Prescribing in renal impairment

• some drugs cause nephrotoxicity
  • e.g. NSAIDs causing interstitial nephritis
• some drugs are renally excreted
  • e.g. vancomycin
• some drugs are both
  • e.g. gentamicin
• some drugs are ineffective
  • bendroflumethiazide, nitrofurantoin
    • anitbacterial efficacy of nitrofurantoin based on renal secretion into UT

• use eGFR b/c Cr is crude and may be incorrect
  • use MDRD formula- useses Cr, adjusts for age, sex, ethnicity
• BNF states cautions/contrainidcation based on degree of impairment:
  • stage 1= >90mL/min/1.73m^2 w/ other evidence of kidney damage
  • stage 2= 60-89 w/ other evidence
  • stage 3= 30-59
  • stage 4= 15-29
  • stage 5 (renal failure)= <15

• aminoglycosides
  • nephrotoxic- use w/ extreme caution
• metformin
  • incr risk of lactic acidosis
• nitrofurantoin
  • not effective if GFR= <45 ml/min
• potassium supplements/potassium sparing diuretics
  • risk of hyperkalaemia
• lithium
  • reanlly excreted with narrow therapeutic range (careful monitorring needed if used)
• NSAIDs
  • avoid in CKD
  • can exacerbate fluid overload and oedema

generally renal patients are more at risk of ADR

• goal is to prevent further injury and facilitate recovery of renal function
  • asses circ vol and fluid administration
  • prevent/treat hyperkalaemia and metabolic acidosis
  • discontinue nephrotoxic drugs
  • adapt dose of renally excreted drugs 
    • reduce dose sizes/incr dose interval
  • supportive measures 
    • diuretics etc