Toxicology Flashcards
Toxidrome
signs and symptoms that are characteristic of a toxic substance ingestion
Anticholinergic toxidrome
“red as a beet, dry as a bone, blind as a bat, mad as a hatter, and hot as a hare”
Combative and delirious Tachycardic Dry mucus membranes and dry skin Pupils dilated, non-reactive Diminished bowel sounds, distended bladder
Anticholinergic differential diagnosis
Antihistamines Tricyclic antidepressants Phenothiazines (anti-psychotic) Belladonna alkaloids (atropine, scopolamine) Certain mushrooms
What is Clinical Toxicology?
Determination of the presence of toxic materials as a reason for illness or symptoms
Ordered by a physician for medical care
- –Negative screen suggests other cause for signs/symptoms
- —Positive screen relevant if consistent with signs/symptions
Broad coverage drugs of abuse prescription drugs OTC drugs household or industrial poisons plants
Urine (best), blood, gastric, meconium, oral fluid (saliva-forensic, pre-employment)
Rapid result turnaround
Reduced level of proof (accuracy)
Which tests should be rapid (
Acetaminophen-Tylenol
Salicylates-Aspirin
Ethanol
Iron (ideally with U[T]IBC or transferrin)
Dig, CBZ, VPA, Phenobarb, Theo, Li, Phenytoin
COHgb and metHgb by CO-Oximeter
Methanol and ethylene glycol (2-4 hr TAT) – —-not common
Urine drugs of abuse (qualitative by immunoassay)
—-Cocaine, opiates, barbiturates
—-Amphetamines, propoxyphene, PCP, tricyclics if prevalent in area
What is Forensic Toxicology?
Determination of the presence of toxic materials as they pertain to legal matters
Post-mortem – determination of cause of death
-Blood, urine, tissue – quantitation (blood, tissue) common
Driving – EtOH and possibly others
Drugs of abuse –compliance with legal limits
-Probation
-Pre-employment (esp. Federal)
-Limited menu of drugs in urine, oral fluid, sweat
Onerous requirements and regulations common
-Chain of custody
-Testimony may be required
Acetaminophen
Active ingredient in Tylenol® and many other “non-aspirin pain relievers”
—Component of “multi-symptom” cold meds
Overdose can lead to irreversible and fatal hepatic failure
One of few drugs with specific antidote:
N-acetylcysteine (Mucomyst)
100% effective when given w/in 8 hrs of ingestion
How is Acetaminophen metabolized?
Usually via glucuronidation, and sulfation sometimes to a quinone
How is Acetaminophen Toxicity assessed?
Rumack nomogram >200 mg/L @ 4 hr Probable risk >150 mg/L @ 4 hr possible risk T1/2 >4 hrs bad sign Samples before 4 hrs may not reflect peak & would under-estimate risk
Acetaminophen Measurement?
Immunoassay Enzymatic Arylacylamidase plus o-cresol condensation (blue) Positive interference from bilirubin Therapeutic range: 10-20 mcg/mL
Urine spot screening can detect routine use, not just overdose situations (potential clinical false positive)
—-Not recommended – serum quantitation needed
Salicylates
Aspirin – acetylsalicylic acid (ASA)
Was once the leading cause of childhood poisoning
Rapid hydrolysis to salicylate (active metabolite)
Salicylic acid – keratolytic gels
Oil of wintergreen (methyl salicylate)
enhanced toxicity due to inc. CNS penetration
Salicylamide – not hydrolyzed to salicylate
Salicylate Toxicity
Uncouples oxidative phosphorylation
metabolic acidosis
hyperthermia
CNS stimulation
hyperventilation
respiratory alkalosis
Tinnitus – ringing ears
Done nomogram more
controversial
Beware units
mg/dL vs mcg/mL (mg/L)
Salicylate measurment?
Trinder’s reaction Most common (cheap and stable rgt) Fe3+ complexes with salicylate Req. serum blank due to non-specificity 2-3 mg/dL common Salicylamide does not react (not hydrolyzed)
Immunoassay
Enzymatic – salicylate mono-oxygenase
Ethanol
Most commonly abused drug
10 mg/dL = 0.01% (w/v)
0.08% (80 mg/dL) is legal limit in all states
Legal limit defined in terms of (whole) blood alcohol concentration (BAC), not S/P
May be lethal in naive drinkers at 400 mg/dL
Ethanol Distribution and Metabolism
Distributes in total body water
plasma/serum – 93-95% H2O
rbc – 70-75% H2O
whole blood – 85% H2O
S/P EtOH = 1.14 (1.09-1.18) x BAC
Metabolism is zero order (when >20 mg/dL)
15 (11-22) mg/dL/hr in males
18 (11-22) mg/dL/hr in females
rate increases with continued alcohol use
Medical ethanol results may be used in forensic situations, whether you like it or not
Ethanol Measurement
Enzymatic – alcohol dehydrogenase
Ethanol + NAD+ ------> Acetaldehyde + NADH
Linearity 10 – ~600 mg/dL (variable)
Beware evaporation in open tubes/cups (esp. calibrators or controls that sit)
Iron
Corrosive – GI hemorrhagic necrosis
Shock, acidosis improvement liver failure
Maximum serum levels at 4-6 hrs post ingestion
500 µg/dL – serious toxicity likely
>1000 µg/dL – may be fatal
Trf sat’n >100% indicates free iron, likely toxicity
Deferoxamine chelation – “vin rosé” urine
affects iron assays – wait 4 hrs
Stat availability required
UIBC/TIBC probably optional but desirable
Carbon Monoxide
Colorless, odorless, tasteless gas Density ≈ air (0.97 @20°C) Formed from: incomplete combustion smoking heme metabolism (↑ in in vivo hemolysis)
Binds reversibly to Hgb:O2 binding site Hgb:CO affinity ≈ 250x Hgb:O2 affinity Hgb:CO binding also inc. Hgb:O2 affinity Decreased delivery to tissues CO also binds to Mgb and cytochrome a3 CO reference ranges: rural non-smoker :
CO measurement
CO-Oximeter multi-wavelength spectrophotometer associated w/ blood gas instrument hemolyzer very short path length cuvet matrix coefficient calculation of: HgbO2, HHgb (deoxy), COHgb, metHgb Results presented as % of total Hgb Rarely (usually post-mortem) measured by GC Decomposition affects spectrophotometric assay Sample is stable (cf ABG, metHgb)
CO treatment
Remove from source Oxygen administration Dissociation half-life: 5-6 hrs on room air 1.5 hrs on 100% O2 25 minutes @ 2-3 atm O2 (COHgb >25%) Hyperbaric chamber
Methemoglobin
Hemoglobin with ferric (Fe3+) iron
Does not bind O2
Oxidative environment always forming metHgb
Countered by two enzyme systems w/in rbc
Increased formation from :
Nitrites (vasodilators, inhalation)–“locker room”, “rush”
Chloroquine, Primaquine – anti-malarials
Dapsone – Pneumocystis Rx
Sulfonamide antibiotics
Lidocaine, benzocaine – local anesthetics
Congenital susceptibilities exist
Methemoglobin treatment
Treatment - methylene blue
Reduces ferric metHgb to ferrous HHgb
Methemoglobin measurement
CO-Oximeter
older models had interference from methylene blue
Visual – metHgb is chocolate brown
MetHgb is unstable
Collect and transport on ice (not req’d for COHgb)
Do not freeze
Measure w/in 4-8 hrs
Volitiles
Methanol Isopropanol Acetone Ethanol Other solvents Acetonitrile – some nail polish removers Ethyl acetate - some nail polish removers Ether (diethyl) – automotive starting fluid Methylene chloride – paint strippe
Methanol
Source: some antifreeze windshield washer fluid Effects: not a significant CNS depressant formaldehyde and formic acid metabolites anion-gap metabolic acidosis optic neuropathy blindness
Methanol Treatment?
Treatment block ADH formation of formaldehyde Administer ethanol to serum level of 100-150 mg/dL OR 4-methylpyrazole (Fomepizole) Both act as competitive inhibitors of ADH HCO3- - metabolic acidosis as needed folate – traps formate hemodialysis
Isopropanol
Source: rubbing alcohol is 70% isopropanol ~2-2.5x CNS depressant activity as EtOH Metabolized to acetone (T1/2 = 3.6 hr) No EtOH Rx – IPA is more toxic than acetone Supportive therapy Hemodialysis
Acetone
Source:
isopropanol metabolism
nail polish remover
ketosis (
Volatiles measurement.
Measure by GLC Use n-propanol as internal standard Direct injection – req. periodic column replacement Headspace – column lasts “forever” sample + int. std. + NaCl in sealed vial heat (45°C) for 10-30 minutes sample the vapor (20-250 µL) and inject Uses low oven temperature (~40°C) Can also measure other solvents with higher oven temperature MeOH by enzymatic assay (non-commercial)
Ethylene glycol
Some CNS depression Complexes calcium (oxalic acid) CaOx xtals mechanically damage nephron Treatment EtOH to 100-150 mg/dL blocks metabolism 4-methyl pyrazole (Fomepizole) as alternative Hemodialysis if >500 mcg/mL (50 mg/dL) Correct acidosis and hypocalcemia Measurement Blood – GLC, not suitable for average lab Enzymatic assay (non-commercial) Urine – UV lamp, fluorescein in most antifreeze
Chromatography drug sceens
TLC – thin layer chromatography GLC – gas-liquid chromatography GC/MS – GLC/mass spectrometry LC-MS (incl. TOF) Require time, capital and experience commitment All require sample preparation steps All require skilled interpretation
Mass Spectrometer
Specific detector system for GLC or HPLC
Compounds exiting chromatograph are excited and ionized by one of several energetic methods
Excited compounds break at weaker bonds, yielding characteristic fragment ions as well as neutral fragments
Mass filter analyzes charged fragments
Increased sensitivity over FID and NPD
Increased specificity (structural information)
TIC
Total ion chromato.
Plot of abundance of all ions detected by mass spectrometer vs retention time (time since injection)
Only identifying info is retention time
Mass spectrum
Histogram of mass:charge ratio (m/z) vs abundance at a single point in time
Molecular ion – m/z representing the unfragmented molecule
Not necessarily present
Base peak – most abundant ion
Spectrum is normalized to base peak = 100
SIM
MS: Selected Ion Monitoring (SIM)
Full scan (prev. slide) useful to id unknowns or from large list of potential compounds
Comprehensive drug screen
If targeting specific compound(s), look for (3) ions “unique” for each compound
Ratio two ions to the third
Enhanced sensitivity and specificity
Confirmation of positive EIA drug screen
Specific compound assays
Multiple (Selected) Reaction Monitoring
Used to quantitate known compounds:
Immunosuppressants
Vitamin D (25-OH D2 and D3)
Steroids (e.g., testosterone in women and children)
Time of Flight (TOF) MS
Higher mass resolution and range
Gives exact MW of compounds (nnn.nnnn)
MALDI-TOF (matrix-assisted laser desorption-ionization) - useful for bacterial id
Toxic Metal: LEAD
Lead – no known biological function
Paint – pre-1972, up to 35%. Post
Lead Toxicity
Inhibits PBG synthase → ↑ DALA in urine Blocks Fe2+ incorp. into heme → ↑ ZPP ZPP = zinc protoporphyrin Ferrochelatase Binds to many protein sulfhydryls Deposited in bone Permanent effect on developing mental fxn
Lead Testing
CDC, Oct. 1991: test all children below the age of 6 yrs action limit of 10 mcg/dL (now 5 mcg/dL) CA DPH – CHDP testing req. approved lab OSHA – occupational testing req. approval Measure in whole blood only
Metals Measurement
Reinsch – urine As, Hg, Sb, Bi; but NOT Pb
Obsolete
Atomic absorption
Graphite furnace – higher sensitivity for Al, As, Pb
Cold vapor – mercury as the hydride (AA or atomic fluorescence)
Single element per assay
ICP-MS – inductively-coupled plasma mass spectroscopy
High sensitivity and universal detector
Multiple elements per assay
Expensive instrument
LeadCare – lead only POC disposable sensor.
Drugs of Abuse
Amphetamines Barbiturates Benzodiazepines Cannabinoids (THC, marijuana) Cocaine LSD Methadone Opiates PCP (Phencyclidine) Tricyclic antidepressants (TCAs) Measure by homogeneous immunoassay
