Australian categorisation system for prescribing medicines in pregnancy

The Australian categorisation system and database for prescribing medicines in pregnancy have been developed by medical and scientific experts based on available evidence of risks associated with taking particular medicines while pregnant. This information is presented for the use of health professionals prescribing medicines to pregnant women. It is not presented as medical advice to health professionals or the public.

On this page: What does the Australian categorisation system take into account? | Situations for which the pregnancy category may not be valid | Why do some products have more than one pregnancy category? | The Australian categorisation system is not hierarchical | Definitions of the Australian categories for prescribing medicines in pregnancy

What does the Australian categorisation system take into account?

Most medicines cross the placenta. The categorisation system has taken into account the known harmful effects of medicines on the developing baby, including the potential to cause:

• birth defects
• unwanted pharmacological effects around the time of birth, which may or may not be reversible
• problems in later life

The categorisation system does not take into account the rare circumstance of an idiosyncratic reaction in the neonate to a medicine that crosses the placenta.

Situations for which the pregnancy category may not be valid

The pregnancy categorisation system only applies to recommended therapeutic doses in women. It cannot be assumed that the classifications assigned to individual medicines are valid in situations such as:

• Overdose
• Occupational exposure
• Other situations in which the recommended therapeutic dose has been exceeded

Why do some products have more than one pregnancy category?

While some medicines are genuinely teratogenic, and carry a category X, for most medicines the risk of developing birth defects is also dependent on:

• Systemic exposure of the mother
• Exposure of the fetus, which may be affected by:
  • Dose
  • Route of administration
  • Dosing regimen

Thus, a low dose, limited topical application of a medicine for a particular indication may have a less restrictive category (such as A) compared to a more restrictive category for the same medicine given long-term or at higher doses orally for a different indication.

The Australian categorisation system is not hierarchical

The Australian categorisation system differs from the US FDA categorisation. The categorisation of medicines for use in pregnancy does not follow a hierarchical structure.

• Human data are lacking or inadequate for drugs in the B1, B2 and B3 categories
• Subcategorisation of the B category is based on animal data
• The allocation of a B category does not imply greater safety than a C category
• Medicines in category D are not absolutely contraindicated during pregnancy (e.g.anticonvulsants)

Due to legal considerations in Australia, sponsor companies have, in some cases, applied a more restrictive category than can be justified on the basis of the available data.

For pharmaceutical products containing two or more active ingredients, the categorisation of the combination is based on the active ingredient with the most restrictive pregnancy categorisation.

Definitions of the Australian categories for prescribing medicines in pregnancy

Category A

Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.

Category B1

Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed.

Studies in animals have not shown evidence of an increased occurrence of fetal damage.

Category B2

Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed.

Studies in animals are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage.

Category B3

Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed.

Studies in animals have shown evidence of an increased occurrence of fetal damage, the significance of which is considered uncertain in humans.

Category C

Drugs which, owing to their pharmacological effects, have caused or may be suspected of causing, harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible. Accompanying texts should be consulted for further details.

Category D

Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human fetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Accompanying texts should be consulted for further details.

Category X

Drugs which have such a high risk of causing permanent damage to the fetus that they should not be used in pregnancy or when there is a possibility of pregnancy.