RENAL - Prescribing in Renal Disease Flashcards
(17 cards)
What are the main issues encountered in renal impairment?
- Reduced renal excretion/toxic metabolites
- Drug sensitivity increased - even if eliminstion is unimpaired
- Side efects can be tolerated poorly
- Some drugs just aren’t effective during renal impairment
Describe GFR
- Volume of fluid filtered from renal glomerular capillaries into Bowman’s capsule per unit time
- Measured using inulin (invasive, time-consuming and expensive)
Define creatinine clearance and how it is an overestimation of GFR
- Volume of blood plasma cleared of creatinine per unit time
- Uses serum creatinine - eliminated by TUBULAR SECRETION as well as glomerular filtration
How is creatinine formed and why is it generally higher in men?
- Breakdown product of dietary meat and creatinine phosphate found in skeletal muscle
- Higher muscle mass in men - 110-150ml/min (men) and 100-130ml/min (women)
Describe CKD-EPI
- Recommended method for estimating GFR and calculating drug doses in most patients with renal impairment
- Adjusted for body surface area and utilizes serum creatinine, age and sex as variables
- Routinely used by clinical laboratories to report eGFR
Describe the relationship between serum creatinine and creatinine clearance.
- Non-linear
- Serum creatinine increases as renal function decreases
How is eGFR altered at extremes of muscle mass?
- Reduced muscle mass (frailty, low BMI, amputees will lead to an over-estimation of GFR
- Increased muscle mass (body builders) will lead to an underestimation of GFR
- Creatinine Clearance or Absolute Glomerular Filtration Rate should be used to adjust drug doses in patients < 18kg/m2 or >40kg/m2
- The Cockcroft and Gault formula (Creatinine Clearance) is the preferred method for estimating renal function in >75 years
What is absolute GFR and how can it be calculated?
- Determined by removing the normalisation for BSA (Body Surface Area) from the eGFR
- GFR (Absolute) = eGFR x (individual’s body surface area/1.73)
How is ideal body weight calculated?
Ideal body weight (kg) = Constant + 0.91 (Height -152.4)
* Constant = 50 for men, 45.5 for women
What are some drugs requiring dose adjustment in patients with renal impairment?
- DOACs (Apixaban, Edoxaban, Rivaroxaban)
- Antibiotics such as the Cephalosporins
- Allopurinol (for gout prophylaxis)
- Diuretics
- NSAIDs
- Opioids
Give examples of nephrotoxic drugs leading to direct tubular toxicity and how do they do this.
GENTAMICIN
- Renal excretion leads too accumulation
- Gentamicin reaches 100x higher urine than serum concentration and accumulates in proximal renal tubular cells causing damage
Give examples of nephrotoxic drugs leading to hypersensitivity reactions and how do they do this.
PPIs can cause a chronic TIN
Antibiotics/NSAIDS can cause AIN
Vancomycin AIN
Give examples of nephrotoxic drugs leading to reduced blood flow and how do they do this.
NSAIDS
- Inhibition of prostaglandins
- Reduced GFR and AKI
Why are single doses or loading doses in patients with renal impairment often the same as in those with normal renal function?
- Problem lies in drug accumulation and significantly longer half-life
What are the 3 main approaches to altering drug administration in patients with renal impairment?
- Increase the interval between doses (e.g. administer once daily instead of twice daily)
- Decrease the dose
- A combination of dose reduction and extended interval
What are some ways some drugs can be less effective in renal impairment?
- Reduced activation of drugs by kidneys
- Increased sensitivity to certain medications - and therefore experience more side effects
What are some medications that should be withheld during AKI and why?
- Contrast media, ACE-inhibitors and Angiotensin Receptor Blockers (ARBs), NSAIDs, Diuretics
- Can exacerbate AKI
- Contrast media is not absolutely contraindicated but carries more risk of nephropathy in patients with pre-existing renal impairment
