General practice

Cross sectional database analysis of antidepressant prescribing in general practice in the United Kingdom, 1993-5

^a Pharmacy Department, Wirral Hospital (NHS) Trust, Clatterbridge Hospital, Wirral L63 4JY, ^b Royal College of General Practitioners Unit for Mental Health Education, Division of General Practice and Primary Care, St George's Hospital Medical School, London SW17 0RE, ^c Lilly Industries, Dextra Court, Basingstoke RG21 2SY

Correspondence to: Mr Donoghue.

Consensus guidelines for the treatment of depression in general practice were published in 1992.¹ We investigated whether the prescription of antidepressants in general practice had changed since these guidelines and related educational materials had become available through the Defeat Depression Campaign and the Royal College of General Practitioners' senior mental health education fellowship.²

Methodsand results

Cross sectional data for two periods of 12 months ending June 1993 and June 1995 were obtained from the database of the doctors' independent network (DIN-LINK); this is maintained by the independent company Compufile (Woking, Surrey), which provides general practice data mainly to the pharmaceutical industry. It contains data from 100 general practices (377 general practitioners, 750 000 patient records) across the United Kingdom that use AAH Meditel practice computer systems. Prescriptions for antidepressants linked to a general practitioner's diagnosis of depression were included in the study. Antidepressants that accounted for less than 2% of the total were excluded. The effective dose of tricyclic antidepressants was taken as 125 mg daily from the consensus guidelines¹ and that of selective serotonin reuptake inhibitors as the value in the manufacturers' data sheets.

Since 1993 the number of prescriptions issued for the treatment of depression increased overall by nearly 33%. The prescription rate for all antidepressants increased, but the increase was much lower in the older tricyclic antidepressants (12.4%) than in the selective serotonin reuptake inhibitors (133.8%). The number of people receiving an effective dose increased from 41% in 1993 to 53% in 1995. For amitriptyline, clomipramine, and dothiepin the percentage of prescriptions for an effective dose and the average dose prescribed changed only marginally (table 1).

Table 1--Prescription of antidepressants to patients with diagnosis of depression
------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                     Tricyclic antidepressants                                   Selective serotonin reuptake inhibitors
------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                  Total older
                                  Total   Amitriptyline  Clomipramine  Dothiepin  tricyclics   Lofepramine  Fluoxetine     Paroxetine  Sertraline       Total
------------------------------------------------------------------------------------------------------------------------------------------------------------------
No of prescriptions:
 1993                             58646      10763          2413         18777      31953        4864          5720           2710        1329           9759
 1995                             77738      11873          2693         21334      35900        6317         13675           6480        2657          22812
Increase in numbers (%) of
 prescriptions between
 1993 and 1995                19092 (32.6)  1110 (10.3)  280 (11.6)  2557 (13.6)  3947 (12.4)  1453 (29.9)  7955 (139.1)  3770 (139.1)  1328 (99.9)  13053 (133.8)
1993:
 No of prescriptions with
 dose specified                   37091      7754           1828         14383      23965        4090          5422           2523        1091           9036
 No (%) of prescriptions at
 effective dose               15145 (40.8)  442 (5.7)    278 (15.2)  2188 (15.2)  2908 (12.1)  3205 (78.4)  5422 (100)    2519 (99.8)   1091 (100)   9032 (99.9)
1995:
 No of prescriptions with
 dose specified                   52633      8193           1992         16847      27032        5318         13203           6101        1720          20283
 No (%) of prescriptions at
 effective dose               28113 (53.4)  640 (7.8)    240 (12.1)  2666 (15.8)  3546 (13.1)  4309 (81.0) 13203 (100)    6076 (99.6)   1720 (100)   20258 (99.9)
Average dose (mg/day)*:
 1993                                        55.4           63.8         75.8                    131.5        21.3            22.2        81.4
 1995                                        58.5           58.9         77.1                    134.7        21.4            22.7        79.8
------------------------------------------------------------------------------------------------------------------------------------------------------------------
*Based only on prescriptions with dose specified.

Comment

In this large population the number of prescriptions for antidepressants issued to patients with a diagnosis of depression increased substantially between 1993 and 1995. We emphasise, however, that antidepressants are far from being the only effective treatment for depression.

Prescriptions for all antidepressants increased but more for selective serotonin reuptake inhibitors than for tricyclic antidepressants. This suggests that general practitioners are not prescribing selective serotonin reuptake inhibitors to patients who have been taking tricyclic antidepressants long term.

Encouragingly, the percentage of patients receiving an effective dose of antidepressant increased, but this is accounted for entirely by the much greater increase in prescribing of selective serotonin reuptake inhibitors than tricyclic antidepressants. Although for the older tricyclic antidepressants the proportion of prescriptions for an effective dose and the average doses prescribed were unchanged, we note that the British National Formulary still has not adopted the consensus guidelines on antidepressant doses. However, Kerr found that only 52% of general practitioners would prescribe tricyclic antidepressants at a dose lower than that recommended by the consensus guidelines³ compared with 86% in our study. This may reflect a difference between actual prescribing practice and what general practitioners say about their practice. Doctors may consider that low doses of tricyclic antidepressants offer effective treatment. They may be unaware of, or do not believe, the consensus guidelines or the results of clinical trials showing that tricyclic antidepressants prescribed at these doses are not beneficial in the treatment of depression. They may also lack confidence in prescribing at higher doses or fear that patients will find effective doses intolerable because of side effects.

So far as we are aware low doses of tricyclic antidepressants are ineffective. Failure to treat depression effectively contributes to relapse and the development of recurrent and chronic depression¹ and may be a contributory factor in suicide.⁴ One study found that a large proportion of patients receiving long term treatment with antidepressants at low doses were still moderately to severely depressed during follow up.⁵ Further research is urgently needed to determine why general practitioners continue to prescribe tricyclic antidepressants at low doses and to investigate the consequences of such prescribing on a large scale.

Funding: Access to the database was made possible and travelling expenses were reimbursed through a grant by Dista Pharmaceuticals, part of Lilly Industries.

Conflict of interest: None.

1. Paykel ES, Priest RG. Recognition and management of depression in general practice: consensus statement. BMJ 1992;305:1198-202.
2. Turton P, Tylee A. Evaluation in setting up a large scale educational programme--principles and problems. Education for General Practice 1995;6:226-9.
3. Kerr MP. Antidepressant prescribing: a comparison between general practitioners and psychiatrists. Br J Gen Pract 1994;44:275-6. [Medline]
4. Isacsson G, Holmgren P, Wassermen D, Bergman U. Use of antidepressants among people committing suicide in Sweden. BMJ 1994;308:506-9. [Abstract/Free Full Text]
5. Ali IM. Depression in primary care: a study of long term antidepressant users [MSc thesis]. Cardiff: University of Wales, 1994.

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