Abstract
Antibiotics are a group of medicines used for treating infections caused by bacteria and certain parasites but are not effective against viral or fungal infection.
They are also called antibacterial or antimicrobials and work by killing the organisms or stopping them from multiplying.
Antibiotics are commonly prescribed during pregnancy; however, the specific medication must be chosen carefully as most antibiotics might be safe while some are not.
Safety depends on various factors, including the type of antibiotic, gestational age, dose and duration of the use of the antibiotics.
They are usually grouped together based on mode of action as each only works against certain types of organisms; therefore, different antibiotics are used for different infections.
Antibiotics are a group of medicines used for treating infections caused by bacteria and certain parasites but are not effective against viral or fungal infection.
They are also called antibacterial or antimicrobials and work by killing the organisms or stopping them from multiplying.1
Antibiotics are commonly prescribed during pregnancy; however, the specific medication must be chosen carefully as most antibiotics might be safe while some are not.
Safety depends on various factors, including the type of antibiotic, gestational age, dose and duration of the use of the antibiotics.
They are usually grouped together based on mode of action as each only works against certain types of organisms; therefore, different antibiotics are used for different infections.
• Classification of Antibiotics According to Groups
Penicillin – phenoxymethylpenicillin, flucloxacillin and amoxicillin
Cephalosporins – cefaclor, cefadroxil and cefalexin
Aminoglycosides – gentamicin and tobramycin
Macrolides – erythromycin, azithromycin and clarithromycin
Tetracyclines – tetracycline, doxycycline
Clindamycin
Sulfonamides and trimethoprim – co-trimoxazole
Metronidazole and tinidazole
Quinolones – ciprofloxacin, levofloxacin and norfloxacin
Antibiotics Grouping by Mechanism of Action
C) Protein Synthesis Inhibitors
Guidelines for Prescribing an Antibiotic during Pregnancy
Antibiotics should only be used if no other treatment option will suffice
Should be avoided during the first trimester when possible
Safe medication tested on pregnant women should be chosen
Monotherapy single prescriptions rather than polypharmacy are preferred when possible
Lowest possible dose and duration of use proven effective should be given
Advise patients not to use over-the-counter medications during antibiotic treatment2
Antibiotics Used during Pregnancy
Common antibiotics that are generally considered safe during pregnancy include:
Penicillins (amoxicillin and ampicillin)
Cephalosporins
Erythromycin
Penicillins and cephalosporins are the drugs of first choice in pregnancy.3 The penicillins interfere with cell wall synthesis and are bactericidal.
Tetracyclines are not recommended as they can discolour developing baby’s teeth.4
Clinical Information and New Antibiotics
Older antibiotics are usually prescribed as they are tested in pregnancy. For newer antibiotics, there is very little clinical information available regarding the effect on pregnancy and fetus as they are not tested. However, in some cases, despite the lack of formula testing and lack of evidence during pregnancy, obstetricians are faced with risks versus benefits choices if there are no other alternatives.
If the benefits of prescribing a new antibiotic during pregnancy outweigh the potential risks, the antibiotic in question is chosen.5
When choosing an antibiotic, physicians should consider the effectiveness, risk of adverse effects and resistance rates in the local community.
Regardless of which antibiotic is chosen for initial empiric therapy, the regimen should be revised as necessary after microbial culture susceptibility results are available.
The choice of antibiotic mainly depends on
How severe the infection is
Type of infection
Renal and liver function test
Dosing schedule
Other medications used
Common or even rare side effects
A history of having an allergy to a certain type of antibiotic
Quinolones, tetracyclines and aminoglycosides should be avoided in pregnancy, unless the infection is severe or life-threatening.6 (British National Formulary appendix 4: Pregnancy)
Because only a few controlled scientific studies have addressed whether drugs are safe to use during pregnancy, physicians usually rely on data from animal research and from the collective experience in practice to decide. In 1979, the US Food and Drug Administration (FDA) developed a classification system for drugs, including anti-infectives, and their potential harmful effects on an unborn child.
The FDA Drug Category System
The FDA list of pharmaceutical pregnancy categories helps doctors to know the prenatal safety of medications. The categories are A, B, C, D and X. Drugs within category A have been found to be safe for use in pregnant women, whereas drugs within category X have been found to be harmful to fetuses and should not be used by pregnant women.7
Antibiotics used during pregnancy should fall into either category A or category B on the FDA list.
Category A
Controlled studies fail to demonstrate a risk to the fetus in the first trimester and no evidence of risk in later trimesters. The possibility of fetal harm appears remote.
Category B
Animal reproduction studies have not demonstrated a fetal risk, but there are no controlled studies in pregnant women. Animal reproduction studies have not shown an adverse effect (other than a decrease in fertility), but which was not confirmed in controlled studies of women in the first trimester (and there is no evidence of risk in later trimesters).
Category C
Animal studies have revealed adverse effects on the fetus, and there are no controlled studies on women and animals available. Drugs in this category should be given only if the potential benefit justifies potential risk to the fetus.
Category D
There is positive evidence of human fetal risk, but the benefits of use in pregnant women may be acceptable despite the risk (serious disease for which safer drugs cannot be used or are ineffective).
Category X
Studies on animals or humans have demonstrated fetal abnormalities, or evidence of fetal risk based on human experience, or both. The drug should not be used by women who are or may become pregnant.
Birth defects associated with antibiotics defined within category X include anencephaly, choanal atresia (a blockage of the nasal passage), transverse limb deficiency, diaphragmatic hernia, eye defects, congenital heart defects and cleft palate.7
In general, unborn babies are most likely to be harmed in the first trimester of pregnancy. However, the use of sulfa antibiotics is safe in early pregnancy. Later in pregnancy, it can cause jaundice in the newborns and should not be used.
Effects of Antibiotics during Pregnancy
It is important to remember that the choice of an antibiotic relies on multiple factors, including the targeted organism, the possibility for resistance and the potential for adverse effect on pregnancy.
Metronidazole is now considered safe in most cases according to the new research.
Nitrofurantoin may be recommended for recurrent urinary tract infections and should be stopped at 36 weeks (or immediately if labour is imminent before). There is a small risk of baby’s red blood cells destruction if taken within a few days before delivery.
Trimethoprim should not be used during the first trimester. It blocks the effects of folic acid, which is crucial during pregnancy and preconception as it reduces the risk of developing neural tube and other birth defects.
Streptomycin can cause hearing loss in the baby, and tetracycline can discolour baby’s teeth.
