Baclofen toxicity in a patient with subclinical renal insufficiency

Baclofen, a centrally acting gamma-aminobutyric acid agonist is a commonly used pharmacotherapy for spasticity of spinal origin. It is primarily excreted by glomerular filtration with a clearance proportional to creatinine clearance. We describe a 39-year-old quadriplegic women who, over a 16-week period, developed clinical signs of baclofen toxicity confirmed by progressively rising serum baclofen levels while on a conventional stable dosing regimen. During this period blood urea nitrogen and creatinine concentrations were normal and stable (9mg/dL and 0.8mg/dL, respectively). However, creatinine clearance values were consistently low (55 to 60m/min), suggesting renal insufficiency as the underlying cause. After a decrease in baclofen dosage, evidence of baclofen toxicity resolved. Clinicians should be alert to signs of evolving baclofen toxicity even in patients on an apparently stable regimen. Baclofen dosage adjustments based on systemic baclofen level may play a role in optimizing the clinical management of spasticity.