Toxicology Oral Boards

Contains everything from Pharmacology and Toxicology

Absorption

• movement of drug from site of admin to body

  • pH dependent

  • Blood: 7.35-7.45

  • Saliva: 6.5-7.5

  • Gastric Juices: 1-2

  • Urine: 4.5-8

  • CSF: 7.3

Premeation

• part of absoprtion

• hydrophillic

  • polar

  • blood over tissues

  • higher clearance

• hydrophobic/lipophillic

  • often nonpolar

  • favors organic solutions

  • favors tissue

  • lower clearance

  • permeates BBB

First pass effect

• part of GI metabolism

• drug is metabolized in liver before reaching systemic circulation

  • reduces active drug available

  • oral admin

Enterohepatic recirculation

• GI metabolism

• drug goes liver, bile, intestine, liver, repeat

  • longer duration of action

  • oral admin

  • drug can be toxic because drug concentration builds up

Rule of 9’s

• When pH is fixed difference between pH and pka is expressed in 9’s

Distribution

movement of drug from central compartment to peripheral

Factors that affect distribution

• solubility

• blood flow

• cardiac output

• protein binding

• lipid content of tissues

displacement

• aspirin and albumin

• less albumin means higher distribution and increase in toxic side effects

• drugs bound to albumin do not distribute well into tissues

• drug drug interactions are possible: aspirin and warfarin

Volume of distribution

• Vd=dose/conc

• needs to be in L/Kg

• high vd is greater than 1: decrease in blood conc

• equal vd is equal to 1: blood conc = tissue conc

• low vd is less than 1: high tissue conc

Metabolism

drug is made into a form that is easier to excrete from the body

Phase I

redox reactions make drugs more polar for excreation

• redox, hydrolysis

• CYP3A4, CYP2D6

  • poor

  • intermediate

  • extensive

  • ultra-rapid

Phase II

conjugation adds functional groups

polar drug is polarized further

transferases add groups

• Glucuronidation (MOST COMMON)

• Actylation 

• Glutathionylation 

• Sulfation 

• Methylation

Elimination

Organs involved

• kidney

• gall bladder

• lungs

• GIT

• breast milk

• sweat

• hair

• nails

• salvia

Route of administration

highest bio-availability: IV

lowest availability: topical, transdermal

Drug dosing

Why are some drugs in prodrug form?

• more stable

• activated when metabolized

• increase bioavailability

3 things to achieve correct dose

1. speed of onset of action

2. intensity of effect

3. duration of action

Quantitative Dose curve

• Quantitative curves plot response to a drug against its concentration. 

  • Drug response vs. drug concentration

• Emax: max response of drug

• EC50: conc at which drug produces 50% of max effect

• ED50: median effective dose

• potency: dose required to produce a response

  • lower dose=more potent

• Efficacy: ability to produce greatest possible effect

Quantal Curve

• Quantal curves plot the rate of an outcome occurring in a population against the drug dose

  • The percent of individuals’ responses vs. the drug dose.

• TD50: median toxic dose

• LD50: median lethal dose

• Therapeutic index: ratio that compares toxic dose to effective dose

Pharmacokinetics

what the body does to the drug

One compartment model

• one homogeneous compartment

• instant distribution

• linear clearance

• Alcohol

Two compartment model

• central and peripheral

• non homogeneous distribution

• logarithmic clearance

Zero order elimination

constant amount of compound per unit of time

1st order elimination

constant fraction of compound per unit of time

half-life

time required for drug concentration to reduce by 50%

• t1/2=.693/k

Pharmacodynamics

what drug does to the body

competitive inhibitor

compound that binds directly to receptor and inhibits drug from binding, no effects observed

Allosteric activator

substrate binds to an alternate binding site on receptor which increases binding affinity

• AKA Inverse agonist

Allosteric inhibitor

compound introduces a conformation change and drug no longer fits the active site

Agonist

substrate that binds to the receptor and activates it

Full agonist

max activity and full saturation

partial agonist

partial activation and some saturation

Inverse agonist

decreases the activity below the basal level

Competitive antagonist

• competitive inhibitor

• no change in Emax

noncompetitive antagonist

• allosteric inhibitor

• decreases Emax

• no change in EC50

Time Action Curves

1. time to onset of action

2. time to peak effect

3. duration of action

4. carryover effects

Receptors

a protein in the membrane that binds to ligands and activates pathways

Samples from living subjects

• urine

• oral fluid

• blood 

• hair

• fingernails and toenails

PM samples

• blood

• urine

• VH

• liver

• stomach contents

• bile

• CSF

• lung

• kidney

• brain

• SQ fat/muscle

Conditions that affect drug concentration PM

• PM redistribution

• time interval

• trauma to the body

• puterfaction

• autolysis

PM Blood

• heart

• peripheral (femoral or subclavian

• NaF/k-oxalate

Urine PM

• lags behind blood conentration profile

• urine may drain in PM interval

• NaF preservative preferred

Vitreous humor PM

• isolated area of the body

• good stability

• all available fluid should be collected separately

Liver PM

• usually most valubale

• metabolites

• high drug concentration

• plenty of sample

• take deep right lobe sample

Gastric Contents

• oral ingestion prevalent

• measure entire volume

• removed and test apparent dosage forms

Bile PM

• excretory fluid that concentrates many drugs

• remove gall bladder

• measure volume

• preserve with NaF and freeze

CSF PM

• Good for drugs affecting CNS

• protected therefore less subject to contamination

• useful for detection of glucose and lactate in cases of hypoglycemia

GPCR

• G protein coupled receptors

• binds to lingands

• triggers downstream signaling

  • Cannabinoids: CB1, CB2

  • cholinergic, muscarinic

  • adrenergic, alpha, beta

  • Opioid: Mu, Kappa, Delta

Ligand-gated ion channels

protein embedded in cell membrane that opens to allow specific ions to flow across the channel. Ligand must be present to be able to open the channel

• cholinergic, nicotinic

• GHB, NSAIDs, GABA

Inducers

drugs that induce P450 expression by increasing the rate of synthesis or reducing the rate of degradation

Inhibitors

drugs the reduce P450 expression

• Imidazole, suicide

Pharmacogenomics

branch of pharmacology which deals with the influence of genetic variation an a drug response in patients by correlating gene expression or SNPs with a drug efficacy or toxicity

Pharmacogenetics

genetic difference in metabolic pathways which can affect individual responses to drugs, both in terms of therapeutic effect and adverse effects

Tolerance

diminished response to alcohol or other drugs over the course of repeated or prolonged exposure

• can be overcome

• mechanisms:

  • decrease synthesis of receptors

  • increase metabolic enzymes

    • more enzymes =less efficacy of drug

    • activity of metabolic enzymes may be overcome by INCREASING the dose of the drug to produce clinical effects

Tachyphylaxis

appearance of progressive decrease in response to a given dose after repetitive administration of an active substance

• Mechanisms

  • mass cellular response causes cell to emply protective mechanisms to produce less significant cell response

  • cannot be overcome

  • rapid response to large, initial dose of drug

  • decrease synthesis of receptors

  • kinases add phosphate residues

  • endocytosis

Autonomic NS

regulates involuntary physiological processes including heart rate, blood pressure, respiration, digestion, and sexual arousal

Ganglion

a collection of neuron cell bodies

Affector (sensory)

the structure that is stimulated to relay a message to CNS

Effector (motor)

the structure that is stimulated for to get final response

• smooth muscle cells

• cardiac muscle

• exocrine glands

• endocrine glands

Sympathetic NS

fight or flight

• thoracolumbar division

  • preganglionic nerves: SHORT

  • postganglionic nerves: LONG

• Acetylcholine (Ach)→ NE or Epi

  • switches to NE or EPI at ganglion=pre to post ganglionic at synaptic cleft

• Adrenergic system (synthesize, store, and release NE)

  • stimulatroy effects

    • pupil dilation

    • decrease salivation

    • bronchodilation

    • tacycardia

    • decreased peristalsis

    • decreased urination

Adrenergic receptors

• Alpha 1

  • G protein, STIM

  • agonist: phenephrine

  • antagonist: ends in -osin

• Alpha 2

  • presynaptic cleft

  • G protein, INHIBIT

  • agnoist: inhibits NE release

• Beta 1

  • G protein, STIM

  • Agonist: isoproterenol

  • Antagonist: ends in -olol

• Beta 2

  • G protein, STIM

• Beta 3

  • G protein, STIM

  • inhibits urination

Parasympathetic NS

rest and digest

• cholinergic system (synthesize, store and release Ach)

  • nicotinic

    • focus on the heart

    • ligand gated

  • Muscarinic

    • GPCR

  • Stimulatory effects

    • miosis

    • vasodilation

    • bronchoconstriction

    • bradycardia

    • increase peristalsis

    • increase urination

Cholinergic receptors

• Nicotinic

  • Nn=neuron or ganglion

    • blockers: competitive inhibition of agonsits of parasympathetic and sympathetic

  • Nm=muscular

    • depolarizing

      • binds to and activates Ach

      • irreversible

    • non-depolarizing

      • binds to receptor without activation

      • short, reversible

• Muscarinic

  • GPCR

  • focus on contraction of bladder and GIT

  • M1, M3, M5 excitatroy

  • M2, M4 inhibitory

• Animuscarinics=antags of parasympathetic

Anoxia

absence of oxygen to the tissue

hypoxia

decrease of oxygen supply to tissues

Carbon Monoxide

• odorless gas, less dense than air

• Fatalities=%COHb>50%

• CO affinity for Hb is 200-300 times greater than O2 and binds just as easily and does not come off easily

Bohr Effect

How CO2 affects Hb affinity for oxygen

• High CO2+ low pH= less O2 bound

Haldane effect

How O2 affects Hb affinity for CO2

• High O2=low CO2

CO Analysis

• Spectrophotometry

• Conway diffusion

• GC-headspace/mass spec

• Sample MUST contain Hb

Conway microdiffusion

• conway cell

• 2 wells

  • outside-specimen+sulfuric acid

  • center well-PdCl2

• seal and incubate at RT for 2 hours

• PdCl2 is reduced to form a black or silver mirror in the center of well

GC for CO

• CO must be separated from blood for analysis

• TCD or FID needed

• collect headspace through a gas syringe

Cyanide

• rapidly acting and lethal poison

• death occurs within minutes after ingestion

• cyanide and cyanogenic products

CN- toxicity

• stops cellular respiration by inhibitng electron transport at cytochrome c oxidase step

• 3 inhibitors

  • cyanide ion

  • rotenone

  • antimycin A

CN- detoxification

• Rhodanese

• major route is enzymatic conversion to thiocynate

Hydrogen Sulfide

• product of organic decomposition

• rotten egg smell

Toxicokinetics of hydrogen sulfide

• rapidly absorbed through the lungs

• partially oxidized by hemoglobin and liver enzymes to thiosulfate

Toxicity of Hydrogen sulfide

• similar to CN-

  • inhibits cytochrome c oxidase

Inhalants

• describes volatile compounds that may be inhaled accidentally or intentionally

• no classification system based on chemical structure

• includes

  • aliphatic hydrocarbons

  • halogenated HC

  • aromatic HC

  • halogenated oxygen containing compounds

  • alkylnitrites

Mechanisms for abuse

• inhaled directly from container

• order of the high

  • Bagging>huffing>sniffing

Inhalant metabolism

• unchanged in exhaled air and metabolites in air ans urine

• phase 1 and 2 in the liver

Inhalant analysis

• Glass tube

• minimal headspace

• anticogulant

• tight seal

• use GC-FID, GC-ECD, GC-MSD

Drugs used in DFC

• alcohol

• opioids

• GHB

• DPH

• Z drugs

• Benzos

Drugs tested for in workplace drug testing

• Cocaine

• amphetamines

• marijuana

• phencyclidine

• opioids

Reasons to drug test

• applicant

• reasonable suspicion

• post accident

• follow-up

• voluntary

• random

Urine as a specimen

Advantages

• readily available waste produce

• easily collectable and non-invasive

• drug and drug metabolites concentrated

• aqueous media which is easily extracted

Disadvantages

• single specimen which cannot correlate concentration with physiological behaviors

• sample concentration varies

• indicates use only at time of collection

• principally measures metabolites of drugs

• subject to adulteration with non-observed collection

screening vs confirmatory testing

Screening

• immunoassay

  • ELISA, EIA

  • identify positive and negatives

Confirmatory

• instrumental

  • LCMS, GCMS

  • See if drug is there at the cutoff concentration

Tox ELISA

• Concentration of target analyte inversely proportional to absorption/colorimetric change

• Based on competitive binding btwn enzyme labeled Ag and target analyte

• Steps:

  • Ab is bound to solid substrate

  • competitive binding btwn enzyme labeled Ag and target analyte

    • binding on analyte conjugate to substrate activates enzyme which produces color change

  • high levels of analyte=less Ag binds=no color change

  • low levels of target analyte=more Ag binds=color change

• increased sensitivity for heterogeneous mixtures, good for low concentrations

EMIT assay

• concentration of analyte is proportional to color change

• based on competitive binding btwn analyte and enzyme labeld Ag for limited binding site. Enzyme is INACTIVATED when bound to Ag

• Steps:

  • Ab is bound to solid substrate

  • competitive binding with analyte conjugate and target analyte

  • high levels of analyte=less conjugation binding=color change

  • low levels of analyte=more conjugation=no color change

• used for urine, less sensitive, no was steps

Oral Fluid

• mix of saliva, cellular debris, oral mucous, drainage, blood

• 1 mL is collected from mouth

• just now be offered for drug testing

Hair Drug testing

• solid sample

• longest detection window

• difficult to adulterate

GFAAS

• source of light is radiation

• atomization chamber in which sample is vaporized (1500-2800 C)

• monochromator selects specific light wavelength

• photomultiplier tube that detects absorbance

ICP-MS

inductively coupled plasma-mass spec

• sample is prepared as a solution or solid samples

• high temperature argon plasma atomizes the sample

• ions are separated by quadrupole

• abundance of each ion is detected

heavy metal

any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations

metallothionein

family of small, highly conserved, cysteine rich metal binding proteins that are important for zinc and copper homeostasis

Aluminum

• found in earth’s crust

• multiple uses

• stored in bone

• dialysis exposure

• occupational exposure

• analysis

  • GFAAS, ICP-MS

Al pharamcokinetics

• 5-10 mg enters the body daily

• poorly absorbed orally or by inhalation

• accumulates in bone and lung tissue

• t1/2 is 8h-8y

Al toxicity

• believed to be related to its ability to compete with other cations

• bones and CNS

• bone softening

  • antacids due to phosphate reduction

  • uremic dialysis patients

    • replaces Ca

Arsenic

• used therapeutically for over 200 years

• exposure can come from anywhere

• different forms

  • organic, arsine

• known human carcinogen

Mees lines

• white discoloration of nails

• often occurs at the base of the nail

Cadmium

• very toxic

• carried through body metallothionein

• t1/2 is 10-30 years

• interacts with functional macromolecules

• analysis

  • ICP-MS

  • GFAAS

• Itai-Itai disease

Lead

• found in environment

• inorganic and organic forms are toxic