Australian experts have called for the government to change the way pregnancy-relevant medications are approved and funded through the PBS.
New Australian research has revealed that ondansetron accounts for the largest proportion of PBS expenditure for antiemetics dispensed to pregnant women – despite not having a listing for its use in pregnancy.
That’s according to recent findings published in Acta Obstetricia et Gynecologica Scandinavica, which found that ondansetron accounted for more than half of the total PBS expenditure for antiemetics dispensed to pregnant women despite only being dispensed to 19.2% of the cohort included in the study.
Researchers used data from Maternity1000 – a historical, population-level cohort administrative dataset containing details on every pregnant woman who gave birth in Queensland between July 2013 and June 2018 – and Queensland Perinatal Data Collection records that were linked with PBS claims data to explore trends and differences in pregnant women accessing antiemetic medications throughout their pregnancy.
The three antiemetic medications that were examined were metoclopramide, ondansetron, and prochlorperazine.
Data from 297,630 women were included in the study. The distribution of women in terms of their socioeconomic status, as measured by their Index of Relative Socioeconomic Disadvantage quintile, where lower scores indicate greater socioeconomic disadvantage, was uneven: 54,579 women in quintile 1 (18.3% of the total sample), 48,703 in quintile 2 (16.4%), 75,815 in quintile 3 (25.5%), 73,357 in quintile 4 (24.6%), and 45,176 in quintile 5 (15.2%).
Most of the women were aged 20-34 years (222,054; 74.6%), were born in a country other than Australia (217,165; 73.0%), had previously been pregnant (206,676; 69.4%), experienced a singleton birth (293,169; 98.5%), were of a healthy weight according to their BMI (152,006; 51.1%), and gave birth through the public hospital system (205,790; 69.1%).
Metoclopramide accounted for the largest proportion of PBS-listed antiemetics dispensed to pregnant women over the course of the study (78.7% of all dispensings), followed by ondansetron (19.2%) and prochlorperazine (2.1%).
“The highest volume of antiemetic dispensings occurred in the middle socioeconomic quintile (Q3), reflecting the higher number of pregnancies in this group,” wrote the researchers.
“Notably, when prevalence was calculated to account for differences in the underlying number of pregnancies within a socioeconomic quintile, results for all three medications were highest among women in the most socioeconomically disadvantaged quintiles (Q1 to Q3) and declined progressively across the two least disadvantaged groups (Q4 and Q5).”
For metoclopramide, the five quintiles from Q1 to Q5 accounted for 21.9%, 17.4%, 26.3%, 22.6%, and 11.7% of prescriptions dispensed. The distribution across the five quintiles was similar for ondansetron: 21.9%, 18.4%, 27.0%, 22.0%, and 10.6%.
Despite not having PBS approval for treating nausea and vomiting in pregnancy, ondansetron accounted for the greatest proportion of total PBS expenditure for antiemetic medications (AUD $172,966, or 53.5%), which the researchers attributed to “substantial off-label use and leakage of public funds”.
Metoclopramide (45.2%) and prochlorperazine (1.3%) accounted for a smaller proportion of PBS expenditure.
“These expenditure patterns partly reflect differences in total medication costs (i.e., the combined patient contribution and public subsidy), with prochlorperazine being the least expensive, followed by metoclopramide, and ondansetron being the most costly,” wrote the researchers.
Further examination of the association between socioeconomic status and antiemetic dispensing patterns revealed that the poorest 50% of women accounted for roughly 70% of total PBS expenditure for metoclopramide, ondansetron, and prochlorperazine.
“Because official subsidised options are so limited, doctors frequently rely on system workarounds to ensure patients on low incomes can afford necessary treatment,” said Dr Hannah Jackson, a health economist and recent PhD graduate from the University of Technology Sydney who served as the first author on the study.
Associate Professor Luke Grzeskowiak, a clinical pharmacist and research fellow from Flinders University who co-authored the paper with Dr Jackson, likened the workarounds used by doctors as a “Robin Hood” scenario.
“Providing medicines outside of PBS restrictions is seen as an acceptable workaround, because it’s helping vulnerable women get necessary treatment they would otherwise not be able to afford,” he told media.
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“With fewer medications subsidised on the PBS, pregnant women with lower financial capacity must rely on a narrow selection of older therapies, while those with more means can pay out-of-pocket for non-PBS medications which may be more suitable.”
Dr Jackson called for policymakers to update the nation’s medication funding structures by expanding the range of pregnancy-relevant medications approved and subsidised under the PBS.
“Without reform, the current policy framework will continue to perpetuate socioeconomic inequalities, incentivise prescribing outside of standard regulatory safeguards, and lead to potential inefficiencies in public spending,” said Dr Jackson.
“Ultimately, expanding PBS access to both new and repurposed existing medications will create a more dynamic, evidence-based health policy system that is truly responsive to pregnant women’s health needs.”
The study was not without its limitations, however. The range of limitations affecting the study included the assumptions that all antiemetics dispensed during pregnancy were used purely for the management of nausea and vomiting, and that women did not move their place of residence (which could impact their socioeconomic status) throughout the course of their pregnancy.
“[Furthermore,] there are difficulties associated with assigning the initial date of a pregnancy within our dataset, as the end date for pregnancy (i.e., the date of delivery) is recorded as the month and year of birth, with the date being recorded as the first of the month in each instance (as a privacy protection mechanism),” the researchers noted.
“Consequently, dispensings in the final month of pregnancy may be missed.”
