Does a patient with tongue numbness after taking levofloxacin (levofloxacin) require a kidney function evaluation?

Tongue Numbness After Levofloxacin: Kidney Evaluation

Tongue numbness following levofloxacin administration represents a neurological adverse effect rather than a renal complication, but kidney function evaluation is still warranted because levofloxacin is 80% renally eliminated and renal impairment increases the risk of CNS toxicity through drug accumulation.

Understanding the Adverse Reaction

Neurological Manifestation

• Tongue numbness is a recognized neurological adverse effect of fluoroquinolones, similar to the circumoral paresthesias commonly seen with streptomycin 1
• Levofloxacin can cause various CNS effects including dizziness, tremor, involuntary movements, and dysarthria, occurring in approximately 0.5% of patients 1
• Case reports document orofacial dyskinesia, involuntary tongue movements, and other neurological symptoms with levofloxacin, particularly in elderly patients with renal insufficiency 2, 3

Mechanism of Toxicity

• Fluoroquinolones inhibit γ-aminobutyric acid (GABA) receptors and activate N-methyl-D-aspartate (NMDA) receptors in the CNS, leading to neurological symptoms 2
• These effects are concentration-dependent and more likely when drug levels accumulate 3

Why Kidney Evaluation Is Necessary

Renal Elimination Profile

• Levofloxacin is 80% cleared by the kidneys as unchanged drug through both glomerular filtration and tubular secretion 1, 4, 5
• Renal clearance ranges from 96 to 142 mL/min in patients with normal kidney function 4
• The plasma elimination half-life extends from 6-8 hours in normal renal function to substantially longer in renal impairment 4

Risk Factors for Accumulation

• Creatinine clearance <50 mL/min requires dosage adjustment to prevent drug accumulation 1, 4
• Age-related decline in renal function increases risk, even when serum creatinine appears normal 4, 6
• Case reports show neurological toxicity correlating with elevated serum levofloxacin levels in patients with unrecognized renal impairment 3

Clinical Evidence

• In one reported case, a 67-year-old patient developed tremor, chorea-like movements, and visual hallucinations with a serum levofloxacin level of 3.6 mcg/mL 3
• An 85-year-old patient with slight renal impairment on chronic levofloxacin developed dysarthria and involuntary movements, with serum level of 2.55 mcg/mL and CSF level of 1.12 mcg/mL 3
• Both cases resolved completely after drug discontinuation 3

Recommended Evaluation

Immediate Actions

• Discontinue levofloxacin immediately upon recognition of neurological symptoms 2
• Measure serum creatinine and calculate creatinine clearance using the Cockcroft-Gault equation 1
• Assess for other risk factors: advanced age (>60 years), concurrent medications affecting renal function, dehydration 4, 6

Baseline Kidney Function Assessment

• Calculate creatinine clearance rather than relying on serum creatinine alone, as elderly patients may have reduced renal function despite normal creatinine due to decreased muscle mass 4
• If CrCl is <50 mL/min, the patient was likely receiving an inappropriately high dose 4
• Document whether proper dose adjustment was made: for CrCl 20-49 mL/min, dosing should be reduced to 750-1000 mg three times weekly 1

Monitoring Considerations

• Renal function should be monitored at least yearly in patients on fluoroquinolones, or more frequently (every 1-6 months) if CrCl <60 mL/min 1
• Elderly patients are at higher risk for both renal impairment and CNS toxicity and require closer monitoring 4, 6

Clinical Pitfalls to Avoid

• Do not assume normal renal function based on serum creatinine alone in elderly or low-muscle-mass patients 4
• Do not restart levofloxacin without confirming adequate renal function and implementing appropriate dose adjustment 4
• Recognize that neurological symptoms may be mistakenly attributed to old age rather than drug toxicity 6
• Be aware that symptoms can occur even with "therapeutic" doses if renal clearance is impaired 3

Alternative Management

• If continued fluoroquinolone therapy is necessary and renal function is impaired, consider moxifloxacin (not renally eliminated) as an alternative, though long-term safety data are more limited 1
• For patients with CrCl <50 mL/min requiring levofloxacin, reduce frequency to three times weekly while maintaining the mg/kg dose 1