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Safety of medicines taken during pregnancy

Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2013.

Introduction

Some medicines and drugs are known to cause fetal harm if taken during pregnancy. Medicines should only be taken if the expected benefits to the mother are greater than the risk to the mother and to the baby. Essential medicines should be taken in the lowest possible dose and for the shortest possible time during pregnancy. The risks of fetal malformation are greatest during the first trimester (the first 12 weeks of gestation). The effect of withdrawal on the newborn baby should be carefully assessed if medicines such as antidepressants are taken during the third trimester (after 28 weeks).

Rarely, problems have also been reported when medicines such as finasteride have been taken by the male partner.

Drug licensing authorities classify medicines according to their risk in pregnancy. Data is limited; many available medicines have not yet been assessed or classified, and unclassified medicines may or may not be be safe during pregnancy. Classifed drugs may be reclassified as new information becomes available.

Australian TGA classification

When prescribing medicines in pregnancy, it is useful for health professionals to access the Australian Government Department of Health and Aging Therapeutic Goods Administration (TGA)'s comprehensive database, a categorisation system for prescribing medicines in pregnancy.

The definitions of each category are copied below together with examples of the classification of some drugs used to treat skin conditions (TGA website accessed 8 June 2013).

Category A

Category A medicines 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.

Examples of Category A medicines: chlorhexidine, clindamycin , erythromycin, intralesional triamcinolone, penicillin, prednisone and other systemic steroids, topical steroids, sulfasalazine.

Category B

Medicines allocated Category B are subcategorised based on animal data, with human data lacking or inadequate.

Category B1: Medicines 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 foetal damage.

Examples of Category B1 medicines: anakinra, azelaic acid, calcipotriol, gabapentin, imiquimod, loratidine, an antihistamine, ustekinumab mupirocin, terbinafine, ustekinumab.

Category B2: Medicines 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 foetal damage.

Examples of Category B2 medicines: benzyl benzoate, dapsone, cetirizine, an antihistamine, dithranol, etanercept, metronidazole, nicotinamide, permethrin.

Category B3: Medicines 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 foetal damage, the significance of which is considered uncertain in humans.

Examples of Category B3 medicines: aciclovir, apremilast, cyproterone 2mg daily, eflornithine, gamma benzene hexachloride, griseofulvin, ingenol, itraconazole, ivermectin, ketoconazole, mebendazole, melatonin, pimecrolimus, spironolactone, voriconazole.

Medicines in Category B do not imply greater safety than medicines in Category C.

Category C

Category C medicines are medicines which, owing to their pharmacological effects (risk based on the mechanism of action of the medicine), have caused or may be suspected of causing harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible.

Examples of Category C medicines: adalimumab, alefacept, amitriptyline, ciclosporin, fusidic acid, infliximab, ipilimumab, minoxidil, rifampicin, rituximab, secukinumab, tacrolimus.

Category D

Medicines in Category D are not absolutely contraindicated during pregnancy. However, there is a higher risk of malformations. Category D medicines have caused, are suspected to have caused, or may be expected to cause, an increased incidence of human foetal malformation or irreversible damage. These medicines may also have adverse pharmacological effects.

Examples of Category D medicines: azathioprine, colchicine, cyclophosphamide, cyproterone >10mg daily, dabrafenib, doxycycline fluconazole, hydroxychloroquine, hydroxyurea, methotrexate, minocycline, mycophenolate, nitrogen mustard, podophyllotoxin, thioguanine, vemurafenib, vitamin A.

Category X

Medicines in Category X are absolutely contraindicated in pregnancy with a high risk of permanent damage (ie, these medicines are teratogenic).

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

Examples of Category X medicines: acitretin, oral isotretinoin, leflunomide, thalidomide.

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