Bipolar disorder in the South African private health sector: Longitudinal analysis of prevalence, comorbidities and prescribing patterns

Abstract

Bipolar disorder (BD) is a chronic affective disorder characterised by mood changes, fluctuating between depressive symptoms and manic symptoms. It is one of the psychiatric illnesses that have contributed to the chronic disease burden in South Africa. The overall goal of this study was to assess possible changes, over a six-year period (2010-2015), in the prevalence and incidence of BD, and its coexisting chronic disease list (CDL) conditions as well as changes in the medicine prescribing patterns in the private health sector in South Africa by using medicine claims data. Manuscript 1 conveyed on the findings of the investigation into the trends over a six-year period in the prevalence and incidence of BD and the prevalence of coexisting CDL conditions in patients with BD. The study followed a retrospective cohort study, analysing medicine claims data for the period 1 January 2010 to 31 December 2015. An open cohort design was used to determine trends in the incidence and prevalence rate of BD (ICD-10 code F31) over a six-year study period, whereas a closed (N = 1 228) cohort design was used to investigate the prevalence of coexisting CDL conditions in BD patients. The incidence rate per 1 000 beneficiaries was determined using 2010 as index year. Bipolar disorder patients represented 0.6% (N = 968 131) and 0.8% (N = 843 792) of the total patient population on the database in 2010 and 2015, respectively. The majority of BD patients were females, representing 0.8% (2010) (N = 521 387) to 1.0% (2015) (N = 445 626) of the total number of female patients on the database. The mean age of the BD patients was 43.6 (15.8) years (95% CI 43.2-44.0), with the majority (96.4%, n = 5 471) older than 18.2 years in the index year (2010). Prevalence rate of BD increased from 5.9 (2010) to 7.9 (2015) per 1 000 beneficiaries, whereas incidence rate per 1 000 beneficiaries was 2.3 in 2011 vs. 2.1 in 2015. Female BD patients have higher incidence rates (2.9 in 2011 vs. 2.6 in 2015) than males (1.7 in 2011 vs. 1.6 in 2015). The number of BD patients in the closed cohort (N = 1 228) with one or more coexisting CDL condition increased by 20.5% from 2010 (n = 594) to 2015 (n = 716); however, the increase in the mean number of coexisting CDL conditions per BD patient was practically insignificant (P > .01; Cohen’s d-value < .8). BD patients newly registered with hypertension (P < .0001), hypothyroidism (P < .0001), hyperlipidaemia (P < .0001), type 2 diabetes mellitus (P < .0001), epilepsy (P = .0065) and rheumatoid arthritis (P = .0253) increased. Hypertension, hyperlipidaemia and hypothyroidism combined was the most prevalent three chronic conditions-combination in BD patients. Manuscript 2 reported the findings of the investigation into the possible changes, over a 6-year period, in the medicine prescribing patterns for patients with only BD. The study followed a longitudinal open cohort design to analyse retrospective data of patients identified with the diagnosis code ICD-10, F31, for bipolar disorder, on reimbursed medicine claims, from 1 Jan. 2010 to 31 Dec. 2015. These patients did not have any of the other coexisting CDL conditions that are covered through the prescribed minimum benefits as indicated in the South Africa Medical Scheme Act (131 of 1998). Change in medicine prescribing patterns was assessed by measuring the following: i) different types of active pharmaceutical ingredients; ii) frequency of monotherapy (include only one active pharmaceutical ingredient) or combination therapy (include more than one active pharmaceutical ingredients, based on the last month’s prescription(s) of a patient in 2010 and 2015; iii) average number of medicine items per prescription per patient per year; and iii) average number of prescriptions per patient. The study population consisted of 3627 patients in the index year (2010) and increased to 4332 in 2015. The study population was predominantly female, with a male: female ratio of 1:2.3 in 2010 and 1:1.88 in 2015. Major changes took place in the psychopharmacological prescribing during the study period. The average number of medicine items per prescription stayed constant at 2 medicine items per prescription per patient throughout the study years. The number of prescriptions per patient increased observably from 7.08(5.63) [6.94-7.23] in 2010 to 7.50(5.59) [7.37-7.63] (P = .00001, Cohen’s d-value = .4) in 2015. The proportion of patients on combination therapy increased from 44.6% (2010) to 48.7% (2015). The most prevalent combination therapy in 2010 and 2015 was lamotrigine in combination with quetiapine or with a selective serotonin re-uptake inhibitor, or with bupropion or with valproate. The proportion of patients receiving anticonvulsants (35.4% vs. 34.7%), antidepressants (31.9% vs. 36.1%) and atypical antipsychotics (16.2% vs. 23.2%) as monotherapy increased significantly (P = .0001) from 2010 to 2015; the proportion of patients receiving lithium decreased marginally (4.9% vs. 4.2%) (P = .302). The increase in combination therapy and the constant high use of antidepressant as monotherapy should be further investigated in the private-insured BD population in South Africa.