Abstract
Abstract
Aim:
This study determined the transfer of intramuscular interferon β-1a into human milk and provides an estimate of infant exposure to this antiviral in six women chronically receiving intramuscular interferon β-1a (Avonex®, Biogen Idec, Research Triangle Park, NC).
Methods:
Interferon β-1a was measured at various times at steady state in milk samples collected from women receiving interferon β-1a at 30 μg/week.
Results:
Average milk concentrations were 46.7, 97.4, 66.4, 77.5, 103.1, 108.3, 124, and 87.9 pg/mL at 0, 1, 4, 8, 12, 24, 48, and 72 hours, respectively, after dosing. Using the highest value measured (179 pg/mL), the estimated relative infant dose would be 0.006% of the maternal dose.
Conclusions:
These data clearly suggest that interferon β-1a does not penetrate the milk compartment significantly and that levels in milk are far subclinical. No side effects were noted in any of the breastfed infants.
Introduction
With the advent of better therapies and with clinical studies showing no significant difference in the long-term prognosis of MS patients who choose pregnancy, the safety of immune-modulating drugs in pregnancy and lactation has become an important topic. Because so many patients with MS are now becoming pregnant and wanting to breastfeed their infants, the use of interferon β has become an important issue for breastfeeding mothers.
Interferons are large glycoproteins (22,500 Da) made and released by lymphocytes in response to the presence of viruses, bacteria, parasites, or other stimulants. They produce these effects by activating immune cells, such as natural killer cells and macrophages, and increase the activation of T lymphocytes. Unfortunately, their mechanism for down-regulating the autoimmune response in MS is not known. Interferon β-1a is a purified glycoprotein that has an amino acid sequence identical to natural fibroblast-derived human interferon β. The pharmacokinetics of interferon β-1a are unusual. The peak plasma concentration following intramuscular dosing is found at 3–15 hours after injection, and the elimination half-life is exceedingly low (10 hours). The route of administration (intramuscular vs. subcutaneous) does not appear to affect the pharmacodynamic or the pharmacokinetic profile of interferon β-1a, although the frequency of dose is important. 2 Although the plasma levels are virtually undetectable soon after injection, the biological effects last for approximately 4 days. 3
Interferons are a family of naturally occurring proteins that are produced by most eukaryotic cells, such as fibroblasts and macrophages, in response to viral infections and other biological inducers. Interferons, in general, mediate many activities, including antiproliferative and immunomodulatory activities. Three major interferons have been distinguished: α, β, and γ. Although most interferons have overlapping and distinct biological activities, for MS, only the β interferons are used clinically.
Presently, there are no data that characterize the transfer of β interferons into human milk following their administration in patients with MS who are breastfeeding. To date, no study has attempted to quantify the transfer of interferon β into human breastmilk.
Subjects and Methods
Study protocol
Six breastfeeding mothers who were presently being treated with intramuscular interferon β-1a (Avonex®, Biogen Idec, Research Triangle Park, NC) (30 μg/week) were enrolled in the study. All mothers were orally consented by the primary investigator; the procedure included a complete explanation of the study and a written consent. The study design was approved by the Texas Tech University Institutional Review Board (Amarillo, TX), and written informed consent was obtained from all participants.
Each patient was asked to record the time and dose of the injection of interferon-β along with the time each milk sample was collected. Other information such as the mother's body weight, date the drug was initiated, any other drugs currently being used, the infant's date of delivery, infant gestational age at birth, infant sex, and infant body weight both at birth and current were also recorded and sent on a data collection sheet. (Demographic data from patient 6 were not returned, but the data on interferon levels are included in Table 2.)
Breastmilk sampling procedure
Because the degree of transfer of some medications is a function of lipid content and to avoid the complications of fore and hind milk lipid variations, milk samples were collected by the mothers after fully pumping each breast for 12 minutes with an electric breast pump. Samples from both breasts were mixed together as one. Samples were collected at zero-time prior to injection and then at 1, 4, 8, 12, 24, 48, and 72 hours after injection. Each mother served as her own control. The breastmilk samples were then decanted into Nunc CryoTube™ tubes (Thermo Scientific, Waltham, MA) and frozen for transport. The samples were then sent by overnight transport to our laboratories and stored at −80°C.
Measurement of serum interferon β-1a in human milk
Interferon β-1a levels were measured by an enzyme-linked immunosorbent assay kit from R & D Systems, Inc. (Minneapolis, MN). Milk fat was first extracted using chloroform, and the aqueous phase was subsequently analyzed by enzyme-linked immunosorbent assay. Chloroform (1:1 ratio) was added, and the tube was vortex-mixed until a thick emulsion was obtained. The tubes were then centrifuged at 1,000 g for 30 minutes. The supernatant was removed from the lipid–chloroform layer by decanting into a fresh tube. Again, it was centrifuged at 1,000 g for 30 minutes. The supernatant was carefully removed and assayed. Control milk samples were treated similarly to patient samples using spiked aliquots of interferon β-1a added to control milk samples. The limit of detection with this assay was 20 pg/mL.
Results
The relevant demographic characteristics of the women and infants are summarized in Table 1. The mothers had a mean (range) age of 34.8 (31–43) years. Body weight had a mean (range) of 71.8 (59–88) kg. All mothers had a clinical diagnosis of multiple MS and had been on interferon for months to years so they could be assumed to be at steady state on the days of this study. All received the same dose of 30 μg of interferon β-1a (Avonex) intramuscularly weekly.
Ranges are given in parentheses.
For the five infants (three boys and two girls) for whom demographic data were returned, mean (range) age was 14.6 (6–23) months. Infant body weight had a mean (range) of 9.6 (7.7–11.8) kg. Mean (range) gestational age was 38 (36–39) weeks. None was exclusively breastfed; all were receiving solid foods to some degree. None of the mothers reported any symptoms or concerns about the well-being of their infants.
Table 2 shows the interferon β-1a concentration in milk samples. Many of the samples were below our limit of detection (20 pg/mL). Milk levels ranged from a low of 32.9 pg/mL to a high of 179 pg/mL. Average milk concentrations were 46.7, 97.4, 66.4, 77.5,103.1, 108.3, 124, and 87.9 pg/mL at 0, 1, 4, 8,12, 24, 48, and 72 hours, respectively. No untoward effects were noted in any of the breastfed infants.
Data are pg/mL of milk.
ND, not detected (below the limit of detection [20 pg/mL]).
Discussion
As more women with the diagnosis of MS choose pregnancy, more neonates will be potentially exposed to immunomodulator therapy. Our study attempted to quantify the amount of interferon β-1a that enters human milk.
As a group, interferons are transported around the body completely bound to T lymphocytes and other immune cells. As such, their transport and/or diffusion into human milk would be expected to be low because of their bound state, poor plasma levels, and large molecular weight.
The data above clearly suggest that the transfer of interferon β-1a into human milk is negligible at the doses commonly administered intramuscularly in patients with MS. To place this in perspective, each of the patients in this study was receiving 30 million pg weekly of interferon β-1a. Using the highest reported milk level of 179 pg/mL, the relative infant dose would only be 0.006% of the maternal dose. All other data points were far less than this one.
The molecular weight of a drug along with its lipophilicity and plasma levels attained are the most important factors when determining if any drug will enter the milk compartment. Any drug with a molecular size of greater than 1,000 Da, and without a specific transport system, is generally excluded from the milk compartment. At this time, there is no known transporter for interferons into human milk. Drugs that are highly bound to plasma proteins or cells also fail to produce significant levels in human milk, simply because they are not free in solution to diffuse across this tight endothelial barrier.
Few studies of interferon use in breastfeeding mothers exist. In one case report, following treatment with a massive intravenous dose of 30 million units (6,000,000 pg) of interferon α N3 in a breastfeeding patient, the amount of interferon α transferred into human milk was 894, 1,004, 1,551, 1,507, 788, and 721 units at 0 (baseline), 2, 4, 8, 12, and 24 hours, respectively. 4 Hence, even following a massive intravenous dose with this interferon, no change in breastmilk levels was noted from baseline.
The oral absorption of interferons is controversial and but is believed to be minimal. 5 Interferons are relatively nontoxic unless extraordinarily large doses are administered parenterally. Interferons are sometimes used in infants and children to treat idiopathic thrombocytopenia in huge doses.
With these results we believe that it should be quite safe for mothers to breastfeed their infants while undergoing interferon β-1a therapy intramuscular therapy. The infants in our study showed no acute adverse affects that might be associated with the use of interferon β-1a despite prolonged exposure to this drug during lactation.
Footnotes
Disclosure Statement
No competing financial interests exist. The authors have no financial or relationship of any kind to the manufacturer of interferon β-1a.