Use of Proton Pump Inhibitors After Antireflux Surgery
Use of Proton Pump Inhibitors After Antireflux Surgery
The analysis was conducted as a population-based, descriptive follow-up study of patients undergoing first-time ARS during the period 1 January 1996 to 31 December 2010.
We used data from three different sources: the Danish National Registry of Patients, the Danish National Prescription Registry and the Danish Person Registry.
The Danish National Patient Registry contains data on all non-psychiatric hospital admissions since 1977 and data on outpatient contacts since 1995. Discharge diagnoses are coded according to the International Classification of Disease V.10 (ICD-10) since 1994, and surgical procedures are coded according to the Nordic Classification of Surgical Procedures (NCSP) since 1996. In Denmark, ARS has not been a high-volume procedure in the private hospital sector and less than 0.5% of all ARS have been performed at private hospitals. The Danish National Registry of Patients therefore allows true population-based study regarding ARS.
The Danish National Prescription Registry contains data on all prescription drugs redeemed by Danish citizens since 1995. Drugs are categorised according to the Anatomical Therapeutic Chemical (ATC) index. Prescription data include the date of dispensing, the substance, the brand name and the quantity expressed by the defined daily dose (DDD).
The Danish Person Registry contains data on vital status (date of death) and migrations in and out of Denmark.
All data sources were linked by use of the Central Person Registry number, a unique identifier assigned to all Danish citizens since 1968 that encodes gender and date of birth. All linkage occurred within Statistics Denmark, a governmental institution that collects and maintains electronic records for a broad spectrum of statistical and scientific purposes.
We extracted data for all patients who had undergone ARS in the period 1996–2010. Since fundoplication is by far the most commonly used method for ARS, we restricted our analyses to this type of operation. Only patients with first-time elective ARS (index ARS) coded as either open fundoplication (JBC00) or laparoscopic fundoplication (JBC01), and who were ≥18 years at surgery, were eligible for the study. Eligible patients were followed from their index ARS to the end of follow-up (31 December 2011) or time of censoring, whichever came first. Patients were censored on day of death, day of emigration or day of repeated ARS (re-ARS) after their index ARS.
Data on all redeemed prescriptions for eligible patients were extracted from 1995 to 2011. Index prescription of PPI (ATC: A02BC) was defined as the first PPI prescription redeemed more than 30 days after the index ARS. This precaution was taken because of the assumption that some patients may have been discharged after surgery with a prescription of PPI, 'just to be on the safe side'. Use of PPI in the year before index ARS was categorised as use of 0 DDD, 1–89 DDD, 90–179 DDD and ≥180 DDD.
Long-term use of PPI was defined as an average of at least 0.5 DDD per day (equalling an average of 180 DDD per year) from a given date until end of follow-up. The first date fulfilling this criterion was considered start of long-term use. It was not necessarily synchronous with index PPI prescription, but could occur later, whenever the criteria were fulfilled during follow-up.
Design
The analysis was conducted as a population-based, descriptive follow-up study of patients undergoing first-time ARS during the period 1 January 1996 to 31 December 2010.
Data Sources
We used data from three different sources: the Danish National Registry of Patients, the Danish National Prescription Registry and the Danish Person Registry.
The Danish National Patient Registry contains data on all non-psychiatric hospital admissions since 1977 and data on outpatient contacts since 1995. Discharge diagnoses are coded according to the International Classification of Disease V.10 (ICD-10) since 1994, and surgical procedures are coded according to the Nordic Classification of Surgical Procedures (NCSP) since 1996. In Denmark, ARS has not been a high-volume procedure in the private hospital sector and less than 0.5% of all ARS have been performed at private hospitals. The Danish National Registry of Patients therefore allows true population-based study regarding ARS.
The Danish National Prescription Registry contains data on all prescription drugs redeemed by Danish citizens since 1995. Drugs are categorised according to the Anatomical Therapeutic Chemical (ATC) index. Prescription data include the date of dispensing, the substance, the brand name and the quantity expressed by the defined daily dose (DDD).
The Danish Person Registry contains data on vital status (date of death) and migrations in and out of Denmark.
All data sources were linked by use of the Central Person Registry number, a unique identifier assigned to all Danish citizens since 1968 that encodes gender and date of birth. All linkage occurred within Statistics Denmark, a governmental institution that collects and maintains electronic records for a broad spectrum of statistical and scientific purposes.
Patients and Follow-up
We extracted data for all patients who had undergone ARS in the period 1996–2010. Since fundoplication is by far the most commonly used method for ARS, we restricted our analyses to this type of operation. Only patients with first-time elective ARS (index ARS) coded as either open fundoplication (JBC00) or laparoscopic fundoplication (JBC01), and who were ≥18 years at surgery, were eligible for the study. Eligible patients were followed from their index ARS to the end of follow-up (31 December 2011) or time of censoring, whichever came first. Patients were censored on day of death, day of emigration or day of repeated ARS (re-ARS) after their index ARS.
Use of PPI
Data on all redeemed prescriptions for eligible patients were extracted from 1995 to 2011. Index prescription of PPI (ATC: A02BC) was defined as the first PPI prescription redeemed more than 30 days after the index ARS. This precaution was taken because of the assumption that some patients may have been discharged after surgery with a prescription of PPI, 'just to be on the safe side'. Use of PPI in the year before index ARS was categorised as use of 0 DDD, 1–89 DDD, 90–179 DDD and ≥180 DDD.
Long-term Use of PPI
Long-term use of PPI was defined as an average of at least 0.5 DDD per day (equalling an average of 180 DDD per year) from a given date until end of follow-up. The first date fulfilling this criterion was considered start of long-term use. It was not necessarily synchronous with index PPI prescription, but could occur later, whenever the criteria were fulfilled during follow-up.
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