Dr Phil Kieran: My teenage daughter is listless after antibiotic

Fatigue is one of those symptoms which is incredibly hard to pin down medically. Picture: iStock 

My 13-year-old daughter had a chest infection recently and needed an antibiotic. Though the medication seems to have worked, she is quite listless and has difficulty getting out of bed in the morning. Could this be a reaction to the antibiotic or a lingering effect of the infection?

Fatigue is one of those symptoms which is incredibly hard to pin down medically. Hundreds of variables can contribute to tiredness or low motivation and more often than not we feel significant fatigue not due to any one factor but because many are activated at the same time.

I usually try to classify fatigue or listlessness by the degree to which it is restricting the person. If someone is tired and has difficulty getting up in the morning but still manages to go to school or work, the fatigue isn’t as problematic as it would be for someone who can’t.

In your daughter’s case, the most important question is how long it since her infection occurred? If she were quite sick and only finished the antibiotics a week ago, I wouldn’t be worried that she is still not back to herself fully yet. 

Her body is continuing to divert resources to recover from the infection and her energy levels should return to normal within a week or two. I would be reassured if she had more energy day by day (even if it is a slow increase) and would encourage her to be active when she can, without overdoing it. 

Teenagers may be keen to get back to sport, but may over-exert themselves — waiting until they recover will be more beneficial long term.

If the infection started a number of weeks ago and her recovery seems very static or even getting worse, then I would suggest a review appointment with her GP. 

In this case, I would consider blood tests to see if she has an underactive thyroid, low iron levels, or any signs that what she actually had was glandular fever rather than a bacterial chest infection (there can be significant overlap in symptoms and findings on examination). If all of these were clear, then in most cases, the fatigue will settle down by itself.

Post-infection fatigue syndromes are a complex and variable group of conditions which are still poorly understood. They are defined by severe and often debilitating fatigue, post-exertional malaise (where you feel sick or have a “crash” after minor exertion) and significant brain fog. 

They can follow an unpredictable course and, unfortunately, don’t have any guaranteed treatments.

Antibiotics are amazing medical tools, but also come with a price. They can alter gut bacterial flora, which, in turn, can affect mood and energy levels.

This is one of the reasons we are reluctant to give antibiotics “just in case” as there is a potential harm to using them. These gut bacteria changes will recover, and making sure you eat a healthy diet rich in fibre could help speed up this recovery.

Most fatigue after an infection is short-lived and passes with rest.

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