Drug addiction

Drug addiction is a pathological or abnormal condition which arises due to frequent drug use. The disorder of addiction involves the progression of acute drug use to the development of drug-seeking behavior, the vulnerability to relapse, and the decreased, slowed ability to respond to naturally rewarding stimuli. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) has categorized three stages of addiction: preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect. These stages are characterized, respectively, everywhere by constant cravings and preoccupation with obtaining the substance; using more of the substance than necessary to experience the intoxicating effects; and experiencing tolerance, withdrawal symptoms, and decreased motivation for normal life activities. By the American Society of Addiction Medicine definition, drug addiction differs from drug dependence and drug tolerance.
It is, both among scientists and other writers, quite usual to allow the concept of drug addiction to include persons who are not drug abusers according to the definition of the American Society of Addiction Medicine. The term drug addiction is then used as a category which may include the same persons who, under the DSM-IV, can be given the diagnosis of substance dependence or substance abuse. (See also DSM-IV Codes)

The terms abuse and addiction have been defined and re-defined over the years. The 1957 World Health Organization (WHO) Expert Committee on Addiction-Producing Drugs defined addiction and habituation as components of drug abuse:

    Drug addiction is a state of periodic or chronic intoxication produced by the repeated consumption of a drug (natural or synthetic). Its characteristics include: (i) an overpowering desire or need (compulsion) to continue taking the drug and to obtain it by any means; (ii) a tendency to increase the dose; (iii) a psychic (psychological) and generally a physical dependence on the effects of the drug; and (iv) detrimental effects on the individual and on society.

    Drug habituation (habit) is a condition resulting from the repeated consumption of a drug. Its characteristics include (i) a desire (but not a compulsion) to continue taking the drug for the sense of improved well-being which it engenders; (ii) little or no tendency to increase the dose; (iii) some degree of psychic dependence on the effect of the drug, but absence of physical dependence and hence of an abstinence syndrome [withdrawal], and (iv) detrimental effects, if any, primarily on the individual.

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H3 Pharmaceutical Chemistry

H3 Pharmaceutical Chemistry (Syllabus 9812) is an additional subject being offered to the GCE A-level students in Singapore. It replaces the decades old Special paper (otherwise known as paper "0" in syllabus 9251), a paper that is often taken by students aiming for local/overseas scholarship or simply wants to challenge themselves. The first batch of students will be sitting for their examination in November 2007.

As given under the "Introduction" in the syllabus provided by University of Cambridge, H3 is meant for students with exceptional ability and interest in chemistry. The depth of the knowledge is pitched at college freshmen level, with approximately 140 hours of teaching and self-directed independent learning.
Syllabus

The syllabus is divided into 6 sections as follow:

   1. Effects and development of drugs
   2. Properties of functional groups and intermolecular interactions
   3. Molecular Stereochemistry
   4. Understanding Reaction Mechanisms
   5. Separation and Analytical Techniques
   6. Some classes of drugs

Additional information

The above syllabus is somewhat similar to the optional topics offered by International Baccalaureate chemistry. It overlaps considerably with option B, G and H, which are titled "Medicines and Drugs", "Modern Analytical Chemistry" and "Further Organic Chemistry" respectively. The move from Special paper to H3 is primarily to place more emphasis on independent thinking, learning and creativity. Unlike Special paper, H3 takes the students beyond what is covered in the basic H2 syllabus; it therefore allows students to be exposed to more in-depth knowledge at a younger age.

Teaching materials/notes are mainly obtained from a guide written by the University of Cambridge.

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Process of drug discovery

 Discovery

Discovery is the identification of novel active compounds, often called "hits", which are typically found by screening many compounds (compound library) for the desired biological properties. While a number of approaches toward the identification of hits exist, the most successful of techniques relies on chemical and biological intuition developed through years of rigorous chemical-biological training. Other sources of hits can come from natural sources, such as plants, animals, or fungi. Hits may originate also from synthetic chemical libraries, such as those created through combinatorial chemistry or historic chemical compound collections that are tested en-masse against the biological target in question.
Optimization

Another step in drug discovery involves further chemical modifications in order to improve the biological and physiochemical properties of a given candidate compound library. Chemical modifications can improve the recognition and binding geometries (pharmacophores) of the candidate compounds, their affinities and pharmacokinetics, or indeed their reactivity and stability toward metabolic degradation. A number of methods have contributed to quantitative metabolic prediction, and a recent example is SPORCalc[1].The quantitative structure-activity relationship (QSAR) of the pharmacophore play an important part in finding lead compounds, which exhibit the most potency, most selectivity, best pharmacokinetics and least toxicity. QSAR involves mainly physical chemistry and molecular docking tools (CoMFA and CoMSIA), that leads to tabulated data and first and second order equations. There are many theories, the most relevant being Hansch's analysis that involves Hammett electronic parameters, steric parameters and logP(lipophilicity) parameters.
Development

The final step involves the rendering the lead compounds suitable for use in clinical trials. This involves the optimization of the synthetic route for bulk production, and the preparation of a suitable drug formulation.

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