6 Adverse Effects and Safety

Responding to safety concerns

Anti-infective toxicity can affect the kidneys, hearing, tendons, blood cells, liver, heart rhythm, or nervous system. Before treatment, check for interactions and patient-specific risks; monitor tests appropriate to the medicine. Patients should promptly report severe or new symptoms and check with a clinician or pharmacist before adding medicines or supplements.

Follow the prescriber's instructions. Do not change or stop a treatment on your own unless emergency guidance tells you to; some specific warning signs, such as serious fluoroquinolone symptoms, require stopping the medicine and promptly contacting the prescriber for advice.

Aminoglycoside toxicity

Tinnitus, dizziness, and worsening renal function in a patient receiving gentamicin can signal ototoxicity and nephrotoxicity. Promptly notify the prescriber; anticipate reassessment of the dose or treatment and renal function. Monitoring may include drug levels, renal function, and hearing when appropriate. Toxicity may require dose adjustment or discontinuation.

Fluoroquinolone warning signs

Sudden Achilles tendon pain during ciprofloxacin treatment is a warning sign. Tendon pain or swelling can be a serious fluoroquinolone adverse effect. FDA advice is to stop fluoroquinolone treatment for serious tendon, muscle, joint, or nerve symptoms and promptly contact the prescriber for advice about switching to a non-fluoroquinolone when possible. Tendon injury risk is especially important to consider in patients using corticosteroids.

Metronidazole and warfarin

Metronidazole can increase warfarin's anticoagulant effect, so prothrombin time and INR require careful monitoring as directed. New unusual bruising or bleeding should be reported promptly; patients should not independently stop warfarin or change its dose.

Avoid alcohol and products containing propylene glycol during metronidazole treatment and for at least three days after the course.

Acyclovir and kidney safety

Intravenous acyclovir can cause renal injury. Risk is increased by dehydration, pre-existing renal impairment, or other nephrotoxic medicines; poor oral intake and reduced urine output therefore raise concern. Adequate hydration, renal-function monitoring, and dose adjustment when indicated help reduce risk.

Fluconazole interactions

Fluconazole can increase prothrombin time in patients taking warfarin and can amplify QT-prolonging effects of some medicines, including amiodarone. The care team should review these combinations and determine appropriate monitoring. Liver injury is another important potential concern.

Primaquine precautions

Primaquine can cause hemolytic anemia in people with G6PD deficiency. Quantitative G6PD activity testing is recommended before starting primaquine to prevent relapse of Plasmodium vivax malaria. Pregnancy is also an important precaution.

Amphotericin B and digoxin

Amphotericin B can impair renal function and lower potassium and magnesium. Rising creatinine and low potassium or magnesium warrant attention, particularly when the patient also takes digoxin: low potassium can increase digoxin toxicity and cardiac risk. Monitor renal function, electrolytes, and cardiac status.

Linezolid and serotonergic medicines

Serotonin syndrome, including fatal cases, has been reported when linezolid is used with serotonergic medicines such as SSRIs. The combination requires prescriber review and, if used, careful monitoring for agitation, confusion, tremor, sweating, or fever.

Diarrhea during or after antibiotics

Antibiotic exposure, especially clindamycin, can increase the risk of Clostridioides difficile infection. A patient with frequent watery or significant diarrhea during or after antibiotics should contact a healthcare professional promptly, even if the treatment course has ended. Do not take anti-diarrheal medicine without professional advice.

• QT prolongation