Determination of metabolitesA Story by MedicilonAfter drugs enter the body, they generally undergo physical changes and chemical changes. Physical changes refer to the binding reaction between drugs and biological macromolecules such as plasma protRelated definitions
After
drugs enter the body, they generally undergo physical changes and chemical
changes. Physical changes refer to the binding reaction between drugs and
biological macromolecules such as plasma proteins; chemical changes refer to
metabolic reactions in the body. Metabolic
reactions in the body are also called biotransformations, which are divided
into one-phase metabolism and two-phase metabolism. Phase one metabolism refers
to the oxidation reaction, reduction reaction, and hydrolysis reaction of the
drug in the body. Phase two metabolism refers to the conjugation reaction of
drugs in the body, including: glucuronic acid conjugation, sulfation,
methylation, acetylation, amino acid conjugation, glutathione conjugation, etc.
The MetID team of Medicilon is composed of experienced scientists. We provide
fast and reliable in vivo and in vitro MetID and
reactive metabolite capture services. We also support new drug screening and domestic
and oversees IND filings. Since the establishment of MetID team, Medicilon has
successfully completed multiple different types of research projects for
clients, including challenging peptide MetID research. The
analysis and research of drugs and their metabolites in vivo will provide
scientific basis for the relationship between drug concentration, drug efficacy
and toxicity, as well as the study of drug action mechanism and
pharmacokinetics. Therefore, the progress in recent years has been remarkable
and has become An important branch of drug research and formed a new
discipline. Bioavailability:
The rate and extent to which a drug in a dosage form is absorbed into the
bloodstream. Bioequivalence:
When different preparations of a drug are given the same dose under the same
test conditions, there is no significant statistical difference in the main
kinetic parameters that reflect the rate and extent of absorption. Study the
significance of metabolite determination
2.1
Measuring the distribution of drugs and their metabolites in blood tissues and
organs is an important indicator to measure the effectiveness and safety of
drugs; 2.2
Determine the changes in concentrations of drugs and metabolites over time to
provide reliable pharmacokinetic data; 2.3
Studying the metabolic pathways of drugs, the pharmacological activity of
metabolites, and the speed of generation and elimination is of certain
significance for rational use of drugs, avoiding drug toxicity, and finding new
drugs. 2.4
Conducive to the preservation of biological samples. After biological samples
such as blood are collected, plasma esterase may continue to hydrolyze the
ester drugs in the sample, and other enzymes may also continue to produce
metabolic reactions on the sample drugs. Therefore, enzyme inhibitors are often
added. . 2.5 It
is conducive to the selection of analytical methods for the in vivo metabolic reactions
of most drugs. However, changes in certain groups on the molecular structure of
the drug make the chemical structure of the metabolites very similar to that of
the parent drug, resulting in no major differences in some physical properties
and spectra. Analysis and immunoassay methods often face interference from
metabolites. When you want to determine the content of drugs and metabolites in
biological samples, chromatography is the appropriate choice. Because of its
separation and analysis functions, it can avoid interference from metabolites
or directly Determination of metabolites. 2.6 It
is helpful to select methods for sample separation and extraction. After drugs
are metabolized in the body, the metabolites generated generally increase in
polarity and enhance water solubility. Therefore, when separating and
extracting drugs from biological samples, the polarity and balance between them
are often used. Depending on the difference in dissociation behavior, choose an
appropriate pH buffer and solvent system to separate them. Situations in which
metabolites in the body need to be measured
3.1 When conducting
phase 1 clinical pharmacokinetic trials of drugs,
3.1.1
If active metabolites (pharmacological and toxicological) are known and the
concentration is high enough, it can be determined a) The
study is about its pharmacokinetics, and metabolites need to be measured b)
Only conduct bioequivalence experiments, and metabolites do not need to be
measured when the original drug can be measured. 3.1.2
If there is an active metabolite known, but the concentration is low and
difficult to measure, it does not need to be measured. 3.1.3
If the metabolites will affect the metabolism, distribution and excretion of
the drug, the measurement of the metabolites should be considered when studying
its pharmacokinetic characteristics. However,
it is difficult to judge whether a metabolite is active in the human body,
because its activity is supported by its preclinical data. At this time, you
can refer to the March 2005 version of "Technical Guiding Principles for
Clinical Pharmacokinetic Studies of Chemical Drugs" and FDA's
"Bioavailability and Bioequivalence Studies for Orally Administered Drug
Products - General Considerations" (2003) 3.2 When detecting
the concentration of metabolites in biological samples,
3.2.1
When metabolites can affect the safety and effectiveness of drugs: Pharmacokinetic
studies: Simultaneous determination of concentrations of parent drug and
metabolites, Equivalence
test: The concentrations of the parent drug and metabolites are measured
simultaneously, and the parent drug is used as the main judgment indicator when
evaluating equivalence. 3.2.2
When the activity of the main metabolite is unclear: Pharmacokinetic
studies: determination of parent drug and metabolite concentrations, Equivalence
test: Determination of parent drug concentration. 3.2.3
When the prodrug concentration is very low and the metabolite is the main form
in the body: Pharmacokinetic
studies: determination of parent drug and metabolite concentrations, Equivalence
evaluation: Determine the concentration of metabolites. 3.2.4
Prodrugs: Pharmacokinetic
studies: determination of parent drug (if available) and metabolite
concentrations, Equivalence
test: Determination of metabolite concentration. Biological samples
commonly used for metabolite determination
Biological
samples commonly used for metabolite determination include blood samples
(plasma, serum and whole blood), urine samples, and saliva. Collection
and storage of commonly used biological samples: plasma - add anticoagulant to
whole blood, centrifuge, and take the supernatant; serum - centrifuge the whole
blood, take the supernatant. After blood collection, plasma or serum must be
separated by centrifugation as soon as possible and stored frozen below -20°C.
Urine sample - collect urine samples within a certain period of time after
taking the medicine, record the volume, mix evenly and take a certain amount,
measure the concentration of the drug in the urine, and calculate the
cumulative amount of the drug in the urine within a certain period of time.
Saliva - After gargling for 15 minutes, collect the mixed saliva that naturally
flows out of the mouth or flows out after stirring in the mouth with the
tongue, and centrifuge to take the supernatant. If the sample cannot be
measured in time after collection, it can be refrigerated at 4°C. If it is left
for a long time, it needs to be frozen and stored at -20°C ~ -80°C. Methods for
determination of metabolites
The
determination of metabolites is one of the most classic and very effective
methods in drug metabolism research. Since
the drug will eventually be excreted from the body through one or more
metabolites associated with the parent nucleus, the isolation, identification
and measurement of metabolites can provide a certain understanding of the
drug's metabolic pathway. In recent years, high-speed, efficient and highly
sensitive analytical methods such as HPLC, GC-MS, LC-MS and GC-MS-MS, LC-MS-MS,
LC-NMR and LC-MS-NMR have been used for the analysis of metabolites. Analysis
and determination. 5.1.HPLC method
Since
the content of drugs and metabolites in body fluids is extremely small and
mixed with a large number of endogenous components, only reliable analysis
methods can ensure accurate analysis results. Gas chromatography-mass
spectrometry (GC-MS) is a powerful tool for analyzing trace and even
ultra-trace compounds and is widely used in this field. However, many drugs and
metabolites lack volatility and thermal stability, which limits its
application. In recent years, high-performance liquid chromatography (HPLC) has
been characterized by its wide application range, high separation efficiency,
easy recovery of components, and speed and simplicity. Along with the
development and application of highly sensitive and selective detectors, it has
been used in many analyses. The method has come from behind and has become one
of the indispensable means for analyzing drug metabolites in the body. Because
the content of drugs and metabolites in the body is very small, it is difficult
to collect enough samples to measure the four major spectra, namely infrared,
ultraviolet, nuclear magnetic resonance and mass spectrometry. Therefore, using
HPLC as a tool to identify unknown substances has become one of the difficult
problems that need to be solved. Although LC-MS is effective, it cannot be
widely used because the instrument is expensive. At present, empirically
inferred compounds are still commonly used. In order to remove the interference
of endogenous components and ensure the column efficiency and life of the
chromatographic column, it is extremely important to pretreat biological
samples. 5.1.1
Separation Different
pretreatments are performed for the different biological sample types selected.
For example, blood samples (including serum and plasma) can be loaded directly
for solid phase extraction. However, if the drug binds to protein, the
extraction recovery rate will be reduced. Therefore, the protein in the metabolites
must be removed to release the bound drug to determine the total concentration.
. Obtain a "cleaner" extract, reduce emulsification, and eliminate
interference with the measurement. For saliva samples, centrifugal
precipitation is mainly used to remove mucin, and the supernatant is taken to
determine the drug concentration. Determination of conjugates in urine often
requires acid hydrolysis or enzymatic hydrolysis to hydrolyze the conjugates. Commonly
used protein removal methods: Protein
precipitation method - formation of insoluble salts or salting out and
dehydration. Commonly used protein precipitating agents include organic
solvents (acetonitrile, methanol, ethanol, acetone, etc.), ammonium carbonate
salts, inorganic acids (trichloroacetic acid, perchloric acid, etc.) and heavy
metal salts (mercury salts, tungstates, copper salts, etc.) . It is most widely
used because biological samples treated with organic solvents or acids are
compatible with reversed-phase HPLC analysis. Tissue
enzyme digestion method - proteolytic enzymes, such as trypsin, pepsin, etc. In
recent years, methods for filtering proteins using microporous membranes have
been reported, which have the advantage of being simple and fast, but can only
measure free compounds. Using acidic and alkaline ion exchange resins to remove
proteins that coexist with alkaline and acidic compounds can complete the
purification and enrichment processes at the same time, so it is often used. 5.1.2
Extraction There
are usually two methods for extracting analytes from biological samples: liquid
phase extraction and solid phase extraction, which are especially necessary
when analyzing ultra-trace compounds. Liquid
phase extraction is also called solvent extraction. Commonly used organic
solvents include: n-alcohol, dichloromethane, chloroform, ethyl acetate,
diethyl ether, benzene, n-hexane, etc. and their mixed solutions. Sometimes a
small amount of methanol or ethanol can be added to reduce emulsification. In
order to effectively extract acidic and alkaline drugs, it is usually necessary
to adjust the pH of the sample. Alkaline drugs are generally adjusted to 12
units higher than their pKa, and acidic drugs are adjusted to 12 units lower
than their pKa, so that the drugs are in a non-dissociated state. Easily
extracted. When extracting highly ionized compounds (such as quaternary
ammonium salts or sulfonates) and amphoteric compounds (such as amino acids),
ion pairs must be added for trial production. Acidic compounds generally use
quaternary ammonium salts or tertiary ammonium salts, and alkaline compounds
use alkyl or aryl sulfonates to form ion pairs to improve organic solvents.
Since organic solvents are generally toxic and flammable, evaporation of the
solvent may cause analytes to evaporate. Loss and sometimes emulsification
phenomenon, etc. Therefore, a simpler and more effective extraction method has
become the goal sought. Among
them, solid-phase extraction method shows broad prospects. Classic solid phase
extraction agents include alumina, activated carbon and diatomaceous earth.
Since alumina can selectively adsorb o-phenolic hydroxyl compounds, it is still
commonly used today. It is usually adsorbed in a weakly alkaline medium (around
pH 8), and the impurities are washed away with water and then the analyte is
eluted with acid. Factors
affecting liquid-liquid extraction: pH value of aqueous phase, extraction
solvent and ionic strength, etc. 1)
Aqueous phase pH Alkaline
drugs: pH 2 to 3 units higher than the pKa of the drug; acidic substances: <
pKa 2 to 3 units 2)
Extraction solvent The
selection of the extraction solvent must consider not only the selectivity of
the extraction, but also the convenience of operation. While satisfying the
extraction efficiency, select a solvent with as little polarity as possible to
achieve a suitable recovery rate and reduce interfering substances to lowest. Generally,
the selection can be based on the principle of similar miscibility, and a
solvent with a low boiling point can be selected. When
the properties of the drugs in the sample are unknown, ether and chloroform can
be used as extraction solvents for acidic and alkaline drugs respectively. 3)
Ionic strength Adding
neutral salts, such as NaCl, to the water phase can increase the ionic
strength, causing water molecules in the solution to strongly associate with
inorganic ions, resulting in fewer water molecules associated with the drug,
making the drug solubility in the water phase smaller, and thus Conducive to
organic solvent extraction. 4) The
volume of organic phase and aqueous phase is 1:1 or 2:1 Factors
affecting liquid-solid extraction: Separation
and recovery rate are important indicators reflecting extraction efficiency.
The main factors affecting extraction rate are: 1)
Eluent flow rate - if the flow rate is too fast, the resolution will decrease,
the sample will be lost, the recovery rate will be low, and the reproducibility
will be poor. 2)
Sample loading capacity - the effective loading capacity depends on the
capacity factor of the analyte, the amount of stationary phase and the sample
concentration. Overload, resulting in sample loss. Select
pretreatment and detection methods based on the drug's pKa value,
lipophilicity, solubility, distribution coefficient, etc. A)
Drugs with lipophilic properties are extracted with solvents at appropriate pH
values B)
Methods of selective precipitation of proteins, solid phase extraction, ion
pair extraction or extraction after derivatization for drugs with strong
polarity or hydrophilicity, etc. C) GC
assay for drug selection with volatile properties D)
Select analytical detection methods with spectral or electrochemical
characteristics E) The
extraction and concentration technology should be selected based on the
stability of the drug: avoid using strong acid or strong alkaline solvents for
drugs that are unstable to acids and bases, avoid high-temperature evaporation
of solvents for drugs that are unstable to heat, and avoid exposure to light
for drugs that are unstable to light. The
selection of sample processing steps and analysis methods is shown in the
figure below
5.2 Other methods for
measuring metabolites
Since
drugs are ultimately excreted through one or more metabolites associated with
the parent nucleus, isolation and identification of metabolites can provide a
certain understanding of the drug's metabolic pathway. Special analysis methods
such as GC-MS, HPLC-MS, GC-MS-MS, LC-MS-MS, LC-NMR and LC-MS-NMR analysis
methods can also be used at this time. They have high speed, high efficiency
and high sensitivity. characteristics and absolute specificity. And the
structure of metabolites can be identified while detecting extremely small
amounts of metabolites. Absorbance
ratio, photodiode matrix detection, evaporative light scattering detection, or
the application of dual detectors (UV, fluorescence) are also some special
methods. In the absence of the above techniques, the peak shape and retention
time of each chromatographic peak should be carefully compared. © 2023 Medicilon |
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Added on November 27, 2023 Last Updated on November 27, 2023 Tags: Determination of metabolites AuthorMedicilonCambridge, MAAboutMedicilon is an integrated contract research organization (CRO), providing comprehensive one-stop new drug R&D services for pharmaceutical enterprises and scientific research institutions around the w.. more..Writing
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