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PSF > Solutions And Solubility > Flashcards

Solutions And Solubility Flashcards

1
Q

Extemporaneous formulation (example)

A

Thiamine (vitamin B1) HCL oral liquid
Medium therapeutic index
Moderate technical risk
Therefore a low to moderate risk extemporaneous preparation

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2
Q 
Extemporaneous formulation (example)
Clinical pharmaceutics
A

Drug should be in solution at all strengths (usually 20-100mg/ml)
pH sensitive: specification of ingredients should be checked prior to use
Stability depends on excipients

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3
Q

Optimising solubility (like dissolves like)

A

Acyclovir (aciclovir)
Max solubility in water at 25 degrees exceeds 100mg/ml
At physiological ph acyclovir will exist as unionised form (Mr 225) and a max solubility in water at 37 degrees of 2.5 mg/ml
pH affects solubility and the salt form

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4
Q

What are the pKas of acyclovir

A

2.27 and 9.25

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5
Q

What is the ClogP of acyclovir

A

-0.95

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6
Q

4 types of solutions

A

Oral solution
Oral elixirs (contain ethyl various alcohols as co solvent. Phenobarbital elixir, 10% v/v propylene glycol, 20% v/v ethyl alcohol)
Oral syrups (ca. 85% sugars)
Others eg mouthwashes, gargles, rectal solutions and enemas

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7
Q

Define pharmaceutical oral solutions

A

Liquid preparations in which the therapeutic agent and the various excipients are dissolved in the chosen solvent system

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8
Q

Advantages of oral solutions

A

Ease of use (children or elderly)
Drug is dissolved and readily available for absorption (as long as the drug is soluble at stomach/GI pH it will have a greater bioavailability than solid oral dosage forms
Modification of taste can improve compliance of bitter tasting drugs

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9
Q

Disadvantages of oral solutions

A

Stability - can’t be used for drugs unstable in water e.g. Aspirin
Limited by the solubility of some drugs
Expensive to transport compared to some other dosage forms (adds to overall cost)
Bulky for patients to carry with them

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10
Q

Common excipients

A

Flavours and colours - sweeteners,dyes, etc.
Preservatives including antioxidants
Vehicle - usually purified water
Co solvents A ethanol, propylene glycol, glycerin
Solubility enhancing agents - ie surfactants
Viscosity modifiers
Buffers

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11
Q

Removal of a molecule or an atom from the solid state

A

Formation of a cavity within the solvent - energetically unfavourable as disorder in the matrix increases and there are fewer solvent-solvent interactions
Solute separation from bulk solute - solute-solute interactions are unfavourable but it is entropically viable
Accommodation of the drug molecule into the cavity - the results of favoured solvent-solute interactions which are similar to solvent-solvent interactions (like dissolves like e.g. Polarity)

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12
Q

Drug solubility and dissolution

A

Involved endothermic processes (requires absorption of heat, breakage of solute-solute and solvent-solvent bonds, formation of solute-solvent bonds)
May liberate energy: dissolution occurs when the Gibbs free energy is negative

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13
Q

Legal requirements of drug solubility

A

Drugs and excipients of a solution must be and remain in solution throughout the shelf life of the product
Products are homogenous (uniform)

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14
Q

What causes changes in solubility

A

Changes in pH and or temperature presents challenges to maintaining homogeneity

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15
Q

Solubility at the selected pH may be

A

High - stable, easy to formulate
Moderate - maybe be pH sensitive for example consider using solubility enhancers as co solvents, buffers or surfactants
Low - co solvents and similar approaches do not exchange solubility sufficiently, consider alternative formulations such as suspensions

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16
Q

Very soluble - approx volume of solvent ml per gram of solute

A

<1

17
Q

Freely soluble - approx volume of solvent ml per gram of solute

A

From 1 to 10

18
Q

Sparingly soluble - approx volume of solvent ml per gram of solute

A

From 30 to 100

19
Q

Very slightly soluble - approx volume of solvent ml per gram of solute

A

From 1000 to 10000

20
Q

Practically insoluble

A

> 10000

21
Q

Factors affecting solubility

A

Crystal form
As melting point increases solubility decreases
Chemical factors - substituent type and position
pH will affect the solubility of acids and bases:
- at pH values above pKa the solubility of acidic drugs increases
- at pH values believe pKa the solubility of basic drugs increases
Acid + bases = salt + water
Zwitterions behave as acids at basic pH and bases at acidic pH

22
Q

Polymorphism

A

Ritonavir (antiviral)
2 forms - active and inactive
Presence of the inactive form in the active form will instigate a reaction which results in all active forms converting to the inactive form - lower energy state so this may occur spontaneously

Ranitidine (Zantac) - H2 receptor antagonist

Paracetamol - stable form I monoclinic
Metastable form II orthorhombic
Unstable form III

Cortisone acetate - 5 different polymorphs, four of which are unstable in water and change to a stable form

23
Q

Optimising solubility (like dissolves like)

A

Salt form - salts are often more water soluble than free acids/bases and are usually more stable. Salt form is part of the drug (e.g. Lidocaine HCL not lidocaine)
Modify pH so the salt form and ionised form predominates and solubility is increased. pH may be controlled with a buffer
Co solvents improve solubility for chemicals with poor aq solubility but offer issues wth toxicity which limit use. Complex and difficult to determine optimum properties of mixtures

24
Q

Drug - erythromycin
Aqueous solubility -
Solubility in non aqueous solvent -
Form -

A

Aqueous solubility - slightly soluble
Solubility in non aqueous solvent - soluble
Form - tablets

25
Q

Drug - ibuprofen
Aqueous solubility -
Solubility in non aqueous solvent -
Form -

A

Aqueous solubility - practically soluble
Solubility in non aqueous solvent - freely soluble
Form - oral suspension, tablets, cream, gel

26
Q

Drug - amoxicillin sodium
Aqueous solubility -
Solubility in non aqueous solvent -
Form -

A

Aqueous solubility - very soluble
Solubility in non aqueous solvent - sparingly soluble
Form - injection

27
Q

Drug - amoxicillin trihydrate
Aqueous solubility -
Solubility in non aqueous solvent -
Form -

A

Aqueous solubility - slightly soluble
Solubility in non aqueous solvent - very slights soluble
Form - oral suspension, capsule

28
Q

Excipients for pharmaceutical oral solutions

A 
The aqueous vehicle 
Co solvents 
Buffers
Sweetening agents viscosity modifiers 
Antioxidants 
Preservatives 
Flavours and colours
29
Q

Example of aqueous vehicle excipients

A

Purified water BP or USP
Prepared by distillation, ion exchange or reverse osmosis
Solid residue should be less than 1mg per 100ml
Not to be used for parenteral formulation (use water for injections BP for this instead)
Not tap water as it isn’t purified

30
Q

Examples of co solvent excipients

A

Glycerol (glycerin) - miscible in water. Similar effects to ethanol co solvent

Alcohol USP (CH3CH2OH) - 94.9 -96% v/v ethyl alcohol (ethanol). Co solvent or single solvent. Toxic

Propylene glycol USP - odourless and colourless fool often used as a replacement for glycerol

Polyethylene glycol (PEG) - polymer of ethylene oxide monomers with terminal OH groups. Exact specifications depends on the number of repeating units and MW. Different grades such as PEG 200/400, different properties so different grades used for different chemicals

Surfactants - depends on the critical micelle conc of a drug

Complex calixarenes and cyclodextrins

31
Q

Examples of buffer excipients

A

Control pH
Enhance stability
Buffers should not work in the formulation but not necessarily in the body

Examples

  • phosphate buffered saline pH 7-7.4 (sodium phosphate/ disodium phosphate, 0.8-2%)
  • citrate (Na-citrate, citric acid, 1-5%)
  • acetates (Na-acetate, acetic acid, 1-2%)
32
Q

Sweetening agents excipients

A

Increases compliance of product
Examples: sucrose, liquid glucose, glycerol, sorbitol, saccharin sodium, aspartame

Avoid use of sugar in patients with diabetes mellitus

33
Q

Viscosity modifier excipient examples

A

Product must easily be poured
Examples: non ionic cellulose derivatives (methylcellulose, hydroxymethylcellulose, hydroxypropylcellulose)
Polyvinylpyrrolidone
Ionic polymers (sodium carboxymethylcellulose - anionic, sodium alginate - anionic, polymethylvinylether-maleic anhydride)

34
Q

Antioxidants excipient examples

A

Increase stability of drugs which may degrade by chemical oxidation by inhibition of the initiation and or propagation of free radical generating chain reactions caused by presence of O2 ( e.g. Opiates)

Examples: sodium sulphite, metabisulphites, formaladehyde, ascorbic acid, butylated hydroxyanisole (BHA) and BHT in more lipid rich formulations

Used in low conc
May be used in conjunction with chelating agents which will complex with metal ions

35
Q

Preservatives excipients examples

A

To control the microbial load Ina. Formulation which should be kept below the min inhibitory conc
Require broad spectum antimicrobial activity (gram +ve/-ve, fungi)
Low toxicity

Examples: paraben, sodium benzoate/ benzoic acid

PSF (11 decks)

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