1. INTRODUCTION:

1.1. STUDIES ON SOLUBILITY IMPROVEMENT^1,2:

The most important property of a dosage form is its ability to deliver the active ingredient to its site of action at a rate and amount sufficient to elicit the desired pharmacological response. If the drug is administered by an extravascular route and acts systemically, its potency will be directly related to the amount of drug the dosage form delivers into the blood. Also, if the pharmacological effects of the drug are directly and instantaneously related to the plasma concentration, the rate of absorption will be important because the rate will influence the height of plasma concentration peak and peak time.

Thus, the bioavailability of a drug product is defined in terms of the amount of the active drug delivered to the blood and the rate at which it is delivered.

1.2. Methods Used For Increasing the Dissolution Rate of Poorly Soluble Drugs:

As far as the definition of bioavailability is concerned, a drug with poor bioavailability is the one with – Poor aqueous solubility and/or slow dissolution rate in the biological fluids.

1. Poor stability of the dissolved drug at the physiologic pH.

2. Inadequate partition coefficient and thus poor permeation through the biomembrane.

3. Extensive presystemic metabolism.

The methods are:

1. Micronization: The process involves reducing the size of the solid drug particles between to 1 to 10 microns commonly by spray drying or by use of air attrition methods.

Examples of drugs whose bioavailability have been increased by micronization include griesofulvin and several steroidal and sulfa drugs.

2. Use of surfactants: The surface-active agents enhance dissolution rate primarily by promoting wetting and penetration of dissolution fluid into the solid particles. They are generally used in the concentration below their (CMC) values since above CMC; the drug entrapped in the micelle structure fails to partition in the dissolution fluid. Nonionic surfactants like polysorbates are widely used. Examples of the drugs whose bioavailability have been increased by use of surfactants in the formulation include steroids like spironolactone.

3. Use of salt Forms: Salts have improved solubility and dissolution characteristics in comparison to the original drug. Alkali metal salts of acidic drugs like penicillins and strong acid salts of basic drugs like atropine are more water soluble than the parent drug.

4. Alteration of pH of the Drug Microenvironment: This can be achieved in two ways-in situ salt formation, and addition of buffers to the formulation.

e.g. buffered aspirin tablets.

5. Use of Metastable polymorphs: A metastable polymorphs is more soluble than the stable polymorph of a drug that exhibit polymorphism for example, the B form of chloramphenicol palmitate is more soluble than A and C forms.

6. Solute-Solvent complexation: Solvates of drugs with organic solvents have higher aqueous solubility than their respective hydrates or the original drug. Much higher solubility can be attained by freeze drying such as solute in solution with an organic solvent with which it is known to form a solvate. E.g.1:2 griesofulvin- benzene solvate.

7. Solvent deposition: In this method, the poorly aqueous soluble drug such as nifedipine is dissolved in an organic solvent like alcohol and deposited on an inert, hydrophilic, solid matrix such as starch or micro-crystalline cellulose by evaporation of solvent.

8. Selective Adsorption on Insoluble Carriers: A highly active adsorbent such as the inorganic clays like bentonite can enhance the dissolution rate of poorly soluble drugs such as griesofulvin, indomethaciin and prednesolone by maintaining the concentration gradient at its maximum. The two reasons suggested for the rapid release of drugs from the surface of clay are- the weak physical bonding between the adsorbate and the adsorbent, and hydration and swelling of the clay in the aqueous media.

9. Solid solutions: The three means by which the particle size of a drug can be reduced to submicron level are—

a) Use of solid solution,

b) Use of eutectic mixtures, and

c) Use of solid dispersions.

In all these cases, the solute is frequently a poorly water soluble drug acting as the guest and the solvent is highly water-soluble compound or polymer acting as a host or carrier.

a) A solid solution is the binary system comprising of a solid solute molecularly dispersed in a solid solvent. Since the two components crystallize together in a homogeneous one phase system, solid solutions are also called as molecular dispersions or mixed crystals. Because of reduction in particle size to the molecular level, solid solution show greater aqueous solubility and faster dissolution than eutectics and solid dispersion. They are generally prepared by fusion method where by a physical mixture of solute and solvent are melted together followed by rapid solidification. Such system, prepared by fusion, is often called as melts. E.g. griseofulvin-succinic acid, the griesofulvin from such solid solution dissolves 6 to 7 times faster than pure griesofulvin.

The two mechanisms suggested for enhanced solubility and rapid dissolution of molecular dispersions are:

1. When the binary mixture is exposed to the water, the soluble carrier dissolves rapidly leaving the insoluble drug in a state of micro-crystalline dispersion of very fine particles.

2. When the solid solution, which is said to be in a state of randomly, arranged solute and solvent molecules in the crystalline lattice, is exposed to dissolution fluid, the soluble carrier dissolves rapidly leaving the insoluble drug stranded at almost molecular level.

b) Eutectic Mixture: These systems are also prepared by fusion method. Eutectic melts differ from solid solution in that the fused melt of solute-solvent show complete miscibility but negligible solid-solid solubility i.e. such systems are basically intimately blended physical mixture of two crystalline components. Examples of eutectics include paracetamol-urea, griesofulvin-urea, griseofulvin- succinic acid, etc. Solid solutions and eutectics, which are basically melts, are easy to prepare and economical with no solvents involved. The method however cannot be applied to:

• Drugs which fail to crystallize from the mixed melt,

• Themolabile drugs, and

• Carriers such as succinic acid that decompose at their melting point. The eutectic product is often tacky, intractable or irregular crystals.

c) Solid dispersions: These are generally prepared by solvent or co-precipitation method where by both the guest solute and the solvent are dissolved in a common volatile liquid solvent such as alcohol. The liquid solvent is removed by evaporation under reduced pressure or by freeze drying which results in amorphous precipitation of guest in a crystalline carrier. Example is griesofulvin – PVP.

10. Molecular Encapsulation with Cyclodextrins:3,4,5 The beta- and gamma- Cyclodextrins and several of their derivatives are unique in having the ability to form molecular inclusion complexes with hydrophobic drugs having poor aqueous solubility. These cyclodexrtin molecules are versatile in having a hydrophobic cavity of size suitable enough to accommodate the lipophilic drugs as guest; the outside of the host molecule is relatively hydrophilic.

11. According to Biopharmaceutical Classification System (BCS) drugs can be divided into four classes, depending on their solubility and permeability. Drugs which belong to class II are characterized by low solubility and high permeability. The low dissolution profile of relative insoluble drugs is the rate limiting step in the absorption of a drug from a solid dosage form. Various techniques can be useful to achieve an improvement of dissolution rate. The most popular approaches are the incorporation of the drugs into inert lipidic vehicles such as oils, surfactants dispersions, self- emulsifying formulations and the preparation of solid dispersions (SD) based on cyclodextrin inclusion complexes, polyvinylpyrrolidone and polyethylene glycols 4000 and 6000.

Cyclodextrins (CDs), with lipophilic inner cavity and hydrophilic outer surface, are capable of interacting with a large variety of guest molecules to form non- covalent inclusion complexes (Fig.1).

Fig.1: (a) The chemical structure and (b) the toroidal shape of the â-cyclodextrin molecule.

Chemically they are cyclic oligosaccharides containing at least six D-(+) glucopyranose units attached by α-(1, 4) glucosidic bonds. The three natural CDs, α -, HPβ - and γ -CDs (with 6, 7 or 8 glucose units respectively) differ in their ring size and solubility (Table-1).

Table-1: Some characteristics of α -, HPβ -, γ -, and δ -CD

Type of CD	Cavity Diameter Å	Molecular weight	Solubility (g/100 ml)
Α - CD	4.7-5.3	972	14.5
HPΒ - CD	6.0-6.5	1135	1.85
Γ - CD	7.5-8.3	1297	23.2
Δ - CD	10.3-11.2	1459	8.19

The cavity size of α-CD is insufficient for many drugs and γ-CD is expensive. δ -CD, in general has weaker complex forming ability than conventional CDs. With drugs like digitoxin and spiranolactone, δ -CD showed greater solubilizing effect than α-CD but the effect of δ -CD was lesser than that of HPβ- and γ-CDs. HPβ-CD has been widely used in early stages of pharmaceutical applications due to its ready availability and cavity size suitable for the widest range of drugs. But the low aqueous solubility and nephrotoxicity limited the use of HPβ-CD especially in parenteral drug delivery.

1.3. Complexation with cyclodextrins.

One of the most important characteristics of CDs is their ability to form inclusion complexes. Inclusion complexation involves entrapment of guest molecule totally or partially in the cavity of host molecule without formation of any covalent bonds. CDs are typically host molecules and can entrap a wide variety of drug molecules resulting in the formation of monomolecular inclusion complexes.

The central cavity of the CD molecule is linked with skeletal carbon and ethereal oxygens of the glucose residue. It is therefore lipophilic; the polarity of the cavity has been estimated to be similar to that of the aqueous ethanolic solution. It provides a lipophilic environment into which suitably sized drug molecules may enter and be included. No covalent bonds are formed or broken during CD complex formation, and in aqueous solutions, the complexes are readily dissociated. Free drug molecules are in equilibrium with the molecules bound with in the CD cavity. Measurements of stability or equilibrium constants (Kc) or dissociation constant (Kd) of the drug CD complexes are important properties of a compound upon inclusion.

1.4. Cyclodextrins^6,7,8

Cyclodextrins comprise a family of non-reducing, water-soluble, cyclic oligosaccharides that are unique in having the ability to form molecular inclusion complexes with hydrophobic drugs having poor aqueous solubility. These Cyclodextrin molecules are versatile in having a hydrophobic cavity of size suitable enough to accommodate the lipophilic drugs as guests; the outside of the host molecule is relatively hydrophilic. Thus the molecularly encapsulated drug has greatly improved aqueous solubility and dissolution rate.

Synonyms⁹

Cyclodextrin: Cavitron, Cyclic oligosaccharide, Cycloamylose, Cycloglucan, Encapsin, Rhodocap, Schardingar dextrin.

α-CD: Alfadex, Alpha-cycloamylose, Alpha-cyclodextrin, Cyclohexaamylose, Cyclomaltohexose.

β-CD: Beta-cycloamylose, Betadex, Beta dextrin, Cycloheptaamylose, Cycloheptaglucan, Cyclomaltoheptose.

y-CD: Cyclooctaamylose, Gamma cyclodextrin, Gamma W8.

1.5. Chemistry of Cyclodextrins ^6,7,10

Cyclodextrins are cyclic (α-1,4) – linked oligosaccharides of α-D- glucopyranose units that have a relatively hydrophobic central cavity and hydrophilic outer surface. The most common nature or parent form of Cyclodextrins known are α, β and y-CDs consisting of 6, 7 and 8 D – glucopyranose units respectively, linked by α-1,4 glycosidic bonds into a macro cycle.

Figure 2: Structure of β-cyclodextrin and hydroxypropyl β-cyclodextrin

The chemical structure of these CDs shows that cyclic nature of the molecule and structure of CD takes the shape of a truncated cone. The hydroxyls located at C-2, C-3 and C-6 positions provide the hydrophilic exterior of the cone and are responsible for the aqueous solubility of CDs. Inclusion complexes are formed when a guest molecule (drug) is partially or fully included inside the hydrophobic cavity of CDs without covalent bonding.

It is the unique configuration that gives cyclodextrin their interesting properties and creates the thermodynamic driving force needed to form host guest complexes with a polar molecules and functional groups.

1.6. Physical and chemical properties of cyclodextrins^{7, 10-12.}

a) Solubility:

1. Water: HPβ-CD is very soluble in water. Substitution of the hydroxyl groups of the β-CD disrupts the network of hydrogen bonding around the rim of the β-CD. As a result of disruption of the hydrogen-bonding network, the hydroxyl groups interact much more strongly with water resulting in increased solubility compared to β-CD.

2. Solvents: HPβ-CD is more soluble in solvents than β-CD solvents are octanol, and Iso-propanol.

b) Viscosity:

Unlike β-CD solubility is limited, solutions of HPβ-CD can become viscous. At concentration normally used in applications the viscosity is not a concern the table below shows the viscosity of HPβ-CD at different concentrations and temperatures.

c) Thermal stability:

In case of HPβ-CD, energy is absorbed as water evaporates peaking at about 100°C. The glass transition occurs in this thermogram from about 225-250°C as determined by visual observation using a capillary melting apparatus whereas β-CD melts between 255-265°C.

d) Acid/Base Stability:

Strong acids, such as hydrochloric or sulfuric acids, hydrolyze HPβ-CD. The rate of hydrolysis is dependent upon the temperature and concentration of the acid. The higher the temperature or concentration of the acid, the more rapid is the rate of hydrolysis. Weak acids, such as organic acids do not hydrolyze HPβ-CD.

HPβ-CD is stable in bases. HPβ-CD is synthesize under basic conditions without opening of the β-CD ring. Stability of HPβ-CD is from pH 4.0 to 9.0.

e) Enzymatic stability:

HPβ-CD is not hydrolyzed by β-amylase of glucoamylase. The enzymes require an end group in order to initiate attack. Since HPβ-CD has no end groups, no hydrolysis occurs with these enzymes.

1.7. Method of Manufacture⁹

Cyclodextrins are manufactured by the enzymatic degradation of starch using specialized bacteria (Bacillus macerans,The insoluble β-CD organic solvent complex is separated from the non-cyclic starch, and the organic solvent removed in vacuole so that less than 1 ppm of solvent remains in the β-CD. The cyclodextrin is then carbon treated and crystallized from water, dried and collected. Hydroxyethyl-β-CD is made by reacting β-CD with ethylene oxide, whilst hydroxpropyl-β-CD is made by reacting with propylene oxide.

1.8. Complexation of Cyclodextrins^6,13

The interior of the cyclodextrin cavity is relatively hydrophobic because of the presence of the skeletal carbons and ethereal oxygen, which comprise the cavity,

whereas the cavity entrances are hydrophilic owing to the presence of the primary and secondary hydroxyl groups. As the water molecules located inside the cavity cannot satisfy their hydrogen bonding potential. They are having high enthalpy than bulk water molecules located in the solution. Water inside the cavity tends to be squeezed out and to be replaced by more hydrophobic species. Thus, molecules of appropriate size and stereochemistry can be included in the cyclodextrin by hydrophobic interactions.

1.9. Preparation of Complexes

Cyclodextrin complexes are prepared by the following methods:

a) Physical mixture (PM).

b) Kneading method (MW)¹⁴.

1.10. Safety of Cyclodextrins (CDS):^{10, 12}

The safety of orally administered β-CD has been investigated in several studies with extensive evaluation of hematology, blood chemistry, urinalysis and necropsy. No significant toxic effects were observed in any of these studies after oral administration of β-CD to mice, rats and dogs. The oral safety of HP-β-CD has been assessed in mice, rats and dogs for dosing periods upto 2, 2, and 1 year respectively. Doses reached as high as a 5000mg/kg/day. No adverse effects were noticed. Numerous studies with the parent CDs have shown that their parental toxicity was observed primarily as renal and cytotoxicity (haemolysis and tissue irritation). The parenteral safety of CDs has not yet been established completely.

Handling Precautions⁹

Observe normal precautions appropriate to the circumstances and quantity of material handled. CDs are organic powders and should be handled in a well-ventilated environment. Efforts should be made to limit the generation of dust that can be explosive.

Incompatibilities⁹

The activity of some antimicrobial preservatives in aqueous solution can be reduced in the presence of HP-β-CD.

Storage Conditions:⁹

β-CD and other Cyclodextrins are stable in the solid state if protected from high humidity. Cyclodextrins should be stored in a tightly sealed container, in a cool, dry, place.

1.11. STABILITY STUDIES¹⁵

Stability of a drug can also be defined as the time from the date of manufacture and packaging of the formulation until its chemical or biological activity is not less than a predetermined level of labeled potency and its physical characteristics have not changed appreciably or deleteriously. The environmental factors, ingredients used and the nature of the container can affect stability. Loss of potency usually occurs from a chemical change, the most common reaction being hydrolysis, oxidation and reduction. Potency is determined by means of assay procedure that differentiated between the intact drug and its degradation product.

Table-3: Stability Requirement for Maintenance of Shelf-Life

Temperature °C	Maximum time	Minimum time
37°C	12 months	6.4 months.
45° C	8.3 months	2.9 months.
60° C	4.1 months	3 weeks.
85° C	6 weeks	2.5 days

1.12. Methods for Detection of Inclusion Complex Formation and Determination of Complex Stability Constant:

One of the most interesting properties of CDs is their ability to form inclusion complexes with wide variety of guest molecules. Molecular encapsulation may occur both in solution and solid state. In solution there is equilibrium between complexed and non-complexed guest molecules. In solid state guest molecules can be enclosed within the cavity or may be aggregated to the outside of the CD molecule. Upon inclusion with in the CD cavity a guest molecule experiences changes in its physico-chemical properties. These changes provide method to detect whether guest molecules are really included in the CD cavity.

1. Enhancement of dissolution rate and bioavailability:

The drug-CD complexes often exhibit improved dissolution rate due to enhanced solubility when compared to other formulations of the drug. These two features can provide for an improvement in oral bioavailability when the solubility and the rate of dissolution are limiting the availability of the drug for absorption.

2. Active stabilization:

The nature of stabilization and destabilization depends on the CD used and on the position of the drug inside the CD. Enhanced stability usually results when the area or site of instability of the drug is located fully within the CD cavity.

3. Odour or taste masking:

Through encapsulation within the cyclodextrin cavity, molecules or specific functional groups that cause unpleasant tastes or odour are hidden from the sensory receptors. The resulting formulations have no or little taste or odour and are much more agreeable to the patient.

4. Compatibility improvement:

Different drugs are often incompatible with each other or another inactive ingredient within a formulation.

5. Material handling benefits:

Active ingredients that are oils/liquids or are volatile materials can be difficult to handle and formulate into stable solid dosage forms. Encapsulating these types of substances in a cyclodextrin convert them to a solid powder that has good flow properties and can be conveniently formulation into a tablet by conventional production processes and equipment.

6. As sustained release carriers:

While the hydrophilic CDs (β-CD, HP-β-CD) enhance the solubility, dissolution and bioavailability of the drugs, the hydrophobic CD derivatives such as alkylated and acylated CDs (diethyl-β-CD, triethyl-β-CD, triacetyl-β-CD) are useful as sustained release drug carriers for water-soluble drugs and peptides because they tend to decrease the solubility of the guest molecules.

2. NEED FOR THE STUDY:

The poor dissolution of relatively water insoluble drug such as Efavirenz cause a problem in the formulation of oral dosage forms. This limits its absorption and bioavailability. Several approaches have been followed in improving solubility of such drugs, one being complexation using cyclodextrins.

Cyclodextrins are a group of structurally related saccharides that are formed by enzymatic cyclisation of starch by a group of amylases termed glycosyle transferese. HPβ-cyclodextrins is extensively used to trap certain drug molecules inside its cavity and their by modify their physiochemical and biological activity.

3. OBJECTIVES:

The major objectives of the investigation are as follows:

1. To prepare inclusion complexes of Efavirenz using HPβ-cyclodextrins by microwave technology at different molar ratios.

2. To perform compatibility studies by using IR spectroscopy.

3. To study the phase solubility and stability constant for the intended complexes.

4. To study dissolution performance of inclusion complexes and to characterize the prepared complexes by phase solubility studies, XRD and DSC techniques.

5. To study in vitro drug release performance of different formulations.

6. To perform stability studies as per ICH guidelines.

3.1. PAST WORK ON INCLUSION COMPLEXATION WITH CYCLODEXTRINS:

An extensive work was carried on inclusion Complexation of many drugs with cyclodextrins in order to improve their solubility and bioavailability. Some of them are cited below.

The effect of β-CD on the aqueous solubility and dissolution rate was investigated. The possibility of molecular rearrangement of inclusion complexes were studied using molecular modeling and structural designing. The results offered a better correlation in terms of orientation of celecoxib inside the CD cavity. Phase solubility studies indicated that the solubililty of celecoxib was significantly increased in the presence of β-CD and was classified as AL type, indicating that 1:1 stochiometric inclusion complexes. Solid complexes prepared by freeze drying, evaporation and kneading method were characterized by DSC, XRD and SEM. In vitro studies showed that the solubility and dissolution rate of celecoxib was significantly improved by complexation with β-CD with respect to the drug alone. In the inclusion behavior of hydroxypropyl β-cyclodextrin and natural β- cyclodextrin was studied toward ketoprofen, in order to develop a new oral dosage form with enhanced dissolution rate and bioavailability, and to study the oral pharmacokinetics of ketoprofen in humans, following cyclodextrin complexation. Drug-cyclodextrin solid systems were prepared by kneading, co-evaporation, and freeze-drying. The initial dissolution rate of ketoprofen in the inclusion complexes was 15 fold higher, than that of plain drug powder. The maximal plasma concentration of ketoprofen after the oral administration of inclusion complexes to human volunteers increased about 1.5 fold (7.15 vs 4.65 mg/ml), and there was no significant increase in area under concentration-time curve, AUC0-5 (10.35 vs. 9.35 mg. hr/ml), compared to those of ketoprofen powder alone.⁵⁵

3.2. DRUG PROFILE⁶³ EFAVIRENZ:

Efavirenz (brand names Sustiva and Stocrin) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) and is used as part of highly active antiretroviral therapy (HAART) for the treatment of a human immunodeficiency virus (HIV) type

1. For HIV infection that has not previously been treated, the United States Department of Health and Human Services Panel on Antiretroviral Guidelines currently recommends the use of efavirenz in combination with

lamivudine/ zidovudine (Combivir) or tenofovir/ emtricitabine (Truvada) as the preferred NNRTI-based regimens in adults and adolescents. Efavirenz is also used in combination with other antiretroviral agents as part of an expanded postexposure prophylaxis regimen to reduce the risk of HIV infection in people exposed to a significant risk (e.g. needlestick injuries, certain types of unprotected sex etc.). The usual adult dose is 600 mg once a day. It is usually taken on an empty stomach at bedtime to reduce neurological and psychiatric adverse effects. Efavirenz was combined with the popular HIV medication Truvada, which consists of tenofovir and emtricitabine, all of which are reverse transcriptase inhibitors. This combination of three medications approved by the U.S. Food and Drug Administration (FDA) in July 2006 under the brand name Atripla, provides HAART in a single tablet taken once a day. It results in a simplified drug regimen for many patients.

Chemical properties:

Efavirenz is chemically described as (S)-6-chloro-(cyclopropylethynyl)-1,4- dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one. Its empirical formula is C14H9ClF3NO2. Efavirenz is a white to slightly pink crystalline powder with a molecular mass of 315.68 g/mol. It is practically insoluble in water (<10 µg/mL).

Systematic (IUPAC) name:

(4S)-6-chloro-4-(2-cyclopropylethynyl)-4-(trifluoromethyl)-2,4-dihydro-1H-3,1- benzoxazin-2-one

Molecular weight: 315

Structure:

Pharmacokinetics:

Efavirenz, a non-nucleoside reverse transcriptase inhibitor with activity against HIV, blocks the RNA-dependent and DNA-dependent polymerase activities including HIV replication.

Absorption Absorbed after oral doses; plasma concentrations peak after about 5 hr.

Distribution> 99% bound to plasma proteins.

Metabolism Metabolized mainly by CYP3A4 and CYP2B6.

Excretion About 14-34% of a dose is excreted in the urine as metabolites, and 16-61% in the faeces.

Efavirenz Adverse Reactions / Efavirenz Side Effects:

Rash including Stevens-Johnson syndrome and erythema multiforme; CNS effects e.g. dizziness, headache, insomnia, somnolence, abnormal dreams, fatigue, impaired concentration. Nausea, less frequently, vomiting, diarrhoea, hepatitis, depression, anxiety, psychosis, amnesia and ataxia, stupor, vertigo, abdominal pain, hepatic failure, pancreatitis, convulsions, gynaecomastia, pruritus, blurred vision.

Precautions:

Monitor Consider monitoring cholesterol and triglycerides. Monitor LFTs in Patients with history of hepatitis B and/or C. Hepatic Function Use with caution. Convulsions Use with caution in patients with history of seizures.

Convulsions have been reported. CNS symptoms Reported in 53% of patients. Fat redistribution Redistribution/accumulation of body fat, including central obesity, dorsocervical fat enlargement, peripheral wasting, facial wasting, breast enlargement, and cushingoid appearance, may occur. Hepatitis Monitor liver enzymes in patients with known or suspected history of hepatitis B or C infection and in patients receiving medication associated with liver toxicity. Immune reconstitution syndrome May occur, necessitating further evaluation and treatment. Lipids Increases in total cholesterol and triglycerides have been reported.

Monotherapy Resistant virus may emerge rapidly. Psychiatric symptoms Serious adverse psychiatric experiences have been reported. Patients with a history of psychiatric disorders may be at greater risk. There have been occasional reports of death by suicide, delusions, and psychosis-like behavior. Skin rash Reported in 26% of adults and 46% of children. OverdosageSymptoms Increased CNS symptoms, involuntary muscle contractions.

Special Precautions:

Mild to moderate liver disease; renal impairment. Monitor liver enzymes and cholesterol. Discontinue if severe skin rash or fever develops; known or suspected hepatitis B or infection. History of mental illness or seizures; elderly,Pregnancy, Children.

Other Drug Interactions:

Hormonal contraceptives; antibacterial e.g. rifampicin, rifabutin, clarithromycin; enzyme inducers. St. John's wort may decrease serum level. Ethanol (hepatic and CNS adverse effects). Potentially Fatal: Life-threatening adverse effects when used with terfenadine, astemizole, cisapride, midazolam, triazolam and ergot alkaloids.

Other Interactions:

Food Interactions: High-fat meals increase absorption of efavirenz. Grapefruit juice inhibits its metabolism.

Dosage:

Oral HIV infection Adult: Combined with other antiretrovirals: 600mg once daily. Dosing at bedtime recommended during 1st 2-4 wk of therapy to improve tolerability. Child: Combined with other antiretrovirals: >3 yr, 10-14kg: 200mg; 15-19kg: 250mg; 20-24kg: 300mg; 25-32.4kg: 350mg; 32.5-39kg: 400mg; ≥40kg: 600mg. To be taken once daily.

List of Contraindications Efavirenz and Pregnancy:

Caution when used during pregnancy. Category D: There is positive evidence of human foetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g., if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).

Efavirenz and Lactation:

Contraindicated in lactation

Efavirenz and Geriatic:

Use with caution because of the greater frequency of decreased hepatic, renal, or cardiac function, and concomitant diseases or other drug therapy.

Efavirenz and Other Contraindications:

Severe hepatic impairment; hypersensitivity; lactation

Storage:

Oral Store at 15-30℃

Lab interference:

False-positive results in some urinary cannabinoid tests. Raised liver enzymes and serum cholesterol values.

3.5. POLYMER PROFILE^9,30.

HPβ-CYCLODEXTRIN:

Synonyms:

Beta-cycloamylose; betadex; beta-dextrin; cyclohepta amylase; cycloheptaglucan; cyclomaltoheptose; kleptose.

Functional category:

Solubilizing agent and stabilizing agent.

Empirical Formula:

C42 H70 O35

Molecular Weight:

1541.

Description:

White, practically odorless, amorphous powder, having a slightly sweet taste.

Solubility:

Soluble in 1 in 200 part of propylene glycol, 1 in 50 of water at 20 C, 1 in 20 at 50C.

Stability and storage conditions:

Are stable in the solid state if protected from high humidity, should be stored in a tightly sealed container in cool, dry place.

Safety:

Used in oral pharmaceutical formulations.

Handling Precautions:

Should be handled in a well-ventilated environment. Efforts should be made to limit the generation of dust, which can be explosive.

4.1. METHODOLOGY:

The following materials that either AR/LR grade or the best possible pharma grades available were used as supplied by the manufacturer.

Table No- 4 Materials Used:

S. No.	Materials	Grade	Company
1.	Efavirenz	Pharma	Dr. Reddy’s laboratories, Hyderabad, India.
2.	HPβ-Cyclodextrin	Pharma	Gangwal Chemical Pvt Ltd.
3.	Hydrochloric Acid	L.R.	S.D. Fine Chem. Ltd.
4.	Methanol	L.R.	Renkem, chem., S.A.S. Nagar

4.4. Drug Evaluation Studies:

a) Drug Content Estimation²⁹: Solid dispersions prepared by physical mixture, kneading method were assayed for Efavirenz content by dissolving a specific amount of the complexes in methanol and analyzing for the Efavirenz content spectrophotometrically at 245 nm on a spectrophotometer.

b) In vitro dissolution rate studies Efavirenz -HPβCD complexes:²⁷

Dissolution studies of , its complex with HPβ-CD and its physical mixture was performed using USP dissolution apparatus (USPXX IV) paddle method with 900 ml of 0.1 N HCl as dissolution medium at 37˚C±0.5˚C and 50 rpm. At fixed time intervals, 5-ml aliquots were withdrawn, filtered, suitably diluted, and assayed for content by measuring the absorbance at 245nm using a spectrophotometer. Equal volume of fresh medium at the same temperature was replaced into the dissolution medium after each sampling to maintain its constant volume throughout the study. Dissolution studies were perform in triplicate (n=3) and calculated mean values of cumulative drug release were used while plotting the release curves. The percent drug released at various time intervals was calculated and plotted against time.

Characterization of complexes.

a) X-ray diffraction study:

X-ray diffraction study was done to study the powder characteristics of Efavirenz and its solid dispersions with HPβ-cyclodextrin. X-ray diffractgrams were obtained by Philips diffractometer (PW 1140) and Cu-Kα radiation diffractograms were run at a scanning speed of 2^o/min and a chart speed of 2^o/2cm/ 2θ.

4.6. Stability study^34,35,36

a) Introduction:

In any rational drug design or evaluation of dosage forms for drugs, the stability of the active component must be a major criterion in determining their acceptance or rejection.

Stability of a drug can be defined as the time from the date of manufacture and the packaging of the formulation, until its chemical or biological activity is not less than a predetermined level of labeled potency and its physical characteristics have not changed appreciably or deleteriously.

b) Objective of the Study^37,38

The purpose of stability testing is to provide evidence on how the quality of a drug substance or drug product varies with time under the influence of a variety of environmental factors such as temperature, humidity and light, enabling recommended storage conditions, re-test periods and shelf-lives.

The International Conference on Harmonization (ICH) Guidelines titled “Stability Testing of New Drug substance and Products” (QIA) describes the stability test requirements for drug registration applications in the European Union, Japan and the United States of America.

Stability studies were carried out at 25⁰C/60% RH and 40⁰C/75% RH for the selected formulation for the period of 6 weeks.

c) Method³⁴

The selected formulations were packed in amber-colored bottles, which were tightly plugged with cotton and capped. They were then stored at 25⁰C/60% RH and 40⁰C/75% RH for 6 weeks and evaluated for their physical appearance, drug content and drug excipients compatibility at specified intervals of time.

5. CONCLUSION:

From the present study, the following conclusions can be drawn:

1) Cyclodextrins like HPβCD can be used to prepare inclusion complexes of efavirenz with improved solubility. Phase solubility studies of drug with HPβCD illustrate the solubility enhancement capability of HPβCD, the stability constant (Kc) of EFA: HPβCD complex was found to be 820M^–1.

2) FT-IR and XRD studies indicated the formation of true complexes of EFA: HPβCD prepared by microwave technique.

3) The dissolution of EFA from inclusion complexes prepared by microwave technique was found to be higher than the pure drug and physical mixture. By comparing the first order and zerro order kinetics, it was concluded that it followed the first order kinetics.

4) The solid dispersions prepared by microwave technique (F6) was subjected to short-term accelerated stability studies, which has shown no appreciable change in its physical appearance, drug content value and dissolution profiles.

5) Hence from the above results it can be concluded that microwave technique can be used to formulate inclusion complexes of poorly soluble drugs for improved solubility.

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Received on 13.03.2024 Modified on 15.04.2024

Asian J. Pharm. Tech. 2024; 14(2):163-172.

DOI: 10.52711/2231-5713.2024.00029

1.1. STUDIES ON SOLUBILITY IMPROVEMENT1,2: