12 - Nephrology in the Podiatric Patient Flashcards
What do you NEED to focus on for this lecture?
- Appropriate dosing and adverse side effects of aminoglycosides.
- Mechanism, risk factors and prevention of contrast induced renal failure.
What are the typical aminoglycosides used in podiatric medicine?
- Gentamicin (Garamycin)
- Tobramycin (Nebcin)
- Amikacin (Amikin)
6 licensed in US, but these 3 have indications for LE infections
Gentamicin is used 90% of the time
- A lot of physicians shy away from this because there are fewer side effects and fewer renal impacts, but are a lot more expensive
What are the adverse reactions we see with aminoglycoside use?
- Nephrotoxicity
- Ototoxicity
- Neuromuscular Blockade
Ototoxicity is IRREVERSIBLE ***
Describe the nephrotoxicity seen with aminoglycoside use
- Most feared side effect***
- Usually begins several days after therapy started - may begin sooner or after medication discontinued
- First sign - increase in serum creatinine (but damage may already be done***)
- Usually reversible
- Increased risk when used with Vancomycin
- Don’t combine gentamicin and vanco (nephrotoxicity is increased)
Describe the ototoxicity seen with aminoglycoside use
- Most devastating side effect
- Generally irreversible
- Can manifest as auditory toxicity (feeling of fullness in ears, tinnitus, loss of acuity-high frequency)
- Can manifest as vestibular toxicity (dizziness and nausea, poor balance)
Describe the neuromuscular blockade seen with aminoglycoside use
- Excessive levels of antibiotic accumulate at neuromuscular junction which inhibits acetylcholine release and paralysis results.
- Usually due to rapid administration via IV bolus
Aminoglycosides always infused over 30 minutes
Red man syndrome: massive histamine release
Describe the administration of aminoglycosides
- All parenteral, not absorbed in stomach
- Correlation between dosing and side effects
- Patients that need aminoglycosides usually have many medical conditions
Describe the dosing of aminoglycosides
Aminoglycosides require a loading dose regardless of renal function
- Gentamicin and Tobramycin - 2 mg/ kg
- Amikacin - 7.5 mg/ kg
Maintenance dose is calculated based on renal function. Normal renal function:
- Gentamicin and Tobramycin 3 - 5 mg/kg/day q 8 - 12 h
- Amikacin 15 mg/kg/day q 12 h
So, loading dose is the SAME for everyone, but the maintenance dose is dependent on RENAL function ***
Don’t need to know the actual doses, but should know how it changes for renal function
How do you convert pounds to kg?
1 kg = 2.2 lbs ***
Need to know this for the exam
What is the cockcroft and gault formula?
Creatinine clearance = [(140-age) x weight in kg]/[serum creatinine x 72]
For women, multiply this by 0.85
Normal = 100% or 1.0
It is actually lean body mass, but we don’t test that in the hospital
NEED to know this for renal PBL*** (What impact does age have? What impact does weight have? - Renal function decreases as age increases)
How do you determine the peak and troughs for aminoglycosides?
- Used to determine blood levels
- Usually drawn after third dose
- Peak drawn immediately after dose
- Trough drawn 20-30 minutes before next dose
- Peak is dose dependent
- Trough is time dependent
What does peak depend on?
DOSE
What does trough depend on?
TIME
What should you do if the peak is high and the trough is normal?
Decrease the dose
Timing is okay
What should you do if the peak is low and the trough is normal?
Increase the dose
Timing is okay
What should you do if the peak is normal but the trough is high?
Increase the time (q12 hrs rather than q8 hrs)
Dose is okay
What should you do if the peak is normal and the trough is low?
Decrease the time (q6 hrs rather than q8 hrs)
Dose is okay
Describe the clinical use of aminoglycosides
- Low cost, but safer agents are available
- Severe gram negative infection or sepsis
- Combination with a ß-lactam
- Triple agent combination with a ß-lactam and antianaerobic agent for shotgun therapy for severe diabetic foot infection
What is triple antibiotic combination?
Broad spectrum approach
- Put a patient on one broad spectrum antibiotic initially
- Once you identify the organism, then you narrow your focus
Triple antibiotic approach
- The theory of triple antibiotic coverage (gram positive, gram negative, anarobe bacteria)
- Then, based on your culture, you take them off what they don’t need
- This way you never start a new antibiotic, you just take off what they don’t need
- This is a cheaper method
- Will need to pay attention to creatinine clearance with this method
Describe a urinary tract infection in podiatric patients
Not on exam
NOT tested on this
- Common cause of post-op fever
- Usually occurs around 2 day
- Check urinalysis for presence of leukocytes
- Check CBC or take urine culture
- Always check wound
Describe a fever in the hospital
Following urgery - Benign post-op fever (from anesthesia) Day 1 - Wind (pneumonia) Day 2 - Water (UTI) Day 3 - Wound (post-op infection) Day 4 - Walk (DVT)
Others: medications, constipation
Describe radiographic contrast agents and ARF
- Increases plasma volume
- Osmotic diuresis
- Increase in uric acid and oxalate excretion
- ARF in 24-48h after diuresis in some patients
- Creatinine peaks 3-5 days and returns to normal in 10-14 days
Describe acute renal failure due to radiographic contrast agents
- Pathology occurs in proximal tubule due to intra-tubular obstruction
- Can lead to Acute tubular necrosis
Incidence
- 0-12%
-
What are the risk factors for contrast induced ARF?
KNOW THESE
- **Definite Risk Factors
- Pre-existing renal insufficiency
- Diabetes Mellitus
- **Probable Risk Factors
- Dehydration
- Prior contrast induced ARF
Possible risk factors
- Large contrast load
- Advanced age
- CHF
- Vascular disease
- Proteinuria
- Hyperuricemia
What is the incidence of ARF in diabetic patients
Normal Renal Function 0%
Moderate Renal Insufficiency 1.5-2.0 mg/dl –> 50-76%
Severe Renal Insufficiency > 4.5 mg/dl –> 92-100%
Describe the treatment of contrast-induced ARF
- Once ARF has developed, treatment is usually unsuccessful (with dialysis)
- Emphasis placed on prevention (with hydration)
How do you prevent contrast-induced ARF?
- Identify patient at risk
- Avoid study if feasible
- Hydrate - does not really prevent, but may minimize severity***
- Minimize contrast load
- Avoid repeated studies
Describe the study on the role of osmolality in the incidence of contrast-induced nephropathy
- Level 2 – review of randomized controlled studies
- 1365 patients
- 16.8% incidence in nephropathy
- Iso-osmolality and low-osmolality contrast showed no difference
Different types of contrast didn’t change risk of ARF
Their recommendation is to focus on HYDRATION***
Remember: hydrate, hydrate, hydrate***
