred to under that heading below.

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