Drug interactions with medical plastics

Clinical Recommendations for Managing the Impact of Insulin Adsorptive Loss in Hospital and Diabetes Care

BACKGROUND

Adsorption of insulin to infusion sets impacts patient therapeutic outcomes and, unaccounted for, may exacerbate persistent hyperglycemia or result in therapy-induced hypoglycemia. This article aims to provide recommendations for clinicians involved in intensive care and/or outpatient pump therapy contexts.

METHODS

A dynamic adsorption model is used to evaluate time-varying insulin concentration in the infusion set outflow. Hourly and daily percentage insulin loss to adsorption is examined for neonatal, pediatric, and adult intensive care patients, as well as outpatient children and adults weighing 30, 50, and 80 kg. A short review of preconditioning methods is included.

RESULTS

Insulin adsorption in outpatient pump therapy is most pronounced in the first hour, where as much as 80% of the intended insulin dose may be lost to adsorption. Subsequently, insulin adsorptive loss is typically negligible. Overall, extra care should be taken in the first 1-6 h of a new infusion set, particularly in children or teenagers. Typically, insulin adsorption in the adult intensive care unit is negligible unless infused at low flow rates (<2 mL/h). Insulin adsorption is significant in pediatric and neonatal intensive care, resulting in delivery concentrations as low as 5%-50% of that intended. Thus, it is recommended that preconditioning of insulin delivery lines be carried out prior to infusion initiation in this context. However, no preconditioning method completely removes adsorption, and care should still be taken in the first 1-6 h of insulin dosing.

CONCLUSIONS

Recommendations made in this article are dependent on the insulin concentration and flow rate used in each clinical context.

Capacity of Infusion Lines for Insulin Adsorption: Effect of Flow Rate on Total Adsorption

BACKGROUND

Insulin adsorption to clinical materials has been well observed, but not well quantified. Insulin adsorption reduces expected and actual insulin delivery and is unaccounted for in insulin therapy or glycemic control. It may thus contribute to poor control and high glycemic variability. This research quantifies the problem in the context of clinical use.

METHOD

Experimental insulin adsorption data from literature is used to calculate insulin delivery and total insulin adsorption capacities for polyethylene (PE) and polyvinal chloride (PVC) lines at clinically relevant flow rates and concentrations.

RESULTS

Insulin adsorption capacity decreased hyperbolically with flow rate for both PE and PVC, where low flow scenarios result in greater insulin adherence to infusion lines. When the infusion flow rate was halved from 1 to 0.5 mL/h, twice as much insulin adsorbed to the line. Insulin loss to adsorption resulted in up to ~50% of intended insulin not delivered over 24 hours in a low flow and low concentration context.

CONCLUSION

Material capacity for insulin adsorption is not constant, but increases with decreasing flow. Different materials have different adsorption capacities. In low flow and low concentration contexts, such as in neonatal or pediatric intensive care, insulin loss to adsorption represents a significant proportion of daily insulin delivery, which needs to be accounted for.

A finite element model for insulin adsorption in ICU infusion sets

Insulin adsorption has been observed in ICU delivery lines, and is especially problematic in the delivery of insulin within the neonatal ICU. This paper presents a two state model with adsorptive loss described as a predator-prey term with parameters K_i and B_eq. This model is discretized to N sub volumes along the length of an infusion set. The model was found to converge to a solution for N>~100-150. The model was fit to literature data, and it was found that the total adsorptive capacity of a material (B_eq, U/m²) was hyperbolically related to flow rate. If the average rate constant K_i was used with the hyperbolic relationship, the model was able to describe adsorption dynamics at all 3 examined flow rates for a polyethylene line.

Stability of Cotrimoxazole in Peritoneal Dialysis Fluid

This study examines the stability of both components of the antibacterial combination, cotrimoxazole (trimethoprim and sulphamethoxazole) in peritoneal dialysis fluid stored in polyvinyl chloride bags and glass ampoules at room temperature for up to nine days.

Greater than 10% loss of trimethoprim occurred within three days for admixtures stored in plastic bags, whereas the original concentration remained virtually unchanged after nine days for similar solutions stored in glass ampoules. This indicated that the loss of trimethoprim observed in solutions stored in plastic bags was associated primarily with the nature of the container, presumably due to some form of uptake by or loss through the plastic.

Greater than 10% loss of sulphamethoxazole occurred within two days for all admixtures examined, stored in either glass or plastic containers. This degree of loss was achieved within 12 h for one admixture stored in plastic. There was also the time-dependent appearance of an additional peak in HPLC analyses of these solutions, indicating that loss of sulphamethoxazole was due to chemical decomposition of the drug in the peritoneal dialysis fluid. The shelf-life of such admixtures would be limited by the stability of the sulphamethoxazole component, with the available data suggesting a shelf-life of 12 h for solutions stored at room temperature.

Preparation of a Bulk Preservative Free Morphine Parenteral Solution

This column provides reports that situate and synthesize current developments, issues, innovative clinical procedures, therapeutic methods and promising novel methods of delivery in the related fields of palliative care.

Microbiological Investigations of ReNu Plastic Bottles and the 2004 to 2006 ReNu With MoistureLoc-Related Worldwide Fusarium Keratitis Event

PURPOSES

The purposes of this study were to determine whether the contact lens solution RevitaLens Ocutec (containing the antimicrobial agents alexidine and polyquaternium-1) would inhibit Fusarium organisms when heated in ReNu plastic bottles; whether alexidine would inhibit Fusarium organisms when heated in non-ReNu plastic bottles; and whether an alexidine-neutralizing compound leaches from heated ReNu bottles.

METHODS

RevitaLens and an alexidine solution (0.00045%), previously stored in ReNu bottles at room temperature (RT) and 56°C, were incubated with 7 different Fusarium organisms. The alexidine solution was similarly stored in seven non-ReNu plastic bottles and incubated with these same organisms. To determine if an alexidine-neutralizing compound might be leaching from heated ReNu bottles, phosphate-buffered saline (PBS) was incubated at RT and 56°C in ReNu bottles, combined with alexidine, and then tested for anti-Fusarium capability.

RESULTS

After being heated in ReNu bottles, RevitaLens retained its anti-Fusarium capability, whereas the alexidine solution did not. The alexidine solution heated in seven non-ReNu plastic bottles retained its anti-Fusarium capability. The alexidine solution retained its anti-Fusarium capability when incubated with a PBS solution that had been heated in ReNu bottles, indicating, microbiologically, that an alexidine-neutralizing compound did not leach from the heated ReNu bottle.

CONCLUSIONS

Alexidine uniquely fails to inhibit Fusarium organisms when heated in a plastic ReNu bottle, but not in seven other plastic bottles, whereas the anti-Fusarium capability of RevitaLens (containing the antimicrobial agents alexidine and polyquaternium-1) is unaffected by heating in a ReNu bottle. There does not seem to be an alexidine-neutralizing compound leaching from heated ReNu bottles. An interaction between alexidine and its heated ReNu bottle may have been a critical factor in the worldwide ReNu with MoistureLoc-related Fusarium keratitis event of 2004 to 2006.

Adsorption of radiopharmaceuticals to syringes: setting up a reliable protocol for its assessment

BACKGROUND

It is well known that various drugs, including radiopharmaceuticals, may adsorb to plastic syringes to different extents. Some reports suggest that adsorption can reach levels of almost 50%. The consequence of adsorption of a radiopharmaceutical and subsequent inadequate dosing can include an inappropriate diagnostic response in patients, an increase in the duration of investigation or treatment, and an increase in cost.

AIM

To investigate the extent of adsorption of Tc-succimer to plastic syringes and to set up a reliable protocol for assessment of the extent of retention of drugs to single-use plastic syringes before a new syringe brand and/or radiopharmaceutical are introduced in a nuclear medicine department.

METHODS

Radiopharmaceutical kits from two different manufacturers were compared for retention using syringes from three different producers. To assess the influence of dilution on retention, Tc-succimer preparations were further diluted with sodium chloride solution for injection. Syringes were filled to one-third of their capacity and incubated at room temperature before being emptied into vacuum vials. The radioactivity of the syringes was measured before and after emptying. The extent of retained radioactivity was calculated as a percentage of radioactivity in the syringe before emptying.

RESULTS

Results show that adsorption of Tc-succimer considerably differs between syringe brands. The adsorption of undiluted Tc-succimer in 30 min may exceed 50%.

CONCLUSION

The findings show that measurement of retention in syringes and injection sets should be regarded as an essential aspect of quality assurance before radiopharmaceuticals, syringes and injection sets are used routinely.

A qualitative investigation into the physical stability of polypropylene and polyethylene in liquid isoflurane and sevoflurane

The interaction between medical plastics and drugs is complex. Drug absorption into plastics may affect drug dosage and the migration of plastics' additives into a drug solution may affect drug composition. We investigated the stability of those plastics which may be used in infusion systems to inject liquid volatile anaesthetic drugs directly into an anaesthetic breathing system. Samples of two types of polypropylene from a syringe barrel and plunger and low- and high-density polyethylene from extension tubing were exposed to isoflurane and sevoflurane for 1, 7 or 250 days. All samples were from the same batches. Samples of the plastics (n = 24) and the liquid volatile anaesthetics (n = 24) were subjected to Fourier transform-infrared spectroscopy to produce series of absorption spectra. By reference to control sample absorption spectra, this allows detection of anaesthetic drug absorption into the plastics or migration of the plastics or their additives into the liquid anaesthetics. We found no evidence of migration of the plastic components or their additives into the liquid anaesthetic drugs at any of the exposure periods. Similarly, we found no evidence of absorption of isoflurane or sevoflurane by any of the plastic components during short-term exposure of either 1 or 7 days. However, there was evidence of some absorption of the anaesthetic drugs by the polyethylene plastics after about 8 months' exposure. It would appear that low- and high-density polyethylene and polypropylene are suitably safe for use in infusion systems for the direct injection of isoflurane and sevoflurane into anaesthetic breathing systems.

Stability, compatibility and plasticizer extraction of quinine injection added to infusion solutions and stored in polyvinyl chloride (PVC) containers

The stability of quinine was determined in various diluents and in polyvinyl chloride (PVC) containers. The release of diethyhexyl phthalate (DEHP) from PVC bags into intravenous infusions of quinine was also measured. We used an injection of two doses of quinine; quiniforme at 500 mg and quinimax at 400 mg in either 250- or 500-ml PVC infusion bags containing 5% dextrose, to give initial nominal concentrations of 2 or 1 mg ml(-1) quiniforme and 1.6 or 0.8 mg ml(-1) quinimax, the mean concentrations commonly used in clinical practice. Samples were assayed by stability-indicating high-performance liquid chromatography (HPLC) and the clarity was determined visually. Experiments were conducted to determine whether the stability and compatibility of quinine would be compromised, and whether DEHP would be leached from PVC bags and PVC administration sets during storage and simulated infusion. There was no substantial loss of quiniforme and quinimax over 1- or 2-h simulated infusion irrespective of the diluent, and storage during 8 h at 22 degrees C, 48 or 72 h at 4 degrees C and 96 h at 45 degrees C. Leaching of DEHP was also detected during simulated infusion delivery using PVC bags and PVC administration sets. The quantity was less than 2 microg ml(-1). During storage at 4 degrees C and room temperature the leaching of DEHP was low, but when the temperature was 45 degrees C the quantity was high, 21 microg ml(-1). To minimise patient exposure to DEHP, quinine solutions with all drugs should be infused immediately or stored for a maximum of 48 h at 4 degrees C.

Stability study of fotemustine in PVC infusion bags and sets under various conditions using a stability-indicating high-performance liquid chromatographic assay

The stability and compatibility of fotemustine, a nitrosourea anticancer agent, in 5% dextrose solution with polyvinyl chloride (PVC) containers and administration sets were studied under different conditions of temperature and light. The drug was diluted to 0.8 and 2 mg ml(-1) in 100 or 250 ml 5% dextrose injection solutions for 1-h simulated infusions using PVC bags and administration sets with protection from light. After preparation in the PVC bags containing 5% dextrose, fotemustine was also prepared at the same concentrations and stored at 4 degrees C for 48 h and at room temperature (22 degrees C) or at sunray exposure ( > 30 degrees C) over 8 h with or without protection from light. The solution samples were removed immediately at various time points of simulated infusions and storage, and stored at -20 degrees C until analysis. The physical compatibility with PVC and chemical stability in solution of fotemustine were assessed by visual examination and by measuring the concentration of the drug in duplicate using a stability-indicating high-performance chromatographic assay. When admixed with a 5% dextrose solution, fotemustine 2 and 0.8 mg ml(-1) was compatible and stable over 1-h of simulated infusion using PVC bags through PVC administration sets with protection from light. On the other hand, in the same diluent, fotemustine was compatible and stable with PVC bags for at least 8 h at 22 degrees C with protection from light and for at least 48 h at 4 degrees C with protection from light. There were no pH variation, no visual change, no color change, no visible precipitation and no loss of the drug. Conversely, when the solutions were exposed to light (ambient or solar), the drug concentration decreased rapidly, leading to the production of a degradation product as shown by mass spectral analysis and a discoloration of the solutions. Finally, in all cases, no DEHP (di-2-ethylhexyl phthalate) was detected in the injection solution.

In vitro growth inhibition of Plasmodium falciparum by retinol at concentrations present in normal human serum

To assess the in vitro effect of retinol on Plasmodium falciparum, the standard isolates 3D7, D10, W2 and K1 in continuous culture were exposed to retinol added in concentrations ranging from 10(-7) to 0.1 mumol/l. Parasite growth inhibition was assessed from 3H-hypoxanthine incorporation. Triplicate experiments were performed at physiological pH and in the case of D10, additional experiments were performed at pH 7.2 and 7.6. Final media retinol concentrations were assayed using high performance liquid chromatography. Retinol inhibited growth of both asynchronous and synchronous cultures of 3D7 and D10 and asynchronous cultures of W2 and K1. IC50 values determined from assayed media concentrations ranged from 0.2 to 3.9 mumol/l and were comparable to concentrations in normal human serum (1.0-3.0 mumol/l). IC50 values for asynchronous D10 cultures at pH 7.2 were lower than at pH 7.4 or 7.6 (0.5, 3.9 and 5.0 mumol/l, respectively); results from synchronous cultures were similar. These data suggest that P. falciparum is a retinol-sensitive parasite, especially at pH levels equivalent to those in an acidotic patient. Adjunctive retinol therapy may have a role in clinical management of malaria.

Stability and compatibility studies of zorubicin in intravenous fluids and PVC infusion bags

The stability of zorubicin (ZOR) in admixtures for continuous intravenous infusion was studied. ZOR was reconstituted and diluted to 600 micrograms ml-1 for simulated infusion and to 250 and 1000 micrograms ml-1 for storage in poly(vinyl chloride) (PVC) bags containing 5% dextrose injection or 0.9% sodium chloride injection (0.9% NaCl). Bags were then stored at refrigerated temperature (4 degrees C) and in the dark for 24 h. ZOR concentrations in each admixture were tested by stability-indicating high-performance liquid chromatographic (HPLC) assay with ultraviolet detection. No substantial loss of ZOR was observed during simulated infusions (n = 4) using PVC infusion bags and administration sets over a 1 h infusion. The drug stored at 4 degrees C in the dark in PVC bags showed that it is highly unstable at 250 micrograms ml-1 in 0.9% NaCl injection and in 5% dextrose injection. On the other hand, under the same storage conditions, at 1000 micrograms ml-1, ZOR is more stable in 0.9% NaCl injection (6 h) than in 5% dextrose (4 h). The reported superior stability of the 1000 micrograms ml-1 in 0.9% NaCl can be explained, at least in part, by the difference in pH. Changes in pH, particularly a decrease, seem to affect adversely the stability of ZOR. In fact, ZOR is rapidly converted into daunorubicin, the dominant degradation product, which is more cardiotoxic than the parent drug. Therefore, several precautions must be observed when the commercial product (Rubidazone) is prepared and reconstituted in i.v. fluids and containers.

Stability, compatibility and plasticizer extraction of miconazole injection added to infusion solutions and stored in PVC containers

The stability of miconazole in various diluents and polyvinyl chloride (PVC) containers was determined and the release of diethylhexyl phthalate (DEHP) from PVC bags into intravenous infusions of miconazole was measured. An injection formulation (80 ml) containing a 1% solution of miconazole with 11.5% of Cremophor EL was added to 250-ml PVC infusion bags containing 5% glucose injection or 0.9% sodium chloride injection, to give an initial nominal miconazole concentration of 2.42 mg ml-1, the mean concentration commonly used in clinical practice. Samples were assayed by stability-indicating high-performance liquid chromatography (HPLC) and the clarity was determined visually. Experiments were conducted to determine whether the stability and compatibility of miconazole would be compromised, and whether DEHP would be leached from PVC bags and PVC administration sets during storage and simulated infusion. There was no substantial loss of miconazole over 2 h simulated infusion irrespective of the diluent, and over 24 h storage irrespective of temperature (2-6 degrees C and 22-26 degrees C). All the solutions initially appeared slightly hazy. Leaching of DEHP was also detected during simulated delivery using PVC bags and PVC administration sets. There was a substantial difference between the amounts of DEHP released from PVC bags and from administration sets, and also between the amounts released in solutions stored in PVC bags at 2-6 degrees C and 22-26 degrees C over 24 h. At the dilution studied, miconazole was visually and chemically stable for up to 24 h. The storage of miconazole solutions in PVC bags seems to be limited by the leaching of DEHP rather than by degradation. To minimize patient exposure to DEHP, miconazole solutions should be infused immediately after their preparation in PVC bags.

Stability and compatibility of cisplatin and carboplatin with PVC infusion bags

The availability and compatibility of drugs from solutions infused via PVC infusion bags through PVC administration sets have been examined. No significant drug loss was observed during simulated infusions using PVC infusion bags and administration sets over time periods used in hospitals (cisplatin, 2 h; carboplatin, 1 h). The stability of carboplatin was studied in 5% dextrose. In 0.9% NaCl, we observed that carboplatin could be converted to cisplatin in the presence of chloride ions. With cisplatin, no significant difference was found between infusion solutions (5% dextrose or 0.9% NaCl). The stability of cisplatin (5% dextrose or 0.9% NaCl) and carboplatin (5% dextrose) was also studied in PVC bags after storage in the dark at room temperature. The results show that the drugs were stable over the 9-day storage period studied.

Stability and compatibility studies of cephamandole nafate with PVC infusion bags

A rapid isocratic technique was developed for the analysis of cephamandole nafate and cephamandole in parenteral solutions using high-performance liquid chromatography (HPLC) with UV detection and C18 column. The availability and compatibility of drugs from solutions infused via plastic infusion bags through plastic administration sets have been examined. No significant drugs loss was observed during simulated infusions (n = 4) for 1 h using PVC infusion bags and administration sets. No significant difference was found between infusion solutions (5% glucose or 0.9% NaCl). The stability of drugs was also studied in solution in PVC bags after storage at room temperature and at 4 degrees C without protection from light. The results show the stability of cephamandole nafate during 24 h at room temperature and 7 days storage at 4 degrees C to be satisfactory, irrespective of the infusion solution (5% glucose or 0.9% NaCl). However, an almost immediate and total transformation of cephamandole nafate to cephamandole in 5% glucose has been observed, whereas in 0.9% NaCl both forms were found in similar proportions.

Modeling of solute sorption by polyvinyl chloride plastic infusion bags

Methods for estimating the equilibrium and time-dependent sorption of solutes by polymeric containers have been developed. The methods are specifically applied to the sorption of solutes by polyvinyl chloride (PVC) infusion bags. The methods correlate the partition coefficients and dissociation constant (when appropriate) of the solute, the physical dimensions of the container, and solution pH with single parameters that dictate the shape of the sorption profile. To determine the equilibrium sorption level for PVC containers, the fractional binding of a solute is correlated with its hexane-water and octanol-water partition coefficients. Calculations based on single partition coefficients are less effective in terms of mimicking the behavior of the PVC. To determine the sorption profile (fractional binding versus time), the partition coefficients are related to the fraction binding at a particular time through a single parameter referred to as the sorption number. Equilibrium fractional binding and sorption profiles for various drugs stored in PVC containers are generated with the models and agree well with reported behavior. The effect of pH on the sorption process is also examined.

Stability and compatibility of four anthracyclines: doxorubicin, epirubicin, daunorubicin and pirarubicin with PVC infusion bags

A rapid isocratic technique was developed for the analysis of four anthracyclines (doxorubicin, epirubicin, daunorubicin and pirarubicin) in parenteral solutions using high pressure liquid chromatography (HPLC) with fluorescence detection and a C18 Hypersil ODS column. The availability and compatibility of these drugs from solutions infused via PVC infusion bags through PVC administration sets have been examined. No significant drug loss was observed during simulated infusions (n = 4) for 24 h using PVC infusion bags and administration sets. No significant difference was found between infusion solutions (5% glucose or 0.9% NaCl), except for pirarubicin. The reconstitution of pirarubicin in 0.9% NaCl was impossible, because we observed a precipitation of the compound in solution. The stability of the drugs was also studied in solution, in PVC bags after storage at 4 degrees C with protection from light. The results show the stability of doxorubicin, epirubicin and daunorubicin during 7 days of storage to be satisfactory, irrespective of the infusion solution (5% glucose or 0.9% NaCl). In the case of pirarubicin, the stability of the drug was satisfactory during 5 days of storage in 5% glucose, but beyond, we observed a degradation of the compound with formation of doxorubicin in the infusion solution.

PVC as pharmaceutical packaging material. A literature survey with special emphasis on plasticized PVC bags

In this report the state of the art with respect to PVC as pharmaceutical packaging material is described. A general introduction into the applications of PVC is followed by a description of its production process. The metabolic effects of the monomer of PVC, vinyl chloride and of the most commonly used plasticizer diethylhexylphthalate are mentioned. Special attention is given to the pharmaceutical properties of plasticized PVC bags in comparison to other plastics and the environmental aspects of waste PVC disposal. Although there are emotional and political queries regarding the future use of PVC as a (pharmaceutical) packaging material, we conclude that there is no scientific justification for a total or partial ban of PVC. PVC will remain a fact of life as a cheap, versatile, high-performance and well-investigated plastic material for medical and pharmaceutical applications, to be replaced by newer plastics only for certain well-defined indications where the requirements of the plastic to be used are so specific that it will economically and technically be justified to use another polymer. Community and hospital pharmacists have to be prepared for a role in intake of waste plastic disposables, probably against deposit money, in order to fulfil the logistics needed for recycling.

Prediction of solute sorption by polyvinyl chloride plastic infusion bags

The time course of the sorption of drugs by polyvinylchloride infusion bags has been approximated using a diffusion model in which the plastic is assumed to act as an infinite sink. This model appears to be suitable for estimation of storage times relevant to clinical usage and enables the magnitude of the uptake in a specific time to be described by a single parameter, referred to as the sorption number. This parameter is defined by the plastic-infusion solution partition coefficient, the diffusion coefficient in the plastic, the fraction un-ionized in solution, the volume of the infusion solution, and the surface area of the plastic. An approximation of the model allows a ready estimation of the sorption number from the fraction remaining in solution at a given time. The sorption number can be extrapolated to allow prediction of the effects of time, plastic surface area, solution volume, and solution pH on fractional solute loss. A reasonable correlation was established between the logarithm of this parameter and the logarithm of the octanol-water partition coefficients of various solutes. The model allows the fraction of a solute remaining in a plastic infusion bag at a given storage time to be estimated from the octanol-water partition coefficient of the solute and other readily available data.

The availability of diltiazem: a study on the sorption by intravenous delivery systems and on the stability of the drug

The stability and the sorption by intravenous delivery systems of the calcium antagonist diltiazem dissolved into either 5% dextrose or 0.9% sodium chloride solutions have been investigated, under conditions simulating current clinical practice. Static experiments showed an excellent stability and no sorption after 48 h. Dynamic experiments, at a perfusion rate of 20 mg h-1, showed no sorption of the drug by infusion fluid containers, burettes or administration sets. For end-line filters a temporary decrease of the recovered amount of diltiazem was observed but only with the 0.9% NaCl solution. It is concluded that the stability and the sorption of diltiazem offers no problem with regard to clinical efficacy.

Kinetics of sorption of ionizable solutes by plastic infusion bags

Aqueous solutions of several ionizable substances were stored in plastic infusion bags and the sorption of the substances monitored with time. The substances used were p-nitrophenol, p-toluidine, warfarin sodium [3-(alpha-acetonylbenzyl)-4-hydroxycoumarin sodium salt] and trifluoperazine hydrochloride (10-[3-(4-methyl-1-piperazinyl)propyl]-2-(trifluoromethyl)phenothiazine dihydrochloride). The rate and extent of sorption for each substance varied with pH and was consistent with a preferential uptake of the un-ionized species. The uptake of p-nitrophenol and p-toluidine was adequately described by a diffusion model derived assuming that sorption is rate-controlled by the diffusivity of the solute in the plastic matrix, and that only the un-ionized species was sorbed by the plastic matrix. However, the uptake of warfarin sodium and trifluoperazine hydrochloride was described more accurately by a diffusion model in which the diffusional resistance of the plastic matrix and of an interfacial resistance barrier both contributed to the diffusional resistance encountered in the sorption process. It appeared that the rate of uptake of the un-ionized form of these solutes was diminished due to the influence of interfacial or aqueous diffusional barriers. Solute lipophilicity and degree of ionization appeared to be important factors determining the relative contribution of the respective barriers to the overall diffusional resistance.

Addition of drugs to infusion fluids: pharmaceutical considerations on preparation and use

In most hospitals, the addition of drugs to infusion fluids is carried out by nurses. The preparation involves certain hazards both microbiologically and pharmaceutically. Incompatibilities between drug and fluid or between drugs may result in admixtures which have reduced therapeutic activity or which are even hazardous to the patient. The all-in-one total parenteral nutrition mixtures represent a new way of administering nutrition and has achieved increased popularity both for in- and outpatients. During preparation, which takes place in the pharmacy, several precautions have to be taken to assure a product with acceptable stability. Some of the important incompatibilities are mentioned.