Lecture 1/2: Overview of Drug Absorption and Elimination Pathways Flashcards
(146 cards)
1
Q
What are the key takeaways from this lecture?
A
-need to know how xenobiotics are absorbed
-need to articulate the molecular mechanism of xenobiotic distribution and excretion
-need to explain the various mechanisms of how the body eliminates xenobiotics and drugs
2
Q
What is included when considering drug elimination pathways?
A
cellular transport (influx and efflux into and out of cells)
metabolism
protein binding
3
Q
What is included when considering drug exposure?
A
the AUC
-the concentration of the drug in the plasma (y axis) vs time (x axis)
4
Q
What is included when considering the clinical outcome of a drug?
A
toxicity - too much drug
therapeutic window
suboptimal - not enough drug
5
Q
Where are drugs orally or mucocutaneously absorbed?
A
absorbed largely in the small intestine to the large intestines
-there is some intranasal absorption
-some sublingual absorption
-some rectal or suppository absorption
-some absorption from stomach
-some inhaled
6
Q
Where do molecules need to be to be absorbed?
A
near or on surfaces of mucosa layer to be absorbed
-compounds should be soluble in gut contents
7
Q
What types of molecules are not well abrobed?
A
crystals and gummy stuff is not well abrobed
8
Q
How does overconsumption of food harm the body tissues?
A
glucose - atp - superoxides- destroys tissues
9
Q
If you swallow food in how much time dio you feel satiated?
A
within an hour
10
Q
What does the small intestine do?
A
absorbs nutients which go to the liver
11
Q
What are the salivary glands?
A
parotid
sublingual
submandibular
12
Q
What are the intestines?
A
they are a long continuous tube of mucosal cells running from the stomach to the anus
13
Q
Where does the majority of the absorption of water and nutrients occurs?
A
the intestines
14
Q
What do the intestines include?
A
the small intestine, large intestine, and rectum
15
Q
How long is the small intestine and what is its diameter?
A
20 ft long and one inch in diameter
16
Q
What lines the small intestine and what is it divided into?
A
velvety tissues
duodenum, jejunum, and ileum
17
Q
What is the length and diameter of the large intestine?
A
5 ft long and 3 inches in diameter
18
Q
What is the large intestine divided into?
A
colon and large bowel
19
Q
What does the colon do?
A
it absorbs water form waste which makes stool and this stool enter the rectum which have nerve which create the urge to defecate
20
Q
What does the large colon have the secreted digestive enzymes which help with nutrient absorption?
A
crypts
21
Q
What doe the small colon have that increases teh SA?
A
villi
22
Q
What is absorbed in the large intestine and how is it eliminated?
A
water and is eliminated in urine and the kidneys
23
Q
What is believed to be the major route of absorption for nutrients and drugs?
A
passive transcellular
24
Q
What compounds have the best chance of diffusing across the barrier but have a hard time across the water soluble blood compartment?
A
non charged compounds
25
What compounds are best in absoprtion and why?
ampiphillic because fat can pass membranes and h20 loving can reach actives sites
26
What is the brush border?
refers to the microvilli-covered surface of the epithelial cells in certain parts of the digestive tract, such as the small intestine.
27
What is octanol water partitioning?
octanol-water partition coefficient (often abbreviated as Kow) is a measure of how a substance divides itself between water and octanol (a type of organic solvent).
28
What is the purpose of artificial membranes in pharmacology?
Artificial membranes are widely used in pharmaceutical research and development for several key purposes. These synthetic membranes are designed to mimic the natural biological membranes (such as the lipid bilayer of cells) and are used in various experimental setups to better understand how drugs interact with biological barriers.
-i.e. caco-2 cell lines
29
What is the difference between transcellular and paracellular transport?
Transcellular transport refers to the movement of substances through the cells themselves, from one side of the cell layer to the other. i.e. large molecules
Paracellular transport refers to the movement of substances between the cells, across the tight junctions that seal the epithelial cell layer.i.e small molecules like water
30
What is transport protein?
Carrier Proteins: These proteins change their shape to move a substance from one side of the membrane to the other.
Uniporters: Transport a single type of molecule in one direction.
Symporters: Transport two types of molecules in the same direction (co-transport).
Antiporters: Transport two types of molecules in opposite directions (counter-transport).
Channel Proteins: Unlike carrier proteins, channel proteins form pores that allow molecules (usually ions or water) to pass through the membrane without changing shape.
Ion Channels: Specific to ions (e.g., sodium, potassium, calcium).
Aquaporins: Channels specifically for water molecules.
31
What is carrier mediated cell transport?
a. Facilitated Diffusion (Passive Transport):
No energy required: Facilitated diffusion occurs when a substance moves down its concentration gradient (from an area of higher concentration to an area of lower concentration) without requiring energy (ATP).
Carrier proteins or channels: The substance binds to a specific carrier protein that facilitates its movement across the membrane. The carrier protein helps the substance pass through the hydrophobic lipid bilayer more easily.
Example: The movement of glucose into cells via the GLUT (glucose transporter) proteins is a common example of facilitated diffusion.
b. Active Transport:
Energy required: Active transport moves substances against their concentration gradient (from an area of lower concentration to an area of higher concentration), which requires energy, usually in the form of ATP.
Carrier proteins (pumps): Active transport relies on specialized pump proteins that use energy to move substances across the membrane.
Example: The sodium-potassium pump (Na+/K+ ATPase) is a well-known active transporter that uses ATP to pump sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, against their concentration gradients.
32
What is a cell suspension or adherent cell?
-A cell suspension refers to a culture of cells that are not attached to a surface but are instead floating freely in the culture medium. These cells can exist in a suspended state in a liquid medium.
-Adherent cells refer to cells that attach to a surface, typically a culture dish or flask, and grow as a monolayer on the surface.
33
What is the membrane vesicle cell culture system?
-membrane vesicle cell culture system refers to a specialized method used in cell culture that involves creating membrane vesicles (also known as lipid vesicles or liposomes) and using them to mimic cellular environments or enhance certain cellular functions.
34
Where do components like nutrients and drugs absorbed through the intestinal walls go from there?
they eneter into the blood stream go from high conc to low conc
35
How are undesirable compounds prevented from entering the blood from the intestines?
through protective mechanisms - the gastrointestinal system has both responses to xenobiotics and immunity to protect from pathogenic intrusion
36
Once a drug or xenobiotic is absorbed what can happen?
it can circulate to various organs
37
What can be transported acorss membranes and into tissues?
free drug
38
What do extracellular drugs need to do to exert their actviities?
enter into cells
39
What is free drug also suscpetible to?
elimination and metabolism
40
How can you make a drug reach tumor tissue?
tumors have fast metabolism and great energy requirement and not enough O2 so they have a lactic acid buildup making them acidic so can make drug cationic so it reaches the tumor tissue
41
What are some mathematic models of drugs crossing various barriers?
Small molecules - absoprtion is Fa
inetstinal first pass = Eg = 1 - Fg
hepatic first pass = Eh = 1-Fh
distribution and elimination = perfusion tissue binding and cyps and renal and billiary excretion
biology analog - sc absoprtion
injection site - metabolism
lymphatic - lymph node uptake and metabolism
distrbition and elimination convection/transcytosis
catabolism and target mediated and FcRn
42
How is the systemic fraction of drugs calculated?
F = Fa + Fg * Fh
43
What is included in gut first pass metabolism and absorption?
diffusion and transport across the intestinal epithelium
44
What is included in hepatic first pass metabolism and absorption?
metabolism
excretion in the bile
45
What is convection and the FcRn?
convection refers to the bulk flow of fluid that carries substances through biological barriers (such as capillaries). It’s a passive process where substances are transported with the movement of fluid or bulk flow.
The neonatal Fc receptor (FcRn) is a receptor found on various cells, including endothelial cells and epithelial cells, that is primarily involved in the transport and protection of IgG antibodies and albumin (plasma proteins). - prevents degradation of antibodies and increases half life
46
What are the overall steps of drug distribution and elimination?
absorption --> drug in central compartment (excretion Ke and metabolism Km) ---> tissue distribution Kd ----> protein binding KPB
47
Once a drug is absorbed what occurs and why?
the biotransformation process ensues and it is the bodys way to ameliorate the potential of xenobiotic induced cellular and tissue injury
48
What is elimination?
the biotransformation or metabolism of a drug + excretion
49
What is excretion?
the process of removing the parental drug and its respective metabolites from the body
-the time to excretion is dependent on the physicochemical properties of the drug
-polarity or water solubility of drugs are important
-non polar compounds are lipid doluble and unionized so thty can cross the membrane barrier
50
What are the major routes of excretion?
kidney and urinary
biliary and hepatic
fecal and microbiome
pulmonary - can test this with arithromyocin and breathing mask to test metabolism
51
What are minor routes of excretion?
saliva
skin and sweat
tears
breast milk
vaginal or seminal fluids
52
What is the purpose of xenobiotic clearance?
-to reduce exposure to potentially toxic xenobiotics
53
What are the mechanisms included in clearance?
-dilution or filtration
-reduce absorption
-efflux transporter mediated activities
-vomiting
-diarrhea
-increase excretion mechanisms - renal excretion
-metabolism - cyp450, microbiome
54
What is drug distribution? What is this process dependent on?
the reversible transfer of drug from the blood traversing into the extravascular fluids and into tissues found in the body - fat muscle and nervous tissues
-this is dependent on the amphiphillicity/hydrophobicity of the compound - binding may also be affinity for receptors or plasma proteins
55
What is the volume of the vascular compartment, interstitial space, cellular membrane?
vascular compartment --> 4L can range based on size to (3-5L) - blood volume does not change on size
interstitital space ---> 10L - this changes with size
cellular membrane --> 28L - this changes with size
56
What are the factors impacting tissue distribution? What are some drug physicochemical characteristics?
drug distribution is not equally distributed due to tissue and fluid physicochemical properties
-the lipid solubility of the drug
-the MW of the drug
-the pKa of the drug
-pH of the fluid
-pH of the targeted tissue
-blood flow
-drug binding affinity onto protein and receptors
-membranes
57
What is the relationship between lipid solubility and crossing barriers?
-lipid soluble drug non ionized compounds at physiologic pH can cross cellular barriers
-water soluble compounds ionized compounds at physiologic pH cannot cross the cells membrane without facilitation by active or passive transporters
58
What is the drug molecular weight?
-lower molecular less than 500 daltons are more likely to cross barriers
-higher molecular weight drug will need active transport mechanisms to cross the cellular barriers
59
Where can a drug distribute to?
blood plasma ---> ECF -----> Fat -----> ICF -----> other CSF, peritoneum, synovial fluid (joint fluid), fetus
60
How do drugs of size less than 50 daltons pass from the ecf to the icf across the cell membrane?
bulk flow
61
How do lipophillic drugs 50-600 daltons pass through the cell membrane from the ecf to the icf?
passive diffusion
62
How do polarized or ionized drugs of size greater than 50 daltons get across the cell membrane?
through active transport
63
Can protein bound drugs cross the capillary wall into the ecf?
no
64
Through what mechanisms can drugs traverse across membranes?
paracellular passage
passive diffusion
facilitated diffusion
active transport - takes atp or gtp
-just as an aside - can make a drug a salt to make it amphiphillic to cross through membranes
65
What are some potential reasons as to why cells distant from blood vessels might be resistant to treatment?
-if you take a look at cords of cells surrounding blood vessel in xenograft of a cervix cancer - more cells are proliferating close to the blood vessel - the farther away a cell is from a blood vessel there is ledd oxygen and nutrients and energy and less drug concentration which is why there is less
66
What are some methods to understand distribution and efficacy of drugs?
-multicellular spheroids can be grown in the spinner culture to form spherical aggregates
-multilayered cell cultures or MCCs are frown on permeable support membranes and they are proliferating cells are located predominantly close to the upper and lower surfaces
-studies of drug penetration are usually performed by separating two reservoirs - an mcc or floating an mcc on a meidum with a drug of interest added to the small compartament above the mcc and sampling from the lower reeceving end
-the penetration of the drug through an mcc is usually compared to penetration through the support membrane alone as shown for doxorubicin and 5-fluorouracil
67
What does total drug found in the blood include? How are free drug levels determined?
includes both protein bound and free drug levels - free levels are normally determined using size exclusion membranes - like centrifree
68
What are the proteins present in the blood and ECFs?
human serum albumin, alpha acid protein, and other plasma proteins like lipoproteins
69
What are the things that only unbound drugs can do?
interact with enzymes or receptors be excreted by the kidney
70
Can compounds compete for binding sites on HSA?
yes and tightly bound compounds can have suddenly high free fraction when displaced by other compounds
71
What happens to the volume of distribution with highly protein bound drugs?
it increases
72
How do bound drugs act as a resevoir for drugs?
they cna slowly release and increase the circulaotry half life
73
What type of bound drugs are not biologically active?
protein or fatty acid bound drugs
74
What is drug circulation time dependent on?
drug-protein interaction
75
How does blood flow affect drug distribution?
highly perfused organs normally have higher distributions at earlier time points
76
What is Kc is dependent on?
the permeability of the barriers and compartment pH and drug binding capacity
77
What is the blood flow in terms of percent of cardiac output each organ receives?
liver - 27.8%
kidney - 23.3%
muscle - 6-15.6%
brain - 13.9%
skin - 4%
fat tissue - 2%
placenta - 9%
liver and kidney have the highest
78
What is the volume of distribution?
provides an estimate of how well the drug is distributed
79
What does a Vd less than 0.071 L/kg indicate?
the drug is mainly in the circulatory system
80
What does a Vd more than 0.071L/kg indicate?
the drug has gotten into specific tissues
81
How do you calculate the Vd?
C (concentration of drug in plasma at designated timepoint) = total concentration of drug in system D/ Vd volume of distribution
C = D/Vd
Vd = Q/Cp
Q = dosage
Cp is concentration in the plasma
82
What is the distribution equilibirum equation?
Vss = Dose * AUMC 0-inf / AUC0-inf^2 = CL * MRT
83
What is the elimination phase equation?
VB = CL/kel = dose / AUC0-inf * kel
84
What are the sizes of fluid compartments in the body?
plasma = 0.045L/kg - this is about 4.5% of BW
ECF 0.20L/kg 20% of BW
TBW 0.60L/kg 60% of BW
exampple if a drug has Vd that is 60% of BW this means the drug distrubutes in the TBW compartament
85
What are some things to consider when looking at the site of actions of most compounds relation back to the concentration of the comppund in the plasma?
compounds distribute differentially within the bidy
-plasma protein inding may limit distribution
lipophillic compounds accumulate in fatty tissues
liver kidneys and other excretory organs often show high concentrations of compounds
concentrations in brain are often very different from plasma concentrations
distribtution can be studied using carbon labelled compounds
86
What is drug clearance?
volume of blood in a defined region of the body that is cleared of a drug in unit time
-clearance is a more useful concept in reality than t1/2 or kel since it take into account the blood flow rate
-clearance varies with body weight
-also varies with degree of protein binding
rate if elimination = kel C Vd
87
What is the rate of elimination for the whole body?
CLtC
CLt = KelVd
88
How do you dose a drug?
3-4 half lifes
89
What is total body clearance?
TBC = CLhepatic + CLrenal + CLother
90
What is hepatic clearance?
CLhepatic = CLmetabolism + CLbiliary
91
What is metabolic clearance?
CL:metabolic = fB* CLintrinsic * Qh / fB * CLintrinsic + Qh
92
What is the intrisinc clearance equation?
Vmax/Km = vo/Cu
assumes drug conc is less than Km
93
What is the depletion or half life method?
CLi = 0.693 *liver wt / in vitro t1/2 * amount of liver
94
What does renal elimination regulate? What is excreted?
-electrolyte balance via hormonal secretion (aldosterone)
-water or volume balance (ADH)
-get excretion of nitrogenous waste and drug metabolites - urea, uric acid, creatinine
95
At what age do we excrete our hormones?
40
96
At what age do we secrete our gut microbiome?
60
97
At what age do we tend to get stage ii renal failure?
60
98
What are the three processes of renal excretion?
1. glomerular filtration - elimination via size exclusion
2. active tubular secretion which require active transport across the basolateral and then to out of the apical membrane (basolateral faces the blood and apical faces the lumen)
3. passive tubular reabsorption - normally electrolytes and small molecules
99
How can xenopus oocytes be used with mRNA expression?
can microinject mrna into an oocytes and this will then translate process and insert receptors which you get test to see if the drug gets in and out of them i.e. rOAT
100
What is the impact of drugs on creatinine secretion?
-Drugs that affect renal blood flow (like angiotensin converting enzyme inhibitors (ACE inhibitors) or angiotensin receptor blockers (ARBs))
-Some drugs can inhibit creatinine secretion by the renal tubules, leading to increased serum creatinine levels
101
In glomerular filtration, blood is filtered across a semi permeable membrane into what?
bowmans capsule
102
In glomerular filtration, what is the driving force in the capillaries?
hydrostatic pressure
103
In glomerular filtration what is the filtrate made of?
water, glucose, amino acid, electrolytes, organic solutes
104
What is the level of GFR dependent on?
renal blood flow
105
What are the biological factors that affect GFR?
age
sex - males vs female (males have a greater muscle mass)
disease state (acute disease state changes perfusion like in sepsis)
106
What is glomerular filtration rate? What is it determined by?
the amount of blood filtered by the glormeruli in a given amount of time
-a marker or indication of kidney function
-normally determined by creatnine, cystatin c, or drug markers - like inulin, iothalamate
107
What are the factors that influence GFR?
molecular weight - smaller molecules readily excrete
-plasma protein binding - lipid solubility
-renal blood flow
108
What is the cockcroft-gault equation for an estimation of creatinine clearance?
Male Cr Cl = (140-age) * ideal body weight / serum creatinine * 72
Female Cr Cl = (140-age) * ideal body weight * 0.85 / serum creatinine * 72
normal function is 100
109
What are some examples of direct and indirect drug metabolism?
-microbiome activation of prodrug liberating into activity moiety
-converting active moiety into inactive moiety
-converting compound into toxic drug
110
How do you make a drug longer acting?
add a fatty acid or amino acid onto it which makes it no longer water soluble and it becomes protein bound and we cannot excrete it readily
111
What is the amino acid precursor to serotonin?
tryptophan
112
What is the amino acid precursor to epinephrine?
tyrosine
113
What is albumin?
a carrier protein of lipids or cholesterol or nutrients like building blocks
114
What is cholesterol?
a steroid that plays a role in the in the cell membrane and affects membrane fluidity and plays a role in cell senessance
115
What is the role of lipids in diseases?
lipids and oxidized lipids is why we develop diseases many drugs are carboxyl esterases
116
What is cpt-11 and what is its metabolites?
-cpt-11 kills colon cancer and it metabolizes into sn-38 which is broke down by carboxylesterase-2 which is found in tumors and the liver
-sn-38 is 1000 fold more active and can kill the tumor but how can we harness sn-38 and administer it in a non toxic way - if you get it to cross the BBB it can kill brain tumors
-sn-38 is gluconorated to sn-38G and goes into the gut and bacteria clears it and get massive diarrhea
-sn-38G it inactive and a detoxified metabolite - we can genotype people and can say how severe diarrhea is based on how much bacteria is present which gluconorated SN-38G
117
What is the effect of low extraction efficiency by hepatocytes in series?
hepatic clearance - for low extraction drugs - equation reduces to simple form and ClH = fx unbound x CLINT
-if a drug is highly extracted in the lover then it is less bioavailable
-low extraction drugs are water soluble and high extraction drugs are fatty and water insoluble
118
What are some examples of low extraction drugs or endogenous compounds?
diazepam - valium
phenytoin
theophylline - caffeine - use in kids with asthma or ADHD
bilirubin - comes from hemoglobin breakdown and pregnant women get gall stones from not clearing bilirubin
-these drugs are efficiently absorbed when given orally
-thus bioavailability of orally administered drugs is high
-drug companies look for these types of products as pills are easy to take
119
What is the equation for the hepatic clearance of drugs?
CL H = Q(fx unbound drugs) (CLINT) / Q + (fxunbound)(CLINT)
Q is the liver blood flow
CLINT is the rate of ability of the liver to clear blood of drug if blood flow is not limiting
120
What are some important transporters in hepatocytes to know?
BCRP, MDR1, MRP2
121
How does the liver form bile? What does fecal matter and urine color indicate?
-liver pumps into bile and bile goes into the intestine which becomes fecal matter
-if fecal matter is green high bilirubin
-if urine is yellow high conjugated bilirubin
122
What is hepatic clearance?
the liver removal of drugs and xenobiotics from blood
123
What are the three main factors which impact hepatic clearance?
liver blood flow
liver intrinsic clearance
-fraction of drug not bound to albumin
124
As you get over 60 what happens to conjugated transporter levels?
-as you get over 60 conjugated transporter levels increase due to hormones getting down regulated and blood flow decreases so you need active transporters
-cholesterol accumulates as you get older and causes this hormonal change
-old people get GH to mobilize stem cells to stay young and this can cause cancer
125
What is phase i biotransformation in the liver?
cyp mediated oxidation reactions
-direct modification of primary structure
-cyp450 - oxidative reactions ass a reactive or hydrophillic group OH
-often in er
-rate limiting
-may eliminate or generate toxic molecules
-highly variable - genetic polymorphisms, inhitable, inducible
126
What is phase ii biotransformation in liver?
catalyze covalent binding of drugs to polar ligands - transferases - glucuronic acid - sulfate - glutathione - amino acids
-increase water solubility
-enzymes generally in ER some cytosolic
-often follow phase 1 biotransformation reactions
-frequently use OH or other group added by cyps
-conjugation to polar ligands
-glucuronyl transferase
-sulfotransferase
-glutathione s transferase
127
What is the natural compounds for phase i and phase ii biotransofmration?
cholesterol and sterol like compounds like hormones
128
What is the anatomy of the cytochrome p450s?
they have a porphyrin ring which has an FE inside and put O2 there to oxidize the compound and O2 is donated by anything that has a heme group
129
What are some of the steps in the liver biotransformation and elimination of drug?
1.transport of drugs and xenobiotics from the blood
-liver has unique access to blood
-versatile transporter in liver membrane
2. biotransformation in the liver
-phase i cyp450
-phase ii conjugation
130
What are the types of enzyme kinetics?
kinetics of enzyme catalyzed reaction
-tons of caclulation
-line weaver burk plot
enzyme inhibion
-competitive - km is higher but vmax is same
-non comp - km is same vmax decreases
-uncomp - km decreases vmax decreases - only binds to ES complex so favors it more
y interceopt = -1/km
y intercep = 1/vmax
slope = km/vmax
131
What are some in vitro systems to predict metabolic clearance?
liver microsomes
-high throughput and most common
-mostly oxidative - cyp and fmo
s9 fraction
-high throughput
-phase i and phase ii metabolism
hepatocytes
-low throughput
-cell membrane/transporters
-intracellular concentration
-phase i and phase ii metabolism
132
What are some in vivo systems to predict metabolic clearance?
for animal clearance - can use in silico - fda does not like
133
Is all metabolism hepatic?
no
134
What does the incubation concentration need to be in order to balance assay sensitivty?
incubation concentration less than km
135
Does in vitro need to correlate to an in vivo model?
yes
-fast in vitro clearance generally implies fast in vivo clearance the reverse does not need not be true
136
What are some confounding physical chemical properties when assessing compound stability?
solubility
stability
purity
non specific binding
137
What can affect the real concentration at the enzyme active site?
protein binding
cell penetration
non specific binding
138
Why do in vitro system generally underestimate CLi?
due to non specific binding
139
Can the metabolic stability be too good?
yes in some situations
140
What are the best methods for metabolic stability predictions?
in vitro systems
141
What is the synergy between microbiome and endogenous metabolism?
intestinal bacteria and metabolism
-metabolites are precursors for biosynthesis
-absorption of these precuroses may influence physiology
-physicla impact, immunologic, behavior impacts
-disruption of gut microbiome can ifnluence all of the above
-activation of immune mediators has been shown to correlate with metabolic enzymes sich cyp 450
142
How does the microbiomes interact with the microenvironment?
diet affects the gut microbiome
-so do antibiotics - type number and duraction
143
In terms of precision medicine what impact patient slection and rationalized dosing?
patient selection - drug response related genes
dosing - pharmacokinetics realted genes
144
What goes into coming up with a diagnostic test for genetic polymirphisms? What about when you commercialize the test?
idenitify genetic markers
validate the genomic markers
commercialization - indication with genomic markers
145
What is the clinical significance of DME polymorphism?
-omeprazole is metabolized by cyp2c19
-plasma conc of omeprazole individual with different cyp2c19 genotype following a 20 mg dose
-there are distinct differences in plasma concentrations are observed between cyp2c19 genotypes
-patient geniytoe affects level of omeprazole and gastric pH needed for efficiency
-cant do PK compairsons between genotypes in small number of patients because metabolic capacity can vary on the day - new approaches in metabolomics can help address this though
146
