MCAT

MCAT is a mnemonic device to help clinicians recall antibiotics that should be avoided during pregnancy. Antibiotics are a class of medications used to treat bacterial infections. During pregnancy, they are most commonly prescribed to treat asymptomatic bacteriuria and urinary tract infections (UTIs), as well as to prevent neonatal infections caused by vaginal-rectal group B streptococcus colonization. 

Like with any other medication, the benefit of antibiotic treatment in pregnancy should be weighed against the potential risks to the fetus. To aid in this decision, the Food and Drug Administration (FDA) classifies medications into five different pregnancy categories. Class A and B medications are considered safe to take during pregnancy. Class C and D medications may present a risk to the fetus but may be used if treatment outweighs the risk. Finally, class X medications are contraindicated during pregnancy as they have a proven risk of causing birth defects in unborn babies.  

In addition to the type of antibiotic, the choice of treatment should consider other factors like the trimester of pregnancy, the dose and duration of treatment, and the ability of the medication to cross the placenta. Generally, it is best to avoid therapy during the first trimester of pregnancy when fetal organs are still developing. When possible, antibiotic treatment should be started once the infection is confirmed and be adjusted based on sensitivity tests. Finally, it is preferable to use antibiotics that have been studied for use in pregnancy and to use the lowest effective dose regardless of the chosen treatment.  

The “C” in MCAT stands for chloramphenicol (FDA class C). Due to its severe toxicity, chloramphenicol is no longer used systemically in most countries with access to safer antibiotics. Nonetheless, it is still used in the form of eye ointments to treat bacterial conjunctivitis.  

The main side effect of chloramphenicol is toxicity to the bone marrow, which can lead to anemia and other blood disorders. In newborns, chloramphenicol use can lead to "gray baby syndrome”, where the newborn is anemic and cyanotic, meaning their skin is a pale or grayish-blue color, due to poor oxygenation. This condition occurs because infants, especially premature infants, have immature liver enzymes that cannot metabolize the medication effectively, leading to its accumulation.