Return to PJ Online Home Page
The Pharmaceutical Journal Vol 265 No 7114 September 16, 2000
Pharmacy Practice Research
Papers presented at the British Pharmaceutical Conference, Birmingham, September 10 to 13, 2000 pR50

Can factors influencing the prescribing of oral hypoglycaemic drugs in primary care be identified using national data sets?

By C. Dalton, J. E. Field, K. J. Frenz and H. E. Kendall

Introduction Prescribing rates of oral hypoglycaemics should be highest in populations with a greater prevalence of type 2 diabetes. Factors likely to be associated with increased rates of type 2 diabetes include high proportions of elderly people and of people of non-white origin. Relative efficacy and the presence of contraindications to a particular drug should determine whether metformin or a sulphonylurea is selected as initial drug therapy. For example, metformin is the drug of choice for overweight patients provided the patient has no renal impairment or other conditions likely to lead to lactic acidosis.

Method Prescription analysis and cost (PACT) data for oral hypoglycaemic drugs were extracted for the last five years. Usage of the two most commonly prescribed oral hypoglycaemic drugs, metformin and gliclazide, was calculated using defined daily doses (DDDs). Geographical variation in their usage was then mapped for English health authorities (HAs).
Multiple regression analysis with stepwise elimination was used to examine the relationship between population characteristics and the prescribing of metformin and gliclazide. The dependent variable used was the number of DDDs prescribed per 1,000 patients for January to March, 1999, for each HA. Independent variables were the percentage of residents whose ethnic group was other than white in 19911 (per cent non-white), percentage of patients over 65 years in 1999 (per cent over 65 years), Jarman score in 1991,1 and percentage of patients with a body mass index >30 in 1995 (per cent obese).2

Results In the five years to March, 1999, prescribing of metformin almost doubled. Prescribing of all sulphonylureas increased by 33 per cent; however, gliclazide use more than doubled. There was a threefold variation in prescribing of metformin between HAs and a sixfold variation in prescribing of gliclazide. Prescribing was inconsistent between HAs; two HAs were within the top 10 HAs for metformin prescribing but were in the bottom 10 HAs for gliclazide prescribing, whereas another two HAs were in the top 10 for both drugs.
Multiple regression analysis found that the most significant factor explaining the variation in use of metformin was per cent non-white (P<0.0005). The best model to fit the data included this variable and the per cent obese (P<0.03). Adjusted R2 was 0.28 for the relationship between usage of metformin and these two variables. The only significant factors explaining the variation in use of gliclazide were per cent obese (P<0.02) and Jarman score (P<0.02) (adjusted R2 0.08). Per cent over 65 years did not correlate significantly with prescribing of either drug.

Focal points

  • Prescribing of metformin and gliclazide is inconsistent between health authorities
  • The variation in use of metformin could partly be explained by differences in ethnic mix and in prevalence of obesity between health authorities
  • The variation in use of gliclazide could partly be explained by differences in Jarman scores and in prevalence of obesity between health authorities
  • Prescribing of metformin or gliclazide did not correlate with the percentage of elderly patients in a health authority
  • Differences in population between health authorities are not the prime reason for variation in prescribing of metformin and gliclazide

Discussion Since type 2 diabetes is most prevalent in older people, it was surprising that there was no significant relationship between percentage of patients over 65 years and use of metformin or gliclazide. Gliclazide can be prescribed for patients with renal impairment and hence it would be expected to be used more often for elderly patients than metformin.
The UK prospective diabetes study concluded that metformin should be the drug of choice for overweight patients.3 The prevalence of obesity was not, however, a stronger influence on the prescribing of metformin than on gliclazide.
People of Indo-asian and Afro-Caribbean origin are more likely to develop diabetes than white people and hence the ethnic mix of an HA should be a factor influencing prescribing rates; however only metformin prescribing was significantly related to this factor.
Most of the variation in prescribing of metformin and gliclazide could not be explained by the factors examined in this study. Data for the prevalence of type 2 diabetes in each HA were not available but differences in disease prevalence would not explain why use of metformin and gliclazide is inconsistent between HAs. Further work is required to identify the prime factors influencing the choice of oral hypoglycaemic.

Prescription Pricing Authority, Newcastle

References

1. Department of Health. Public health common data set 1997. Guildford: National Institute of Epidemiology, University of Surrey; 1997.
2. Social and community planning research. Health survey for England 1994-96. London: University College; 1999.
3. UK Prospective Diabetes Study (UKPDS) Group. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). Lancet 1998;352:854-65.