Antibiotic Use in Older Adults: Common Side Effects and High-Risk Medications

Older adults frequently depend on antibiotics to treat bacterial infections, yet age-related physiological changes make them more vulnerable to medication-related complications. Declining organ function, multiple chronic conditions and the simultaneous use of several drugs increase the likelihood of adverse reactions. Understanding which effects are expected, which signal danger and which specific drugs pose heightened risks helps clinicians and caregivers manage treatment more safely.

The impact of aging on drug response

Aging is characterized by gradual loss of tissue mass and reduced physiological reserve. In practical terms, the liver metabolizes drugs less efficiently and the kidneys excrete them more slowly. These changes, combined with common comorbidities such as diabetes, heart failure and hypertension, alter how medications circulate and accumulate in the body. Because many people over 75 take several prescriptions simultaneously, interactions can amplify side effects that might be mild in younger populations.

How antibiotics work and why side effects develop

Antibiotics kill or inhibit bacteria responsible for infections of the throat, lungs, urinary tract, skin, eyes and ears. While these drugs remain essential for treating bacterial disease, they also disturb the balance of helpful microbes and interact with existing medications. Most patients experience only temporary issues such as nausea or stomach discomfort, yet roughly one third of high-risk older outpatients report notable side effects that require monitoring or intervention.

Adverse drug reactions versus side effects

Side effects are expected, generally mild responses that appear soon after therapy begins and usually resolve within days. An adverse drug reaction (ADR) is more serious, carries potential for long-term harm and often prompts discontinuation or substitution of the medication. The line separating the two becomes thinner in seniors because even minor symptoms—if combined with frailty, dehydration or impaired cognition—can escalate quickly.

Common side effects in older adults

Digestive tract issues: About one in ten seniors experiences vomiting, diarrhea, nausea, loss of appetite, stomach pain, indigestion or bloating. These symptoms tend to improve after the drug course ends, but severe fluid loss can lead to instability and falls.

Allergic reactions: Roughly one in five patients is sensitive to penicillins or cephalosporins. Typical manifestations include wheezing, coughing, sneezing, skin rash and throat tightness. Most reactions respond to antihistamines, yet any sign of airway compromise warrants immediate care.

Muscle, joint and bone complications: Between 10 % and 15 % of older recipients of fluoroquinolones, statins or proton pump inhibitors report muscle weakness (myopathy), joint pain or bone loss. High potassium or low sodium levels may produce irregular heartbeat, tingling or dizziness. Long-term use heightens the risk of fractures, peripheral neuropathy and gastrointestinal bleeding.

Factors that raise the risk of ADRs

• Inappropriate medication prescription (IMP): Under-, over- or misprescribing when safer alternatives exist.
• Diminished liver function: Slows metabolism of cardiovascular and other agents, allowing accumulation.
• Reduced renal clearance: Extends the half-life of many antibiotics and adjunct drugs.
• Comorbid conditions: Heart failure, diabetes and immune disorders modify drug distribution and effect.

Five medications older patients should approach cautiously

Levofloxacin and ciprofloxacin: These fluoroquinolones treat urinary, respiratory and skin infections. Potential problems include nerve damage, insomnia, dizziness, tendon pain and gastrointestinal discomfort. The U.S. Food and Drug Administration has advised limiting their use for uncomplicated urinary or sinus infections when other options are available. (See FDA safety communication at fda.gov.)

Non-steroidal anti-inflammatory drugs (NSAIDs): Ibuprofen, naproxen and aspirin can exacerbate hypertension, provoke peptic ulcers, trigger gastrointestinal bleeding and precipitate acute kidney injury, particularly in individuals older than 75.

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Zolpidem: Marketed for insomnia, this hypnotic increases drowsiness, dizziness and balance problems that contribute to falls, fractures and traffic accidents. Behavioral therapies or structured exercise programs generally offer safer alternatives for sleep disturbances in seniors.

Diphenhydramine (Benadryl): Although indicated for allergies, the medication’s anticholinergic properties may cause confusion, blurred vision, delirium and memory impairment. Because it is often purchased over the counter for sleep, unmonitored use is common.

Megestrol: Prescribed for appetite stimulation and certain cancers, megestrol is eliminated through the kidneys. Age-related renal decline can lead to drug accumulation and toxicity, making routine dosing unsuitable for many older adults.

Practical considerations for safer antibiotic therapy

When an infection is suspected, clinicians are advised to confirm bacterial etiology before prescribing antibiotics, avoiding their use for viral illnesses such as influenza or the common cold. Dose adjustments based on renal and hepatic function, shorter treatment durations and regular review of the full medication list help reduce complications. Patients and caregivers should report new symptoms promptly, even if the effects appear minor.

As populations age, balancing effective infection control with medication safety becomes increasingly complex. Vigilant prescribing, close monitoring and informed self-advocacy remain the cornerstones of minimizing antibiotic side effects in older adults.

Crédito da imagem: Elderly Care Systems