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Questions and Answers
Which term is used to describe the fraction of an administered drug that reaches the systemic circulation?
Which term is used to describe the fraction of an administered drug that reaches the systemic circulation?
What factor can lead to incomplete bioavailability during oral administration?
What factor can lead to incomplete bioavailability during oral administration?
What is commonly used to assess bioavailability between oral and intravenous drug administration?
What is commonly used to assess bioavailability between oral and intravenous drug administration?
When comparing the oral dose to the intravenous dose for a drug with a bioavailability of 0.1, what would be the oral dose relative to the intravenous dose?
When comparing the oral dose to the intravenous dose for a drug with a bioavailability of 0.1, what would be the oral dose relative to the intravenous dose?
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What main factor might skew the measurement of bioavailability from an oral dose compared to an intravenous dose?
What main factor might skew the measurement of bioavailability from an oral dose compared to an intravenous dose?
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What is bioavailability (F) specifically defined as?
What is bioavailability (F) specifically defined as?
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Which factor does NOT influence the rate of absorption of a drug?
Which factor does NOT influence the rate of absorption of a drug?
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Which type of drugs is primarily administered through inhalation methods?
Which type of drugs is primarily administered through inhalation methods?
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What is the main advantage of using modified-release formulations?
What is the main advantage of using modified-release formulations?
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In the context of drug absorption, how does food intake affect the absorption of medications?
In the context of drug absorption, how does food intake affect the absorption of medications?
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For which route of administration is the bioavailability considered to be 1?
For which route of administration is the bioavailability considered to be 1?
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How does the absorption of basic drugs generally occur in the stomach?
How does the absorption of basic drugs generally occur in the stomach?
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What effect does rapid elimination of a drug have on its plasma concentration with regular oral dosing?
What effect does rapid elimination of a drug have on its plasma concentration with regular oral dosing?
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Which factor does NOT influence the rate of absorption from intramuscular injections?
Which factor does NOT influence the rate of absorption from intramuscular injections?
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What is a key characteristic of the nasal mucosa that supports intranasal drug absorption?
What is a key characteristic of the nasal mucosa that supports intranasal drug absorption?
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Which method is typically used to achieve a prolonged absorption of drugs from an injection site?
Which method is typically used to achieve a prolonged absorption of drugs from an injection site?
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Why is inhalation rarely used to achieve systemic drug effects?
Why is inhalation rarely used to achieve systemic drug effects?
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What is the purpose of subdermal implants in hormonal contraception?
What is the purpose of subdermal implants in hormonal contraception?
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Which type of drug is commonly administered intranasally for acute migraine treatment?
Which type of drug is commonly administered intranasally for acute migraine treatment?
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How does the absorption of insulin glargine occur after subcutaneous injection?
How does the absorption of insulin glargine occur after subcutaneous injection?
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Which factor is least likely to affect the bioavailability of a drug administered via inhalation?
Which factor is least likely to affect the bioavailability of a drug administered via inhalation?
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Study Notes
Oral Administration Bioavailability
- Bioavailability (F) is the fraction of the administered dose reaching the systemic circulation.
- Oral bioavailability can be complete (F=1) or incomplete (F<1). Factors contributing to incomplete bioavailability include:
- Incomplete absorption due to the drug not fully dissolving or being adsorbed onto gut contents.
- Inadequate lipid solubility for absorption.
- First-pass metabolism in the gut lumen, gut wall, or liver before reaching systemic circulation.
- Bioavailability is independent of drug dose (same proportion absorbed between large and small doses).
- Bioavailability comparison: comparing plasma concentration after oral vs. intravenous administration.
- Area under the plasma concentration-time curve (AUC) is used because oral and intravenous dosing have different concentration-time profiles.
Rate of Absorption
- The rate of absorption for oral administration is determined by the drug's movement from the gut lumen to the systemic circulation.
- Factors influencing the rate of absorption:
- Gastric emptying: basic drugs are poorly absorbed in the stomach, resulting in a delay.
- Food: slows gastric emptying and drug absorption.
- Decomposition or first-pass metabolism: reduces drug reaching circulation without affecting the absorption rate.
- Modified-release formulations: control drug release, reducing frequent dosing and improving adherence.
Absorption Routes
- Routes other than oral administration:
- Intravenous (IV): F=1, 100% of the drug enters the circulation.
- Transdermal (patches): produces low but constant blood concentrations for drugs like nicotine replacement therapy.
- Intradermal and Subcutaneous Injection:
- Bypasses the stratum corneum barrier.
- Limited by blood flow to the injection site.
- Primarily for local effects but can be used for slow absorption, as seen with insulin glargine.
- Subdermal Implants:
- Long-term hormonal contraception.
- Implants release hormones for up to 3 years.
- Intramuscular Injection:
- Rate of absorption depends on blood flow and drug water solubility.
- Depot formulations (e.g., flupentixol decanoate) prolong absorption.
- Intranasal Administration:
- Nasal mucosa offers large surface area and low enzyme activity.
- Used for systemic effects (e.g., triptan drugs) and local effects (e.g., decongestants).
- Inhalation:
- Lungs have high surface area and blood flow but are rarely used for systemic effects.
- Challenges include delivery of nonvolatile drugs and potential for alveolar toxicity.
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