Aminopyridines/administration & dosage; Aminopyridines/pharmacokinetics; Analgesics/administration & dosage; Analgesics/pharmacokinetics; Kidney Diseases/physiopathology; Kidney/physiopathology; Administration, Oral; Adult; Age Factors; Aged; Aging/metabolism; Aminopyridines/adverse effects; Analgesics/adverse effects; Area Under Curve; Biomarkers/blood; Biomarkers/urine; Creatinine/blood; Creatinine/urine; Delayed-Action Preparations; Drug Administration Schedule; Drug Monitoring; Female; Glomerular Filtration Rate; Humans; Kidney/metabolism; Kidney Diseases/blood; Kidney Diseases/diagnosis; Kidney Diseases/urine; Male; Metabolic Clearance Rate; Middle Aged; Prospective Studies; Severity of Illness Index; Young Adult