Quo Vadis Clozapine? A Bibliometric Study of 45 Years of Research in International Context

Abstract

We have carried out a bibliometric study about the international scientific publications on clozapine. We have used the EMBASE and MEDLINE databases, and we applied bibliometric indicators of production, as Price's Law on the increase of scientific literature. We also calculated the participation index (PI) of the different countries. The bibliometric data have also been correlated with some social and health data from the 12 most productive countries in biomedicine and health sciences. In addition, 5607 original documents dealing with clozapine, published between 1970 and 2013, were downloaded. Our results state non-fulfilment of Price's Law, with scientific production on clozapine showing linear growth (r=0.8691, vs. r=0.8478 after exponential adjustment). Seven of the 12 journals with the highest numbers of publications on clozapine have an Impact Factor>2. Among the countries generating clozapine research, the most prominent is the USA (PI=24.32), followed by the UK (PI=6.27) and Germany (PI=5.40). The differences among countries on clozapine research are significantly related to economic variables linked to research. The scientific interest in clozapine remains remarkable, although after the application of bibliometric indicators of production, a saturation point is evident in the growth of scientific literature on this topic.

Keywords: atypical antipsychotics; bibliometry; clozapine; schizophrenia; second-generation antipsychotics.

Figure 1

Growth of scientific production on clozapine. A linear adjustment of the data was carried out, and a fitting to an exponential curve, in order to check whether production follows Price’s law of exponential growth. Linear adjustment: y = 7.0338x − 30.828 (r² = 0.7554). Exponential adjustment: y = 6.7016e^0.0999x (r² = 0.7188).

Figure 2

Growth of scientific production on other AADs. A linear adjustment of the data was carried out, and a fitting to an exponential curve, in order to check whether production follows Price’s Law of exponential growth. Linear adjustment: y = 38.718x − 315.56 (r² = 0.8641). Exponential adjustment: y = 1.6462e^0.2191x (r² = 0.9176). AADs (atypical antipsychotic drugs: Risperidone, olanzapine, ziprasidone, quetiapine, sertindole, aripiprazole, paliperidone, amisulpride, zotepine, asenapine, iloperidone, lurasidone, perospirone and blonanserin).

Figure 3

Evolution of the accumulated scientific production on atypical antipsychotic drugs.

Figure 4

Distribution of publications on atypical antipsychotic drugs and current trend lines in relation to the scientific production from the group “clozapine” and the group “other AADs”. AADs (atypical antipsychotic drugs: Risperidone, olanzapine, ziprasidone, quetiapine, sertindole, aripiprazole, paliperidone, amisulpride, zotepine, asenapine, iloperidone, lurasidone, perospirone and blonanserin).

Figure 5

Evolution of documents on clozapine and other individual AADs.

Figure 6

Differences in the type of publication used between the group “clozapine” and the group “other AADs”. The sections are sorted moving clockwise: Article (61%, 57%); Letter (17%, 15%); Conference document (8%, 15%); Review (6%, 7%); Others (8%, 6%).

Figure 7

Relationship between production of scientific literature on clozapine and other atypical antipsychotic drugs (AADs) and total production in the field of psychiatry and neurology in the world’s 12 most productive countries in biomedicine and health sciences. PI (Participation Index); AADs (Atypical antipsychotic drugs: Risperidone, olanzapine, ziprasidone, quetiapine, sertindole, aripiprazole, paliperidone, amisulpride, zotepine, asenapine, iloperidone, lurasidone, perospirone and blonanserin).

Figure 8

Relationship between production of scientific literature on clozapine and per capita gross domestic product in the world’s 12 most productive countries in biomedicine and health sciences. We have excluded the USA from the graph in order to give a clearer impression of the rest of the countries. GDP (Gross Domestic Product), PI (Participation Index). The economic data were obtained from the website of the World Health Organization (Available online: http://www.who.int/country/es/). Economic data are expressed in international dollars (data 2012). JAP: Japan; SPA: Spain; NET: Netherlands; AUS: Australia; FRA: France; CAN: Canada; GER: Germany; CHI: China; UK: United Kingdom; IND: India.

Figure 9

Per capita Health Expenditure and relationship between production of scientific literature on clozapine and per capita health expenditure and gross domestic expenditure on research and development, in the world’s 12 most productive countries in biomedicine and health sciences. PI (Participation Index). Total Health Expenditure per capita Purchasing Power Parity (PPP) Int. $ (data WHO 2011) (Available online: http://www.who.int/country/es/). Gross Domestic Expenditure on research and development (%). Data OECD 2011, except Australia and Japan (data 2010) and China (data 2009) (Available online: http://www.oecd-ilibrary.org/science-and-technology/gross-domestic-expenditure-on-r-d_2075843x-table1).