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Two-state model:
Two-state model:
A simplified model of receptor activation by agonists. The receptor is hypothesized to be in conformational equilibrium between an inactive conformation R and an active conformation R*, with the equilibrium in the absence of agonist normally favoring the inactive state. Agonists bind preferentially (i.e. with greater affinity) to the active state, and by mass action shift the conformational equilibrium such that a greater proportion of receptors are in the active R* conformation. Inverse agonists shift the conformational equilibrium such that a greater proportion of receptors are in the inactive R* conformation.
United States Pharmacopoeia (U.S.P.):
The United States Pharmacopoeia is a reference volume, published every five years by the U.S. Pharmacopoeial Convention, which describes and defines approved therapeutic agents, as well as sets standards for purity, assay, etc. Agents are included on the basis of their therapeutic value. The U.S.P. is recognized by the F.D.A. as the official standard for the agents described therein.
The purposes of the Pharmacopoeia, as described in the Preface to the first edition in 1820 by Dr. Jacob Bigelow, are to :
1. Select the best, established drugs (those "the utility of which is most fully established and best understood").
2. Set standards of pharmaceutical quality for them (" form from them preparations and compositions in which their powers may be exerted to the greatest advantage ").
3. Name them ("distinguish those articles by convenient and definite names, such as may prevent trouble or uncertainty in the intercourse of physicians and apothecaries").
4. Encourage their use ("the value of a Pharmacopoeia depends upon the fidelity with which it conforms to the best state of medical knowledge of the day. Its usefulness depends upon the sanction it receives from the medical community and the public; and the extent to which it governs the language and practice of those for whose use it is intended:).
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