With therapy using diuretics, milk production can decrease, especially if there was already some lactational deficiency. Displacement of bilirubin from the plasma protein binding in newborns was discussed for furosemide and the thiazides. A risk of kernicterus as a result should not, however, be considered a realistic possibility (see also section 3.6).
Chlorthalidone has a half-life of 44 hours or more. Long-term treatment with 50 mg daily leads to an accumulation with values of up to 0.86 mg/1 of milk. However, because of the very high maternal plasma concentration, there is an M/P ratio of only about 0.06. The maximum dosage an infant would receive would be 0.13 mg/kg daily. This represents 15.5% of the maternal weight-related dosage. No symptoms have been observed as yet in breastfed children (Mulley 1982).
Furosemide has an M/P ratio of 0.5-0.8 (Wilson 1981). There are no indications of any special intolerance in breastfed infants.
With long-term treatment using 50 mg hydrochlorothiazide daily, there was, at most. 0.12 mg/1 milk. The dosage taken iti by the infant would be 0.02 mg/kg daily - that is, 2.2% of the maternal weight-related dosage (Miller 1982).
Spironolactone is a potassium-saving diuretic. As soon as it is absorbed it is changed into the active metabolite, canrenone, which is up to 98% bound to plasma protein. In animal studies, canrenone is carcinogenic in very high doses; no such effect has been observed in human beings. The M/P ratio lies between 0.5 and 0.7. With ongoing treatment of 100 mg daily, a maximum milk concentration of 0.1 mg/1 was found. For the infant, this would mean a daily intake of 0.016 mg/kg - 1.2% of the maternal weight-related dosage (Phelps 1977).
The carbonic anhydrase inhibitor acetazolamide, which is related to the thiazides and is prescribed for glaucoma therapy per os as well as in eye drops, plays a spccial role. Therapeutic doses of lOOOmg/daily per os led to peak values of 2.1 mg/1 milk. Mathematically, this translated into 1.9% of the maternal weight-related dosage for the symptom-free infant described, in whose blood 0.2-0.6 mg/1 of the active ingredient was measured (maternal plasma 5.8 mg/1) (Sodermann 1984). Similar characteristics can be assumed for the eye drops brinzolamide and dorzolamide.
There are insufficient data to make a judgment on amiloride, azosemide, bendroflumethiazide, bumetanide, butizide, chlo-razanil, clopamide, ethacrynic acid, etozolin, indapamide, mefru-side, metolazone, piretanide, polythiazide, torasemide, triamterene, trichlormethiazide, and xipamide.
Recommendation. During breastfeeding, diuretics should not be used primarily for treating hypertonia. However, when such a drug is urgently needed, moderately dosed treatment with hydrochlorothiazide can be undertaken, with attention to the side effects described. If furosemide is indicated, this may also be prescribed. Spironolactone should be used only for special indications, such as primary hyperaldosteronism, ascites, nephrotic syndrome, and the like.
Carbonic anhydrase inhibitors for glaucoma are acceptable. Chlortalidone is contraindicated because of its accumulation, and the other drugs mentioned should not be used because of insufficient experience during breastfeeding. Single doses do not require limitation of breastfeeding, but the therapy should be changed.
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