A newborn has developed jaundice and poor sucking. Which medication is likely responsible for this condition?

The medication most commonly associated with jaundice and poor sucking in newborns is sulfonamide. Sulfonamides can displace bilirubin from its binding sites on albumin, leading to increased levels of unconjugated bilirubin in the infant's bloodstream. This results in a higher risk of jaundice, as the infant's liver is still maturing and may not efficiently process the bilirubin. Poor sucking can also result from the overall effects of the drug on the infant's health and the potential for decreased feeding interest or lethargy.

While tetracycline, phenothiazine, and chloramphenicol may also have side effects, they are not typically linked to jaundice and poor sucking in newborns in the same way that sulfonamides are. Tetracycline can affect bone and teeth development and may have other impacts on neonates, phenothiazines can cause extrapyramidal symptoms, and chloramphenicol is known for serious toxicity, including grey baby syndrome, but sulfonamides stand out in this context for the specific symptoms mentioned.