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Questions and Answers
What is the preferred route for locally treating diseases affecting the female reproductive tract?
What is the preferred route for locally treating diseases affecting the female reproductive tract?
Due to its __________, the vagina allows the movement of molecules and absorption of certain drugs through the epithelium.
Due to its __________, the vagina allows the movement of molecules and absorption of certain drugs through the epithelium.
gaps in connecting links
What is the term used to describe the first pass effect of drugs in the uterus?
What is the term used to describe the first pass effect of drugs in the uterus?
uterine first pass effect
The thickness of the vaginal epithelium remains constant throughout a woman's life.
The thickness of the vaginal epithelium remains constant throughout a woman's life.
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Match the following components of the vaginal mucus with their descriptions:
Match the following components of the vaginal mucus with their descriptions:
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Which enzymes are the most abundant in the outer layers of vaginal mucus and are involved in enzymatic degradation processes of peptide and protein drugs?
Which enzymes are the most abundant in the outer layers of vaginal mucus and are involved in enzymatic degradation processes of peptide and protein drugs?
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What is the normal vaginal pH range for healthy women of reproductive age?
What is the normal vaginal pH range for healthy women of reproductive age?
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During postmenopause, vaginal pH becomes more acidic.
During postmenopause, vaginal pH becomes more acidic.
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Drugs administered vaginally are classified into weak bases (>50%, pKa = 8.5–10.5) and weak acids (~40%, pKa < ____).
Drugs administered vaginally are classified into weak bases (>50%, pKa = 8.5–10.5) and weak acids (~40%, pKa < ____).
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Match the drug properties that influence vaginal absorption with their descriptions:
Match the drug properties that influence vaginal absorption with their descriptions:
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Study Notes
Anatomy and Physiology of the Vagina
- The vagina is a organ capable of absorbing drugs systemically, with various compounds administered vaginally including sodium salicylate, quinine hydrochloride, and hormones.
- The vagina's large surface area and high blood supply facilitate easy absorption of active substances into the bloodstream.
- The vaginal epithelium is composed of squamous cells with gaps in their connecting links, allowing for the movement of molecules and electrolytes and the absorption of certain drugs.
- The vaginal epithelium acts as a physical barrier, with a thickness that varies with age and hormonal changes.
Vaginal Drug Delivery Systems
- Vaginal drug delivery systems can be optimal for treating and preventing vaginal infections, cervical intraepithelial neoplasia, and delivering hormones for hormone replacement therapy.
- The most common drugs administered vaginally are related to the treatment of vaginal infections, spermicides or contraceptive agents, and induction of labor or interruption of pregnancy.
- Avoiding the hepatic first-pass effect and minimizing systemic exposure can lead to lower dosing and reduced side effects.
Factors Affecting Vaginal Drug Delivery
- Physiological factors: menstrual cycle, age, pregnancy, and menopause can affect drug absorption and distribution.
- Physicochemical properties of drugs: molecular weight, lipophilicity, ionization, and surface charge can influence drug absorption.
- Vaginal microflora: Lactobacillus species play a crucial role in defining the environment and can influence drug absorption.
- Enzyme activity: proteases, aminopeptidases, and dipeptidyl peptidases can degrade peptide and protein drugs.
Vaginal pH and Its Effects
- Vaginal pH ranges from 3.5 to 5, maintained by the production of lactic acid by Lactobacillus.
- pH affects drug ionization potential, with many drugs being weak electrolytes.
- Changes in vaginal pH can affect the release profiles of pH-sensitive drugs.
Rectal Drug Delivery
- The rectal route offers a non-invasive, useful route of drug administration when systemic or local effects are required.
- Advantages over the oral route: avoiding hepatic first-pass metabolism, improving bioavailability, and decreasing side effects.
- The rectal route is useful for patients with nausea, vomiting, objectionable taste, or difficulty in swallowing.
Anatomy and Physiology of the Rectum
- The rectum is a temporary storage area for defecation, with a pH of 7.2-7.4 and a fluid volume of 1-3 mL.
- The rectum epithelium is similar to that of the upper GI tract, with a predominant mechanism of transcellular passage across the cell membrane.
- The rectum has a much lower surface area, but is potentially beneficial for drugs with poor gastrointestinal absorption or low solubility.
Factors Affecting Rectal Drug Delivery
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Physiological and pathological factors: stool presence, motility, and bowel movements can affect drug absorption.
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Physicochemical factors: dissolution, stability, and drug contact with the mucosal wall.
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Formulation factors: dosage form and drug-associated factors can influence drug absorption.
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Pathological conditions: inflammatory bowel disease, hemorrhoids, and gastro-intestinal infections can influence drug absorption and efficacy.### Factors Affecting Rectal Absorption of Drugs
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Proctitis (inflammation) can alter drug absorption from the rectum
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Ionized drugs have a higher degree of ionization, leading to higher absorption
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Particle size affects absorption, with smaller particles having a greater surface area to volume ratio, leading to faster dissolution and absorption
Formulation of Rectal Dosage Forms
- The type of formulation used influences the absorption of drugs
- Aqueous and alcoholic solutions can lead to rapid absorption, which is therapeutically valuable in acute convulsive attacks
- Suppositories have slower absorption, dependent on the nature of the suppository base, use of surfactants, and particle size of the active ingredient
Partition Coefficient and Lipophilicity
- LogP measures the lipophilicity or hydrophobicity of the drug molecule
- The lipophilicity of the drug affects its absorption through the transcellular route, with higher lipophilicity leading to greater absorption
- A balance between lipophilicity and hydrophilicity is necessary for effective rectal drug administration
Dissociation Constant and Degree of Ionization
- The existence of a drug in its ionized or unionized form affects drug absorption
- Unionized drugs are more lipophilic and show higher absorption through the transcellular route
- Basic drugs with a pKa near or above the physiological pH of the rectum exist more in the unionized form and show higher absorption
Solubility
- Solubility affects the concentration of the free drug available for absorption
- Higher solubility favors higher dissolution and faster absorption
Particle Size and Liquid Formulations
- Smaller particles have a faster dissolution rate and solubility, leading to faster absorption
- Drugs with a particle size of 50-100 µm show maximum absorption through the rectal route
- Liquid formulations have a faster drug release and solubilization, leading to faster absorption and greater spreading capacity
Solid and Semi-Solid Formulations
- Solid formulations undergo disintegration, liquefaction, and dissolution before drug release and absorption
- Solid formulations have a longer time to obtain a therapeutic effect compared to liquid formulations
- Semi-solid formulations provide better retention time in the rectum, reduce patient compliance issues, and increase drug release
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Description
Learn about the structure and function of the vagina, including its ability to absorb drugs and its composition of squamous cells.
