Abnormal Development - Drugs

From Embryology

Introduction

Thalidomide molecular structure

This page introduces the possible effects of maternal use of legal drugs (therapeutic chemicals/agents) on development. In some cases these drugs are prescribed to treat pre-existing or pregnancy related maternal medical conditions. In all cases, a discussion with a medical practioner should be had prior to any reproductive decision.

The placenta and fetal tissues may deal with drugs differently from adult target tissues. In particular, drugs are "cleared", metabolised and excreted, at a different rate in both the fetus and in newborn infants. In general there is a much lower rate of clearance (More? Infant Drug Clearance Rate).

Legal drugs are classified, usually by each country's appropriate regulatory body, on the safety of drugs during pregnancy. In Australia, the Therapeutic Goods Authority has classes (A, B1, B2, B3, C, D and X) to define their safety (More? Australian Fetal Risk Categories). In the USA, drugs are classified by the Food and Drug Administration (FDA) into classes (A, B, C, D, and X) to define their safety (More? FDA Fetal Risk Categories).

There are also a growing range of herbal drugs which may not have undergone this type of study and classification (More? Herbal Drugs)

The importance of careful evaluation of drugs can be historically demonstrated with the teratogenic effects of thalidomide, a drug given to treat "morning sickness" in the first trimester of pregnancy, which affected musculoskeletal development. (More? thalidomide) This current page also gives examples of some other current drugs which have been shown to impact on development.

Links:

Some Recent Findings

Australia - Advisory Committee on Prescription Medicines

The Australian Drug Evaluation Committee (ADEC) was established in 1963 following the thalidomide experience and in 2010 this committee was replaced by the Advisory Committee on Prescription Medicines (ACPM). The new ACPM advises and makes recommendations to the Therapeutic Goods Administration (TGA) on prescription medicines listed on the Australian Register of Therapeutic Goods (ARTG), established under the Therapeutic Goods Act 1989. There were approximately 54,000 products on the Australian Register of Therapeutic Goods as at 23 May 2008.

Advisory Committee on Prescription Medicines

  • inclusion of a prescription medicine on the Australian Register of Therapeutic Goods (the Register)
  • changes to an entry of a prescription medicine on the Register
  • removal or retention of a prescription medicine on the Register
Links: Advisory Committee on Prescription Medicines

Australian Drug Categories

Legal drugs are classified, usually by each country's appropriate regulatory body, on the safety of drugs during pregnancy. In Australia, the Therapeutic Goods Authority has classes (A, B1, B2, B3, C, D and X) to define their safety. In the USA, drugs are classified by the Food and Drug Administration (FDA) into classes (A, B, C, D, and X) to define their safety. (More? Australian Drug Categories)

  • Pregnancy Category A - Have been taken by a large number of pregnant women and women of childbearing age without an increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.
  • Pregnancy 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.
  • Pregnancy Category B2 - 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.
  • Pregnancy Category B3 - 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.
  • Pregnancy Category C - Have caused or may be suspected of causing, harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible.
  • Pregnancy Category D - 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.
  • Pregnancy Category X - 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.

Teratology

Now consider how different environmental effects during pregnancy may influence developmental outcomes. The terms listed below are often used to describe these environmental effects

  • Teratogen (Greek, teraton = monster) any agent that causes a structural abnormality (congenital abnormalities) following fetal exposure during pregnancy. The overall effect depends on dosage and time of exposure. (More? Critical Periods of Development)
  • Absolute risk the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome)
  • Relative risk the ratio of the rate of the condition among the exposed and the nonexposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers) A high relative risk may indicate a low absolute risk if the condition is rare.
  • Mutagen a chemical or agent that can cause permanent damage to the deoxyribonucleic acid (DNA) in a cell. DNA damage in the human egg or sperm may lead to reduced fertility, spontaneous abortion (miscarriage), birth defects and heritable diseases.
  • Fetotoxicant is a chemical that adversely affects the developing fetus, resulting in low birth weight, symptoms of poisoning at birth or stillbirth (fetus dies before it is born).
  • Synergism when the combined effect of exposure to more than one chemical at one time, or to a chemical in combination with other hazards (heat, radiation, infection) results in effects of such exposure to be greater than the sum of the individual effects of each hazard by itself.
  • Toxicogenomics the interaction between the genome, chemicals in the environment, and disease. Cells exposed to a stress, drug or toxicant respond by altering the pattern of expression of genes within their chromosomes. Based on new genetic and microarray technologies.

Thalidomide

Thalidomide is a drug that was introduced on to the market on October 1, 1957 in West Germany. Thalidomide soon became a drug prescribed to pregnant women to combat symptoms associated with morning sickness. When taken during the first trimester of pregnancy, thalidomide prevented the proper growth of the fetus resulting in horrific birth defects in thousands of children around the world.

It was the linking of newborn abnormalities with the taking of thalidomide by an Australian clinician, William McBride, that identified it as a teratogenic agent causing a "thalidomide embryopathy".[1]

Not all species embryos are affected by the drug in the same way, with human and rabbit being most susceptible to the teratogenic effects. In addition, the effect on human development is also dependent upon the time and dose of the drug exposure, the "critical periods".

Links: Abnormal Development - Thalidomide | Musculoskeletal System - Abnormalities

References

  1. ↑ <pubmed>331548</pubmed>

Reviews

  • Saunders EJ, Saunders JA. Drug therapy in pregnancy: the lessons of diethylstilbestrol, thalidomide, and bendectin. Health Care Women Int. 1990;11(4):423-32.
  • Stephens TD. Proposed mechanisms of action in thalidomide embryopathy. Teratology. 1988 Sep;38(3):229-39.
  • Newman CG The thalidomide syndrome: risks of exposure and spectrum of malformations. Clin Perinatol. 1986 Sep;13(3):555-73.
  • Fletcher I. Review of the treatment of thalidomide children with limb defeciency in Great Britain. Clin Orthop Relat Res. 1980 May;(148):18-25.

Articles

  • Benegbi M. 45 years later...where do we stand? Can J Clin Pharmacol. 2007 Winter;14(1):e37-9. "The Thalidomide Victims Association of Canada (TVAC) was founded in 1988 and is the only organization in North America to work with and for Thalidomide victims. Our mission is to empower our members and to improve their quality of life through various programs and customized services. With the return of Thalidomide on the market, TVAC also took on the mandate of informing the public on the devastating effects of this medication and to promote awareness and caution when using any teratogenic products currently available".
  • McBride WG. Prescription drugs in the first trimester and congenital malformations. Aust N Z J Obstet Gynaecol. 1992 Nov;32(4):386.

Search Pubmed

June 2010 "thalidomide teratogenicity" All (147) Review (57) Free Full Text (11)


Search Pubmed: thalidomide teratogenicity | Thalidomide

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Cite this page: Hill, M.A. (2024, May 3) Embryology Abnormal Development - Drugs. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Drugs

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