10.6 Pharmacology and the Kidneys

Question 1

What equation do we use to determine someone’s GFR (and therefore, if someone has renal impairment) when prescribing medications? What does it take into account?

Answer 1

• Cockcroft-Gault equation
• Takes into account body weight, serum creatinine, and gender

(ABC = Age, Bodyweight, Creatinine)

Question 2

The Cockcroft-Gault equation is unreliable when…

Answer 2

• The patient is at either extreme of bodyweight
• Renal function is changing rapidly

Question 3

Effect of renal impairment on pharmacokinetics (i.e. what the body does to a drug)

Answer 3

• Clearance rate decreases w/ GFR
• Therefore, drugs and subsequent metabolites from drugs stay in the body for longer

Question 4

What are 4 different ways that drugs can alter pharmacodynamics (e.g. drug actions independent of conc) in chronic renal failure?

Answer 4

1. Giver worse adverse effects regardless of conc (worsen complications of CRF, such as hyperkalaema [K sparing diuretics], oedema [NSAIDS], anticoagulation associated w/ uraemia [anticoags/antiplatelets]
2. Drugs may not work without renal clearance (e.g. some diuretics, UTI antibiotics that need to be in the urine)
3. Transient reduction in GFR from hypotension/volaemia
4. Actual nephrotoxicity

Question 5

Give some examples of nephrotoxic drugs

Answer 5

• Aminoglycosides (e.g. gentamicin)
• NSAIDs (interstitial nephritis, nephrotix syndrome)
• Radiocontrast agents

Question 6

Give some examples of drugs that cause a transient reduction in GFR

Answer 6

• Frusemide (diuretic effect)
• Intereference with prostaglandin/ag2 arteriole dilation (e.g. NSAIDs, ARBs, ACEIs)

Question 7

How can drugs falsely cause renal impairment in terms of a certain blood test?

Answer 7

• Drugs which compete w/ creatinine for secretion can elevate serum creatinine, causing apparent (but not necessarily real) renal impairment