Relating Subjective and Objective Pharmacovigilance Association Measures - Clustering Challenges in Biological Network - page 289

number of clusters present in the data. A brief summary of the results is given in
Sec. 15.6.3, and an interpretation is presented in Sec. 15.7.

15.6.1. The Case Study

The AERS database is a large repository, updated quarterly, and the portion con-
sidered here corresponds to the 12 releases for the four quarters of the years 2001,
2002, and 2003, summarizing 462,936 adverse event reports. Altogether, these re-
ports list 12,015 unique adverse reactions and 117,287 unique drug name entries,
so it was not feasible to analyze the entire database. To obtain a representative
subset, the following strategy was adopted. First, the adverse events were ranked
in descending order of reporting frequency and the 100 most frequently reported
adverse events were used as the basis for all of the drug/adverse event associations
considered here. The top 25 of these adverse events are listed in Table 15.1, along
with their frequencies (the term “nos” appearing in this table is an abbreviation for
“not otherwise specified”). Altogether, these 100 terms account for 36.3% of the
total reported adverse events in this portion of the AERS database, despite the fact
that they constitute less than 1% of the distinct adverse events reported. In fact,
the distribution of these events is extremely heavy-tailed, with over half (56.0%)

Table 15.1. The top 25 suspected adverse
drug reactions and their frequencies of ocur-
rance in the AERS database.

No. Adverse Reaction Frequency

1 nausea 19428

2 drug ineffective 15817

3 pyrexia 14387

4 vomiting nos 12096

5 fatigue 10677

6 medication error 9970

7 condition aggravated 9941

8 diarrhoea nos 9385

9 dyspnoea nos 9313

10 pain nos 8757

11 asthenia 8368

12 abdominal pain nos 8332

13 chest pain 8323

14 rhabdomyolysis 7783

15 myalgia 7728

16 headache nos 7463

17 malaise 6907

18 myocardial infarction 6853

19 convulsions nos 6623

20 dizziness 6547

21 dyspnoea 6522

22 headache 6398

23 arthralgia 6358

24 constipation 6143

25 thrombocytopenia 6099