Pharmacology

The Molecular Mass of Medications

Composition of a Medication

• A medication consists of one or more active ingredients, which are chemical molecules responsible for pharmacological properties and undesirable effects.

• Excipients, which are inert molecules without pharmacological effect, are added to the active ingredients.

• Excipients are necessary for the manufacturing, administration, or preservation of the medication, such as binders, solubilizers, and colorants.

• The final medication is an ensemble of chemical molecules composed of the active ingredient(s) + excipients.

Atomic Structure

• An active ingredient is composed of atoms.

• Atoms consist of a nucleus, positively charged, around which negatively charged electrons orbit.

• The nucleus contains protons (positive charge) and neutrons (no charge), making the nucleus positively charged overall.

• In an atom, the number of protons (positive charges) equals the number of electrons (negative charges), making the atom electrically neutral.

Ions

• An atom or molecule that loses or gains one or more electrons becomes an ion.

• If an atom or molecule loses electrons, it loses negative charges and becomes a positive ion or cation (e.g., sodium ion Na+).

• If an atom or molecule gains electrons, it gains negative charges and becomes a negative ion or anion (e.g., chloride ion Cl-).

Molecules and Chemical Bonds

• When atoms associate with each other, they form a molecule, which is an electrically neutral chemical entity.

• Molecules are formed by chemical bonds between atoms, which can be of two types:

• Covalent bonds: electrons are equally shared between two atoms, forming a strong, solid connection.

• Weak bonds: such as hydrogen bonds or Van der Waals forces, which are fragile.

• The nature and number of atoms in a molecule are given by its formula. For example, the formula for water is H2O, meaning a molecule of water consists of 2 hydrogen atoms and 1 oxygen atom.

Molecular Mass Calculation

• Molecular mass is calculated by summing the atomic masses of the different atoms in the molecule, expressed in daltons (Da).

• For example, the molecular mass of aspirin is:

• 9 x carbon (12) = 108

• 8 x hydrogen (1) = 8

• 4 x oxygen (16) = 64

• Total: 108 + 8 + 64 = 180 Da

Types of Active Ingredients Based on Molecular Mass:

• Chemical synthesis: generally have a low molecular mass, between 100 and 1,000 Da (e.g., aspirin).

• Peptides or proteins: generally have a high molecular mass, between 5,000 and 100,000 Da (e.g., insulin).

Influence of Molecular Mass on Pharmacokinetics:

• The molecular mass of active ingredients is an important factor in understanding their behavior in the body.

• Active ingredients with low molecular mass can easily cross the digestive barrier and be absorbed through passive diffusion.

• They can also easily diffuse into most tissues.

• Molecular mass affects the renal excretion of active ingredients.

• The kidneys filter molecules with a molecular mass below 50,000 Da and retain those above this limit.

In conclusion, the molecular mass of an active ingredient depends on its composition in atoms and varies with the chemical origin of the active ingredient. Knowing this mass is important as it helps determine the behavior and pharmacokinetics of active ingredients in the body.