Urinary Toxicology Flashcards
What are the 4 main functions of the urinary system?
- acid-base balance
- electrolyte balance
- ECF volume regulation
- metabolic waste excretion
What are the 4 major reasons that the urinary system is susceptible to toxicants?
- high blood flow coupled with small size - 25% CO (90% to renal cortex, 6-10% to medulla)
- high metabolic demand - 10% of body’s oxygen demand that the active transport of the kidney relies on (PT most susceptible)
- processes involved in concentrating urine also concentrate toxicants - countercurrent mechanism
- metabolic activation of xenobiotics by enzymes within the renal tubular epithelium
What are the renal function markers? When are they affects?
BUN and creatinine
50-70% of nephrons must be damaged before BUN and creatinine elevate
What is the difference between mild renal toxicity and acute renal failure?
MILD - renal function continues using reserve capacity with minimal alterations found on urinalysis (isothenuria, proteinuria) and is completely reversible
ARF - decreased GFR manifests with increased BUN and creatinine, glucosuria, azotemia, aminoaciduria, oliguria/anuria, renal enlargement, and pain + PD/PU, nausea, vomiting
What are the systemic sequelae of acute renal failure? Is it reversible?
dehydration and metabolic acidosis
YES - with appropriate treatment
What is chronic renal failure? What is it characterized by? Is it reversible?
progressive deterioration of renal functions with exhaustion of reserve capacity resulting from long-term exposure to toxicants
PU/PD, isosthenuria, increased BUN and creatinine, uremia, dehydration
frequently irreversible and progresses to end-stage renal disease (ESRD) with permanent loss of renal function
What causes ethylene glycol toxicosis?
ingestion of the colorless, odorless, sweet-tasting liquid found in antifreeze, windshield de-icing agents, brake and transmission fluids, polishes, and photographic/paint solutions
When is ethylene glycol toxicosis most common? What species are most affected? Which are the most sensitive?
fall, winter, spring
dogs*, cats, birds
CATS - high baseline production of oxalic acid
Why is ethylene glycol toxicity so common?
- abundance in households coupled with lack of public awareness of its high potential for toxicity
- palatability: somewhat pleasant taste; dogs likely will not consume if water is available
- low lethal dose
What can delay GI absorption of ethylene glycol?
if food is present in the lumen
What are the 4 steps of ethylene glycol metabolism?
- ethylene glycol is oxidized by alcohol dehydrogenase (ADH) into glycoaldehyde —> 1st rate-limiting step
- glycoaldehyde is more toxic than EG, but it dose not accumulate and is readily metabolized by mitochondrial aldehyde dehydrogenase and cytosolic aldehyde oxidase into glycolic acid and glyoxal —> 2nd rate limiting-steps
- glycolic acid is more toxic, but has a short half-life and is metabolized into oxalic acid via oxidation of glycolic acid oxidase/LDH, formic acid, glycine, and α-hydroxy-β-ketoadipate by conjugation with α-ketoglutarate
- oxalic acid is then excreted in the urine and combine with calcium to form calcium oxalate that is deposited into the renal tubules, brain vasculature, and other tissues
What are the 5 mechanisms of toxicity of ethylene glycol?
- GI tract irritation by EG and calcium oxalate
- CNS depression by EG, glycoaldehyde, and calcium oxalate
- induction of metabolic acidosis and electrolyte imbalances
- cytotoxicity by the production of ROS due to CYP450 inhibition
- mechanical damage by calcium oxalate crystals
What are the 3 stages to ethylene glycol toxicity?
- CNS
- cardiopulmonary/acidotic
- renal toxicity
What are the 2 main toxic principles that causes CNS signs in ethylene glycol toxicity?
mostly EG and aldehydes, but high levels of glycolic acid may also cause CNS effects
Other than CNS signs, what are 4 other signs of stage I of ethylene glycol toxicosis?
- mimics acute alcohol toxicosis
- GIT irritation
- EG increases serum osmolarity, leading to PD/PU
- EG has an osmotic diuretic effect (like ethanol) and may inhibit release of ADH
What are the major clinical signs associated with stage I of ethylene glycol toxicosis?
CNS EFFECT
- inebriatioin and belligerance
- depression, loss of withdrawal and righting reflexes
- progressive ataxia with knuckling over and stumbling
- osmotic diuresis, PD/PU
- hypothermia
- nausea and vomiting due to gastric irritation
What causes stage II of ethylene glycol toxicosis?
CADIOPULMONARY/ACIDOTIC
- accumulation of acidic metabolites, especially glycolic acid
- calcium sequestration as calcium oxalate causes hypocalcemia and impairment of cardiac function