Risk of gynaecomastia associated with cimetidine, omeprazole, and other antiulcer drugs

Introduction

Gynaecomastia (enlargement of true breast tissue as opposed to adipose tissue) was a common clinical finding in case series.*RF 1-3* The differential diagnosis of gynaecomastia depends on physiological and pathological criteria, and pathological gynaecomastia can be further classified into that associated with other medical conditions and idiopathic gynaecomastia. Cimetidine has repeatedly been reported as causing gynaecomastia,*RF 4-7* and ranitidine was associated with gynaecomastia in a single case.8 More recently omeprazole, a proton pump inhibitor also used as an ulcer healing drug, has been associated in more than a dozen cases with the development of gynaecomastia.*RF 9-11* No epidemiological study has been published comparing the incidence of gynaecomastia among the various ulcer healing drugs. We performed a large population based cohort study which provides estimates of the absolute and relative risk of idiopathic gynaecomastia in patients who received cimetidine, misoprostol, omeprazole, or ranitidine, four drugs used primarily for treating peptic ulcer disease. The results are based on information held on British general practitioners' computers.

Methods

Over four million residents in the United Kingdom are enrolled with selected general practitioners who use office computers provided by Value Added Medical Products (VAMP) Research and have agreed to provide data for research purposes. They record medical information in a standard manner and supply it anonymously to VAMP Research on an ongoing basis. Among other items, the recorded information includes the patient's characteristics, medical diagnoses and comments arising from the patient's visit to the general practitioner, referral letters from consultants, and details of stays in hospital. Also, the general practitioners generate prescriptions directly with the computer, and these drugs are automatically transcribed into the patient's computer record. A distinctive attribute of this computerised medical information system is that the general practitioner is asked to provide the indication for each new course of medication. A modification of the Oxford Medical Information System classification is used to enter medical diagnoses, and a coded drug dictionary based on the Prescription Pricing Authority's dictionary is used for the recording of prescriptions. Two recent validation studies determined that information from manual medical records in the general practitioners' offices was recorded on the computer over 90% of the time.^12,13

Study population - For this study, 478 practices contributed information from 1 January 1989 through 15 September 1992. Men between 25 and 81 years old in 1989 and registered with one of these practices entered the study population when they were prescribed cimetidine, misoprostol, omeprazole, or ranitidine during the study period. Men with a history of gynaecomastia before they received one of these drugs during the study period were excluded, as were those with Klinefelter syndrome, testicular cancer, breast cancer, or liver disease or who had used replacement androgen therapy. A total of 81 535 men formed the final study population and were followed until either the first occurrence of gynaecomastia, any malignant neoplasm, liver disease, a diagnosis of alcoholism, use of replacement androgen therapy, transfer to another practice, death, or 15 September 1992, whichever came first (table 1).

Exposure Definition - Thirty days was the most common duration of an antiulcer prescription, accounting for 72% of all prescriptions; 60 days was the second most common duration, accounting for 15% of all prescriptions. Person time was aggregated across calendar time and age groups into two mutually exclusive time windows for each of the four drugs: “current use,” starting from day 1 of each prescription until the earlier of day 60 or the date of the next prescription; and “past use,” from day 61 of each prescription until the earlier of day 120 or the date of the next prescription. The person time beginning from day 120 after each prescription for any ulcer healing drug and continuing until any subsequent prescription was combined into a “non-use” category. Duration of use was defined as the number of consecutive prescriptions (that is, prescriptions that followed within a maximum of 60 days of the same ulcer healing drug) among current users. Duration was categorised as “unknown” when there were less than six months' data in the automated prescription file. Daily dose was estimated according to the strength prescribed and the prescription's instructions as recorded on the computer.

Case ascertainment - We identified among the study population 160 subjects who had a first time diagnosis of gynaecomastia. We reviewed their computerised profiles without knowing their drug use and eliminated six with clear concurrent causes for their breast enlargement (liver disease, two; cancer, three; or trauma, one). To validate the diagnosis of gynaecomastia recorded on a computer for a random sample of half of the 160 subjects, we sent the general practitioners a questionnaire requesting details of some of the clinical features and any correspondence available related to the diagnosis of interest (referral letters, discharge letters). All patients' personal identifiers were suppressed before any material was sent to us. We excluded only one additional patient (trauma) after reviewing the information on these 80 patients.

Cohort analysis - We calculated standardised rates of gynaecomastia for each antiulcer drug, using as an internal standard the distribution of person time for the total study population over categories of calendar time and age groups. We also performed Poisson regression with the generalised linear interactive modelling (GLIM) package14 and obtained similar results.

Nested case-control analysis - A random index date between 1 January 1989 and 15 September 1992 was assigned for each of the 81 535 study members. If the random date of a study member were included in his eligible time at risk (from study entry to end of follow up), we considered the person as an eligible control.15 From the list of eligible controls, we selected a random sample of 1000 controls and compared them with the 153 cases. We used unconditional logistic regression to estimate the relative risk and 95% confidence interval for gynaecomastia within each category of exposure to ulcer healing drugs, using the non-user group as the reference group. We examined duration-response and dose-response relations among current users of cimetidine and we calculated relative risks for other selected drugs implicated in the literature as causing gynaecomastia (box).

Results

In all, 153 men presented with a first occurrence of idiopathic gynaecomastia. Table II presents a summary of the clinical features for the 80 patients for whom we received general practitioners' medical reports. In 12 patients the gynaecomastia did not regress, and five underwent a subareolar mastectomy. In none of the cases was a diagnosis of any other endocrine changes, such as impotence, recorded on computer.

The incidence for age and calendar time standardised among non-users and current users of the four antiulcer drugs is shown in table III. Only cimetidine users had a substantially greater risk of gynaecomastia than non -users: the relative risk associated with current use of cimetidine was 7.2 (95% confidence interval 4.5 to 11.3). The risk among users of the three other antiulcer drugs was not greatly different from the risk among non-users. These estimates of relative risk were virtually identical to the ones obtained in the nested case-control analysis.

Table IV presents the risk among current users of cimetidine broken according to duration of treatment, daily dose, and the joint effects between increasing duration and increasing daily dose. The period at highest risk seemed to be between the seventh and 12th month after starting treatment with cimetidine. Dose was also a major predictor of the occurrence of gynaecomastia, with most of the risk associated with greater than equal to 1000 mg daily. There was a strong synergy of effects between the duration and dose of cimetidine. When we used a common reference group (patients who received six or fewer prescriptions for cimetidine at a dose of 800 mg or less) we found relative risks of 2.0 in those who received seven or more prescription at a dose of 800 mg or less, 4.2 in those receiving six or fewer prescriptions at a dose of 1000 mg or more, and 13.1 in those receiving seven or more prescriptions at a dose of 1000 mg or more.16 The excess relative risk due to interaction between an increasing duration and an increasing dose was 7.9; owing to the small numbers in each group, this estimate of interaction presented some statistical uncertainty.17 The proportion of gynaecomastia among current users of cimetidine with both

Spironolactone (relative risk 9.3 (3.3 to 26.1) and verapamil (9.7 (2.6 to 36.0)) were the only two drugs associated with a risk of gynaecomastia comparable in magnitude with the one for cimetidine (table V).

Discussion

These results indicate that use of cimetidine is associated with clinically importantidiopathic gynaecomastia but that the use of misoprostol, omeprazole, and ranitidine is not. Clinical trials found that up to 0.8% of the subjects exposed to high doses of cimetidine developed gynaecomastia. 5 In our study population there were close to 2000 men who took 1000 mg a day or more; 15 went on to develop gynaecomastia. Despite the obvious differences between the two studies, especially with respect to surveillance of the subjects, estimates of risk for cimetidine are closely comparable, indicating that our source of information and study design had adequate validity to assess this outcome.

A recent publication presented a case series of endocrine adverse effects associated with omeprazole reported to the World Health Organisation Collaborating Centre for International Drug Monitoring.11 The authors suggest that omeprazole causes impotence and gynaecomastia. Our study did not examine the risk of impotence. However, there is no indication in the present study that use of omeprazole is associated with a greatly increased risk for gynaecomastia.

The mechanism by which cimetidine causes gynaecomastia has been discussed by Galbraith and Michnovicz, who showed that giving cimetidine to normal volunteers decreases 2-hydroxylation of oestradiol resulting in an increase in the serum oestradiol concentration.18 In contrast, ranitidine did not affect 2-hydroxylation nor did omeprazole.19 Our results are in agreement with these biochemical findings.

We thank the staff at VAMP, particular Dr Alan D Dean and Ms Anne Costello, and the participating general practitioners for their excellent cooperation with this study. The Boston Collaborative Drug Surveillance Program is supported in part by grants from Bayer AG, Burroughs Wellcome, Ciba-Geigy Corporation, Hoechst AG, HoffmannLa Roche, R W Johnson Phamaceutical Research Institute, Marion Merrell Dow, Pfizer, Procter and Gamble, and Sanofi Winthrop Pharmaceuticals.