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Atenolol / chlorthalidone Pregnancy and Breastfeeding Warnings

Atenolol / chlorthalidone is also known as: Tenoretic, Tenoretic 100, Tenoretic 50

Atenolol / chlorthalidone Pregnancy Warnings

Atenolol-chlorthalidone has been assigned to pregnancy category D by the FDA. Animal studies have revealed evidence of dose-related embryotoxicity and fetotoxicity associated with atenolol, but not with chlorthalidone. Atenolol use in the second trimester of pregnancy has been associated with the birth of infants that are small for gestational age. Some retrospective reviews have shown an increased risk of malformations associated with thiazide diuretics. In addition, neonates born to mothers who are receiving atenolol-chlorthalidone at parturition may be at risk for hypoglycemia and bradycardia. Atenolol-chlorthalidone is considered contraindicated during pregnancy.

Data from controlled human pregnancy have revealed no significant difference in the birth weights of infants whose mothers were taking atenolol or placebo. Some data have shown, however, a significantly decreased fetal heart rate and significantly decreased mean birth weight of infants whose mothers were taking atenolol relative to those taking acebutolol or pindolol. While most studies have shown no significant effects of atenolol, case reports of profound beta-blockade in neonates of mothers who were taking atenolol have been reported. Because of this, observation of affected neonates for bradycardia and hypotension is recommended for 48 hours postpartum. A series of 211 pregnant women who were given chlorthalidone to prevent toxemia of pregnancy has been reported. Patients were entered into the study at gestation week 16, and were given chlorthalidone 50 mg once a day or placebo in a single-blinded fashion. There were significant decreases in the serum sodium and potassium in the treated patients, especially between gestation months four through nine. There appeared to be no benefit from the drug since there were no differences in blood pressure or the incidence of edema or proteinuria between the groups. The average height and weight of the offspring of treated patients was significantly higher; there were no deaths and no malformations. Placental weights were significantly greater among women who received chlorthalidone, but no differences in the amount or nature of amniotic fluid, placental calcification, or number of placental infarctions were observed. The authors speculated whether the increased placental size in the treated group was related to alterations in glycogen metabolism. The Collaborative Perinatal Project monitored 50,282 mother-child pairs, of whom 233 were exposed to thiazide or related diuretics during the first-trimester. An increased risk of malformations was found for thiazide diuretics. Use of thiazides after the first trimester does not seem to carry this risk. Thiazide diuretics may, however, pose metabolic risks to the mother and fetus (hyponatremia, hypokalemia, thrombocytopenia, hyperglycemia), and may have a direct effect on smooth muscle, resulting inhibition of labor. The Michigan Medicaid surveillance study showed no association between some thiazide diuretics and congenital defects (written communication, Franz Rosa, MD, Food and Drug Administration, 1994). This report is a summary of information from two studies, one in which 390 of 104,000 pregnant women from 1980 to 1983, and one in which 567 of 229,000 pregnant women from 1985 to 1992 received a related drug, hydrochlorothiazide (HCTZ). In the first study 28 total defects and 6 cardiovascular defects were observed (25 and 4 were expected, respectively). In the second study, 24 total defects and 7 cardiovascular defects were observed (22 and 6 were expected, respectively). Cleft palate was not observed in either study. These data do not support an association between HCTZ and congenital defects, and are considered pertinent to other thiazide diuretics. Cases of neonatal thrombocytopenia associated with antepartum administration of thiazide diuretics have been reported.

Atenolol / chlorthalidone Breastfeeding Warnings

Milk atenolol levels may be four times higher than maternal serum levels. Symptoms of bradycardia, peripheral cyanosis, and hypothermia have been reported in a nursing infant whose mother was taking atenolol 50 mg orally every 12 hours. The authors calculated that the atenolol exposure to the nursing infant was 9% of the mother's daily dose. Because of this, observation of nursing infants for bradycardia and hypotension is recommended during breast-feeding. In addition, neonates born to mothers who are breast-feeding may be at an increase risk for hypoglycemia. There are no data on the safety of chlorthalidone during breast-feeding. There are data for a related drug, hydrochlorothiazide (HCTZ). A peak milk concentration of HCTZ of 125 ng/mL was measured between 4 and 12 hours after a daily dose in a woman who was taking HCTZ 50 mg/day. A simultaneously measured maternal serum HCTZ level was approximately 275 ng/mL. There were no detectable drug levels or electrolyte abnormalities in the baby's blood. The authors calculated that, if a 1-month-old infant takes approximately 600 mL of milk per day, and the mean milk HCTZ level is approximately 80 ng/mL, the infant would be exposed to approximately 0.05 mg HCTZ daily. This usually represents an insignificant amount of HCTZ to the infant such that adverse effects in the nursing infant are unlikely.

Atenolol is excreted into human breast milk at a ratio of 1.5 to 6.8 when compared to the concentration in plasma. Thiazides are excreted into human milk in low concentrations. Neonates born to mothers who are receiving atenolol-chlorthalidone and are breast-feeding may be at an increased risk for hypoglycemia and bradycardia. The manufacturer recommends that caution be used when administering atenolol-chlorthalidone to nursing women.

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