3 - Renal Function

Question 1

Describe the stages of kidney function based on GFR?

Answer 1

• Stage 1 = normal or high; 90 and over
• Stage 2 = 60-90; mildly decreased
• Stage 3a = 45-59; mildly to moderately decreased
• Stage 3b = 30-44; moderately to severely decreased
• Stage 4 = 15-29; severely decreased
• Stage 5 = < 15; kidney failure

Question 2

What is creatinine?

Answer 2

By-product of muscle metabolism (result of creatine phosphate dephosphorylation)

Question 3

How is creatinine excreted?

Answer 3

Kidney, through glomerular filtration and active tubular secretion

Question 4

What happens to creatinine clearance and serum creatinine when kidneys aren’t functioning normally?

Answer 4

• Creatinine clearance decreases

- Serum creatinine increases

Question 5

At what level is eGFR valid up to?

Answer 5

60 mL/min/1.73 m^2

Question 6

What are some limitations to using equations to estimate renal function?

Answer 6

• Use only in adults (>18 y/o)
• Only valid if renal function is stable
• Not validated in px w/ “markedly abnormal body composition” (ex: extreme obesity, cachexia, paralysis, amputation, pregnancy)
• Estimation may be inaccurate in px following vegetarian diets, taking creatine supplements, or taking medications that inhibit tubular secretion of creatinine (ex: trimethoprim, fenofibrate)

Question 7

When would a 24 h urine collection be required to estimate GFR?

Answer 7

• Extremes of age and body size
• Severe malnutrition or obesity
• Disease of skeletal muscle
• Paraplegia or quadriplegia
• Vegetarian diet
• Rapidly changing renal function
• Pregnancy

Question 8

How do you determine if a medication requires dosage adjustments for renal dysfunction?

Answer 8

• In general, most renally eliminated medications will not need major dosage adjustments until px GFR falls below 50-60 mL/min/1.73 m^2
• Once they fall below this level, renally eliminated drugs may require dosage decreases or dosage interval increases

Question 9

What should be done for a drug w/ a narrow therapeutic index given to a pt will Clcr below 50-60?

Answer 9

More detailed calculations are needed to maintain efficacy and prevent toxicity

Question 10

Would hepatically metabolized drugs need a dosage change for renal dysfunction?

Answer 10

If they have active metabolites that are renally eliminated (renal dysfunction would cause the active metabolites to accumulate and cause toxicity)

Question 11

Which drugs require dosing adjustments w/ renal dysfunction?

Answer 11

• Saxagliptin
• Metformin
• Ramipril
• EC ASA
• Varenicline
• Gabapentin

Question 12

What are some drugs that can affect how you interpret serum creatinine?

Answer 12

• Septra
• Fenofibrate
• HCTZ (only if pt is severely dehydrated from the drug)

Question 13

What is important to note about colchicine for pt w/ renal dysfunction?

Answer 13

• Don’t repeat dose for at least 2 weeks b/c colchicine can accumulate in the joints
• For Clcr under 30, could give 0.3 mg for the next 3-5 days after initial dose to make sure the gout attack is cleared

Question 14

What is allopurinol used for?

Answer 14

• As prophylaxis for gout b/c decreases production of uric acid
• Generally recommended for px w/ more than 2 gout attacks per year

Question 15

What is the dosing of allopurinol for renal dysfunction?

Answer 15

• Clcr of 10-20 mL/min should use max 200 mg/day

- Want to start at 50 mg/day and increase every 2-5 weeks to achieve desired uric acid levels (less than 360 umol/L)

Question 16

What should be done when a pt is starting allopurinol therapy?

Answer 16

• Use an anti-inflammatory while allopurinol levels are rising (allopurinol may cause a flare when it is being initiated)
• Can do daily colchicine 0.3 mg for 3 months

Question 17

Describe the dosing changes required for saxagliptin if Clcr is 30-45 or if below 30. What other considerations need to be made?

Answer 17

• Clcr under 50 = 2.5 mg once daily
• If blood sugars are high, must alter other meds to fix it
• If dose isn’t changed, pt will start accumulating the drug and will have a higher chance of experiencing adverse effects

Question 18

Describe the dosing changes required for metformin if Clcr is 30-45 or if below 30.

Answer 18

• If pt has Clcr 30-45 before starting metformin, may begin at initial dose of 250 mg w/ close monitoring and titration (max 1000 mg/day)
• If pt Clcr falls between 30-45 during metformin therapy, consider risks and benefits; if continuing, dose reduction of 50% (max 1000 mg/day) is recommended w/ close monitoring
• Use contraindicated if Clcr under 30 b/c can cause lactic acidosis

Question 19

Describe the dosing changes required for ramipril if Clcr is 30-45 or if below 30.

Answer 19

• If starting an ACE inhibitor w/ Clcr under 40, max 5 mg/day
• If already on ACE inhibitor and Clcr starts to decrease, most of the time will leave it and monitor
• D/c if pt experiences hypotension, hyperkalemia, or rapid increases in serum creatinine; leave it if pt is still experiencing hypertension

Question 20

Describe the dosing changes required for ASA if Clcr is 30-45 or if below 30.

Answer 20

• Low dose aspirin has more risks than benefit, so normally not an issue
• Wouldn’t recommend taking aleve or advil

Question 21

Describe the dosing changes required for varenicline if Clcr is 30-45 or if below 30.

Answer 21

• Normal dose = 0.5 mg once daily for 3 days, then 0.5 mg BID for 4 days, then 1 mg BID for 12 weeks
• Clcr 30-45 = no dosing adjustment
• Clcr > 30 = initiate 0.5 mg daily; max dose 0.5 mg BID

Question 22

Describe the dosing changes required for gabapentin if Clcr is 30-45 or if below 30.

Answer 22

• Virtually 100% renally eliminated
• Clcr 30-45 = max dose 200-700 mg BID
• Clcr 15-29 = max dose 200-700 mg once daily
• Clcr 15 = 100-300 mg once daily