Dysphagia at 1 Year is Associated With Mean Dose to the Inferior Section of the Brain Stem

PURPOSE

Dysphagia is a common toxicity after head and neck (HN) radiation therapy that negatively affects quality of life. We explored the relationship between radiation therapy dose to normal HN structures and dysphagia 1 year after treatment using image-based datamining (IBDM), a voxel-based analysis technique.

METHODS AND MATERIALS

We used data from 104 patients with oropharyngeal cancer treated with definitive (chemo)radiation therapy. Swallow function was assessed pretreatment and 1 year posttreatment using 3 validated measures: MD Anderson Dysphagia Inventory (MDADI), performance status scale for normalcy of diet (PSS-HN), and water swallowing test (WST). For IBDM, we spatially normalized all patients' planning dose matrices to 3 reference anatomies. Regions where the dose was associated with dysphagia measures at 1 year were found by performing voxel-wise statistics and permutation testing. Clinical factors, treatment variables, and pretreatment measures were used in multivariable analysis to predict each dysphagia measure at 1 year. Clinical baseline models were found using backward stepwise selection. Improvement in model discrimination after adding the mean dose to the identified region was quantified using the Akaike information criterion. We also compared the prediction performance of the identified region with a well-established association: mean doses to the pharyngeal constrictor muscles.

RESULTS

IBDM revealed highly significant associations between dose to distinct regions and the 3 outcomes. These regions overlapped around the inferior section of the brain stem. All clinical models were significantly improved by including mean dose to the overlap region (P ≤ .006). Including pharyngeal dosimetry significantly improved WST (P = .04) but not PSS-HN or MDADI (P ≥ .06).

CONCLUSIONS

In this hypothesis-generating study, we found that mean dose to the inferior section of the brain stem is strongly associated with dysphagia 1 year posttreatment. The identified region includes the swallowing centers in the medulla oblongata, providing a possible mechanistic explanation. Further work including validation in an independent cohort is required.

The Strength of Compressed Tablets: Part I. The Measurement of Tablet Strength and its Relation to Compression Forces

A motorised single-punch eccentric tablet machine has been fitted with instruments to measure the forces operating during the compression cycle. Apparatus has also been designed to measure the resistance to crushing of the final compact. Sodium chloride was compressed at varying pressures and the relationship between compaction forces, ejection force, strength and voidage investigated.

The effect of granule properties on the pore structure of tablets of sucrose and lactose

Air permeability and liquid penetration of tablets of sucrose and lactose have been measured. The tablets had been compressed over a wide pressure range from granules which varied in bulk density, size and strength. The degree to which inter- and intra-granular pore structure within the tablet was sustained varied with these properties; low pressure, high density, high strength and large size promoting a more open but less uniform structure. Such structures allowed rapid penetration of liquid through a coarse pore network which isolated a large fraction of the total pore space. Thus tablets of high permeability gave low final degrees of saturation whereas less permeable tablets became fully saturated.

The Strength of Compressed Tablets: Part II. The Bonding of Granules during Compression

The deformation of tablet granules has been followed over a wide pressure range by preparing and compressing sucrose granules with coloured surfaces. By examination of the fracture of the compacts in a strength test, it has been possible to determine the structural role of the granule at these pressures.

The Strength of Compressed Tablets

Examination of the fracture of tablets in a strength test has revealed two types of failure. Where the interparticulate bond is strong, fracture occurs across the grains and the strength of tablet is a simple function of the particle size. If the interparticulate bond is weak, fracture occurs around the grain and particle size has little effect. A thin coating of stearic acid was used to weaken the interparticulate bond when the effect of grain size on strength disappeared or was reversed. The relation of bonding and capping is discussed and it is shown that capping can be reduced by weakening the interparticulate bond.

Modulite: a simple solution to a difficult problem

The development of HFA-based pMDIs has proved difficult due to differences in the physico-chemical properties of CFC and HFA propellants. However, the development of solution formulations instead of suspensions has provided a way to formulate products whose cloud characteristics can be modulated in a controlled manner by permitting different formulation and device hardware variables. The new approach has proved successful in formulating several different drugs including steroids and has now been applied to developing a formoterol Modulite solution formulation characterized by good chemical stability, delivery performance, and clinical results.

The formulation and evaluation of a CFC-free budesonide pressurised metered dose inhaler

Although dry powder inhalers are well established for the delivery of corticosteroids, the pressurised metered dose inhaler remains the preferred and most cost effective presentation. To design an HFA solution formulation which matched marketed CFC products (Pulmicort and Desonac DA) two elements of the Chiesi Modulite system, the addition of a non-volatile component and the actuator orifice diameter, were varied. These variables, which were shown by in vitro tests to influence the fine particle dose and its mean particle size in different ways, could be permuted to give an aerosol cloud with size characteristics very close to the comparator products. The likelihood that this would confer clinical equivalence is reinforced by a pharmacokinetic analysis which showed that the chosen HFA solution formula gave similar systemic absorption from the lung as Pulmicort. The equivalence in aerosol characteristics was sustained when the pressurised metered dose inhalers (pMDIs) were used with spacers. The Chiesi Jet and the AstraZeneca Nebuhaler, when used with their respective pMDIs, reduced likely oropharyngeal deposition to the same extent and gave a similar increase in the fine particle dose.

Modulite: a means of designing the aerosols generated by pressurized metered dose inhalers

Although popular, the pressurized metered dose inhaler generates coarse, fast moving clouds so that the fraction reaching the lung is small. These shortcomings can be redressed by Modulite which permutes the following variables: the non-volatile components of a solution formula, the actuator orifice geometry, the volume of the metered solution and the vapour pressure of the propellants. This permits the design of aerosols with chosen particle size and plume speed. This facilitates co-ordination of dose generation with inspiration, reduces oropharyngeal deposition and provides a mechanism for targeting drug delivery to different parts of the lung. These principles are exemplified by designing an HFA-propelled beclometasone dipropionate product which closely matches existing products which use chlorofluorocarbons.

Targeted delivery of inhaled drugs: current challenges and future goals

Past success of topical delivery to the lung stems more from the therapeutic nature of drugs used rather than the delivery device. Both the pressurized metered dose inhaler (pMDI) and the dry powder inhaler (DPI) are inefficient, placing a small fraction of the dose at the site of action. Most of the drug deposits in the mouth and is swallowed. Modifications to the pMDI may redress this by improving the coordination of dose generation and inspiration, or by the use of spacers. The DPI can be improved by the use of special excipients. Nevertheless, fundamental weaknesses that limit improvements in targeting drugs to the lung remain. Ideally, a stationary or slow-moving cloud of a selected particle size distribution should be generated at the source by the device. The rate of cloud generation should be such that a patient can accommodate it during a slow inspiration. Many new devices are in development, harnessing one or more of these principles. Respimat (Boehringer Ingelheim, Ingelheim am Rhein, Germany), a soft mist inhaler, shows particular promise. It generates a fine slow-moving cloud over a period exceeding 1 second and incorporates many design features to win patient acceptance.

Modulation of aerosol clouds produced by pressurised inhalation aerosols

The inclusion of non-volatile components such as glycerol or polyethylene glycol in hydrofluoralkane (HFA) solution formulations for pressurised metered dose inhalers (pMDIs), greatly increases the particle size of the aerosol. Cloud characteristics can be further modulated by permuting this factor with the choice of propellant and the dimensions of the actuator, to give a chosen fine particle dose and particle diameter. This principle has been used to design solutions which closely match the performance of chlorofluorocarbon based suspension formulations containing beclomethasone dipropionate, budesonide and ipratropium bromide as assessed for pharmaceutical equivalence using the Andersen Cascade impactor.

The effect of flow rate on drug delivery from the Pulvinal, a high-resistance dry powder inhaler

Dry powder inhalers vary widely in their resistance to flow. When the resistance is high, airway resistance can be neglected and inspiration rates will be determined primarily by the device. Provided that the patient can generate adequate flow rates to aerosolize the dose, variability of emitted dose and fine particle dose should be reduced. For in vitro simulation, these concepts are explored using a Pulvinal device. In conditions likely to be encountered in patient use, the emitted dose showed little dependence (80-102 micrograms) as the flow rate increased from 28 to 63 L/min. The fine particle dose was more sensitive, increasing by a factor of 1.6 from 22 to 35 micrograms. These variations are less than those observed with the Turbohaler, a device of intermediate resistance and very much lower than those observed with the Rotahaler, a low-resistance device.

Assessing lung deposition of inhaled medications. Consensus statement from a workshop of the British Association for Lung Research, held at the Institute of Biology, London, U.K. on 17 April 1998

In vitro measurements of aerosol fine particle fraction (FPF) using particle-sizing apparatus (e.g. the twin impinger, multi-stage liquid impingers, cascade impactors) have a key role to play in the development of new pharmaceutical products and in quality control. However, use of in vitro methodology to attempt to predict lung deposition in vivo is of limited value due, in part, to the inability of current apparatus to mimic upper and lower airway anatomy satisfactorily. Estimates of FPF based on cut-off points ranging from 5-7 microns generally overestimate lung deposition as measured in vivo by gamma scintigraphy. We recommend that: 1. multistage apparatus (minimum five stages) be used to characterize particle size distribution adequately, over the range 0.5-5.0 microns; 2. where possible, measurements should be made at a range of rates and profiles of flow reflecting those likely to be generated using the inhalation device in clinical practice (including use by young and elderly patients with varying degrees of airflow obstruction); 3. encouragement should be given to the further development, standardization, and validation of apparatus with a 'throat' which more closely resembles the human oropharynx and larynx. Pharmacokinetic methods can give a good estimate of total, but not regional, lung deposition, with drugs which are either not absorbed via the gastrointestinal tract, or whose absorption can be blocked by co-administration of charcoal, thus avoiding confounding by absorption of drug substance deposited in the oropharynx and subsequently swallowed. Techniques which rely on evaluation of a timed fractional output of drug substance in the urine are susceptible to the inherent variability of rate of absorption across the respiratory epithelium. We recommend that consideration should be given to the further refinement and validation of PK methods which would more clearly identify the fractional dose deposited in the lung. Lung-imaging methodology, e.g. gamma scintigraphy, employing formulations radiolabelled with gamma-ray-emitting radionuclides such as 99mTc, can measure total lung deposition and oropharyngeal deposition, provided that the radiolabelling process is appropriately validated and suitable corrections are made for attenuation of gamma rays by body tissues. An estimate of regional lung deposition can be made by drawing 'regions of interest' on the scintigraphic image; the precision of this measure is limited by the two-dimensional (2-D) nature of most images which mean that there is an overlay of structures of interest (alveoli, small and large airways), which is most marked centrally. Three-dimensional (3-D) imaging techniques (e.g. single photon emission computed tomography, SPECT, and positron emission tomography, PET) have the potential to give more detailed data on regional lung deposition, but are currently more expensive, employ higher radiation doses, and are less well validated than 2-D (planar) imaging. We consider that, of the available imaging modalities, planar gamma scintigraphy represents current best practice for the assessment of lung deposition from inhaler devices where regional differences may be important. The methodology should be optimized by the adoption of generally accepted standards for radiolabelling, imaging, attenuation correction, and interpretation. It is important that deposition in all sites (device, oropharynx, lungs, stomach) should be quantified. Consideration should be given to refining the concept of regions of interest to coincide more closely with anatomical lung structures. Statistical methods to compare the size distributions of drug and radiolabel in validation experiments should be developed. In the longer term it is envisaged that three-dimensional imaging may play a more important part in evaluating lung deposition; an optimal three-dimensional anatomical model of lung zones of interest needs to be developed.

General factors influencing drug delivery to the lung

The first devices to be developed for the delivery of bronchodilators and corticosteroids for the treatment of asthma were the pressurised metered dose inhalers (pMDIs). While pMDIs are viewed as patient friendly, they are associated with some serious disadvantages, such as considerable oropharyngeal deposition (due to the speed of delivery of the dose) and poor patient co-ordination of inhalation and activation. This has resulted in the development of alternative systems, such as the dry powder inhaler (DPI). However, DPIs also have problems, as there are difficulties in handling, measuring and metering fine particles. New devices, such as the Easi-breathe and Diskus inhalers, are now being introduced to overcome some of these problems. The ideal device is one that will produce a large proportion of respirable particles in the emitted dose. It must also deliver precise and uniform doses of drug to the patient. Further innovations are required to achieve these goals.

A clinically relevant modification to existing inhaler therapy

A modified formulation of inhaled salbutamol and a new inhaler device were studied in a group of 11 moderate-to-severe asthmatic patients. Changes in airway calibre (FEV1, Vmax30) were measured before and after inhalation of the new formulation, and compared with changes following inhalation of conventional salbutamol. A standard Rotahaler was used as a reference for the new inhaler. The study was conducted as a two-part randomized, double-blind cross-over trial. We found a significantly greater bronchodilatation of the larger airways using the modified drug in the Rotahaler. The new inhaler did not show any superiority over the Rotahaler, contrary to expectations from in vitro work. A slightly shorter model may better reflect the in vitro results. The study has implications for inhalation therapy in general.

Current innovations in drug delivery

It is almost twenty years since the attention of the pharmaceutical industry was focussed on an alternative strategy--improving existing medicines by better control of the site, duration and intensity of the drugs they contain. Whilst site specificity remains a major objective for future medicines, progress has mainly come from devices which modulate the duration and intensity of drug action. In their most advanced form, they will deliver their contents in response to a physiological or pathological demand such as a diabetic's glucose level. However, practical devices have been limited to passive dosage forms which either speed up or slow down the rate of systemic absorption in a controlled manner. Oral, rectal, percutaneous and parenteral routes have been energetically explored and several products have been successfully marketed. Oral administration has dominated invention. Future advances will embrace the concepts of variable or pulsed release in order to meet particular therapeutic criteria. Equally important will be the extension of transit time in order to increase the uptake of some poorly absorbed drugs, or to extend dosage intervals to twenty-four hours. Attempts to more closely approach constant release rates at the end of the release period, to devise efficient formulae which carry drug loadings in excess of eighty per cent, or to invent formulae which, whilst retaining precision, are cheaper and more easily manufactured are less innovative aspects of this important field. The commercial success of percutaneous presentation of glyceryl trinitrate has prompted further refinement of this principle and guidelines for exploitation are now clearer. The development of acceptable penetration enhancers remains an important element in extending this principle to a wide range of drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of granules prepared by pan granulation and by massing and screening

Granules of lactose and calcium phosphate were prepared by pan granulation and by massing and screening. Capillary forces and the gentle action of tumbling in the pan were inadequate to compact the fine cohesive calcium phosphate but were highly effective with the less cohesive lactose where the absence of shear gave very high densification. Whereas massing and screening provided the necessary forces for consolidating calcium phosphate, with lactose a more open structure resulted which further dilated during screening. Increase in both moisture content and time of mixing increased granule density but the degree varied with both method and material as did granule shape, strength and compressibility.

The effect of starch type, concentration and distribution on the penetration and disruption of tablets by water

The effect of starch type, and its concentration and distribution, on the pore structure of tablets of aspirin and magnesium carbonate has been measured using air permeability and liquid penetration techniques. The addition of starch had no significant effect on the pore structure of the dry tablet but caused disruption and alteration of this structure when penetrated by water. When each starch was incorporated into the granules in wet massing the rate of disruption decreased in the order potato, maranta, wheat, corn, waxy corn and rice; but a more complicated pattern was produced when the starch was added to the granules as a pre-dried powder. Maximum breakup efficiency of magnesium carbonate tablets was produced when 10 % potato starch was incorporated internally and the tablet compacted to a porosity of 28 %.

An investigation of the pore structure of tablets of sucrose and lactose by mercury porosimetry

The pore structure of tablets has been investigated by mercury porosimetry. Tablets, when prepared from ungranulated powder, showed a narrow pore size distribution, the mode of which decreased from 9 to 1 μm over the pressure range studied. Granulation caused the size distribution of tablet pores to widen. Large robust granules, compressed at low pressures, gave tablets with a bimodal pore size distribution. Decrease in granule size and strength, promoted a more uniform tablet structure and fine, friable, granules, compressed at high pressures, gave tablets with almost the same structure as those prepared from ungranulated powder.

Some observations of the penetration and disruption of tablets by water

The effect of compressibility, particle size, granulation and the addition of starch on the pore structure on tablets of aspirin, calcium carbonate, lactose, magnesium carbonate, phenindione and sucrose has been measured using air permeability and liquid penetration techniques. The addition of starch to the various materials produced no significant effect on the pore structure of the dry tablet but caused disruption and alteration of this structure when the tablet was penetrated by water. This disruptive effect produced by starch depends on the compressibility of the constituent material and the pressure used to form the tablet.

The influence of wet and dry granulation methods on the pore structure of lactose tablets

The conditions of wet granulation influenced the pore structure of lactose tablets, prepared over a wide range of tabletting pressures. Dry granulation, on the other hand, only influenced pore structure when slugging pressures were high, the granules were coarse and tabletting pressures were low. Mercury porosimetry revealed intense granule fragmentation when dry granulated materials were compressed. The effect of the change of pore size distribution on liquid penetration into tablets is discussed.

The effect of distribution of magnesium stearate on the penetration of a tablet by water

Magnesium carbonate powder and granules were compressed and the tablets characterized by their permeability to air and penetration by liquids. To the same materials, magnesium stearate was added, its distribution being varied by varying its concentration, the size of the base material and the method of mixing. The inhibition of penetration by liquids is roughly proportional to the concentration of magnesium stearate and very susceptible to the method of mixing. The influence of granule size on its distribution was seen mainly as a change in the uniformity of penetration.