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What effect does a hygroscopic base have on mucosal membranes?
Which base would provide a rapid drug release for a drug that is more soluble in water than in oil?
What is an example of a slow-release agent used in suppositories?
Which of the following ingredients is used for deodorizing flatulence in suppositories?
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Which component of a suppository base is hygroscopic?
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How does the volume of a suppository determine its formulation?
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In an antiemetic suppository, which ingredient acts as a suspending aid?
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Which formulation characteristic is important for the cocoa butter-base suppository?
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What is one advantage of using suppositories for drug delivery?
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Which of the following is a disadvantage of rectal drug delivery?
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What is a common issue that may affect vaginal absorption of medications administered via pessaries?
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Suppositories avoid certain issues associated with oral administration. Which of the following is NOT one of them?
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How does the first pass metabolism affect the effectiveness of rectally administered drugs?
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What might impede the self-administration of suppositories for patients with arthritis?
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What is a reason that rectal absorption can be erratic?
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Which method can help facilitate the insertion of a rectal suppository?
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Which vein is responsible for draining the superior rectal vein into the hepatic portal vein?
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What is the primary factor that can significantly affect rectal drug absorption?
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Which type of drug absorption occurs with hydrophobic base suppositories?
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What characteristic of a suppository base can make it hygroscopic?
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Which statement is true regarding the middle and inferior rectal veins?
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What is a notable feature of glycogelatin as a suppository base?
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Which factor does NOT typically affect rectal absorption?
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What is the relationship between the superior rectal vein and first pass hepatic metabolism?
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Which of the following can enhance drug solubility for rectal absorption?
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What must be adjusted when formulating suppositories that contain more than 5% w/w drug?
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If a drug with a 'displacement value' of 2.0 displaces how much base when 1.0 g of the drug is used?
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What is the formula for calculating the displacement value (DV) of a drug?
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Which of the following drugs has the highest displacement value?
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If a drug has a displacement value of 1.5 when calculated with cocoa butter, what will its DV be with a PEG base?
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What is the density of cocoa butter used in the displacement value calculations?
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What weight of base is needed when preparing a suppository containing 1.0 g of drug, considering its displacement?
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Which factor influences the displacement value of a drug?
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What is the purpose of moistening powder with mineral oil before blending with melted base?
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What should be done with suppositories before they have completely hardened?
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Which of the following is a common ingredient in hormone replacement pessaries?
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What is the correct density of glycerinated gelatin used in formulary calculations?
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How much base is required for a pessary containing 500 mg metronidazole?
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Which stage of the suppository preparation involves minimizing handling to prevent melting?
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What is the purpose of allowing slow cooling and congealing of the melted mixture?
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In what form are suppositories and pessaries typically delivered?
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Study Notes
Rectal blood circulation
- Superior rectal vein drains into the hepatic portal vein
- The portal vein leads to the “first-pass hepatic metabolism” of drugs
- Middle and inferior rectal veins drain directly into general systemic circulation
- Little “first-pass hepatic metabolism” of the drug occurs in the middle and inferior rectal veins
Rectal Drug Absorption
- Hydrophobic base suppositories melt into a very thin layer of mucous that allows the drug to be passively diffused
- Hydrophilic base suppositories dissolve and mix with the mucous layer where the drug is then passively diffused
Factors affecting rectal absorption
- The type of base used
- The type of drug
- The solubility of the drug in the vehicle (surfactant may be needed)
- The concentration of the drug
- The particle size of the drug
Hydrophilic Base: Glycogelatin
- Glycogelatin is made up of: Glycerin + Gelatin + Water (e.g. 70:20:10)
- It is not used as much as cocoa butter or PEG bases
- Glycogelatin is good for laxative suppositories
- Used for vaginal suppositories (e.g.paracetamol, morphine)
- It can also deliver: anti-inflammatories, anti-emetics and anti-nausea drugs, sedatives/tranquilisers, antihaemorrhoidals, hormones, antibacterials, antifungals, contraceptives
Advantages of suppositories and pessaries
- Ease of administration by a professional or by the user
- Easy to remove or flush out if necessary
- Useful for young children and the elderly
- Provides rapid, targeted drug delivery when systemic delivery is unsuitable
- Limits systemic exposure to the drug
- Partially avoids first-pass intestinal and hepatic metabolism allowing > 30% of the dose to reach systemic circulation unchanged
- Allows for large doses to be delivered
Advantages of suppositories and pessaries (cont’d)
- Can be used in unconscious and disabled patients
- Can be used in infants and young children
- Avoids problems with oral administration:
- Taste or smell
- Drug degradation in the stomach acid
- Nausea and vomiting
- Pre-surgical need to keep stomach empty
Disadvantages of suppositories and pessaries
- Drug absorption is slower vs. oral or IV administration
- Percentage absorption is variable and unpredictable
- Not suitable for drugs with a narrow therapeutic range
- Potential for mucosal irritation
- Potential for triggering defecation and loss of product from the rectum
- Diarrhoea and GI disease reduce absorption
Disadvantages of suppositories and pessaries (cont’d)
- Menstruation can affect vaginal absorption
- Leakage of melted product
- Can be difficult for arthritics to self-administer
- Cost of production is high
Drug release rates from different bases
- Oily bases promote slow drug release for oil-soluble drugs, and rapid release for water-soluble drugs
- Water-miscible bases produce a moderate drug release for oil-soluble drugs, and slow to fast release for water-soluble drugs
Preparing cocoa butter suppositories
- Wash hands, wear rubber or vinyl gloves
- Remove the suppository from its wrapping
- Moisten the suppository if necessary
- Lubricate the mould if required
- Pour the stirred melt into the mould quickly in one movement
- Allow the suppository to cool and congeal slowly
- Trim excess if needed
- Carefully remove the suppository from the mould
- Wrap and put into a container
- Label and dispense
Formulating suppositories
- Suppositories have a fixed volume determined by the volume of the mould
- When formulating suppositories with >5% w/w drug, we need to allow for the volume of the base “displaced” by the drug and reduce the quantity of the base in the mixture accordingly
Displacement Values
- Drugs have a “displacement value” (DV) or “density factor”
- The DV is the number of grams of active ingredient that displaces 1 gram of base
- DV = Density of drug / density of cocoa butter
- Reference books usually list DVs relative to cocoa butter base which has a density of 0.9 g/mL
Examples of DVs
- Boric acid: 1.5
- Codeine phosphate: 1.1
- Hydrocortisone: 1.5
- Morphine HCl: 1.6
- Paracetamol: 1.5
- Phenobarbital: 1.2
- Zinc oxide: 4.0
Displacement Values relative to PEG bases
- PEG bases have a density of 1.09 g/mL (about 1.20 times the density of cocoa butter)
- To calculate the DV relative to PEG, divide the DV relative to cocoa butter by 1.2
- For example, boric acid DV vs. cocoa butter 1.5, DV vs. PEG 1.5 / 1.2 = 1.25
Examples of Vaginal Pessaries
- Hormone replacement pessary: Progesterone 200 mg (active), Silicon dioxide 35 mg (suspending aid), Polyethylene glycol base qs (base)
- Antibiotic for vaginal vaginosis: Metronidazole 500 mg (active), Glycerinated gelatin base qs (base)
Summary
- Suppositories and pessaries are solid dosage forms designed to deliver drugs to the rectum or vagina.
- Some suppositories are designed to deliver drugs locally, while others are designed to deliver drugs systemically.
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Description
Explore the intricacies of rectal blood circulation and drug absorption through this quiz. Understand the differences in absorption based on drug solubility and base types, including hydrophilic and hydrophobic suppositories. Test your knowledge on the factors affecting these processes.
