Narcotic drugs: biochemical pharmacology. New York: Plenum Press.
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Chicago: Clouet, Doris H. Narcotic Drugs: Biochemical Pharmacology.. Set language NL EN. Contact Live chat offline E-mail: libservice ugent. You are not connected to the UGent network. Ingang koepelzaal gesloten IIngang koepelzaal gesloten CRI HC p These disorders can change receptor binding, alter the level of binding proteins, or decrease receptor sensitivity. Aging tends to affect pharmacodynamic responses through alterations in receptor binding or in postreceptor response sensitivity see table Effect of Aging on Drug Response. Pharmacodynamic drug—drug interactions result in competition for receptor binding sites or alter postreceptor response.
From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Merck Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge. Common Health Topics. The free radicals that are generated cause oxidative stress, lipid peroxidation, DNA damage, and hence cytotoxicity. These effects are particularly responsible for the antitumor property of a drug like doxorubicin.
Drugs containing ester functions R 1 COOR 2 such as procaine are hydrolyzed by a variety of non-specific esterases in liver, and plasma while drugs with amide bonds are hydrolyzed by amidases in the liver. The polypeptide drugs such as insulin and growth hormones are hydrolyzed by peptidases in the plasma and erythrocytes. The metabolites resulting from hydrolysis reactions are subjected to phase II biotransformation reactions before excretion in the bile or urine. They require participation of specific transferase enzymes and high energy activated endogenous substances.
Most of the conjugation reactions result in detoxification of the drug although in some cases conjugation reactions result in bioactivation of drugs. The following is a summary of the different types of phase II biotransformation reactions;. Glutathione-S-transferases catalyze the enzymatic conjugation of xenobiotics with the endogenous tripeptide glutathione, glutamylcystenylglycine GSH.
The xenobiotics with suitable electrophilic centres such as the epoxides and nitro groups can be subjected to nucleophilic attack by glutathione Figure 9.
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The final product, mercapturic acid is easily excreted from the body. Glutathione conjugation reactions for a drug with a suitable nucleophilic centre leads to the formation of mercapturic acid which is easily excreted from the body. This is the conjugation of a drug or xenobiotic with glucuronic acid.
Many functional groups are subject to glucuronidation.
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The benzoyl group in morphine, an analgesic and the amine group in meprobamate a sedative can undergo glucuronidation. A drug with a benzoyl group can undergo glucoronidation by a transferase as shown below:. A number of aromatic compounds are transformed by phase I reactions to form epoxide intermediates. The epoxides are reactive electrophilic species that can bind covalently to proteins and nucleic acids to bring about toxic effects.
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These epoxides are detoxified via the nucleophilic attack of water molecule on one of the electron deficient carbon atoms of the oxizane ring as shown below:. Acetylation is achieved by cytosolic enzymes known as N-acetyl transferases which catalyze transfer of acetate from acetyl co-enzyme A to primary aromatic amine or hydrazides figure Acetylation reations leading to the formation of N— Acetylsulfanilamide, the final metabolite of the antimicrobial agent sulfanilamide which is secreted from the body.
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Most of the methyl transferases are cytosolic enzymes. They utilize S-adenosyl methionine SAM as the methyl donor. The final metabolite, thiopurine, has antineoplastic properties and is used as an anticancer agent Figure Many adverse drug reactions can be traced to an improper balance between bioactivation and detoxification reactions. For example, when the analgesic acetaminophen is given at normal therapeutic doses, it undergoes glucuronidation and sulfation reactions that terminate the action of the drug and hasten its elimination.
However, some of the drug is bioactivated via Cyt P to form N-acetylbenzoquinimine, a reactive intermediate that can be detoxified by conjugation with glutathione GSH. When excessive doses of the drug are given, glucuronidation and sulfation reactions become saturated and more acetaminophen is bioactivated via Cyt P This imbalance leads to high concentrations of N-acetylbenzoqunonine which cannot be sufficiently eliminated by the limited concentrations of gluthathione.
This metabolite binds covalently to cellular protein thiols and initiates hepatotoxicity leading to hepatic necrosis. Problem 1: Describe how you can determine the partition coefficient of a labeled drug. Solution: The partition coefficient of a drug is its differential distribution between the hydrophobic and hydrophilic phases. The distribution of the drug between these two phases can be determined by allowing equilibration of a radioactively labeled drug between aqueous buffer containing the drug and a cell membrane preparation obtained by homogenization and fractionation of a tissue sample.
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The ratio of drug concentration in the membrane to the concentration in the aqueous phase gives the partition coefficient. When the ghosts are prepared in 14 C glucose, it will be possible to monitor the rate of release or uptake of the labeled 14 C glucose from the membranes into the aqueous environment. When log 10 C was plotted vs time h a linear response was obtained with a slope of — 0.
Calculate the following pharmacokinetic parameters;. Once the apparent volume of distribution is known for a particular drug the amount of drug that must be given to achieve a desired concentration can be determined from. For a practical loading schedule, the maintenance interval should be lowered to say 8. The analytical method of assaying paracetamol relies on the introduction of a nitro group into the molecule after the removal of plasma proteins through precipitation. The resultant nitrophenol compound which is formed has a deep yellow colour in an alkaline medium and absorbs at nm Figure Describe how you would construct the standard curve for determination of paracetamol concentration.
These are the classical approaches to drug discovery that do not initially involve detailed scientific study they include the following;.
This is the discovery of drugs based on traditional medical knowledge. The best example is the documented analgesic effects of extracts from opium poppy that led to the isolation of morphine from the plant and the subsequent synthesis of related analgesics. This is the accidental discovery of novel drugs based on the ingenuity of a scientist investigating a problem initially unrelated to the observed phenomenon; examples of such discoveries include the observation by Alexander Flemmings that penicilliummould could inhibit the growth of bacteria.
This finding led to the discovery of antibiotics. Discovery of therapeutic usefulness of a side effect e. An example of discovery arising from studies of endogenous agents in test animals is the anticoagulant action of the venom from the Malayan viper that led to the identification of the anticoagulant ancrod. These are those approaches that form a basis for the rational design of drugs and include the following;. This is the screening of a large number of natural products, chemical entities, large libraries of peptides, nucleic acids and other organic molecules for biological activity.
This approach may lead to identification and development of new drug molecules. This is the profiling of natural products of related plant species screening using either liquid or gas chromatography mass spectrometry to determine active metabolites that may be present in novel crude herbal medical preparations.
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This is the most advanced technique for drug discovery. It entails virtual screening or docking of compounds on the 3-D- structure of a known receptor based on homologies of the test drug molecules with a known test parent drug.
In silico screening can form a basis for the modification of a known drug molecule to determine possible therapeutic applications and may lead to the development of putative drugs against new targets. Selection of molecules for further study is usually conducted in animal models of human disease and the pharmacological tests include both the in vitro and in vivo studies after the initial screening for biological activity.
For instance, antibacterial activity of drugs is assessed by their ability to inhibit growth of a variety of micro-organisms, while hypoglycemic drugs are tested for their ability to lower blood pressure. The in vitro methods include incubation of a parent compound with various subcellular fractions such as microsomes, individual recombinant drug metabolizing enzymes from cells or tissue slices.
The in vivo studies involve working on typical animal models such as dogs or rats.