Royal College of Surgeons in Ireland
Coláiste Ríoga na Máinleá in Éirinn
Multigroup multilevel segmented regression models &
prescribing variation within the Preferred Drugs
Scheme in Ireland
Ron McDowell, Tom Fahey
HRB Centre for Primary Care Research, RCSI, Dublin
Overview
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The Preferred Drugs Scheme
Objectives
Change in level models
Data & methods
Results
Comments
Conclusions
Preferred Drugs Scheme
• Ireland spends 50% per capita above the EU average on
drugs/pharmaceuticals.
• 2014: €1.3 billion (12% of the Health Service Executive’s
budget) spent on prescription medication.
• 2013: introduction of the “Preferred Drugs Scheme” by the
Medications Management Programme. 10 medication groups to
date including Proton Pump Inhibitors (PPI), heart medications,
psychotropics.
– Preferred drug chosen on grounds such as clinical efficacy,
international guidelines and cost.
Objectives
• To examine the impact of national guidelines on the prescribing
of the preferred Proton Pump Inhibitor (PPI) [Lansoprazole] in a
cohort of older adults in Ireland between 2011 and 2015,
distinguishing between new and pre-existing patients.
• To examine where the variation lies: between patients, practices
or both?
• Note: Ireland has high levels of sustained PPI prescribing
Change in level models
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Segmented Regression Model
Interrupted Time Series Model
Latent Growth Curve Model
Other data features e.g. groups, clusters to take account of
Preference sensitive care : more than 1 recognised treatment option
Data & methods
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Medication Reconciliation cohort: Jan 2011-Sept 2015
21,481 patients; 41 GP practices in Ireland
Adults aged 65+ years
Data aggregated to obtain the number of PPI and Lansoprazole
prescriptions per patient per calendar quarter per practice
• Logistic segmented regression model with random effects.
• 2 groups of interest: patients who received PPI between Jan
2011 –March 2013 & April 2013-Dec 2015 and those who only
had them from April 2013 onwards.
• Models fit using MLWin/runMLwin.
Results
• 3.1 million prescriptions: Jan 2011-Sept 2015.
• 5.1% (158,824) for one of 5 PPIs of which 24.2% (38,487) for the
preferred drug, Lansoprazole. Most common: Omeprazole (31.4%).
• 89.2% (11,162) of the 14,242 patients who received at least one PPI
prescription received scripts in at least two calendar quarters
Percentage of preferred prescriptions by drug group
20
15
5
10
Guidelines issued: 15 April 2013
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Percentage
25
30
Jan 2011-Sept 2015
2011: Q1
Q3
2012: Q1
Q3
2013: Q1
Q3
2014: Q1
Q3
Lansoprazole: PPI drug group
Simvastatin: Statin drug group
2015: Q1
Q3
Results
Lansoprazole: Standardised Ratio: Proportion of all PPI Prescriptions
Jan 2011-Sept 2015
0
1
Ratio
2
3
Guidelines: April 2013
2011: Q1
Q3
2012: Q1
Q3
2013: Q1
Q3
2014: Q1
Q3
2015: Q1
Q3
Results
• Practices which prescribed Lansoprazole among pre-existing PPI
patients after April 2013 tended to prescribe it in new patients (ρ=0.32,
95%CI (0.14,0.49))
2
1
April 2013
0
Variance
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4
Between practice/patient
variation
Q1 2011
Q1 2012
Q1 2013
Q1 2014
Time
Between practices: pre-April 2013: existing patients
Between practices: post-Apr 2013: existing patients
Between practices: post-Apr 2013: new patients
Between persons: pre-Apr 2013: existing patients
Between persons: post-Apr 2013: existing patients
Between persons: post Apr 2013: new patients
Q1 2015
Comments
• Limitations: no practice-level/prescriber variables
• Models do not as yet include potentially time-varying patientlevel covariates:– age, gender, insurance status, polypharmacy, contact with
practice prior to April 2013.
• Change the definition for inclusion: 2 or 3 consecutive PPI
prescriptions each within 30 days of each other. Results hold.
• Results are in line with expectations- changes in prescribing
patterns tend to be very gradual
Conclusions
• Appears to have been some changes in prescribing patterns of
PPIs with introduction of the Preferred Drug Scheme among
older adults
• More marked among the patients starting PPIs after guidelines
were introduced rather than pre-existing patients
• Most of the variation is due to differences in patients rather than
practices-yet to be explained.
• Less variation in prescribing of Lansoprazole among newer
patients.
• Models can be refined and developed further to address more
specific research questions and to take account of further
features of the data.