Primary Care Pharmacy September 2000 Vol 1 No 4 p103-104

Audit

ACE inhibitors and angiotensin II antagonists for hypertension

By Theresa Garfoot, BSc, MRPharms Elizabeth Reid, BSc, MRPharms and Judith Cantrill, MSc, FRPharms

Auditing the use of drugs that affect angiotensin is discussed in this article

The current British Hypertension Society (BHS) guidelines¹ recommend that a thiazide diuretic or beta-blocker should be the initial drugs of choice for the treatment of hypertension, unless the patient has either a contraindication to these agents or a compelling indication for another class of drug. Many studies have been conducted with older drugs to establish their efficacy and to determine their effects on long-term morbidity and mortality from cardiovascular events. However, until recently, lack of outcome data for newer anti-hypertensive agents remained a problem.
With the formation of primary care groups (PCGs) and a renewed focus on evidence-based and cost-effective prescribing, the use of clinical guidelines is becoming increasingly common. The treatment of hypertension is now seen as a priority, with the release of the national service framework for cardiovascular disease and the inclusion of coronary heart disease in many PCG health improvement programmes. Prescribing Analysis and Cost (PACT) data for South Manchester PCG showed a significant variation in the prescribing of angiotensin converting enzyme (ACE) inhibitors and angiotensin II antagonists. Adherence to the BHS guidelines, with reduced prescribing of newer, more expensive anti-hypertensives, was seen as a way of reducing costs in this area and making resources available for other developments (eg, to allow increased statin prescribing).
It was decided to audit the prescribing of hypertension in one general practice using PACT data and BHS guidelines. The chosen practice was identified as being a relatively high prescriber of ACE inhibitors. The aim was to determine whether ACE inhibitors and angiotensin II antagonists were being used appropriately within the current guidelines, paying particular attention to first-line prescribing.

Methods

The audit was based at a five-partner general practice with approximately 7,000 patients and fully computerised patient records. Patients were selected for the audit using the surgery's database. All relevant drug names (ie, all ACE inhibitors and angiotensin II antagonists) were entered into the computer and this generated a list of patients who were either currently taking or had previously taken one or more of these drugs (regardless of indication). This list was then used to view the patient's records by entering their patient number into the computer. Patients were excluded from the audit if:

• there was no hypertension heading in the current problem list
• the drug was being prescribed for a different condition (eg, congestive cardiac failure)
• the drug was not currently being prescribed

Towards the end of the allocated time for data collection, every fifth eligible case was selected, as there was a large number of patients and little time. A data collection form was designed for the purpose of the audit and was piloted using several patient records. The parts of the pilot form that did not achieve the desired outcomes were then altered to produce the final audit form.
Two sets of data were collected. First, drugs prescribed for the treatment of hypertension were recorded in chronological order. This information was documented using a table on the data collection form. The current therapy (ACE inhibitor or angiotensin II antagonist) was selected from a list on the form and any other current medication for hypertension was also documented.
The second part of the data collection form was used to determine any concurrent conditions or contraindications that the patient might have that would affect the choice of treatment. The data were collated and assessed against the BHS guidelines for the appropriateness of prescribing.

Results

Initial analysis of PACT data showed that newer, more expensive drugs, such as angiotensin II antagonists were rarely prescribed but, as expected, the prescribing of ACE inhibitors was relatively high. They were the second most commonly prescribed cardiovascular drugs and accounted for 28 per cent of the total prescribing costs for that British National Formulary chapter. However, this did not establish whether prescribing was appropriate. This could only be determined by looking at practice records.
The practice computer system provided a list of 528 patients who had either previously taken or were currently taking an ACE inhibitor or angiotensin II antagonist. In total, 521 of these patients were prescribed an ACE inhibitor for any indication, with enalapril being the most commonly prescribed. Only seven patients had been prescribed an angiotensin II antagonist. A total of 264 of these patient records were reviewed and 83 (31.5 per cent) were included in the audit.
Thirty-six patients (67 per cent) were prescribed an ACE inhibitor first-line (Figure 1) with calcium channel blockers being the next most frequent. Of those patients prescribed other drugs, 17 per cent were given a beta blocker and 14 per cent a thiazide diuretic first-line. Of the 36 patients who were prescribed an ACE inhibitor first-line, 21 (58 per cent) had no contraindications or concomitant conditions that would affect the choice of therapy. The other 15 (42 per cent) had one or more contraindications to thiazide diuretics or beta blockers, or had concomitant conditions that may have affected the choice of therapy.

Discussion and conclusions

The results of the audit in this practice indicate that ACE inhibitors are commonly prescribed first-line for the treatment of hypertension, contrary to the recommendations of the current BHS guidelines. However, angiotensin II antagonists are rarely prescribed.
The choice of agent prescribed first-line is one that could have a significant impact on a practice's budget, as ACE inhibitors incur much higher costs than thiazide diuretics or beta-blockers. These agents should be restricted to patients in whom conventional therapy is contraindicated or to those who have existing conditions that affect the choice of therapy, such as diabetes or heart failure. Where a patient has a contraindication to either a thiazide diuretic or beta-blocker the other should be tried first-line.
Problems with the audit include the limited time available because it was carried out as a preregistration project. The number of patients involved meant that it was not possible to screen all records, so the data does not give the full picture for prescribing in hypertension at the practice.
The computer system at the practice was only installed in 1988 and patients' records were added gradually. Existing written records were screened but only major events added to the system. It cannot be guaranteed that a full drug history was obtained for patients diagnosed prior to this time. Given more time, written records and computer records would both have been consulted. In addition, anti-hypertensives have several indications, therefore, it can be difficult to determine what they are being used to treat.
The results of the audit were fed back to all of the general practitioners at one of their regular practice education meetings, and case studies as above were discussed.
The practice continues to receive prescribing support on a sessional basis and the audit will be repeated to look for improvement. Comparative trials with established and newer anti-hypertensives are under way and local guidelines may need to be revised in the light of the results.

Reference

Miss Garfoot is a resident pharmacist at the South Manchester University hospitals NHS trust, Miss Reid is the medicines management pharmacist for South Manchester primary care trust and Miss Cantrill is clinical senior lecturer at the University of Manchester