Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles.
News of a formulary of clinical evidence is most welcome (1); it
is to be regretted that the British National Formulary (BNF) which gave
rise to the idea is itself not referenced, and levels of evidence not
quoted.
Whilst compiling a distance learning paper on contraceptive drug
interactions, it became clear that very little robust evidence exists on
which to base advice about the need for additional contraception. The BNF
is widely used at the consultation as the most up to date source of
information. The Australian equivalent publication is referenced, and in
these days of evidence based medicine, this is to be welcomed, and would
help the clinician to make decisions about the individual patient.
I
enquired to the editor of the BNF the reason for the new inclusion in
edition 35 (March 1998) of retinoids in the interaction section (appendix
1) with oral contraceptives. This states "oral tretinoin reduces efficacy
of progestogen-only (POP) and possibly combined oral (COC) contraceptives
". I was given the information that tretinoin was listed because the
Summary of Product Characteristics for Vesanoid states that it causes
diminution of the contraceptive efficacy of the progestogens. 3 papers
were provided on request by Roche Pharmaceuticals on which the advice was
based.
Berbis (2) reported a small case study, and showed that the only
patient using Microval (0.03mg levonorgestrel) had elevated levels of
plasma progesterone between days 19 and 22 of 3 acitretin treatment cycles
(while no effect was found in the 9 patients using combined oral
contraception). The conclusion by the author was that ovulatory levels of
progesterone indicated that the Microval had failed to act contraceptively
in those cycles; this fails to demonstrate appreciation of the
mechanisms by which progestogen only oral contraception works , as
preventing ovulation is not always observed, and 2 other actions
(endometrial thinning and mucus thickening) are usually accepted as the
major factors. Geiger (3) includes the unreferenced conjecture that
retinoids may interfere with mucus thickening in progestogen-only
contraceptive users, as they act on the differentiation of epithelia
including the mucosal type. The third paper (4) is a review article ,
offering no additional information but concluding that COC is the
contraceptive method of choice . There have been no reported pregnancies
in users of progestogen-only or combined oral contraceptives taking
retinoids (5).
Teaching family planning doctors and nurses about the
principals of contraception highlights the confusions in this area for
both clinicians and patients; the circular arguments illustrated above
would indicate that the time has come to consider a change to the BNF.
Levels of evidence and references to all new entries to the drug
interaction appendix would be of value.
Dr Alyson Elliman SCMO Croydon Community Health NHS Trust
Refs
1. Godlee F, Smith R, Goldmann D. Clinical Evidence. BMJ 1999;318:1570-1
2 Berbis Ph, Bun H, Geiger JM et al Acitretin (RO10-1670) and
oral contraceptives:interaction study. Arch. Dermatol. Res 1988; 280: 388-
9
3. Geiger JM, Baudin M, Saurat JH. Teratogenic Risk with Etretinate
and Acitretin Treatment Dermatology 1994; 189: 109-116
4. Lehucher Ceyrac D, Serfaty D, Lefrancq H. Retinoids and
Contraception. Dermatology 1992; 84: 161-170
5. Stockley. Drug Interactions. Pharmaceutical Press 1996 p 475
I look forward to seeing Clinical Evidence when it appears.
Hopefully it will meet the criterion of providing information whose value
exceeds the cost of acquiring it. So far as I know, the cost-benefit
equation for medical information was suggested by Ed Huth (1) and used to
explain physician use of knowledge resources by Curley and Connelly (2)
1. Huth EJ Needed: an economics approach to systems for medical
information [editorial]. Annals of Internal Medicine. 103(4):617-9, 1985
Oct.
2. Curley SP. Connelly DP. Rich EC. Physicians' use of medical
knowledge resources: preliminary theoretical framework and findings.
Medical Decision Making. 10(4):231-41, 1990
British National Formulary
Sir
News of a formulary of clinical evidence is most welcome (1); it
is to be regretted that the British National Formulary (BNF) which gave
rise to the idea is itself not referenced, and levels of evidence not
quoted.
Whilst compiling a distance learning paper on contraceptive drug
interactions, it became clear that very little robust evidence exists on
which to base advice about the need for additional contraception. The BNF
is widely used at the consultation as the most up to date source of
information. The Australian equivalent publication is referenced, and in
these days of evidence based medicine, this is to be welcomed, and would
help the clinician to make decisions about the individual patient.
I
enquired to the editor of the BNF the reason for the new inclusion in
edition 35 (March 1998) of retinoids in the interaction section (appendix
1) with oral contraceptives. This states "oral tretinoin reduces efficacy
of progestogen-only (POP) and possibly combined oral (COC) contraceptives
". I was given the information that tretinoin was listed because the
Summary of Product Characteristics for Vesanoid states that it causes
diminution of the contraceptive efficacy of the progestogens. 3 papers
were provided on request by Roche Pharmaceuticals on which the advice was
based.
Berbis (2) reported a small case study, and showed that the only
patient using Microval (0.03mg levonorgestrel) had elevated levels of
plasma progesterone between days 19 and 22 of 3 acitretin treatment cycles
(while no effect was found in the 9 patients using combined oral
contraception). The conclusion by the author was that ovulatory levels of
progesterone indicated that the Microval had failed to act contraceptively
in those cycles; this fails to demonstrate appreciation of the
mechanisms by which progestogen only oral contraception works , as
preventing ovulation is not always observed, and 2 other actions
(endometrial thinning and mucus thickening) are usually accepted as the
major factors. Geiger (3) includes the unreferenced conjecture that
retinoids may interfere with mucus thickening in progestogen-only
contraceptive users, as they act on the differentiation of epithelia
including the mucosal type. The third paper (4) is a review article ,
offering no additional information but concluding that COC is the
contraceptive method of choice . There have been no reported pregnancies
in users of progestogen-only or combined oral contraceptives taking
retinoids (5).
Teaching family planning doctors and nurses about the
principals of contraception highlights the confusions in this area for
both clinicians and patients; the circular arguments illustrated above
would indicate that the time has come to consider a change to the BNF.
Levels of evidence and references to all new entries to the drug
interaction appendix would be of value.
Dr Alyson Elliman
SCMO Croydon Community Health NHS Trust
Refs
1. Godlee F, Smith R, Goldmann D. Clinical Evidence. BMJ 1999;318:1570-1
2 Berbis Ph, Bun H, Geiger JM et al Acitretin (RO10-1670) and
oral contraceptives:interaction study. Arch. Dermatol. Res 1988; 280: 388-
9
3. Geiger JM, Baudin M, Saurat JH. Teratogenic Risk with Etretinate
and Acitretin Treatment Dermatology 1994; 189: 109-116
4. Lehucher Ceyrac D, Serfaty D, Lefrancq H. Retinoids and
Contraception. Dermatology 1992; 84: 161-170
5. Stockley. Drug Interactions. Pharmaceutical Press 1996 p 475
Competing interests: No competing interests