Extended release of timolol from nanoparticle-loaded fornix insert for glaucoma therapy

We have developed a cylindrical insert that can be inserted in the fornix for extended release of glaucoma drug timolol. The insert is prepared by incorporating timolol-loaded nanoparticles into a poly hydroxyl ethyl methacrylate (p-HEMA) matrix. A 1-mm diameter, 7.5-mm long insert with 25% (w/w) particles can release timolol for about 10 days at an average rate of about 15 μg/day, which may be therapeutically effective. The increase in particle fraction increases drug loading, but also increases the release duration. The net effect of increasing the particle fraction is a significant increase in release duration, but a decrease in daily drug release rates, in the first few weeks. The release duration increases to about 1 and 3 months on increasing the particle fraction to 50% and 75%, respectively. The average daily release rates in the first 3 weeks are 15, 9, and 3 μg/day for the inserts with 50%, 75%, and 100% (w/w) particles, respectively. The mechanism of release is hydrolysis of the ester bond that links timolol to the propoxylated glyceryl triacrylate matrix, and thus the release profiles fit a first order reaction model. The water content of the inserts decreases from 31% to almost zero on increasing the particle loading from 25% to 100%. The rate constant for the hydrolysis decreases with an increase in particle loading in the insert most likely due to the reduction in the water content. The inserts can be packaged in wet conditions and stored in a refrigerator, but the inserts will exhibit a burst release caused by release of the drug from the particles into the p-HEMA matrix during the shelf life. Also, the magnitude of drug release after the initial burst is reduced due to the storage. The burst effect could potentially be avoided by packaging the inserts in a dry state, with hydration before insertion.

Seasonal Variation in Essential Oil Content and Composition of Thyme, Thymus serpyllum L. Cultivated in Uttarakhand Hills

Thymus serpyllum L. grown in Kumaon region of Western Himalaya was investigated for essential oil content and composition in different seasons. The oils of fresh samples were obtained by hydrodistillation. The yield of essential oil (% v/w) during different seasons varied from 0.07 to 0.28% with the highest in summer season, at vegetative stage. The oils were analyzed by GC and GC-MS. Major components of all the samples were thymol (19.4-60.1%), γ-terpinene (0.3-13.8%) and p-cymene (3.5-10.4%). The results clearly indicated that season has significant effect on quality and quantity of thyme oil.

Insulin initiation and management in people with Type 2 diabetes in an ethnically diverse population: the healthcare provider perspective

AIM

To explore barriers to prescribing of insulin, particularly delays in initiation, from the perspective of healthcare professionals involved in managing Type 2 diabetes in a multi-ethnic setting.

METHODS

The study was carried out in a UK population with high numbers of people of South Asian (mainly Indian) origin. Semi-structured interviews were conducted with 14 healthcare professionals from primary and secondary care. Analysis involved exploring interview transcripts in terms of themes and sub-themes identified through a process of progressive focusing.

RESULTS

Initiation of insulin therapy was described as challenging in all patients irrespective of ethnicity, but some barriers were perceived to be accentuated because of language needs and lower levels of understanding about diabetes and insulin. Additionally, some South Asians were viewed as more likely than their white European counterparts to be influenced by negative observations and experiences about insulin therapy within community networks. Time restrictions were seen as a barrier that was accentuated in the management of South Asian patients. Participants suggested strategies for overcoming patient barriers; with South Asians these included involvement of families and patient peers and availability of South Asian healthcare providers.

CONCLUSION

The challenge for healthcare providers is to how to address the tension between the optimal clinical time for commencing insulin therapy and the time when the patient feels psychologically ready. To help make these two time points coincide, our findings suggest the need to adopt a holistic approach involving consideration of the cultural context of patients, including their ethnic background.

Effect of thyroxine on fibrinolytic system in rat

Thyroid hormones have many effects on the cardiovascular system. Thyroid dysfunction accelerates atherosclerosis not only through conventional risk factors (dyslipidemia) but they also show a very close relationship with hemodynamic parameters. Thyroxine is determinant of the several components of fibrinolytic system even though the exact relationship is far from clear. Present study was carried out to determine the effect of thyroxine on fibrinolytic parameters such as plasminogen activators (PA) in rat heart, levels of PA and plasminogen activator inhibitor (PAI), glucose in plasma and serum lipid profile. Rats were injected with 50 ug eltroxine/100 gm(-1) body weight intraperitoneally for one week. Compared with controls, thyroxine treatment increased PA activity significantly in rat heart. No changes were seen in PA, PAI and glucose in plasma of two groups of rats. A significant decrease in total cholesterol and LDL-cholesterol levels was seen in serum of treated group resulting in the decrease of LDL/HDL and Total cholesterol/HDL-cholesterol ratios. These results suggest that thyroxine treatment may have considerable clinical significance. It raised PA activity in heart as well as reduced cholesterol content in blood. It is possible that thyroxine treatment may confer a beneficial effect on cardiovascular risk.

Cervical mediastinoscopy: re-evaluation of an old technique in era of new imaging technology

CONTEXT

With the advent of modern anatomical and functional imaging technologies, application of cervical mediastinoscopy has decreased in diagnosis and staging of mediastinal diseases.

AIM

To evaluate the usefulness of cervical mediastinoscopy in assessing the mediastinal disease when imaging modalities are non-diagnostic.

SETTINGS AND DESIGN

Retrospective analysis of records of a tertiary care hospital.

PATIENTS AND METHODS

Thirty-nine patients with mediastinal pathology of varied aetiologies underwent cervical mediastinoscopy. Pre- and post-operative diagnosis was compared.

RESULTS

In 34 out of 39 cases (87.5%), cervical mediastinoscopy provided a confirmatory final diagnosis. One case had a major complication in the form of recurrent laryngeal nerve palsy.

CONCLUSION

Cervical mediastinoscopy is useful, minimally invasive modality in a scenario where anatomical and functional imaging tools are non-diagnostic.

Transport of topical anesthetics in vitamin E loaded silicone hydrogel contact lenses

Transport of surface active anesthetic drugs through silicone hydrogel contact lenses containing nanosized vitamin E aggregates is explored for achieving extended anesthetics delivery. Commercial silicone hydrogel contact lenses release most ophthalmic drugs including local anesthetics for only a few hours, which is not adequate. Here we focus on creating dispersion of highly hydrophobic vitamin E aggregates in the lenses as barriers for drug diffusion for increasing the release durations. This approach has been shown previously to be successful in extending the release durations for some common hydrophilic ophthalmic drugs. The topical anesthetic drugs considered here (lidocaine, bupivacaine, and tetracaine) are hydrophilic at physiologic pH due to the charge, and so these cannot partition into the vitamin E barriers. However, these surface active drug molecules adsorb on the surface of the vitamin E barriers and diffuse along the surface, leading to only a small decrease in the effective diffusivity compared to non-surface-active hydrophilic drugs. The drug adsorption can be described by the Langmuir isotherm, and measurements of surface coverage of the drugs on the vitamin E provide an estimate of the available surface area of vitamin E, which can then be utilized to estimate the size of the aggregates. A diffusion controlled transport model that includes surface diffusion along the vitamin E aggregates and diffusion in the gel fit the transport data well. In conclusion, the vitamin E loaded silicone contact lens can provide continuous anesthetics release for about 1-7 days, depending on the method of drug loading in the lenses, and thus could be very useful for postoperative pain control after corneal surgery such as the photorefractive keratectomy (PRK) procedure for vision correction.

Presentations of pyogenic liver abscess in one UK centre over a 15-year period

BACKGROUND AND AIM

Pyogenic liver abscess (PLA) has been a condition of high mortality, improving over recent decades with combined antibiotic and percutaneous drainage. We aimed to identify the presenting features, diagnosis, microbiology, treatment and outcome for patients over a 15-year period at an inner-city hospital.

METHODS

Patients with an appropriate discharge diagnosis were identified and case records retrospectively analysed.

RESULTS

A total of 73 patient records were analysed. Common presenting features were anorexia, abdominal pain, fever, vomiting and weight loss with raised white cell count, C-reactive protein, alkaline phosphatase and hypoalbuminaemia. The delay following symptom onset to presentation was a mean of 17.3 days. The inclusion of PLA as a possible diagnosis on admission was only considered in 1% of cases. Positive blood or abscess culture was achieved in 63% of cases. We recorded a hospital mortality rate of 11%.

CONCLUSIONS

In this sample, PLA was rarely considered as a possible diagnosis at presentation. There are common presenting features, which should prompt early investigation. Our microbiological yield was lower than in some studies and may be due to the early empirical use of antibiotics, without microbiological guidance. Percutaneous drainage and antibiotic treatment remain the mainstay of management. The underlying cause for PLA is often not identified. Emerging septicaemia or underlying malignancy were strong predictors of mortality.

Interaction of ionic surfactants with cornea-mimicking anionic liposomes

The interaction of surface-active molecules with lipid bilayers is ubiquitous both in biological systems and also in several technological applications. Here we explore the interaction of ionic surfactants with liposomes whose composition mimics the ocular epithelia. In this study, liposomes with a composition mimicking ocular epithelia are loaded with calcein dye above the self-quenching concentration. The liposomes are then exposed to surfactants, and the rate of dye leaked from the liposomes due to the interaction of surfactants is measured. Both cationic and anionic surfactants at various concentrations and ionic strengths are explored. Results show that the liposome bilayer permeability to the dye increases on exposure to the surfactants, leading to the release of the dye trapped in the core. However, the dye release stops after a finite time, suggesting a transient increase in permeability followed by healing. The leakage profiles exhibit two different timescales for the cationic surfactant but only one timescale for the anionic surfactant. The total dye leakage increases with surfactant concentration, and at a given concentration, the dye leakage is significantly higher for the cationic surfactants. The timescale for the healing decreases with increasing surfactant concentration, and increasing ionic strength increases the dye leakage for the anionic surfactant. These results show that the surfactant binding to the lipid bilayer increases the permeability while the bilayers heal likely because of the surfactant jump from the outer to the inner leaflet and/or rearrangement into tighter aggregates.

Extended cyclosporine delivery by silicone-hydrogel contact lenses

Cyclosporine A (CyA) is effective in treating chronic dry eyes and contact lens mediated dry eyes. CyA is delivered through eye drops of an oil-in-water emulsion, which has a small residence time in the eyes, leading to low bioavailability. Here we explore delivery of CyA from contact lenses to provide controlled and extended drug delivery with an increased bioavailability due to enhanced ocular residence time. Loading and release profiles of CyA from commercial contact lenses are presented to show that 1-DAY ACUVUE® releases CyA for about a day and extended wear silicone hydrogel (SiH) lenses release CyA for about 2-weeks. The longer duration from SiH lenses compared to the 1-DAY ACUVUE®lens is due to larger partition coefficients in the gel. A novel approach is presented for increasing release duration from the SiH lenses to the desired 1-month through incorporation of Vitamin E. The results show that Vitamin E loaded lenses can provide CyA release within the therapeutic window for a period of about a month. This pilot study demonstrates the promising potential of delivering CyA from contact lens for treatment of chromic dry eyes and contact lens mediated dry eyes.

Molecular transport through surfactant-covered oil-water interfaces: role of physical properties of solutes and surfactants in creating energy barriers for transport

Mechanisms of molecular transport across oil-water interfaces covered by nonionic surfactants are investigated using coarse-grained molecular dynamics simulations. Resistance of the surfactant monolayer to the solute transport is shown to be controlled by dense regions in the monolayer. The dense regions are formed on both sides of the dividing surface and the barrier to the solute transport is created by those of them experiencing unfavorable interactions with the solute. Resistance to the transport of a hydrophobic (hydrophilic) solute increases with the excess density of the head (tail) group region of the monolayer, which in turn increases with the length of the surfactant head (tail) group. Barriers for solute transport through surfactant monolayers are also influenced by the solute size. However, the extent of this influence is determined by the monolayer thickness and the solute structure and composition. For example, it is shown that resistance offered by thin monolayers to transport of linear oligomers is relatively insensitive to the solute length. The barrier sensitivity to the length of these solutes increases with the monolayer thickness. In addition to the static barriers, the solute transport is shown to be affected by dynamic barriers due to a nonadiabatic coupling of the monolayer surface with the solute position and configuration. This coupling leads to deviations of the system dynamics from the minimum energy path. The deviations are most significant in the neighborhood of the static energy barrier, which effectively leads to an increase of the barrier for the solute transport.

Chemical investigation of the essential oil of Thymus linearis (Benth. ex Benth) from western Himalaya, India

Thymus linearis (Benth. ex Benth) was collected from five distinct locations of western Himalaya (India) during the summer season. The hydro-distilled essential oil (yield 0.84-0.95%) was analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). A total of 56 constituents, representing 81.55% to 98.11% of the total oil composition, were identified. Thymol (52.28-66.65%), p-cymene (1.81-21.60%) and γ-terpinene (1.94-12.48%) were the major constituents in all populations. Other constituents identified in significant amounts were carvacrol, p-cymen-8-ol, borneol, terpinen-4-ol and thymol methyl ether. The presence of high phenol and essential oil contents in this species make it a suitable substitute for common thyme oil.

A rare coronary anatomy comprising dual (Type IV) left anterior descending arteries and an anomalous left circumflex artery from the right coronary artery

We present the case of a rare coronary anomaly in a 64-year-old male who presented with exertional angina. The right coronary artery (RCA) was dominant, giving origin proximally to an anomalous left circumflex (LCX) artery and a left anterior descending (LAD) artery which supplied the conventional mid and distal LAD territory. The left main artery (LM) arose from the left coronary sinus and branched into a large first septal and an intermediate artery. There was associated non-critical atherosclerotic disease. We report this because of the rare division of the LAD area of supply by arteries from both coronary sinuses (dual LAD) with an anomalous LCX also arising from the proximal RCA. The clinical implications are discussed.

Tonsillectomy and adenoidectomy for obstructive sleep apnea in sickle cell anemia

OBJECTIVE

To evaluate the effects of Tonsillectomy and Adenoidectomy (T&A) on Obstructive Sleep Apnea (OSA) secondary to Upper Airway Obstruction (UAO) in children with Sickle Cell Disease (SCD).

METHODS

Twenty eight children with SCD and history of snoring, with or without adeno tonsillar hypertrophy, were evaluated for UAO and OSA.

RESULTS

Eight children were confirmed to have OSA by multichannel polysomnography and underwent T&A. Follow up examination showed symptomatic clinical and objective improvement in sleep study parameters in OSA.

CONCLUSIONS

T&A appears to be a safe, effective option to treat selected patients with OSA due to UAO in SCD children.

Current and Emerging Detoxification Therapies for Critical Care

Toxicity resulting from prescription drugs such as tricyclic antidepressants and cardioactive steroids, as well as drugs of abuse and exposure to environmental chemicals, represents a major need for detoxification treatments. Particles and colloids, antibody fragments (Fab), and indirect treatment methods such as macroemulsions, are currently being developed or employed as detoxification therapies. Colloids, particles, and protein fragments typically mitigate toxicity by binding to the toxin and reducing its concentration in vital organs. Indirect methods such as macroemulsions and sodium bicarbonate act directly on the affected organs, rather than the toxin. In this review, key design parameters (i.e. binding affinity, biocompatibility, pharmacokinetics) are discussed for each type of detoxification treatment. In addition, some of the latest research in each area is reviewed.

Tracheal necrosis with surgical emphysema following thyroidectomy

Tracheal necrosis after thyroidectomy is an extremely rare event with only a few published reports. We present a case of a 65-year-old male who developed rapidly progressive surgical emphysema of face and upper thorax on the seventh day following total thyroidectomy. Prompt surgical exploration of neck revealed a tracheal rent at the level of the second tracheal ring. This hole was then refashioned into a formal tracheostomy. Patient had an eventful recovery. Tracheostomy was closed by the 14th day. The complication was probably related to tracheal injury sustained due to electro-coagulation and subsequent secondary infection.

Interaction of cationic drugs with liposomes

Interactions between cationic drugs and anionic liposomes were studied by measuring binding of drugs and the effect of binding on liposome permeability. The measurements were analyzed in the context of a continuum model based on electrostatic interactions and a Langmuir isotherm. Experiments and modeling indicate that, although electrostatic interactions are important, the fraction of drug sequestered in the double-layer is negligible. The majority of drug enters the bilayer with the charged regions interacting with the charged lipid head groups and the lipophilic regions associated with the bilayer. The partitioning of the drug can be described by a Langmuir isotherm with the electrostatic interactions increasing the sublayer concentration of the drug. The binding isotherms are similar for all tricyclic antidepressants (TCA). Bupivacaine (BUP) binds significantly less compared to TCA because its structure is such that the charged region has minimal interactions with the lipid heads once the BUP molecule partitions inside the bilayer. Conversely, the TCAs are linear with distinct hydrophilic and lipophilic regions, allowing the lipophilic regions to lie inside the bilayer and the hydrophilic regions to protrude out. This conformation maximizes the permeability of the bilayer, leading to an increased release of a hydrophilic fluorescent dye from liposomes.

Bupivacaine binding to pegylated liposomes

BACKGROUND

Local anesthetic drugs, such as bupivacaine, can cause severe toxicity. Lipid emulsions have been proposed and used clinically for treating such cases. Liposomes may be an alternative for overdose treatment because of their unique structures and surface charges, which allows them to act as high affinity drug "sinks" and remove bupivacaine from solution.

METHODS

We conducted in vitro experiments with unilamellar and multilamellar anionic, polymer-coated liposomes to determine the amount of bupivacaine bound to liposomes in buffer solutions as a means of assessing the liposome-drug affinity. Binding experiments were also done in human serum to determine the liposomes' ability to compete with serum proteins for binding drug molecules.

RESULTS

Unilamellar liposomes sequestered 60%-65% and 77%-85% of bupivacaine from buffer at 1.45 and 2.9 mg lipid/mL, respectively. The increased lipid loading increased the drug uptake at all drug concentrations measured (P = 0.001, 0.002, <0.001, and 0.003 for 5, 20, 35, and 50 microM, respectively). Multilamellar liposomes bound more drug per unit mass, with 71%-90% of the total bupivacaine bound at a phospholipid concentration of 1.45 mg lipid/mL. When comparing unilamellar and multilamellar liposomes at 1.45 mg lipid/mL, the multilamellar liposomes were significantly better at 3 of the 4 drug concentrations measured (P = 0.002, 0.001, 0.001, and 0.08 for 5, 20, 35, and 50 microM, respectively). In human serum samples, unilamellar liposomes (2.9 mg lipid/mL) reduced the unbound (free) drug by 36% (P = 0.037), 56% (P = 0.022), 47% (P = 0.042), and 50% (P = 0.018) for bupivacaine concentrations of 5, 20, 35, and 50 microM, respectively.

CONCLUSIONS

The anionic, pegylated liposomes exhibit high binding for bupivacaine, both in buffer and in human serum. These results suggest that an IV injection of liposomes could be useful for the treatment of bupivacaine toxicity through drug redistribution.

Tear Dynamics Model

PURPOSE

Quantitative understanding of tear dynamics may help in developing better ophthalmic drug delivery vehicles and dry eye treatments. This paper attempts to develop a comprehensive model that can predict the effect of physiological parameters on various issues related to tear dynamics.

METHODS

The model is based on mass balances of water and solutes such as glucose, sodium, potassium, and chloride. The mass balances require models for the drainage of fluid through the canaliculi and the transport of tears and solutes through the conjunctiva. The model parameters are obtained by simulating Ussing-chamber experiments. The differential equations for the unsteady balances are solved numerically.

RESULTS

The model predicts that under normal conditions, the tear volume, tear osmolarity and potential are 7.1 microl, 297.6 mM, and -15.1 mV, respectively. The model also predicts that the conjunctiva is secretory and contributes about 25% of the total tear production. We also predict the effect of evaporation on tear physiology and show that an increase in evaporation increases osmolarity, reduces tear volume, and increases conjuctival secretion. Additionally, the new tear dynamics model helps assess the effect of osmolarity of the instilled drops, insertion of punctum plugs and use of moisture chamber as treatments for dry eyes. Furthermore, the model is used to predict the effect of modulation of specific transport pathways, which is proposed as a potential remedy for dry eyes, on conjuctival secretion and total tear volume.

CONCLUSIONS

Most of the predicted results agree with the reported experimental results, at least qualitatively. However, some predictions disagree with experiments suggesting that further improvements in the model are needed. The model developed in this paper can improve our understanding of tear dynamics and also serve as a tool to evaluate the efficacy of various modalities at treating dry eyes.

A Mathematical Model for Ocular Tear and Solute Balance

PURPOSE

In this paper we develop a mathematical model that can predict the steady-state tear film thickness and the dynamic tear film thickness and the solute concentration after instillation of a solute-laden fluid in the eye.

METHODS

The mathematical model developed in this paper is based on a balance between the inflow and outflow of tears into the tear film. It incorporates a tear drainage model and a model that relates the tear film thickness to the meniscus radius of curvature. To predict the solute concentrations, the tear balance is coupled with the solute balance. The differential equations for the unsteady balances are solved numerically.

RESULTS

The model predicts that the tear film thickness depends on a number of physiological factors, such as rates of tear production and evaporation, geometry and modulus of the canaliculi, and surface tension and viscosity of tears, and varies from about 3 to 15 microm. The model also predicts that the drainage time for an instilled volume of 15 microl is 1283 s. Additionally, the time required for the tracer concentration to decay to 1% of the value immediately after instillation of a drug-laden 40 microl drop is about 2480 s. Similarly, the time for intensity decay for a radioactive tracer after 25 microl instillation is about 1566 s. Also, the model predicts that the fraction of the instilled drug that reaches the cornea is about 1.3% for topical application of timolol.

CONCLUSIONS

The predicted results agree reasonably with the reported experimental results, at least qualitatively. The model developed here can serve as a useful tool to develop a more precise understanding of various issues related to tears and also evaluate the effect of various parameters on the tear volume.

The Effect of Water Hydraulic Permeability on the Settling of a Soft Contact Lens on the Eye

PURPOSE

Silicone-elastomer soft contact lenses (SCLs) adhere to the cornea during wear, whereas silicone-hydrogel soft contact lenses exhibit adequate on-eye movement. One explanation for the observed immunity to binding of silicone-hydrogel lenses is that some interstitial water is expelled during blinking, therefore maintaining a more stable post-lens tear film (PoLTF). We examine quantitatively whether or not water can be squeezed by hydrodynamic flow through a silicone-hydrogel membrane driven by the applied lid force during a blink.

METHODS

A rigid, porous-disk model of a contact lens was devised to calculate the relative settling rates of a permeable versus a completely impermeable SCL. The settling rate depended strongly on the value of the hydraulic permeability for pressure-driven water flow through the lens. Because the hydraulic permeability of water through silicone-hydrogel materials is not well-known, we measured this value. At steady state, water was forced through flat membranes of representative lens materials under known pressure drops. The resulting volumetric flows were measured by following the transient rise height of water in a vertical, precision-bore glass capillary. Darcy's law permitted calculation of the hydrodynamic permeability.

RESULTS

The settling-rate model indicated that tear can be squeezed through a SCL only when the Darcy-law hydrodynamic permeability is greater than about 10 microm2 (i.e., greater than 10 Darcy). Our measurements for silicone and HEMA hydrogel membranes reveal hydrodynamic permeabilities of the order 10(-8) microm2, almost 9 orders of magnitude smaller than that necessary to initiate hydrodynamic flow through a SCL.

CONCLUSIONS

We conclude that the squeeze-through mechanism cannot quantitatively account for the observed on-eye movement of silicone-hydrogel lenses. Also, we find that the lid-applied pressure cannot squeeze enough water out of a SCL during a blink to stabilize the PoLTF. Neither a squeeze-through nor a squeeze-out mechanism can maintain a stable PoLTF and prevent adherence.

Comparison of internal sphincterotomy with topical diltiazem for post-hemorrhoidectomy pain relief: a prospective randomized trial

AIM

To assess the efficacy of internal sphincterotomy compared with application of topical 2% Diltiazem ointment after hemorrhoidectomy for pain relief.

SETTINGS AND DESIGN

Prospective randomized study.

MATERIALS AND METHODS

In an 18-month period, 108 subjects with uncomplicated Grade 3/ 4 hemorrhoids were enrolled in the study and were randomized into two equal groups: Subjects in Group A underwent internal sphincterotomy at time of primary surgery while those in Group B received 1 g of 2% Diltiazem ointment locally, thrice daily for seven days. Postoperative pain perception was measured using visual analog score (VAS) and on the basis of number of analgesic tablets (Tab tramadol 50 mg) required in each group. Time to discharge, time to return to work and incidence of complications measured and compared.

STATISTICAL ANALYSIS USED

Statistical techniques applied were Student T test, Chi-square and Fisher's Exact Test.

RESULTS

There were 102 analyzable subjects (Group A: 50 and Group B: 52). The mean VAS score was significantly less in the internal sphincterotomy group from the fourth postoperative day onwards compared to topical Diltiazem (2.23 vs. 3.72; P =0.031). Similarly, the mean requirement of analgesic tablets [10.54 vs. 15.40; P =0.01] was much lower in Group A. There was no significant difference in terms of time to discharge and time to return to work between the two groups. The incidence of complications was more with the internal sphincterotomy group (11.5% vs. 3 %; P =0.488).

CONCLUSIONS

In patients undergoing hemorrhoidectomy, addition of surgical internal sphincterotomy results in lesser pain in the postoperative period as compared to those receiving topical application of Diltiazem.

Importance of Taylor dispersion in pharmacokinetic and multiple indicator dilution modelling

Mass transfer in tissues is typically studied by multiple indicator dilution (MID) studies. Several of these studies have shown that drug concentrations can be modelled by axially distributed models. In this paper, we determine the Taylor dispersion coefficient that describes the degree of axial mixing for the MID models, while accounting for the presence of red blood cells in the capillaries. The capillaries are treated as well mixed with no radial concentration gradients. The concentration in tissue is treated as position and time dependent and the partial differential equations for mass transport are averaged using the method of multiple timescales. The calculated values of the dispersion coefficient are in reasonable agreement with the values reported in literature, suggesting that Taylor dispersion is an important contributor to dispersion in tissues. We also show that the average equations for the barrier-limited drugs reduce to the commonly used Sangren-Sheppard model. In this case, Taylor dispersion is not significant in comparison to the dispersion caused by drug exchange between the capillary and the tissue. Additionally, we utilize the average equations for both flow-limited and barrier-limited drugs in pharmacokinetic models. These simulations show that neglecting the dispersion coefficient could cause significant effects in the dynamic drug concentration profiles and thus lead to incorrect estimation of parameters if the experimental data from MID studies are fitted to a model that neglects Taylor dispersion.