eMJA: PBS/RPBS cost implications of trends and guideline recommendations in the pharmacological management of hypertension

Letters

PBS/RPBS cost implications of trends and guideline recommendations in the pharmacological management of hypertension

Ben D Ewald and Brita Pekarsky

MJA 2002; 176 (4): 189-190

To the Editor: The article by Nelson et al estimates Pharmaceutical Benefits Scheme and Repatriation Pharmaceutical Benefits Scheme (PBS/RPBS) savings if hypertensive patients on monotherapy were prescribed the agents recommended in guidelines; however, the analysis contains algebraic errors and insufficient sensitivity analyses. The question of excessive costs through the use of expensive agents for which there is no evidence of increased benefit for most patients is an important one, but the estimates of extent of overuse should be methodologically sound. The three main concerns we have with the paper's estimates are as follows:

The total number of patients on monotherapy in Box 3 of the article adds to 1.1 million, whereas elsewhere the authors state that 60% of all 1.2 million Australian patients treated for hypertension are on monotherapy, giving an estimate of 0.72 million. (These estimates of 60% and 1.2 million are not referenced in the article.) One reason for this discrepancy is that the authors have treated the sum of column 4 in Box 2 as patients, not patient-years of treatment (some patients are on dual or triple therapy), leading to a 40% overestimate of numbers of patients on monotherapy reported in Box 3.
Utilisation of prescription drugs is recorded by PBS/RPBS only if the cost to patient is subsidised. Therefore, PBS/RPBS expenditure divided by total patient numbers (Box 2) underestimates consumer cost for diuretics and β-blockers, both of which cost less than the non-concessional co-payment. Of total PBS/RPBS scripts, 16% are for non-cardholders, and the cost per script to these patients is about three to four times the prevailing 1998 cardholder co-payment. As a rough estimate, total consumer cost for these agents may need to be doubled, and their omission is therefore material. Although non-concessional patients still have a saving, it is less than that estimated in the article.
Sensitivity analysis should have been performed on the following critical assumptions: (1) proportion of use for hypertension for each class of drugs, (2) the number of unsubsidised users of diuretics and b-blockers, and (3) the proportion of patients on each agent who are on monotherapy.

It is vital that the current scrutiny by all stakeholders of PBS/RPBS expenditure be informed by reasonable estimates of inappropriate utilisation. The contribution made by the authors in developing a technique to estimate appropriate use for this group of drugs is valuable. However, use of unreferenced estimates of key variables, insufficient application of sensitivity analyses, algebraic errors and inappropriately combining PBS with non-PBS data may cloud rather than shed light on this issue.

Nelson MR, McNeil JJ, Peeters A, et al. PBS/RPBS cost implications of trends and guideline recommendations in the pharmacological management of hypertension in Australia, 1994–1998. Med J Aust 2001; 174: 565-568. <PubMed>
PBS expenditure and prescriptions. January 2000 to December 2000. Canberra: Commonwealth Department of Health and Aged Care, 2001. Available at <http://www.health.gov.au/pbs/pubs/pbbexp/pbdec00/index.htm>.

(Received 28 Aug 2001, accepted 21 Nov 2001)

Centre for Clinical Epidemiology and Biostatistics, University of Newcastle, Newcastle, NSW.

Ben D Ewald, Lecturer in Epidemiology.

Department of General Practice, University of Adelaide, Adelaide, SA.

Brita A Pekarsky, Senior Lecturer in Health Economics.

Correspondence: Dr B D Ewald, Centre for Clinical Epidemiology and Biostatistics, University of Newcastle, David Maddison Building, Newcastle, NSW 2300. bewaldATcceb.newcastle.edu.au

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In reply: PBS/RPBS cost implications of trends and guideline recommendations in the pharmacological management of hypertension

Mark R Nelson, John J McNeil, Anna Peeters and Henry Krum

MJA 18 February 2002 176 (4: 190

In reply: We thank Pekarsky and Ewald for their comments.

It is difficult to estimate the percentage of patients on monotherapy from any source. We used data from IMS Health (http: //www.ims-global.com/) to determine the number of person-years of exposure to drugs prescribed with a principal indication of hypertension. Some of these drugs were prescribed as a sole agent if the script was for this single drug alone. Exposure for such agents was expressed as a percentage of the total exposure of this drug. For example, angiotensin-converting enzyme (ACE) inhibitors were sole agents in 63.9%. In the other 36.1%, the co-prescribed drugs may have been another antihypertensive drug or another type of drug altogether. Corresponding figures for calcium-channel blockers were 61.3%, for diuretics 53.6%, and for b-blockers 60.0%. As an approximation, we used the estimation that 60% of patients were likely to have been on monotherapy for hypertension. Adding the number on monotherapy for each drug gives an estimate of 1.2 million for the total population on monotherapy for hypertension. Therefore, the total number on drugs is likely to be greater than the 1.2 million as estimated in our article. However, the essential figure is that of 1.2 million for monotherapy, which we stand by.

It is true that a minority of prescriptions (16%) are written for people without a concession card and that these are more likely to pay the full cost of a cheaper drug. Our economic perspective was that of the PBS/RPBS. Hence, consumer costs were only included where the government made a copayment. It is acknowledged in the Methods section that "with some drugs, the patient copayment covers the total cost; in these instances the Commonwealth makes no contribution to the cost and these prescriptions are not recorded in the PBS/RPBS data" (page 566). It is also stated in the Discussion that the PBS/RPBS captures "much more of the cost of the newer, more expensive agents than thiazide diuretics or b-blockers" (page 567).

We chose to limit our sensitivity analysis to the key issue of redistribution of agents after initiation of monotherapy. The data we presented allow interested parties to conduct their own further sensitivity analyses, such as those suggested by Pekarsky and Ewald.