Drug distribution in human milk

Editor, – The Adverse Drug Reactions Advisory Committee (ADRAC) was most interested in the article 'Drug distribution in human milk' (Aust Prescr 1997;20:35-40). In particular, the authors indicated that selective serotonin reuptake inhibitors (SSRIs) were probably safe in breast-feeding women, but that more data were needed. In this context, the ADRAC wishes to provide some relevant data from 4 reports which are strongly suggestive of breast milk transfer of maternal SSRIs to the neonate.

In one report, a 5-month-old breast-fed baby of a mother taking fluoxetine was found to have hyperglycaemia and glycosuria, which resolved after weaning. A second case describes a mother taking paroxetine whose breast-fed baby became agitated, unsettled and had difficulty feeding; the outcome is unknown. The third report is of a 5-month-old baby who initially became agitated for a few days whilst her mother took sertraline, but this settled spontaneously. In the final case, a breast-feeding mother began sertraline therapy at 10 days postpartum and took it for about 3 months. During the mother's drug therapy, the baby remained somnolent, with low muscle tone, hearing problems and suspected developmental difficulties, all of which improved markedly when the mother discontinued the drug.

Alain Rohan
Adverse Drug Reactions Advisory Committee
Symonston, A.C.T.

Editor, – I refer to the article 'Drug distribution in human milk'. I found it very interesting and useful, and will of course keep it for future reference as the previous articles covering this subject are rather dated.

However, there is one major omission which is not only germane to my practice, but I am sure is more important than some of the individual areas that were covered. This is the appearance of antihypertensive drugs in breast milk, particularly with respect to the ACE inhibitors. Although some authorities regard these as being completely innocuous, there are some drug inserts that seem to indicate otherwise.

I would be very interested if a supplementary table could be provided, covering not only the ACE inhibitors, but the calcium channel antagonists, beta blockers and the other more minor drugs used in the treatment of hypertension.

Michael Laver
Consultant Physician
Mildura, Vic.

K.F. Ilett, J.H. Kristensen, R.E. Wojnar-Horton and E.J. Begg, the authors of the article, comment:
We are grateful to Dr M. Laver for his enquiry on the distribution and likely infant dose of antihypertensive drugs in breast feeding. In our article, we set out to discuss those drugs/groups that, in our experience, are commonly used during lactation. However, we appreciate that different practitioners may see specialised groups of patients and have a need for information on drugs other than those that we covered. We hope that the Table below will provide a succinct summary of the available data for a range of different antihypertensives. We reiterate that the 'Further Reading' texts listed in our article provide a comprehensive data summary of distribution and safety data for a broad range of individual drugs, and that this information is also available from Obstetric Drug Information Services in all States.

Distribution of antihypertensive drugs into human milk, calculated infant dose and interpretation of data
Infant dose3(%)
Drug/Group1 M/P ratio2 Average Maximum

Comments and recommendations for breast feeding

Ace inhibitors
Captopril 0.012-0.03 0.009 0.014 Low exposure. Considered safe.
Enalapril (enaloprilat) 0-0.14 0.27 ND Low exposure. Considered safe.
Calcium channel blockers
Diltiazem 1 ND 0.9 Low exposure. Single case report. Considered safe.
Nifedipine 1 ND 1.5 (including
Low exposure. Considered safe.
Verapamil 0.23-0.94 ND 0.4-1.1 Low exposure. Considered safe.
Beta blockers
Atenolol 1.1-6.8 8.4 19.2 Significant quantities in milk. One report of bradycardia in an infant. Consider an alternative where possible. If used, observe infant for signs of beta blockade.
Labetalol 0.22-1.51 0.06 0.33 Low exposure. Considered safe.
Metoprolol 2-3.6 0.7 3.2 Moderate exposure. Considered safe, but observe infant for signs of beta blockade.
Propanolol 0.5-0.85 0.3 0.4 Low exposure. Considered safe, but observe infant for signs of beta blockade.
Sotalol 2.2-8.8 21.8 42 Significant exposure. No adverse effects seen in infants, but advisable to use an alternative.
Other antihypertensives
Clonidine 1.5-3.6 6.4 7.9 Moderate exposure. No adverse effects reported in infants. May inhibit prolactin and reduce milk secretion. Advisable to use an alternative.
Hydralazine 0.49-1.36 ND 0.8 Low exposure. Considered safe.
Methyldopa 0.17-0.46 1.6 3.2 Moderate exposure. Considered safe.

1 active metabolites in parenthesis

2 individual value, means or range from selected studies

3 infant dose in mg/kg as % maternal dose in mg/kg. Data from selected studies

ND no data available

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