Drug Solubility and Complexation

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Questions and Answers

What is the significance of poorly soluble drugs forming an intermolecular complex with soluble materials?

It improves their solubility, allowing for better absorption and effectiveness.

Explain why most complexes are considered macromolecular and inactive.

They are often too large to cross lipid membranes and remain inactive until dissociated into smaller, active molecules.

How do cyclodextrins improve the properties of poorly soluble drugs?

They create inclusion complexes that enhance solubility by encapsulating the drug within their hydrophobic interior.

What is a common method to increase the aqueous solubility of poorly soluble acids and bases?

<p>Converting them into their salt forms can significantly increase their aqueous solubility.</p> Signup and view all the answers

List two uses of nonaqueous solutions in pharmaceuticals.

<p>They are used for stability and as depot injections.</p> Signup and view all the answers

What are fixed oils, and provide an example of their use in pharmaceutical preparations.

<p>Fixed oils are non-volatile oils that act as solvents, such as almond oil used in oily phenol injections.</p> Signup and view all the answers

How do polyhydric alcohols function as solvents in pharmaceutical products?

<p>They enhance solubility and stability, acting as cosolvents, like propylene glycol in Diazepam Injection.</p> Signup and view all the answers

Discuss the role of Dimethylsulfoxide (DMSO) in drug formulations.

<p>DMSO aids in drug penetration through the skin and is mainly used in veterinary medicine.</p> Signup and view all the answers

Why is ethyl ether not used internally in therapeutic applications?

<p>Ethyl ether is considered too volatile and can be harmful when used internally.</p> Signup and view all the answers

Give an example of a miscellaneous solvent and its application in pharmaceuticals.

<p>Isopropyl myristate is used in cosmetics and certain topical formulations.</p> Signup and view all the answers

Flashcards

What is complexation in pharmaceutics?

A process where poorly soluble drugs are made more soluble by forming a complex with a soluble material. This usually involves forming a macromolecular complex, which is inactive in terms of crossing lipid membranes.

How do cyclodextrins work to enhance drug solubility?

Cyclodextrins are ring-shaped molecules with a hydrophobic inner cavity and a hydrophilic outer surface. Poorly soluble drugs can fit inside the cavity, forming an inclusion complex, which increases their water solubility.

What is chemical modification for drug solubility?

Turning poorly soluble acids or bases into their salt forms can significantly increase their water solubility. This involves changing the chemical structure of the drug to make it more polar.

What are nonaqueous solvents used for?

Nonaqueous solvents are used to dissolve drugs that are not soluble in water. They offer advantages like increasing stability and providing a depot effect for slow release.

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What are fixed oils and their applications in pharmaceutics?

Fixed oils, like almond oil and castor oil, are traditionally used for injection and external applications. They dissolve poorly water-soluble drugs and provide a slow release.

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What are alcohols used for in pharmaceutics?

Ethyl alcohol is commonly used externally as a cooling agent and in some lotions due to its ability to dissolve certain drugs. Industrial methylated spirit (IMS) is a denatured form of ethyl alcohol.

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What are polyhydric alcohols used for in pharmaceutics?

Polyhydric alcohols like propylene glycol and polyethylene glycol (PEG) are widely used as solvents in various pharmaceutical formulations due to their excellent solubility properties.

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What is dimethylsulphoxide (DMSO) and its application?

Dimethylsulphoxide (DMSO) is a highly polar solvent that enhances drug penetration through the skin. It is commonly used in veterinary medicine.

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What is ethyl ether and its application?

Ethyl ether is a volatile and flammable solvent used mainly as an extraction agent for crude drugs. It's not used internally for therapeutic purposes due to its toxicity.

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What are some miscellaneous solvents in pharmaceutics?

Isopropyl myristate and isopropyl palmitate are commonly used in cosmetics as solvents and emollients. Xylene is a solvent used for dissolving earwax.

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Study Notes

Complexation

  • Poorly soluble drugs combined with soluble materials form soluble intermolecular complexes.
  • Most complexes are macromolecular and inactive, unable to cross lipid membranes.
  • Complex formation is easily reversible.
  • Many complexes aren't water-soluble, contributing to prolonged drug release.
  • Example: Polyvinylpyrrolidone (PVP) plus iodine improves iodine's aqueous solubility.
  • Another example: Cyclodextrins are a series of glucopyranose units forming hollow cylinders (conical shape).
  • The inside of cyclodextrins is hydrophobic, while the outer part is hydrophilic.
  • Poorly water-soluble drugs can fit inside cyclodextrins, creating a freely water-soluble inclusion complex.

Chemical Modification

  • Poorly soluble acids and bases can be converted to salts to improve aqueous solubility.
  • Example: Sodium phosphate salts of hydrocortisone, prednisolone, and betamethasone.

Nonaqueous Solutions

Uses

  • Stability: Propionate and benzoate esters of testosterone and estradiol provide depot effects.

Choice

  • Factors affecting choice include toxicity, irritancy, sensitization, flammability, cost, stability, and compatibility with other excipients.
  • Parenteral product choices are further limited.

Classification of Nonaqueous Solvents

1. Fixed Oils of Vegetable Origin
  • Non-volatile oils derived from plants, mainly fatty acid esters of glycerol.
  • Examples: Almond oil (oleic acid), castor oil (miconazole eye drops), olive oil, sesame oil, maize oil, cottonseed oil, soya oil.
  • Used in emulsions and parenterals.
2. Alcohols
  • Examples: Ethyl alcohol (external use, cooling, salicylic acid lotion) industrial methylated spirit (IMS), isopropyl alcohol (diclophane/abuse/denaturation).
3. Polyhydric Alcohols/Glycols
  • Toxic.
  • Examples: Propylene glycol (Diazepam injection, Co-trimoxazole IV Infusion, Chloramphenicol Ear Drops, hydrocortisone ear drops), Peg400 (cosolvent with water/glycerol, water-miscible ointment bases, clotrimazole topical solution).
4. Dimethyl Sulphoxide (DMSO)
  • Highly polar.
  • Aids drug penetration through skin, mainly for veterinary drugs.
  • Example: Idoxuridine for human skin application.
5. Ethyl Ether
  • Not used internally (therapeutic).
  • Cosolvent with alcohol in some collodions.
  • Used in crude drug extraction.
6. Miscellaneous Solvents
  • Examples: Isopropyl myristate/isopropyl palmitate (cosmetics) and xylene (ear drops/dissolves ear wax).

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