DRUG THERAPY DURING PREGNANCY
To help guide therapy the FDA has developed a classification for the safety of drugs during pregnancy as follows:
Class A: Drugs that have undergone controlled studies in pregnant patients and have been found to be safe. Unfortunately, no allergy or asthma medications fall into this category.
Class B: These drugs have not undergone rigorous testing in pregnant patients, but adverse effects have not been detected in either animal or human studies. Several asthma medication fall into this category, including ipratropium, salmeterol, terbutaline, cromolyn sodium, nedocromil, zileuton, and zafirlukast.
Class C: Adverse effects have been detected in animal studies, but not yet in human studies. The corticosteroids: prednisone, beclomethasone, flunisolide, fluticasone, and triamcinalone, as well as the bronchodilators: theophylline, albuterol, bitolterol fall into this category.
Class D: These drugs have well demonstrated adverse effects on human foetal health. These drugs should not be used in pregnant patients.
Class X: These drugs are contraindicated in pregnancy.
Antihistamines
Oral Antihistamines: systemic antihistamines should not be prescribed during the first quarter of pregnancy. After this period, second generation (such as non sedating) antihistamines are preferred.
Topical antihistamines, chromones and topical steroids should be considered first choice of drugs because of their low dosage and their rapid action (few minutes for topical antihistamines, some hours or days for chromones and topical steroids)
Cromolyn: is a mast cell stabilizer. The nose and eye drops take about 2 to 5 days to produce clinical effects. No severe systemic or severe Transient burning and stinging is attributed to the preservative. Nedocromil appears to be more potent than cromolyn.
Lodoxamide (Lomide)is an antiallergy compoundanda potent mast cell stabilizer, initially produced for asthma, but now only used in eye drops. It exerts its anti allergy properties within half an hour of administration.
Topical antihistamines: Levocabastine (Livostin) eye drops and nasal solutions are at least as effective and in some cases more effective than, sodium cromoglycate. Levocabastine is well tolerated.
Because the safety profile of these compounds is very favourable since the nasal and/or conjunctival absorption is almost absent. These pharmacologic properties should promote these compounds to the forefront in the strategy for allergy treatment of rhinitis and conjunctivitis during pregnancy. The onset of action is also very fast.
Steroids
They are without teratogenic effects. Systemic steroids should be prescribed only for the most serious allergic disorders. Topical steroids (at the recommended dose for treating asthma and skin conditions) should be the first choice. One the basis of safety profile the newer ones should be preferred due to their reduced or almost absent absorption.
Chromones
As these compounds are almost without side effects, they can be used during pregnancy without significant problems.
Theophylline
They can pass through the placenta barrier, causing foetal arrhythmias.
Anticholinergics
They are without teratogenic effects, but the cost benefit ratio is not very favourable.
Adrenergics
Vasoconstrictors should be used only for a few days; Bronchodilator must be used as needed.
Allergen immunotherapy during pregnancy
Allergen immunotherapy is now recognised as an efficacious means of treating patients affected by rhinitis and/or allergic asthma. The literature confirms that when Immunotherapy is carefully implemented it can yield significant results and notable improvements in symptoms. Immunotherapy has proved to be efficacious in the treatment of rhinitis and asthma in the pregnant patient as well. The safety concerns of the mother and the newborn, the incidence of miscarriages, foetal and neonatal deaths, congenital malformations, and toxaemia have not been seen to be any higher than in control groups of untreated pregnant patients and the general population. Even in the few cases in which immunotherapy caused systemic reactions, when these have been promptly treated, no miscarriages or foetal abnormality have been caused.
On the basis of these findings, it can be concluded that immunotherapy can be continued in women already under treatment before pregnancy, if they meet the following requirement:
- They are in the maintenance phase or
- On high doses if in the initial incremental phase
- They have benefited before from this therapy
- They have not shown any increased risk to systemic reactions
It is usually advisable to reduce the dose in order to further reduce the risk of systemic reactions, and since the highest incidence of systemic reactions, and since the highest incidence of systemic reactions is seen in the phase of increasing doses, caution suggests that immunotherapy should be suspended if the treatment is in the initial stages when pregnancy is discovered. It is not, therefore, advisable to initiate immunotherapy during pregnancy for the following reasons:
- The risk of untoward systemic reactions, which are more frequent in the initial incremental dosage stage
- The lack of benefit from the first low dosage administration of immunotherapy;
- And the difficulty of foreseeing which patients will benefit from the therapy, especially in the case of asthma.
Summary of the Profile of allergy drugs used during pregnancy
Drug category Pregnancy category*
Steroids C
Antihistamines B
Chromones B
Adrenergics C
Theophylline C
Anticholinergics C
* FDA category B = no evidence of risk in humans; FDA category C = risk cannot be ruled out
Considering toxicities of drugs, the following principles should guide drug therapy:
The Australian Drug Evaluation Committee 4th Edition of Prescribing medicines in pregnancy
Categorisation consists of the following categories
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 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 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 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 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 may have 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
Commonly used drugs in Allergy and their Categorisation
Antitussives
Preventative aerosols and inhalations
The benefits of asthma control outweigh any potential for an adverse pregnancy outcome.