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January 28, 2012

Pharmacological Management of Heart Failure


Treatment of Chronic Heart Failure aims to relieve symptoms, to maintain a euvolemic state (normal fluid level in the circulatory system), and to improve prognosis by delaying progression of heart failure and reducing cardiovascular risk. Drugs used include: diuretic agents, vasodilator agents, positive inotropes, ACE inhibitors, beta blockers, and aldosterone antagonists (e.g.spironolactone).
ACE inhibitor therapy is recommended for all patients with systolic heart failure, irrespective of symptomatic severity or blood pressure.ACE inhibitors improve symptoms, decrease mortality and reduce ventricular hypertrophy. Angiotensin II receptor antagonist therapy,particularly using candesartan, is an acceptable alternative if the patient is unable to tolerate ACEI therapy.
Diuretic therapy is indicated for relief of congestive symptoms. Several classes are used, with combinations reserved for severe heart failure:
* Loop diuretics (e.g. furosemide) – most commonly used class in CHF, usually for moderate CHF.
* Thiazide diuretics (e.g. hydrochlorothiazide) – may be useful for mild CHF, but typically used in severe CHF in combination with loop diuretics, resulting in a synergistic effect.
* Potassium-sparing diuretics (e.g.Spironolactone) – used first-line use to correct hypokalaemia.
As with ACEI therapy, the addition of a β-blocker can decrease mortality and improve left ventricular function. Several β-blockers are specifically indicated for CHF including: bisoprolol, carvedilol, nebivolol and extended-release metoprolol.
Digoxin (a mildly positive inotrope and negative chronotrope), once used as first-line therapy, is now reserved when the adequate control is not achieved with an ACEI, a beta blocker and a loop diuretic.There is no evidence that digoxin reduces mortality in CHF, although some studies suggest a decreased rate in hospital admissions.It is contraindicated in cardiac tamponade and restrictive cardiomyopathy.
by
Akshaya Srikanth,
Pharm.D Intern
RIMS Hospital, Kadapa
INDIA

Differential Diagnosis of Wide QRS Complex Tachycardia

-Ventricular tachycardia (about 80% of cases ).
-SVT with abnormal interventricular conduction (15-30 %):
*SVT with BBB aberration (fixed or functional).
*Pre-excited SVT (SVT with ventricular activation occurring over an anomalous AV connection ).Their ECG can be indistinguishable from VT originating at the base of ventricle.(1-5 % of all)
*SVT with wide QRS due to abnormal muscle-muscle spread of impulse.( surgery, DCM)
*SVT with wide complex due to drug or electrolyte-induced changes. (hyperkalemia. Class Ia ,Ic drugs or Amiodarone)
-Ventricular paced rhythms 
SVT vs VT 
-The majority of patients with VT have structural heart disease, In SVT they may or may not have.
-Patient with VT are older.
-Patients with SVT more often have history of previous similar episodes .
-Overall appearance of patient is not accurate.
-The widespread impression that hemodynamic stability indicates SVT is erroneous and can lead to dangerous mistreatment.
-Physical findings that indicate presence of AV dissociation (cannon A waves, variable-intensity S1,variation in BP unrelated to respiration) if present are useful.
-Termination of WCT in response to maneuvers like Valsalva, carotid sinus pressure, or adenosine is strongly in-favor of SVT but there are well-documented cases of VT responsive to these.
-Diagnostic injection of verapamil or beta-blockers should be discouraged. (prolonged hypotension).
-QRS duration:70% of VTs have QRS duration more than140, but no SVT has it. VT is probable when QRS  more than 140 with RBBB and more than160 with LBBB pattern.Anti arrhythmic drugs may prolong QRS. Some patients with VT may have QRS of 120-140 specially in those without structural heart disease.
by
Akshaya Srikanth, Dr.S.Chandra Babu*
Pharm.D*, *Asso.Professor of Medicine
RIMS Medical College, Kadapa, A.P
INDIA

LEARN ECG IN 5 MINUTES - A SIMPLE GUIDE TO ECG



Normal P waves 
Height less than 2.5 mm in lead II 
Width less than 0.11 s in lead II 
Abnormal P waves see in right atrial hypertrophy, left atrial hypertrophy, atrial premature beat, hyperkalaemia

Normal PR interval 
0.12 to 0.20 s (3 - 5 small squares) 
Short PR segment consider Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome (other causes - Duchenne muscular dystrophy, type II glycogen storage disease (Pompe's), HOCM) 
Long PR interval see first degree heart block and 'trifasicular' block 

Normal QRS complex 
Less than 0.12 s duration (3 small squares) 
for abnormally wide QRS consider right or left bundle branch block, ventricular rhythm, hyperkalaemia, etc.
no pathological Q waves 

Normal QT interval 
Calculate the corrected QT interval (QTc) by dividing the QT interval by the square root of the preceeding R - R interval. Normal = 0.42 s. 
Causes of long QT interval 
Myocardial infarction, myocarditis, diffuse myocardial disease 
Hypocalcaemia, hypothyrodism 
Subarachnoid haemorrhage, intracerebral haemorrhage 
Drugs (e.g. sotalol, amiodarone) 
Hereditary - Romano Ward syndrome (autosomal dominant) ,Jervill + Lange Nielson syndrome (autosomal recessive) associated with sensorineural deafness 

Normal ST segment  - no elevation or depression 
Causes of elevation include acute MI (e.g. anterior, inferior), left bundle branch block, normal variants (e.g. athletic heart, Edeiken pattern, high-take off), acute pericarditis 
cCauses of depression include myocardial ischaemia, digoxin effect, ventricular hypertrophy, acute posterior MI, pulmonary embolus, left bundle branch block 

Normal T wave 
Causes of tall T waves include hyperkalaemia, hyperacute myocardial infarction and left bundle branch block 
Causes of small, flattened or inverted T waves are numerous and include ischaemia, age, race, hyperventilation, anxiety, drinking iced water, LVH, drugs (e.g. digoxin), pericarditis, PE, intraventricular conduction delay (e.g. RBBB)and electrolyte disturbance.
Please share your comments & suggestions
by
Akshaya Srikanth, Dr.Chandra Babu*
Pharm.D Internee, *Asso.Professor of Medicine
RIMS Medical college, Kadapa.

Needle-free nanopatch vaccine delivery system

The needle-free nanopatch vaccine delivery system is coming soon after a consortium of investors put up $15 million for its development. The money will enable University of Queensland's Professor Mark Kendall to continue his work on the technology. It is described as the biggest breakthrough in vaccine delivery since the invention of the syringe more than 150 years ago.
The nanopatch has thousands of small projections to deliver vaccines to abundant immune cells in the skin, doing away with needles plunged into muscle where there are few immune cells. Early stage testing in animals has shown a nanopatch-delivered flu vaccine is effective with only 1/150th of the dose compared to a syringe. The nanopatch is also expected to cut needle stick injuries and cross contamination. This would avoid needle borne diseases like HIV and hepatitis. And it does not need refrigeration like traditional vaccines.
Prof Kendall of the Australian Institute for Bioengineering and Nanotechnology, said that's one of the most exciting things about the new technology because it will dramatically cut costs and make transportation easier. He said, “In Africa about half of vaccines aren't working properly because of a breakdown in the cold chain…The nanopatch also offers a way to stop needle-stick injuries during vaccination.” He explained that the idea came to him about eight years ago when he was bored at a conference and “started doodling”.
Money from the Federal Government's innovation investment fund has helped establish the new company Vaxxas, which will commercialise the nanopatch. The investment is led by OneVentures, with co-investors Brandon Capital, the Medical Research Commercialisation Fund (MRCF) and US-based HealthCare Ventures.
OneVentures General Partner Dr Paul Kelly said the significance of the million investment was not just in its size. “This investment syndicate includes both local and international investors, which is a real vote of confidence in the Nanopatch approach and an appreciation of the potential of the technology to revolutionize vaccine delivery worldwide,” Dr Kelly said. Dr Kelly will join the Board of Directors of Vaxxas, along with Brandon Capital Partners Managing Director Dr Stephen Thompson; HealthCare Ventures Managing Director Douglas E. Onsi; and UniQuest General Manager of Life Sciences Dr Dean Moss.
Dr Thompson said launching Vaxxas as a company was a critical next step for the Nanopatch technology. “In Australia, we invest heavily in our excellent research and development capability but have a relatively poor record of taking those technologies to world markets,” he said. “The syndicate's investment in Vaxxas is consistent with its willingness to work with Australia's leading research institutes, including the AIBN, to transform this exciting research effort into a commercially useful product. We need to convert the promise of the technology into a reality.”
Mr Onsi said the Nanopatch had the potential to transform vaccine delivery for the pharmaceutical industry and for patients around the world. “HealthCare Ventures searches globally for the most promising innovations in life sciences and we are very pleased to make our first Australian investment in Vaxxas,” he said.
Source: Nano Medicine
by
Akshaya Srikanth
Pharm.D Internee
Hyderabad, India

January 26, 2012

Why Tuberculosis Is So Hard to Cure ?????


When microbes divide, you usually get more of the same: A cell splits up and creates two identical copies of itself. But a new study shows that's not true for mycobacteria, which cause tuberculosis (TB) in humans—and that may explain why the disease is so difficult to treat. Mycobacteria divide asymmetrically, generating a population of cells that grow at different rates, have different sizes, and differ in how susceptible they are to antibiotics, increasing the chances that at least some will survive. Researchers hope the findings will help them develop drugs against those cells that are especially hard to kill.
"It is incredible that we are finding such basic things out only now," says immunologist Sarah Fortune of at the Harvard School of Public Health in Boston, the paper's lead author. "But it reflects the fact that mycobacteria are relatively understudied."
More than a third of the world's population is estimated to be infected with Mycobacterium tuberculosis. Most people's immune system can keep the bacteria in check, but there is a lifetime chance of 1 in 10 that the dormant infection will progress to TB; the disease still kills 4000 people every day. Tuberculosis treatment is a combination of antibiotics taken for half a year or more—a major drawback, because patients often quit therapy prematurely, increasing the risk of drug-resistant strains emerging. Scientists have assumed that mycobacteria are so hard to kill because dormant cells exist even in patients with active disease and these cells are far less susceptible to antibiotics than metabolically active bacteria.
But Fortune and her colleagues found a second, more surprising mechanism. They cultured M. smegmatis, which is closely related to M. tuberculosis but faster growing, in a tiny chamber with a constant flow of nutrients, allowing them to watch single live cells growing and replicating. Unlike other rod-shaped bacteria, such as E. coli, mycobacterial cells divided asymmetrically, creating a tapestry of cell types with widely different sizes and growth rates, the team reports online today in Science.
By labeling the cell wall of the mycobacteria with a fluorescent dye and observing the new, unstained cell wall growing at the poles, the researchers found that daughter cells mainly grow at their "old" pole. As the new end, created by the cell division, grows older, it matures and the cell elongates faster. And as the cells go through numerous divisions, cells with poles of many different "ages" emerge, leading to the wide variety in growth rates.
Importantly, the cells also differed in their susceptibility to antibiotics: While "older," fast-growing cells were more susceptible to the drugs isoniazid and cycloserine; younger, slower-growing cells were more susceptible to rifampicin. "When I started working on mycobacteria, the assumption was that all the bacteria are indistinguishable. This is the first mechanistic insight into why the cells are phenotypically different," says Fortune. The asymmetry is a way for mycobacteria to keep their population diverse, she says, just like viruses create diversity by mutating frenetically.
"This is an important study, because it shows that our way of thinking that populations are the sum of equal organisms is incorrect," says immunologist Stefan Kaufmann of the Max Planck Institute for Infection Biology in Berlin. "As we look at individual microbes, we find diversity." Kaufmann cautions, however, that most of the experiments were done with M. smegmatis and need to be verified with M. tuberculosis. "But this could explain, at least in part, why tuberculosis is so hard to treat," he says. "And it could pave the way for a rational search for new combination therapies composed of drugs that attack the different types of bacteria."
Source: Science Careers
by
Akshaya Srikanth
Pharm.D Internee
Hyderabad, India

Learn Chest X-ray in 5 minutes

General pattern of seeing a X-Ray is described below:
PED In O Sonia BA-Tra Hi DiL
Part , exposure and development, inspiratory or expiratory film, orientation, soft tissue shadows, bony cage, trachea and mediastinum, hilar shadow, diaphragm and costophrenic angle, lung fields.
akshaypharmd.blogspot.com
1.First of all describe the part of body in x-ray e.g (chest) look its view i.e A.P or P. A view.
P.A view is taken to see lungs and heart while AP view is taken to see posterior lung cage, scapula. 
PA or AP means the direction from which X-Rays are made to project upon body.
2. See the exposure of film whether overexposed or underexposed.
3. Now describe whether film is taken in expiration or inspiration.
4. Find out the orientation of patient on x-ray : check out orientation of patient on x ray by measuring distances between lateral end of manubrium and medial end of clavicle in case of centrally oriented patient this distance will be equal, to take an x ray in centralized form ask patient to fold both of hands and both of shoulders must touch the plate.
if any of distance is less or shadow is overlapped, patient will have that orientation, that means if patient has removed his left shoulder than right side clavicle will be overlapped with sternum.
5. see soft tissue shadows- like lymphnodes, etc
6. see bony cage- see ribs, cartilages, extra ribs, fracture
7. look for trachea and mediastinum: heart will be explained seperately later in this section.
8. look for hilar shadows
9. Look for diaphragm: look whether diaphragm is flat or curved, its postion, normally lies at 5th -6th ribs
10. look for costophrenic angles, cardiophrenic angle: look whether these angles are obliterated or not, obliterated in case of pleural effusion. But in case of consolidation of lung these angles are not obliterated still you see radio opaque areas, however these consolidation are accompanied by small circular gas filled spot, indicating bronchovascular markings.
11. look for lung fields : looks for homogenous or heterogenous opacity, hypertranslucency, cavity, fibrosis, calcifications, millets etc.

Now look for these heading in details below
  1. Part and View: part i.e chest, view i.e A.P or P.A view, P.A view is taken to see the lung and heart, while AP view is taken to see posterior lung cage, scapula.
    • Inspiration is done to expand the lung fields, as diaphragm descends down, the principle behind that is that which ever part is closed to X- ray plate is clearly viewed.
    • PA view is done to minimize bony markings like spine, bony cage, posterior end of ribs are hard so clearly visible in chest x-ray, however anterior part of ribs is fiague, so its shadow becomes light.
2. Exposure and Development:
    • Normal Exposure: shadow of vertebral column is faintly visible, intervertebral spaces not clearly visible, and shadow of trachea is normally visible upto the level of clavicle as a translucent shadow.
    • Over Exposure: vertebral column along with intervertebral spaces will be clearly visible, posterior part that is spine will be clearly visible.
    • Translucency of trachea is lowered down the level of clavicle may be upto the bifurcation of trachea.
    • Translucency of the lung field will increase and density and opacity of heart will reduce and heart becomes more central and narrow.
Under Exposed: faint shadow of vertebral column will not be visible at all, translucency of trachea will not be clearly visible, opacity of heart will increase. 

3. Orientation Of the Patient:
What is centrally oriented x – ray? 
  • If the x ray is taken when patient is having hand folded and both of shoulders are touching the plate.
  • In this case distance between medial end of clavicle and lateral border of vertebrae column will be almost equal in x ray.
  • Right anterior orientation: only right shoulder touching the plate and left is away, in both left and right orientation there will be overlapping of medial end of clavicle and lateral border of vertebrae.
What is importance of orientation?
  • In right orientation, trachea will be shifted to left, in x ray, heart will appear to be shifted left or it will show cardiomegaly. 
  • In left orientation heart will appear central, and aortic knuckle, pulmonary conus not visible, tubular appearance of heart in left orientation.
4. Soft tissue shadows: 
Abnormalities : abnormality of lymph nodes, calcified (appear dense-more dense than bone) and matted.
Subcutaneous emphysema- vertical linear multiple translucent band like shadow.

5. Bony Cage: 
cartilages donot have any shadow, from the age of 25 years, cartilages start ossifying, so densly visible. 
How to detect cardiomegaly in X ray? 
First divide heart shadow in 2 parts from centre by vertical line, now from that line see greatest curves on both left and right side, means there will be to parallel line touching that vertical line, say them (a, b), and say x= a+b
Now measure the transverse diameter of thorax by joining the 2 costophrenic angles and say it to be (y).
If x> y/2 than it is cardiomegaly.

6. Hilar shadows: 
Centre of hilum is place from where vessels originate, it is formed by arteries and viens with small contribution from the walls of the major airways.
  • The most important vessel in hilum is Basal artery or descending branch of pulmonary artery. On right side it is clearly visible (basal art) width is about 7-19mm when visible on left side it is about 1-2 mm less than right side, generally not visible on left side due to overlapping by heart. 
  • The centre of right hilum is at the level of 3 rd rib anteriorly and 6th rib in the axilla- in a normal inspiratory film.
  • Ring like shadows around hilum is end of bronchus and solid shadows are blood vessels.
7. Diaphragm and CostophernicAngles: 
Centre of right dome of diaphragm is 5 to 6.5 ant rib in normal insp. Film. Centre of left dome of a diameter is .5 to 2.5 lower than the right. 
The curvature of the dome of diaphragm : drop a perpendicular from centre to line coming from angles it is around 1 to 1.5 cm
8. Lung Fields: any lesion should not be defined in reference to lobes but as ZONES.
  • Upper zone- from 2nd costal cartilage to axilla
  • Middle zone- between 2nd and 4th costal cartilage.
  • Lower zone- below 4th costal cartilage.
  • Horizontal fissure is normally visible in 70% of individual .
  • Transverse fissure in PA view.
  • Oblique fissure is not visible in PA view.
  • The level of horizontal fissure in normal inspiratory film is at the level of right hilum, 10 degree inclination or depression is accepted as normal.
  • Upper zone vessels are less prominent but lower zone vessels are more prominent due to gravitational effects.
Please share your comments and suggestion 
Prepared by
AKSHAYA SRIKANTH, Dr.S.Chandra Babu*
Pharm.D Intern,*Asst.Professor of Medicine
RIMS hopsital, Kadapa, India

Strategies to Formulate Lipid-based Drug Delivery Systems

Orally administered water-insoluble drugs have become increasingly important in therapy, and lipid-based drug delivery systems have become an essential tool in the development of formulations for these compounds. Lipid-based formulations have been marketed for a variety of drug classes such as HIV protease inhibitors (e.g., ritonavir, lopinavir, sequinavir, tipranavir, amprenavir), immunosuppressants (cyclosporine, sirolimus), and calcium regulators (e.g., calcitriol, paricalcitol). It is estimated that 40% of new drug candidates are water insoluble, and thus may require delivery in a system such as a lipid-based formulation.
A lipid-based drug delivery system typically is composed of lipids and surfactants, and may also contain a hydrophilic co-solvent. Many of them are characterized as Self-Emulsifying Drug Delivery Systems (SEDDS) such that they form an emulsion upon gentle agitation in water. Emulsions are considered metastable systems, with droplet sizes of 100-1000nm. Other formulations, Self-Microemulsifying Drug Delivery Systems (SMEDDS), form microemulsions that are thermodynamically stable systems. Microemulsions have droplet diameters <100 nm, and are visually transparent or translucent. The drug is generally present in the dosage form dissolved in the formulation, and should remain solubilized after dispersion of the dosage form in the GI tract. Absorption by the intestinal mucosal cells is facilitated by the rapid release of drug from the high surface area of the small emulsion or microemulsion droplets.

An ideal oral lipid-based dosage form must meet a number of demands:
  1. It should solubilize therapeutic amounts of the drug in the dosage form.
  2. It should maintain adequate drug solubility over the entire shelf-life of the drug product (generally 2 years) under all anticipated storage conditions.
  3. It should provide adequate chemical and physical stability for the drug and formulation components.
  4. It must be composed of approved excipients in safe amounts.
  5. Once ingested, it should facilitate dispersion of the dosage form in the intestinal milieu and maintain drug solubilization in the dispersed form.
  6. It should adapt to the digestive processes of the GI tract such that digestion either enhances or maintains drug solubilization.
  7. It should present the drug to the intestinal mucosal cells such that absorption into the cells and into the systemic circulation is optimized.
These requirements can render formulation and evaluation of lipidbased systems quite challenging. Despite their importance, design of lipid-based formulations to meet these challenges is still largely an empirical exercise. This review will outline some guidelines and strategies in developing these formulations, addressing the challenges of each of these requirements and highlighting examples of successful lipid-based formulations.
Solubilization
Table 1    -    Excipients used in oral lipid-based formulations
36882-tbl1.jpgZoom In

Table 1 summarizes the excipients available to the formulator to solubilize a drug candidate in a lipid-based formulation. While the lipids (fatty acid derivatives) are the core ingredient of the formulation, one or more surfactants, as well as perhaps a hydrophilic co-solvent, may be required to aid solubilization and to improve dispersion properties. Surfactants are categorized by their Hydrophilic-Lipophilic Balance (HLB) number, with a low value (≤10) corresponding to greater lipophilicity and a higher value (≥10) corresponding to higher hydrophilicity. As a guideline as a starting point for formulation design, most of the lipids used in these oral formulations have a known “required HLB” value (generally available from the vendors), which corresponds to the optimal HLB for the surfactant blend necessary to emulsify the oil in water. For example, the required HLB of medium chain triglyerides (glyceryl tricaprylate/caprate) is ~11, while that of long chain triglycerides (vegetable oil) is ~6. The surfactants polysorbate 80 and sorbitan monooleate have HLB values of 15 and 4.3, respectively. Thus a blend of 63/37 blend of polysorbate 80/sorbitan monoleate will emulsify the former, and a 16/84 blend will emulsify the latter. Co-solvents used in lipid-based formulations include propylene glycol, ethanol, PEG400, glycerol, and diethylene glycol monoethyl ether.
Possible combinations for lipid-based formulations thus approach an endless number, but a consideration of the structure and physical-chemical properties of the drug candidate may allow one to narrow the search. For example, if the drug is an amine, it may be soluble in oleic acid by formation of an ion pair, as exhibited by marketed formulations of ritonavir and ritonavir/lopinavir. Hydrophobic non-ionizable drugs (generally characterized by a Log Poctanol/water≥3) may be solubilized by long chain or medium chain triglycerides and/or by combination of a lipid with a low HLB surfactant such as phosphatidylcholine/medium chain triglyceride or oleoyl macrogolglycerides. Less hydrophobic drugs (viz., Log Poctanol/water ≤3) may be solubilized by monoglycerides or propylene glycol monoesters, or by combinations of these lipids with high HLB surfactants or hydrophilic co-solvents. Often a combination of low HLB and high HLB surfactants give superior solubilization, which may also optimize the dispersion properties described later. Screening studies can be carried by mixing the required drug amount in the formulation and examining visually or microscopically for the presence of drug crystals, followed by more accurate determination of solubility values of drug in the most promising formulations by HPLC. High throughput screening systems have been employed to increase efficiency. For example, a robotic liquid dispenser was used to prepare a series of nilvadipine SMEDDS formulations by combinations of oil, surfactant, and ethanol, and identify the optimal low HLB/high HLB blend. Statistical and experimental design studies, such as a simplex lattice mixture or a central composite design, have also been used to optimize and develop SMEDDS formulations of celecoxib and bufalin, respectively. Nevertheless, as pointed out in the review by Rane and Anderson, prediction of drug solubility in lipid vehicles is difficult due to the dominant role played by interfacial effects and the possible presence of complex microstructures. While it is difficult to predict optimal formulations based solely on physicochemical properties of the candidate, some progress has been made. Thi et al. examined 10 different compounds with varying properties in SMEDDS formulations; optimal drug logPo/w for solubility in the SMEDDS formulation was found to be between 2 and 4.
Frequently, toxicology studies will have been carried out with waterinsoluble drug candidates in lipid vehicles. Constraints may be different for the two situations; safety requirements of excipients will be more stringent for clinical formulations, but doses will likely be lower. Nevertheless, toxicology vehicles for a given drug may provide a starting point for development of a First-in-Human and subsequent formulations. 
Dispersion
Zoom In
Figure 1 - Ternary phase diagram of an oil-surfactant water system, based on a C12E10-oleic acid-water system.
Formulations that exhibit sufficient solubility of the drug candidate should be examined for emulsification and dispersion properties in aqueous vehicles. A preliminary screen can be carried out by microscopic observation of the formulation when mixed with water. Vigorous mixing, accompanied by diffusion and stranding mechanisms, occurring at the water/formulation interface is indicative of an efficient emulsification. Absence of drug precipitate after complete mixing of the formulation with aqueous medium is another requirement. Particle size measurement of emulsion droplets by laser light scattering or other techniques is useful to select promising formulations. Construction of ternary phase diagrams is a method frequently used to determine the types of structures resulting from emulsification and to characterize behavior of a formulation along a dilution path. An example is shown in Figure 1; the line from A to B represents dilution of a formulation consisting initially of 35% surfactant/65% oil, passing through regions of a water-in-oil microemulsion and a lamellar liquid crystal until reaching a stable bicontinuous oil-in-water microemulsion after dilution. It is often unnecessary to construct the entire phase diagram, but an understanding of the structures arising on a dilution path of a given formulation is important to assure formation of stable dispersed structures upon dilution. Appropriate combinations of low HLB and high HLB surfactants frequently lead to smaller emulsion droplet size than single surfactants. These more complex combinations can be examined by pseudo-ternary phase diagrams, wherein a given surfactant blend and/or oil blend would serve as the oil or surfactant apex of the diagram; co-solvents can be examined similarly as part of the oil or surfactant blend.
Dispersion properties can be examined and optimized as part of an experimental design study. For example, genistein SEDDS formulations were optimized by a three-factor, three-level Box-Behnken design. Droplet size after dilution, turbidity, and dissolution percentage of drug after 5 minutes and 30 minutes were the variables examined to optimize a formulation consisting of glyceryl monolinoleate, medium chain triglyceride, polyoxyl 35 castor oil, caprylocaproyl macrogolglyceride, and diethylene glycol monoethyl ether. Similarly, a D-optimal mixture design was used to select compositions of SMEDDS formulations of albendazole, with dispersion performance, droplet size, dissolution efficiency, and time for 85% drug release as the factors examined. The optimal formulation was polyoxyl 35 castor oil, polysorbate 80, acidified PEG-400, and propylene glycol monocaprylate. The same type of design was used to optimize a SEDDS formulation of lacidipine, with droplet size, optical clarity, drug release, and emulsification efficiency as the factors examined. The optimized formulation was composed of oleoyl macrogolglycerides, glycerol monocaprylate/caprate, polysorbate 80, and polyoxyl 35 castor oil.
Ideally, drug solubility and dispersion should be examined together. While presence of a co-solvent may enhance solubility of the drug in the dosage form, high amounts of hydrophilic co-solvent may lead to drug precipitation after dispersion due to diffusion of the co-solvent away from the emulsion droplet into the bulk aqueous phase. Mohsin et al. observed rapid precipitation of fenofibrate after dilution of formulations composed of high amounts of hydrophilic co-solvents (e.g., propylene glycol) and surfactants (e.g., polysorbates). If sufficient amounts of lipid (medium chain triglyceride) were present, formation of supersaturated systems sometimes resulted which nevertheless retarded precipitation for adequate time. Experimental design studies examining both drug solubility and dispersion properties can aid in identifying formulations with optimal behavior with respect to both factors. For example, a simplex lattice experimental design approach was used to optimize SEDDS formulations of curcumin based on ethyl oleate, PEG400, and polyoxyl 35 castor oil.

Digestion

The actions of intestinal lipases can have a profound effect on the behavior of lipid-based formulations in the GI tract, and must be considered in their design. It has long been recognized that non-dispersible but digestible lipids such as triglycerides can be metabolized by lipases to mono-/di-glycerides and fatty acids which will emulsify any remaining oil. Thus, the presence of high amounts of surfactants may be unnecessary to assure creation of the requisite small particle sizes and large surface areas for drug release. In 2000, Pouton proposed a classification system for lipid-based formulations based on the formulation components and the dependence on digestion to facilitate dispersion; this is shown in Table 2. Type I formulations, being composed simply of drug in triglyceride or mixed glycerides, require digestion in order to be dispersed. Dispersibility of the other classes of formulations is less dependent on digestion since low HLB (Type II) or high HLB (Type III) surfactants are included. A fourth category Type IV, was added in 2006, consisting of surfactant/cosolvent mixtures without lipid. However, the lower oil content of Type IIIA and especially of Type IIIB and Type IV formulations increases the risk of drug precipitation upon mixing with the intestinal milieu, due to diffusion of the co-solvents and high HLB surfactant away from the emulsion droplet. Furthermore, surfactants in the formulation may also be digested by intestinal lipases and hence lose their solubilizing power, leading to drug precipitation. Thus, in vitro dissolution testing in biorelevant media (i.e., simulated intestinal fluids) such as those developed by Dressman should be used to evaluate candidate formulations. Studies by Cuine et al. with a series of danazol lipid-based SMEDDS formulations showed that higher surfactant content led to smaller droplet size after in vitro dispersion, but under digestion conditions high surfactant content led to a greater occurrence of drug precipitation and lower bioavailability in dogs. More comprehensive evaluations can be carried out by in vitro lipolysis models as described by Mullertz. For example, in studies by Dahan, formulations of long chain triglycerides (LCT), medium chain triglycerides (MCT), short chain triglycerides (SCT), and aqueous suspensions of griseofulvin were examined in the in vitro lipolysis model and in rat bioavailability studies. Both the in vitro model and in vivo studies showed a rank ordering of drug solubilization of MCT > LCT > SCT > aqueous suspension, with a correlation r2 >0.98.
Table 2    -    Pouton’s Classification of Lipid-Based Delivery Systems
Zoom In

Absorption

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Figure 2 - Processes of dispersion, digestion, and absorption occurring for a lipid-based formulation.
Efficient absorption of the drug by the intestinal mucosal cells is of course the ultimate goal of any oral lipid-based formulation. Figure 2 shows the processes that occur in the intestinal milieu for a lipid-based drug formulation. First the components are dispersed to form lipid droplets (for Type I formulations) or emulsion droplets (for Types II-III), followed by lipolysis and solubilization of the digestion products by bile acids, forming colloidal mixed micelles. It is believed that drug then partitions from the emulsion oil droplets and bile salt mixed micelles to be absorbed by the mucosal cells of the intestinal wall. Even if only a very small proportion of drug is actually in solution in the intermicellar space available for absorption, the colloidal species quickly replenish the soluble portion to be absorbed. Testing in animals of candidate formulations is generally used pre-clinically to evaluate bioavailability of drugs in lipid-based systems. While rats and dogs are the species most widely employed, the pig has more recently been suggested as being more relevant and comparable to humans in eating behavior and in GI physiology. Alternatively, absorption can be monitored by isolated intestinal membranes. For example, absorption of ibuprofen from a medium chain triglyceride/diglyceryl monooleate/polyoxyl 40 hydrogenated castor oil microemulsion was evaluated in rat isolated intestinal membrane in an Ussing chamber. deally, absorption should be optimized along with solubilization and dispersion under biorelevant conditions. This is similar to the approach of Liu et al., who used a central composite design to optimize oil/surfactant/co-surfactant ratio in a SMEDDS formulation of oridonin, examining the factors solubility, droplet size after dispersion, and in situ intestine absorption rate.
Ultimately, the success of any lipid-based formulation will be determined in humans. Clinical results of experimental and marketed lipid-based oral formulations of poorly soluble drugs has been reviewed by Fatouros et al. One of the first compounds delivered by a SEDDS formulation was cyclosporine. The Sandimmune formulation, introduced in 1981, contains corn oil, ethanol, glycerol, and linoleoyl macrogolglycerides; it forms a crude emulsion upon dispersion in water. Neoral is a SMEDDS cyclosporine formulation introduced in 1994; it contains corn oil mono-di glycerides, polyoxyl 40 hydrogenated castor oil, ethanol, propylene glycol, and α-tocopherol. In clinical studies with transplant patients, Neoral gave a higher AUC (3028 vs. 2432 μg • h/L), a higher Cmax (892 vs. 528 μg/L), and a shorter tmax (1.2 vs. 2.6 h) relative to Sandimmune. Several oral HIV protease inhibitors have also been formulated in lipid systems. Ritonavir was originally marketed in 1996 as a hard gelatin capsule with a semi-solid, lipid-based formulation composed of caprylic/capric triglycerides, polyoxyl 35 castor oil, citric acid, ethanol, polyglycolized glycerides, polysorbate 80, and propylene glycol. In 1998, after a less-soluble polymorph of the drug appeared, the product was re-formulated as a soft gelatin capsule with a liquid formulation containing ethanol, oleic acid, and polyoxyl 35 castor oil. A second generation product, ritonavir/lopinavir has been marketed in a oleic acid/polyoxyl 35 castor oil/propylene glycol. Another protease inhibitor, tipranavir, is marketed in a mono-/di-glycerides of caprylic/capric acids/polyoxyl 35 castor oil/propylene glycol/ethanol formulation. Another interesting example is the HIV protease inhibitor sequanavir: the lipid-based formulation (Fortovase), which contains medium chain mono-diglycerides, povidone, and α-tocopherol, gave a 3-fold higher oral bioavailability compared to a conventional capsule formulation of the drug’s mesylate salt (Invirase), even though the salt has a 1000-fold higher aqueous solubility than the free base used in Fortovase (2.2.mg/mL vs. 0.017 mg/mL).

Stability

Maintaining adequate chemical and physical stability of lipid-based drug formulations delivery systems can also present challenges. As already reviewed, unsaturated lipid components can undergo lipid peroxidation. This can be minimized by use of saturated medium chain (C6-C12) triglycerides and by use of appropriate anti-oxidants. Phenol-based anti-oxidants such as Vitamin E (α-tocopherol), butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and propyl gallate can act synergistically with oxygen scavengers such as ascorbic acid and its lipid-soluble counterpart, ascorbyl palmitate. With regard to physical stability, liquid or semi-solid fill formulations in hard or soft gelatin capsules must be carefully designed in order to ensure compatibility of the fill with the capsule shell.

Conclusions

While it is apparent that lipid-based formulations will continue to be an important tool to formulate poorly soluble drugs, design of these formulations can be a challenge. In their excellent review, Porter et al. recently outlined seven guidelines for design of lipid-based formulations, as summarized below:
  1. It is critical to maintain drug solubility in the formulation, after dispersion, and after digestion.
  2. Properties of the colloidal species formed after processing in the GI milieu are probably more important than properties of the formulation itself in enhancing absorption.
  3. Higher proportions of lipid (>60%) and lower proportions of surfactant (<30%) and cosolvent (<10%) generally lead to more robust drug solubilization after dilution.
  4. Medium chain triglycerides may afford greater drug solubility and stability in the formulation, but long chain triglycerides facilitate more efficient formation of bile saltlipid colloidal species and thus may afford higher bioavailability.
  5. Type IIIB SMEDDS formulations give lower droplet sizes after dispersion. However, they are more dependent on the surfactant properties employed, and non-digestible surfactants generally give higher bioavailability.
  6. Dispersion of Type IV formulations (surfactant/cosolvent) are likely more efficient if two surfactants are used rather than a single one.
  7. Type IV formulations may give higher drug solubility, but must be designed carefully to assure that drug does not precipitate after dispersion.
These guidelines are important ones to keep in mind when designing oral lipid-based formulations for poorly soluble drugs. As further experience is gained with design and use of these formulations and the database of successful formulations grows, it is to be hoped that design of these formulations will become less of an empirical exercise and more rational in its approach. As this happens, the utility of lipid-based formulations can only grow.  Source: NDDS Tech Review, APDR, Drug Delivery system.
by Akshaya Srikanth, Pharm.D Intern