Is the use of clenbuterol during pregnancy associated with an increased risk for the fetus?

Fråga: Is the use of clenbuterol during pregnancy associated with an increased risk for the fetus?

Sammanfattning: No information concerning the use of clenbuterol during early pregnancy in humans has been found and no teratogenic properties of the drug have been revealed. An increased frequency of congenital aplasia cutis in humans has been discussed in connection with the use of clenbuterol and antithyroids in animal feed.

Svar: Clenbuterol is a beta-2-agonist with general properties and side-effects similar to those of salbutamol (1). Clenbuterol is not registered in Sweden but is available for human use in eg Germany and Italy. Its main use in humans is as a tocolytic agent.

The drug has also been extensively used among athletes as it has been said to provide a protein anabolic response that could be performance enhancing (1), but the drug is mainly used in veterinary practice as a food additive to increase the growth of the animals.

No information concerning any teratogenic properties in humans has been found in the literature. We have found one study, however, where clenbuterol was fed to pregnant rats and decreased fetal body weight was noted (2).

Clenbuterol concentrations in fetal, placental and maternal plasmas were measured in nine patients at 9-12 weeks gestation following therapeutic abortion. The placental concentration of clenbuterol was about three times higher than that of maternal plasma. Beta-receptors are well developed early in gestation and consequently dose-dependent responses to maternally administered clenbuterol can be expected (3).

Other drugs with pharmacological properties similar to those of clenbuterol, such as salbutamol and terbutaline, are classified in group A in Fass, which means that the drug has been extensively used by pregnant women in common antiasthmatic doses without any increased risk of teratogenicity.

Clenbuterol poisoning has been reported in Spain and France (4) due to consumption of bovine liver and/or meat. Clenbuterol is added to the animal feed with antithyroid drugs such as methimazole and thiamazole and an increased frequency of scalp defects (aplasia cutis) in humans has been noted in the areas where the cases of poisoning have occurred (5). 1 Drugline nr 09859 (year 1993) 2 Maltin CA, Delday MI, Hay SM: The effect of clenbuterol administration in utero and throughout lactation on pre- and post-natal muscle development in the rat. Growth Dev Aging 1990; 54: 143-150 3 Pelkonen O, Tuimala R, Kauppila A: Placental transfer of clenbuterol early in human pregnancy. Eur J Clin Pharmacol 1982; 22: 403-406 4 Martinez-Navarro JF: Food poisoning related to consumption of illicit beta-agonist in liver. Lancet 1990; 336; 1311 5 Martinez-Frias ML, Cereijo A, Rodriguez-Pinilla E, Urioste M: Methimazole in animal feed and congenital aplasia cutis. Lancet 1992; 339: 742-743