Pharmacology: Bioavailability and Therapeutic Success

Reasons for Therapeutic Plan Failure

There are three primary reasons why a therapeutic plan may not achieve the expected results:

• 1. Inadequate Drug Selection: When the selected drugs are not appropriate for the condition.
• 2. Adverse Effects: The appearance of adverse effects that hinder treatment.
• 3. Patient Non-compliance: When the patient does not meet the requirements of their therapy.

Factors Affecting Drug Distribution Volume

The following factors contribute to the reduction of the volume of distribution of drugs in the body:

• Age
• Sex
• Nutritional status
• Weight

Key Pharmacokinetic Parameters

• Minimum Toxic Concentration (CMT): The concentration level from which toxic effects begin to appear.
• Minimum Effective Concentration (CME): The level at which the pharmacological effect begins.
• Therapeutic Margin: The plasma level range between the CME and CMT.
• Maximum Concentration (Cmax): Represents the maximum plasma concentration reached after the extravascular administration of a drug, relating to the maximum amount of drug absorbed.
• Time (Tmax): The time required to reach the maximum concentration of the drug in the blood after extravascular administration.
• Area Under the Curve (AUC): A parameter used in the determination of bioavailability; it is directly proportional to the fraction of the absorbed dose and represents the total amount of drug that reaches the systemic circulation.

Understanding Bioavailability

Bioavailability is a term indicating the relative measure of the amount of drug that reaches the systemic circulation and the speed with which this process occurs.

Methods for Assessing Bioavailability

• Blood data
• Urinary excretion data
• Clinical methods

Drug Equivalence and Alternatives

• Pharmaceutical Alternatives: Products containing the same therapeutic species, but not necessarily in the same amount or dosage form.
• Chemical Equivalent: Refers to two or more dosage forms containing the identical amount of the same active ingredient.
• Pharmaceutical Equivalents: Medications containing identical amounts of the same active ingredient, but not necessarily the same excipients.
• Bioequivalence: Two drugs are bioequivalent if, being pharmaceutical equivalents or alternatives, their bioavailability after administration of the same molar dose of the active ingredient is analogous, to the point that plasma level curves can overlap and efficacy and safety are essentially identical.
• Therapeutic Equivalent: Drugs are considered therapeutically equivalent if they contain the same active molecular part and present, from a clinical viewpoint, the same efficacy and safety as the reference medicine, for which efficacy and safety have been established beforehand.
• Clinical Equivalence: This means that the same drug, present in two or more dosage forms, leads to a similar effect in vivo, which is appreciated through the response of therapeutic agents or by monitoring a symptom or disease.

Sources of Pharmaceutical Information

• Secondary Sources: International Pharmaceutical Abstracts, Merck Index.
• Mixed Sources: Iowa Drug Information Service (IDIS).
• Primary Sources: Scientific journals and magazines.
• Tertiary Sources: Textbooks.