How to Do a Pre-Formulation Study: Fluoxetine and Its Recommendation.
Introduction
An important drug development feature is to find an active compound that is ideal to the human body in terms of absorption into the systemic circulation, distributed to the proper site of action, metabolised efficiently and effectively, excreted well from the body and should be non-toxic [1].
Why do a preformulation study?
Pre-formulation studies help in improving a lead compound and make it to its optimal usage. That is improving in:
physiochemical,
pharmaceutical,
pharmacokinetics,
pharmacodynamic,
pharmacological,
and safety characteristics [1].
Following the identification of a new chemical compound that is suitable for development, the formulator will have to produce dosage forms [1]. Initially, this may involve the production of an injectable form suitable for early efficacy and toxicity testing and subsequently, there will be a need to develop the final dosage form, which generally will not be an injection. The challenge for the formulator is to develop the initial and final dosage forms to the highest quality in the shortest time. This process is best achieved when certain physicochemical properties of the drug substance are investigated, understood, and effectively utilised: this is pre-formulation [1,2].
Selectivity is very important to the success of any pre-formulation program. To achieve this, it is suggested that the data, as they become available, be analysed to decide which areas need further analysis [1,2]. This allows pharmaceutical companies to utilize less time and resources on the formulation as a basic understanding of the compound has already been achieved; hence an educated approach on the formulation can be accomplished. Ultimately, it is the shift from an injectable to a tablet which could be taken orally.
Pre-formulation
Before beginning
It is important to glance into the following factors of your compound:
innovative molecule or abbreviated,
therapeutic category of the drug compound,
amount of drug substance available,
physicochemical properties of the drug,
physicochemical properties of excipient and possible interaction with drug,
therapeutic dose/potency of a compound,
the category of the dosage form to be prepared,
stability parameters [1-3].
Goals of the preformulation
The goals of the studies are:
selection of the correct form of the drug substance (solid, liquid, gas) based on a type of dosage form development,
evaluation of physical and chemical properties of drug substance,
to understand the biopharmaceutical properties of the drug,
to reduce drug development time and cost,
to produce safe, effective and reproducible drug delivery system [1-3]
Areas of the study
Preformulation study helps to:
establish the new drug molecule’s identity,
characterize physicochemical properties of the new drug molecule,
determine drug and excipients compatibility,
correlate pharmacokinetics and biopharmaceutical properties,
establish a kinetic rate profile of the new drug,
optimize the preclinical and clinical process,
provide necessary data for the development of analytical methods,
produce safe, innovative, stable cost-effective dosage form [1-3].
What does a pre-formulation study contain?
1. Background
Compound
Chemical name
Chemical structure
Empirical formula
Molecular weight
CAS, ATC code, UNII code
Lot numbers
Solvent of recrystallization
Purity and impurities
Therapeutic category
Anticipated dose
2. Organoleptic properties
3. Microscopic examination
4. Physical characteristics
Density
Compressibility
Particle size
Surface area
Static charge
Flow properties
Hygroscopicity
Polymorphism
Spectral property
5. Solution properties
pH of 1% Solution
pK
Log P
Solubility
Effect of solubilizing agents
Partition coefficient (n-octanol/water)
Dissolution rates
Volume of distribution
Metabolism
Protein binding
6. Stability
Heat
Humidity
Light
Acidic
Alkali
Oxidative conditions
Shelf life
Storage condition
7. Drug excipient compatibility studies
8. Solution stability
9. Recommendations
A pre-formulation study example: Fluoxetine
Fluoxetine: compound LY-110140
The following shows the preformulation of fluoxetine and the recommendation it should need to produce a successful dosage form.
There is a lot of information that needs to be gathered. Here are the websites that I could find almost everything. It is a challenge to find good and reliable sources that confidently describe the wanted compound. Below are reliable sources of information that can be used for preformulation.
1. Background
Compound: LY-110140
Chemical name: (±)-N-Methyl-3-phenyl-3-(a,a,a-trifluoro-p-tolyloxy) propylamine hydrochloride
Chemical structure:
Empirical formula: C17H18F3NO, HCl
Molecular weight: 345.8 gmoles-1
CAS: 54910-89-3 (fluoxetine); 59333-67-4 (fluoxetine hydrochloride)
ATC code: N06AB03
ATC code (veterinary): QN06AB03
UNII code: I9W7N6B1KJ (fluoxetine hydrochloride); 7C4D25ST1T (R-fluoxetine hydrochloride)
Lot numbers: NDC 49884-734
Solvent of recrystallization: LY-110140 was recrystallized from a mixed solvent consisting of methanol and water.
Purity: LY-110140 is around 99.6% as detected by liquid chromatography. The column, test solution, mobile phase, flow rate, detection, injection, run time and relative tension must follow British Pharmacopoeia standards for fluoxetine.
Impurities: Impurities A and B consisted of 0.25% and impurity C consisted of 0.15%.
A. R = OH: (1RS)-3-(methylamino)-1-phenylpropan-1-ol
B. R = H: N-methyl-3-phenylpropan-1-amine
C. (3RS)-N-methyl-3-phenyl-3-[3-(trifluoromethyl)phenoxy]propan-1-amine
Therapeutic category: Selective serotonin re-uptake inhibitors; antidepressant; anti-bulimic.
Anticipated dose: eq 40mg base; eq 20mg base; eq 15mg base; eq 10mg base.
Fluoxetine Capsules – 20 mg daily single dose, can be increased to 80 daily. Most widely used dosage form.
Fluoxetine Tablets – 20 mg daily single dose, can be increased to 80 daily.
Fluoxetine Oral Solution – 20 mg daily single dose, can be increased to 80 mg daily. Depends on manufacturer oral solution in terms of how much 20 mg goes into a selected amount of millilitres.
Anticipated dose in children age 7 years and over:
Fluoxetine Capsules – 10 mg daily single dose, can be increased to 20 daily after 1 to 2 weeks.
Fluoxetine Oral Solution – 10 mg daily single dose, can be increased to 20 mg daily after 1 to 2 weeks. Depends on manufacturer oral solution in terms of how 20 mg goes into a selected amount of millilitres.
In low-weight children, this may be increased after several weeks to 20 to 30 mg daily, if required. The dose in adolescents and heavier children may be increased to 20 mg daily after 2 weeks; further increases to 60 mg daily may be made after several weeks, as necessary.
2. Organoleptic properties
LY-110140 is a white or almost white crystalline powder, odourless, and almost tasteless powder.
Fluoxetine is a 50:50 racemic mixture of R- and S-fluoxetine.
3. Microscopic examination
LY-110140 has a range distribution of 7.35 - 75.64 μm, 100% of particles are less than 75.64 μm respectively. The crystals are slightly needle-like shape but on overall there is no predominate shape. The compound can precipitate in needle-like crystals. Coating cores with LY-110140 in the large needle-like form can be difficult, it is advisable to mill or otherwise reduce the particle size of the LY-110140 to less than about 50 μm.
4. Physical characteristics
Density: 1.16 gcm-3
Compressibility: LY-110140 compresses suitably with no physical damage, suitable for tablets manufacturing. Tests have shown that 0.312 gcm-3 untapped and 0.581 gcm-3 tapped showed a 46.3% compression [(tapped-untapped)/untapped x 100].
Particle size: LY-110140 has a range distribution (D) of 7.35-75.64 μm; using the Malvern Laser diffractometer wet method. 100% of particles are less than 75.64 μm respectively.
Particle volume in percentage: D10, D50, D100.
Some attention must be given to the particle size of fluoxetine. The compound can precipitate in needle-like crystals, which can be quite large. Coating cores with fluoxetine in the large needle-like form can be difficult, and it is advisable to mill or otherwise reduce the particle size of the fluoxetine to less than about 50 μm before using it in the present product and process.
Surface area: 21.3 A2 topological polar surface area. The surface area of LY-110140 was found to be 0.57 m2g-1, milling through micronization process to increase surface area around 2.10 m2g-1 should be considered.
Static charge: The static charge of LY-110140 causes a problem in manufacturing; hence the granulation process must be initiated to reduce any static charge and showed a significant improvement in the manufacturing of LY-110140.
Flow properties: LY-110140 does not exhibit good flow characteristics. The addition of Cellulose microcrystalline, Croscarmellose sodium, Silicon dioxide and Magnesium stearate improved the formation of granulation and flowability of LY-110140 and the manufacturing process for tableting and capsule filling. Granulation was significantly improved which improved the flow properties of LY-110140.
Hygroscopicity: LY-110140 was placed in desiccators maintained at > 80% relative humidity at room temperature (25ºC ± 2 ºC) for 24 hours to allow the API to hydrate. The percent water content by KF was taken and found to be 0.46% which was similar to the initial value of 0.3%. The pharmacopoeial specification was NMT 0.5%, hence the API has not been found to be hygroscopic. No degradation has been detected.
Polymorphism: No evidence of polymorphism was obtained.
Spectral property: UV max (methanol): 227, 264, 268, 275 nm. Infra-red absorption spectrophotometry can be found in the British Pharmacopoeia.
Solution properties
pH of 1% Solution: 4.5 - 6.5
pKa: 9.4
Log P: 4.05
Solubility: Sparingly soluble in water and dichloromethane; freely soluble in alcohol and methyl alcohol; practically insoluble in ether. Solubility of LY-110140 in solvents:
Effect of solubilizing agents: LY-110140 was moderately soluble in an aqueous environment, attempt to increase solubilisation with the addition of a salt, HCl, and through co-crystallization was highly successful in the increase of LY-110140 solubility. The use of croscarmellose sodium as an excipient provides superior drug dissolution and disintegration.
Partition coefficient (n-octanol/water): 1.8 at pH 7 and 25°C
Dissolution rates: Powder dissolution profile for various forms of LY-110140 Prozac® illustrates how intrinsic dissolution can be modified through co-crystallization.
Sarafem® Fast release technology shows in vitro dissolution of compound LY-110140.
Volume of distribution: 20-45 Lkg-1 LY-110140 reaches the blood-brain barrier very successfully.
Metabolism: LY-110140 appears to be extensively metabolized, likely in the liver, to norfluoxetine and other metabolites. Norfluoxetine, the principal active metabolite, is formed via N-demethylation of fluoxetine. Norfluoxetine appears to be comparable pharmacologic potency as fluoxetine. Fluoxetine and norfluoxetine both undergo phase II glucuronidation reactions in the liver. It is also thought that fluoxetine and norfluoxetine undergo O-dealkylation to form p-trifluoromethylphenol, which is then subsequently metabolized to hippuric acid.
Protein binding: High (94.5%)
Stability
During forced degradation studies LY-110140 undergo extensive degradation under acidic, photolytic, and oxidative stress conditions, degrades to a mild extent in basic and neutral conditions, and is stable to thermal stress. There is no interference of excipients or degradation products in the analytical determination. LY-110140 is a stable compound under normal conditions.
Heat: The thermo-labile property of LY-110140 was clearly observed when it was exposed to dry heat at 80ºC for 24 hours. Melting point of LY-110140 157.5-158.7 °C. When heated to decomposition this product produces toxic fumes.
Humidity: LY-110140 samples were exposed to different temperature 40ºC/50ºC and humidity 10%/75% for different time 1-4 weeks. LY-110140 was stable except marked degradation with lactose was seen.
Light: Photolytic condition was found to be labile on exposure to light in acid, alkali, or neutral conditions. The rate of photolysis was in the order of acid > base > water. LY-110140 Oral Solution should be protected from light.
Acidic: 15% degradation was observed subjected to heating in 0.1N HCl for 12 hours.
Alkali: found to be similar to a great extent to the acidic condition.
Oxidative conditions: LY-110140 was found to be highly labile to oxidative hydrolysis in 3% H2O2 at room temperature after 24 hours. 60% of degradation was found.
Shelf life: 5 years at 15-25°C
Storage condition: LY-110140 is stable in polyethylene bottles or foil packs for at least 5 years.
Drug excipient compatibility studies
All excipients are compatible with LY-110140. Ingredients used from Sarafem®, strength: 10 mg 15 mg and 20 mg. These excipients are useful in oral the dosage routes, such as tablets, capsules and solution.
Solution stability
The stability of commercially available LY-110140 solution diluted with common pharmaceutical diluents was tested. LY-110140 syrup, containing fluoxetine 4mg/mL (as the HCl salt), was diluted to 1 and 2mg/mL in each of the following: deionized water; Simple Syrup, BP; Simple Syrup, USP; Aromatic Elixir USP; and grape cranberry drink. Fluoxetine hydrochloride 1 or 2mg/mL was stable for eight weeks with these diluents if stored at 5 or 30°C. LY-110140 appears to be chemically stable in solution and has been reported to degrade significantly only when the pH is less than 1.
Tests were done with LY-110140 on various aqueous solutions, water/sediment systems, and activated sludge-amended medium. The samples were placed in the dark and in a growth chamber fitted with fluorescent lamps simulating the ultraviolet output of sunlight. Over a period of 30 days, fluoxetine was hydrolytically and photolytically stable in all aqueous solutions. Results indicate that fluoxetine is relatively recalcitrant to hydrolysis, photolysis, and microbial degradation.
However, the British Pharmacopoeia does state that LY-110140 Oral Solution should be protected from light. Oxidative conditions in solution were found that LY-110140 to be highly labile to oxidative hydrolysis in 3% H2O2 at room temperature after 24 hours and that 60% of degradation was found.
Recommendations
LY-110140 should undergo the process of micronization to increase surface area and produce a smooth surface as a slight needle-like shape is noticed. It is advisable to mill or otherwise reduce the particle size of the LY-110140 to less than about 50 μm as its range is from 7.35 to 75.64 μm. The static charge of LY-110140 causes a problem in manufacturing; hence the granulation process must be initiated to reduce any static charge as it showed a significant improvement in the manufacturing of LY-110140.
Granulation is highly recommended, as LY-110140 does not present good flow characteristics. To increase the formation of suitable granulation the addition of cellulose microcrystalline - a white powder consisting of free-flowing, non-fibrous particles and aids in tableting and granulation for capsule filling should be considered. The addition of croscarmellose sodium, used for direct-compression and wet-granulation processes, should be considered. The addition of silicon dioxide, used in tablet making as an anti-caking agent, adsorbent, disintegrant, or glidant that allows the powder to flow freely when tablets are processed, should be considered. The addition of magnesium stearate, used as a lubricant and diluent in the manufacturing of tablets, capsules and powder dosage forms as well as helping to prevent pharmaceutical ingredients from adhering to industrial equipment, should be considered. These excipients improved the formation of granulation and flowability of LY-110140 and the manufacturing process for tableting and capsule filling. Granulation was significantly enhanced which improved the flow properties of LY-110140. These excipients have been proven to not interact with LY-110140 in any way, keeping the integrity of LY-110140. LY-110140 showed good compressibility characteristics.
Furthermore, LY-110140 was moderately soluble in an aqueous environment and attempts to increase solubilisation with the addition of a salt, HCl, and through co-crystallization were highly successful in the increase of LY-110140 solubility in the aqueous environment. The use of croscarmellose sodium is recommended as an excipient, providing superior drug dissolution and disintegration. This enhances the absorption in the duodenum as HCl salt leaves the LY-110140 due to the pH environment, thereby increasing absorption through the membrane. Compound LY-110140 showed satisfactory dissolution and release of active pharmaceutical ingredients. It is well absorbed from the gastrointestinal tract following oral administration. LY-110140 can be modified as fast releasing technology with 98.9% of LY-110140 released within 20 minutes or it can be modified for a delayed-release technology. The oral solution and delayed-release capsule are bioequivalent. Prozac® Weekly capsules, a delayed-release formulation, contain enteric-coated pellets that resist dissolution until reaching a segment of the gastrointestinal tract where the pH exceeds 5.5. The enteric coating delays the onset of absorption of LY-110140 by 1 to 2 hours relative to the immediate-release formulations. LY-110140 reaches the blood-brain barrier very successfully, which is immensely important for an antidepressant drug.
LY-110140 is stable in solid-state and in the liquid state. LY-110140 is 99.6% pure with little to no impurities. However, in forced oxidative conditions in solution, it was found that LY-110140 is highly labile to oxidative hydrolysis in 3% H2O2 at room temperature after 24 hours and 60% of degradation was found. For the Oral Solution of LY-110140, an antioxidant could be considered but it is not an urgency as under normal conditions, oxidation does not occur to cause enough stability damage. The Oral Solution of LY-110140 medicine should be packaged in amber Type III glass bottles with polypropylene lids, with low-density polyethylene (LDPE) liners and enclosed in outer cartons as photolytic conditions showed an increase in oxidative hydrolysis with compound LY-110140. This type of packaging should be considered so that oxidation will not be initiated.
Published 30th November 2018. Last reviewed 30th December 2021.
Reference
1. Kamlesh J. Wadher, Milind J. Umekar. Pharmaceutical Dosage Form : Basics and Beyond. http://www.bspublications.net/downloads/05805bfacb3933_Ch-1_Pharmaceutical%20Dosage%20form_Kamlesh.pdf. Updated 2018. Accessed November 13, 2018.
2. Qiu Y, Chen Y, Zhang G, Liu L, Porter W. Developing Solid Oral Dosage Forms, Pharmaceutical Theory And Practice. 2nd edition. Elsevier Science; 2016.
3. Brayfield A, Bayer G. Martindale: The Complete Drug Reference. 39th edition. London: Pharmaceutical Press; 2017.
Additional source of information:
South African Medicine Formulary (SAMF),
