Chronic kidney disease (CKD) can significantly impact medication clearance and increase the risk of drug toxicity. Three medications I frequently think about in patients with declining renal function are gabapentin, allopurinol, and digoxin. Here are three case scenarios that represent examples I’ve seen in practice.
- Gabapentin: A 78-year-old patient with CKD has been taking gabapentin 300 mg three times daily for neuropathy. Their eGFR declines to 22 mL/min, but the dose is never adjusted. The patient develops confusion, excessive sedation, and an increase in falls. Gabapentin is eliminated unchanged by the kidneys, and accumulation can cause significant CNS toxicity (excellent board exam nugget). Doses and dosing intervals should be reduced based on declining renal function.
- Allopurinol: A 74-year-old patient with CKD is started on allopurinol 300 mg daily for gout. Within several weeks, they develop a widespread rash, fever, and elevated liver enzymes. Allopurinol is metabolized to oxypurinol, which is primarily eliminated by the kidneys. CKD is an important risk factor for allopurinol hypersensitivity syndrome, a potentially life-threatening reaction. Starting at a low dose and carefully titrating therapy is important.
- Digoxin: An 84-year-old patient taking digoxin for atrial fibrillation develops worsening renal function. They begin experiencing nausea, poor appetite, weakness, and a slow heart rate. Digoxin is primarily eliminated by the kidneys and has a narrow therapeutic index. Accumulation can cause gastrointestinal, neurologic, and potentially life-threatening cardiac toxicity. Renal function, electrolytes, heart rate, and digoxin concentrations should be monitored.
The clinical takeaway is simple: declining kidney function can turn previously tolerated medication doses into potentially toxic regimens. Pharmacists should routinely review renal function and reassess medication dosing to prevent avoidable adverse drug events.
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