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Related Concept Videos

Pharmaceutical Alternatives: Polymorphic Form-Related and Particle Size-Related Therapeutic Nonequivalence01:27

Pharmaceutical Alternatives: Polymorphic Form-Related and Particle Size-Related Therapeutic Nonequivalence

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Changes in polymorphic forms can significantly influence the bioavailability of poorly soluble drugs. Although the FDA defines pharmaceutical equivalence based on having the same active ingredient, dosage form, and route of administration, it does not automatically disqualify products with different polymorphic forms. This means two products with different polymorphs can still be deemed pharmaceutically equivalent. However, polymorphic differences can affect properties like wettability,...
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Antiasthma Drugs: Methylxanthines01:24

Antiasthma Drugs: Methylxanthines

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Theophylline, a member of the methylxanthine class of bronchodilators, has long been used in asthma management. While its exact mechanism of action is not fully understood, it is believed to have multiple effects on various cellular processes.
Theophylline is thought to inhibit phosphodiesterase enzymes, increasing intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). This rise in cAMP and cGMP concentrations stimulates cardiac function,...
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Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism01:21

Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism

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Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
Some polymorphic crystals possess lower aqueous solubility than their amorphous counterparts, leading to incomplete absorption. For instance, the oral suspension of Chloramphenicol, which...
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Adrenergic Agonists: Chemistry and Structure-Activity Relationship01:16

Adrenergic Agonists: Chemistry and Structure-Activity Relationship

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Adrenergic agonists' structure-activity relationship (SAR) determines their selectivity and efficacy. These agonists comprise a phenylethylamine moiety with an aromatic ring and an ethylamine side chain.
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of...
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Nonlinear Pharmacokinetics: Dependence of Elimination Half-Life and Dose Clearance01:23

Nonlinear Pharmacokinetics: Dependence of Elimination Half-Life and Dose Clearance

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The elimination half-life and drug clearance of drugs following nonlinear kinetics can vary with dosage. The Michaelis-Menten parameters and drug concentration influence these factors. As the dose increases, the elimination half-life tends to lengthen, resulting in a reduction in clearance and a disproportionately larger area under the curve. The total clearance can be derived from the Michaelis-Menten equation for drugs following a one-compartment model.
A study on guinea pigs examined the...
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Adrenergic Agonists: Mixed-Action Agents01:28

Adrenergic Agonists: Mixed-Action Agents

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Mixed-action adrenergic agonists, like ephedrine and pseudoephedrine, directly and indirectly affect adrenergic receptors. These agents stimulate adrenoceptors and indirectly release stored neurotransmitters, amplifying the adrenergic response.
Ephedrine and pseudoephedrine lack a catecholamine group, making them less susceptible to degradation by metabolic enzymes. They have increased oral bioavailability and lipophilicity, resulting in a longer duration of action. Their response is reduced by...
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Related Experiment Videos

A monoclinic polymorph of theophylline.

Shuo Zhang, Andreas Fischer

    Acta Crystallographica. Section E, Structure Reports Online
    |December 27, 2011
    PubMed
    Summary

    Researchers discovered a new monoclinic polymorph of theophylline, a compound crucial in respiratory medications. This crystal structure, formed via solvent evaporation, reveals unique hydrogen-bonding patterns leading to molecular dimers.

    Area of Science:

    • Crystallography
    • Solid-state chemistry
    • Pharmaceutical science

    Background:

    • Theophylline is a methylxanthine drug used for respiratory diseases like COPD and asthma.
    • Polymorphism, the ability of a solid material to exist in multiple crystalline forms, can significantly impact drug properties.
    • Understanding different polymorphs is essential for drug formulation and efficacy.

    Purpose of the Study:

    • To synthesize and characterize a novel crystalline form of theophylline.
    • To elucidate the crystal structure and intermolecular interactions of the new theophylline polymorph.
    • To contribute to the understanding of theophylline's solid-state behavior.

    Main Methods:

    • Crystallization of theophylline from a chloroform/methanol solvent mixture under ambient conditions.

    Related Experiment Videos

  • Single-crystal X-ray diffraction to determine the unit cell and atomic arrangement.
  • Analysis of hydrogen bonding and crystal packing.

    • Main Results:

    • A new monoclinic polymorph of theophylline (C(7)H(8)N(4)O(2)) was successfully obtained.
    • The asymmetric unit contains two crystallographically distinct theophylline molecules.
    • Intermolecular N-H⋯O hydrogen bonds were identified, forming dimers between the two unique molecules.

    Conclusions:

    • The study reports a novel monoclinic polymorph of theophylline.
    • The crystal structure reveals specific hydrogen bonding leading to dimer formation.
    • This finding enhances knowledge of theophylline's solid-state polymorphism and intermolecular interactions.