Accuracy of intravenous and enteral preparations involving small volumes for paediatric use: a review.

BACKGROUND: Children often need to be administered very small volumes of medicines that are authorised for use in adults. Neonatal drug delivery is particularly challenging, and doses are often immeasurable with the equipment currently available. AIM: To summarise research to date on the accuracy of intravenous and enteral medicine preparation requiring small volumes (<0.1 mL), with a focus on paediatric use and to identify areas for further work. METHOD: Twenty-three publications were identified for the narrative review via: Web of Science (1950-2016), Cumulative Index to Nursing and Allied Health Literature (1976-2016), Excerpta Medica Database (1974-2016) and International Pharmaceutical Abstracts (1970-2016) searches. Nine additional papers were identified through backward citation tracking and a further 17 were included from the personal knowledge of the review team. RESULTS: Measurement of volumes (<0.1 mL), for enteral and intravenous dosing, accounts for 25% of medicine manipulations within paediatric hospitals. Inaccuracies are described throughout the literature with dose administration errors attributed to technique, calculation, dilution and problems associated with equipment. While standardised concentrations for intravenous infusion and drug concentrations that avoid measurement of small volumes would ameliorate problems, further work is needed to establish accurate methods for handling small volumes during the administration of medicines to children and risk minimisation strategies to support staff involved are also necessary. CONCLUSIONS: This review has revealed a paucity of information on the clinical outcomes from problems in measuring small volumes for children and highlighted the need for further work to eliminate this source of inaccurate dosing and potential for medication error.

Tools for the Individualized Therapy of Teicoplanin for Neonates and Children.

The aim of this study was to develop a population pharmacokinetic (PK) model for teicoplanin across childhood age ranges to be used as Bayesian prior information in the software constructed for individualized therapy. We developed a nonparametric population model fitted to PK data from neonates, infants, and older children. We then implemented this model in the BestDose multiple-model Bayesian adaptive control algorithm to show its clinical utility. It was used to predict the dosages required to achieve optimal teicoplanin predose targets (15 mg/liter) from day 3 of therapy. We performed individual simulations for an infant and a child from the original population, who provided early first dosing interval concentration-time data. An allometric model that used weight as a measure of size and that also incorporated renal function using the estimated glomerular filtration rate (eGFR), or the ratio of postnatal age (PNA) to serum creatinine concentration (SCr) for infants <3 months old, best described the data. The median population PK parameters were as follows: elimination rate constant (Ke) = 0.03 · (wt/70)-0.25 · Renal (h-1); V = 19.5 · (wt/70) (liters); Renal = eGFR0.07 (ml/min/1.73 m2), or Renal = PNA/SCr (µmol/liter). Increased teicoplanin dosages and alternative administration techniques (extended infusions and fractionated multiple dosing) were required in order to achieve the targets safely by day 3 in simulated cases. The software was able to predict individual measured concentrations and the dosages and administration techniques required to achieve the desired target concentrations early in therapy. Prospective evaluation is now needed in order to ensure that this individualized teicoplanin therapy approach is applicable in the clinical setting. (This study has been registered in the European Union Clinical Trials Register under EudraCT no. 2012-005738-12.).

Optimising the use of medicines to reduce acute kidney injury in children and babies.

The majority of medications in children are administered in an unlicensed or off-label manner. Paediatricians are obliged to prescribe using the limited evidence available. The 2007 EU regulation on the use of paediatric drugs means pharmaceutical companies are now obliged to (and receive incentives for) contributing to paediatric drug data and carrying out paediatric clinical trials. This is important, as the efficacy and adverse effect profiles of medicines vary across childhood. Additionally, there are significant age-related changes in the pharmacodynamic and pharmacokinetic activity of many drugs. This may be related to physiological (differential expressions of cytochrome P450 enzymes or variable glomerular filtration rates at different ages for example) and psychological (increasing autonomy and risk perception in teenage years) changes. Increasing numbers of children are surviving life-threatening childhood conditions due to medical advances. This means there is an increasing population who are at risk of the consequences of the long-term, early exposure to nephrotoxic agents. The kidney is an organ that is particularly vulnerable to damage as a consequence of drugs. Drug-induced acute kidney injury (AKI) episodes in children and babies are principally due to non-steroidal anti-inflammatory drugs, antibiotics or chemotherapeutic agents. The renal tubules are vulnerable to injury because of their concentrating ability and high-energy hypoxic environment. This review focuses on drug-induced AKI and the methods to minimise its effect, including general management plus the role of child-specific pharmacokinetic data, the use of pharmacogenomics and early detection of AKI using urinary biomarkers and electronic triggers.

Population pharmacokinetics and pharmacodynamics of teicoplanin in neonates: making better use of C-reactive protein to deliver individualized therapy.

OBJECTIVES: There is uncertainty about the optimal teicoplanin regimens for neonates. The study aim was to determine the population pharmacokinetics (PK) of teicoplanin in neonates, evaluate currently recommended regimens and explore the exposure-effect relationships. METHODS: An open-label PK study was conducted. Neonates from 26 to 44 weeks post-menstrual age were recruited (n = 18). The teicoplanin regimen was a 16 mg/kg loading dose, followed by 8 mg/kg once daily. Therapeutic drug monitoring and dose adjustment were not conducted. A standard two-compartment PK model was developed, followed by models that incorporated weight. A PK/pharmacodynamic (PD) model with C-reactive protein serial measurements as the PD input was fitted to the data. Monte Carlo simulations (n = 5000) were performed using Pmetrics. The AUCs at steady state and the proportion of patients achieving the recommended drug exposures (i.e. Cmin >15 mg/L) were determined. The study was registered in the European Clinical Trials Database Registry (EudraCT: 2012-005738-12). RESULTS: The PK allometric model best accounted for the observed data. The PK parameters medians were: clearance = 0.435 × (weight/70)0.75 (L/h); volume = 0.765 (L); Kcp = 1.3 (h-1); and Kpc = 0.629 (h-1). The individual time-course of C-reactive protein was well described using the Bayesian posterior estimates for each patient. The simulated median AUC96-120 was 302.3 mg·h/L and the median Cmin at 120 h was 12.9 mg/L; 38.8% of patients attained a Cmin >15 mg/L by 120 h. CONCLUSIONS: Teicoplanin population PK is highly variable in neonates, weight being the best descriptor of PK variability. A low percentage of neonates were able to achieve Cmin >15 mg/L. The routine use of therapeutic drug monitoring and improved knowledge on the PD of teicoplanin is required.

Population pharmacokinetics of teicoplanin in children.

Teicoplanin is frequently administered to treat Gram-positive infections in pediatric patients. However, not enough is known about the pharmacokinetics (PK) of teicoplanin in children to justify the optimal dosing regimen. The aim of this study was to determine the population PK of teicoplanin in children and evaluate the current dosage regimens. A PK hospital-based study was conducted. Current dosage recommendations were used for children up to 16 years of age. Thirty-nine children were recruited. Serum samples were collected at the first dose interval (1, 3, 6, and 24 h) and at steady state. A standard 2-compartment PK model was developed, followed by structural models that incorporated weight. Weight was allowed to affect clearance (CL) using linear and allometric scaling terms. The linear model best accounted for the observed data and was subsequently chosen for Monte Carlo simulations. The PK parameter medians/means (standard deviation [SD]) were as follows: CL, [0.019/0.023 (0.01)] × weight liters/h/kg of body weight; volume, 2.282/4.138 liters (4.14 liters); first-order rate constant from the central to peripheral compartment (Kcp), 0.474/3.876 h(-1) (8.16 h(-1)); and first-order rate constant from peripheral to central compartment (Kpc), 0.292/3.994 h(-1) (8.93 h(-1)). The percentage of patients with a minimum concentration of drug in serum (Cmin) of <10 mg/liter was 53.85%. The median/mean (SD) total population area under the concentration-time curve (AUC) was 619/527.05 mg · h/liter (166.03 mg · h/liter). Based on Monte Carlo simulations, only 30.04% (median AUC, 507.04 mg · h/liter), 44.88% (494.1 mg · h/liter), and 60.54% (452.03 mg · h/liter) of patients weighing 50, 25, and 10 kg, respectively, attained trough concentrations of >10 mg/liter by day 4 of treatment. The teicoplanin population PK is highly variable in children, with a wider AUC distribution spread than for adults. Therapeutic drug monitoring should be a routine requirement to minimize suboptimal concentrations. (This trial has been registered in the European Clinical Trials Database Registry [EudraCT] under registration number 2012-005738-12.).

Adverse drug reactions causing admission to a paediatric hospital: a pilot study.

WHAT IS KNOWN AND OBJECTIVE: It is known that adverse drug reactions (ADRs) cause admission to hospital in adults and children. A recent adult study showed that ADRs are an important and frequent cause of hospital admission. The objective of this study is to develop methodology to ascertain the current burden of ADRs through a prospective analysis of all unplanned admissions to a paediatric hospital. METHODS: Prospective observational study over a 2-week period. RESULTS AND DISCUSSION: There were 19 admissions to the main hospital wards related to an ADR, giving an estimated incidence of 4%, with the ADR directly leading to the admission in 71% of cases. There were no deaths attributable to ADR. 33% of the reactions were possibly avoidable. The drugs most commonly implicated in causing admissions were anti-neoplastic agents. The most common reactions were neutropenia, vomiting and diarrhoea. The health burden of ADRs in the paediatric population is likely to be significant. This pilot study will be used to inform a much larger prospective study providing more detailed evidence of the burden of ill-health from ADRs in children. This larger study will add to a body of research aiming to identify drug-related problems within children to aid paediatric pharmacovigilance. WHAT IS NEW AND CONCLUSION: This study provides knowledge regarding the methodology to be used for a larger study investigating ADRs in children. The study will allow authors who wish to replicate the study in their own populations (internationally) to avoid some of the pitfalls in planning a large epidemiological study of paediatric ADRs. The study also provides an estimate of the incidence and problem of admissions caused by ADRs in a UK paediatric population.

Weight-related dosing, timing and monitoring hydrocortisone replacement therapy in patients with adrenal insufficiency.

OBJECTIVE: The objective of this study was to examine the variables determining hydrocortisone (HC) disposition in patients with adrenal insufficiency and to develop practical protocols for individualized prescribing and monitoring of HC treatment. DESIGN AND PATIENTS: Serum cortisol profiles were measured in 20 cortisol-insufficient patients (09.00 h cortisol < 50 nmol/l) given oral HC as either a fixed or 'body surface area-adjusted' dose in the fasted or fed state. Endogenous cortisol levels were measured in healthy subjects. Pharmacokinetic analysis was performed using P-Pharm software, and computer simulations were used to assess the likely population distribution of the data. RESULTS: Body weight was the most important predictor of HC clearance. A fixed 10-mg HC dose overexposed patients to cortisol by 6.3%, whereas weight-adjusted dosing decreased interpatient variability in maximum cortisol concentration from 31 to 7%, decreased area under the curve (AUC) from 50 to 22% (P < 0.05), and reduced overexposure to < 5%. Food taken before HC delayed its absorption. Serum cortisol measured 4 h after HC predicted cortisol AUC (r(2) = 0.78; P < 0.001). CONCLUSIONS: We recommend weight-adjusted HC dosing, thrice daily before food, monitored with a single serum cortisol measurement using a nomogram. This regimen was prospectively examined in 40 cortisol-insufficient patients, 85% of whom opted to remain on the new thrice-daily treatment regimen.

Impaired glycogen synthesis in hepatocytes from Zucker fatty fa/fa rats: the role of increased phosphorylase activity.

AIMS/HYPOTHESIS: The Zucker fatty fa/fa rat develops hyperinsulinaemia, insulin-resistance and severe obesity as a result of a homozygous mutation in the leptin receptor gene. The aim was to characterise the metabolic defect(s) in hepatocytes from fa/fa rats. METHODS: Glucose metabolism and key regulatory enzymes were investigated in hepatocytes from fa/fa and Fa/? rats after short-term culture in the absence of insulin. RESULTS: Hepatocytes from fa/fa rats have higher glucokinase activity and expression of the glucokinase regulatory protein and higher rates of glycolysis and lipogenesis, but lower rates of glycogen synthesis than hepatocytes from Fa/? controls. Insulin caused a similar stimulation of glycogen synthesis in hepatocytes from fa/fa rats as in controls ( > twofold) but did not restore the impaired glycogen synthesis in cells from fa/fa rats. Adenovirus-mediated glucokinase overexpression stimulated glycogen synthesis and glycolysis but aggravated rather than abolished the relative impairment of glycogen synthesis in cells from fa/fa rats. Inhibition of glycolysis with 2,5-anhydromannitol, an inhibitor of glycolysis and gluconeogenesis, increased glucose 6-phosphate concentrations and glycogen synthesis in hepatocytes from Fa/? and fa/fa rats but did not restore the impaired glycogen synthesis in cells from fa/fa rats. Hepatocytes from fa/fa rats had a higher activity of phosphorylase a in the basal state and after incubation with insulin or glucagon and higher total phosphorylase. CONCLUSION/INTERPRETATION: The increased activity of phosphorylase is a major contributing factor to the impaired glycogen synthesis in hepatocytes from fa/fa rats and could contribute to the lipogenic state by a glycogenolytic-glycolytic-lipogenic pathway.

Stress-activated protein kinases in the activation of rat hepatic stellate cells in culture.

BACKGROUND/AIMS: The signal cascades involved in the activation of hepatic stellate cells (HSC) are largely unknown. Factors initiating activation include tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, endothelin, and oxidative stress. In other cell types some of these have been reported to stimulate p38 mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK). We have therefore investigated the role of these kinases in HSC activation. METHODS: HSC were isolated from male Wistar rats. Quiescent experiments were performed on day 2 HSC and transformed experiments on day 15 passage 1 HSC. Kinase activities were determined by immunoprecipitation and phosphorylation of specific substrate proteins and alpha-smooth muscle actin (SMA) expression by immunoblotting. RESULTS: The constitutive activity of p38 MAP kinase was higher in transformed versus quiescent cells. In quiescent cells TNFalpha stimulated p38 MAP kinase and JNK activities 12- and 4-fold respectively and this was halved by 2-mercaptoethanol, an indirect antioxidant. Endothelin-1 activated both kinases in quiescent cells via the endothelin-B receptor, while TGFbeta had no effect. Both 2-mercaptoethanol and a p38 inhibitor (SB202190) inhibited alpha-SMA expression by day 5 cells. CONCLUSIONS: The activation of p38 MAP kinase and JNK by TNFalpha and endothelin, together with the inhibition of this activation by 2-mercaptoethanol, provides indirect evidence supporting their role in HSC transformation. Direct evidence for a role for p38 MAP kinase is provided by the observations that its constitutive activity is higher in transformed versus quiescent cells and that its inhibitor reduces HSC activation in culture as assessed by alpha-SMA expression.

Response to transforming growth factor alpha (TGFalpha) and epidermal growth factor (EGF) in hepatocytes: lower EGF receptor affinity of TGFalpha is associated with more sustained activation of p42/p44 mitogen-activated protein kinase and greater efficacy in stimulation of DNA synthesis.

The epidermal growth factor (EGF) receptor mediates the effects of both EGF and transforming growth factor alpha (TGFalpha). Recent data suggested that EGF acts as a partial agonist/antagonist in hepatocytes, TGFalpha exerting a larger maximal stimulation of DNA synthesis than EGF. To further study the mechanisms involved in mediating the different effects of EGF and TGFalpha, we have examined receptor binding of the two growth factors and their action on the p42/p44 mitogen-activated protein (MAP) kinase activity in hepatocytes. Single-ligand concentration curves and competition experiments showed that the binding affinity to a common population of surface binding sites was about 20-fold lower for TGFalpha than for EGF. MAP kinase activity responded to EGF and TGFalpha with different kinetics. While the two agents produced almost identical acute (5 min) stimulation (peak about fivefold), TGFalpha produced a more sustained MAP kinase activity than EGF. The difference between EGF and TGFalpha was still detectable 24 h after growth factor addition. The results show that in hepatocytes a lower receptor affinity of TGFalpha, as compared to EGF, is associated with a more sustained activation of the MAP kinase and a greater efficacy in the stimulation of DNA synthesis. This suggests that differential interaction of these two agents with the EGF receptor results in differences in the downstream events elicited at a given level of receptor occupancy. The data also are compatible with a role of a prolonged MAP kinase activity in the mitogenic effects of EGF and TGFalpha.

Signalling pathways involved in the stimulation of glycogen synthesis by insulin in rat hepatocytes.

In hepatocytes glycogen storage is stimulated by insulin and this effect of insulin is counteracted by epidermal growth factor (EGF). The mechanism by which insulin stimulates glycogen synthesis in liver is unknown. We investigated the involvement of candidate protein kinases in insulin signalling in hepatocytes. Both insulin and EGF activated extracellular regulated kinase 2 (ERK-2), p70rsk and protein kinase B (PKB) and inactivated glycogen synthase kinase-3 (GSK-3). Whereas EGF caused a greater activation of ERK-2 than insulin, the converse was true for PKB. The stimulation by insulin of ERK-2 was blocked by a mitogen-activated protein (MEK) inhibitor (PD 98059) and of p70rsk by rapamycin. However, these inhibitors, separately or in combination, did not block the stimulation of glycogen synthesis by insulin, indicating that activation of these kinases is not essential for the stimulation of glycogen synthesis by insulin. Mono Q fractionation of hepatocyte extracts resolved a single myelin basic protein (MBP) kinase peak from extracts of EGF-treated cells (peak 1, eluting at 200 mmol/l NaCl) and two peaks from insulin-treated cells (peak 1 eluting at 200 mmol/l NaCl and peak 2 eluting at 400 mmol/l NaCl). In the combined presence of insulin and EGF, activation of peak 2 was abolished. In situ MBP kinase assays and immunoblotting established that peak 1 coincides with ERK-2 and peak 2 is not an activated form of ERK-1 or ERK-2. It is concluded that PKB, which is activated to a greater extent by insulin than EGF, and peak 2, which is activated by insulin and counteracted by EGF, are possible candidates in mediating the stimulation of glycogen synthesis by insulin.

Evidence for a role of glucose-induced translocation of glucokinase in the control of hepatic glycogen synthesis.

Glucokinase reversibly partitions between a bound and a free state in the hepatocyte in response to the metabolic status of the cell. Maximum binding occurs at low [glucose] (<5 mM) and minimum binding at high [glucose] or in the presence of sorbitol or fructose. In this study we determined the binding characteristics of glucokinase in the hepatocyte in situ, by adenovirus-mediated glucokinase overexpression combined with the digitonin-permeabilization technique. We also determined the sensitivity of glycogen synthesis to changes in either total glucokinase overexpression or in free glucokinase activity. Glucokinase overexpression is associated with an increase in both free and bound activity, with an overall decrease in the proportion of bound activity. In hepatocytes incubated at low [glucose] (0-5 mM), glucokinase binding involves a high-affinity binding site with a Kd of approximately 0.1 microM and a binding capacity of approximately 3 pmol/mg total cell protein and low-affinity binding with a Kd of approximately 1.6 microM. Increasing glucose concentration to 20 mM causes a dose-dependent increase in the Kd of the high- affinity site to approximately 0.6 microM, and this effect was mimicked by 50 microM sorbitol, a precursor of fructose 1-P, confirming that this site is the regulatory protein of glucokinase. Glycogen synthesis determined from the incorporation of [2-3H,U-14C]glucose into glycogen at 5 mM or 10 mM glucose was very sensitive to small increases in total glucokinase activity and correlated more closely with the increase in free glucokinase activity. The relation between glycogenic flux and glucokinase activity is sigmoidal. Expression of the sensitivity of glycogen synthesis to glucokinase activity as the control coefficient reveals that the coefficient is greater for the incorporation of 2-tritium (which occurs exclusively by the direct pathway) than for incorporation of 14C label (which involves direct and indirect pathways) and is greater at 5 mM glucose (when glucokinase is maximally sequestered at its high-affinity site) than at 10 mM glucose. The results support the hypothesis that compartmentation of glucokinase in the hepatocyte increases the sensitivity of glycogen synthesis to small changes in total glucokinase activity and that glucose-induced translocation of glucokinase has a major role in the acute control of glycogen synthesis.

Effects of hydroxyl radical scavengers on relaxation of supercoiled DNA by aminomethyl-trimethyl-psoralen and monochromatic UVA photons.

The ability of scavengers of hydroxyl radical (OH radical) to modulate the photosensitized relaxation (induction of the first single-strand break) of supercoiled plasmid DNA with UVA photoactivated 4'-aminomethyl-4,5',8-trimethylpsoralen was examined by comparing the dose reduction factor (DRF: the ratio of fluence required to induce the same degree of relaxation in the absence to the presence of OH radical scavengers). The addition of mannitol, azide, acetate, or formate at concentrations inversely proportional to the value of the rate constants for the scavenging of OH radicals partially attenuated the supercoiled DNA relaxation. The degrees of protection afforded by the four scavengers in the presence of AMT photoactivated by either 334 nm or 365 nm monochromatic photons were similar, giving an average DRF of about 0.25 in all cases. Given the diverse chemical nature of the scavengers and their wide range of concentrations utilized, these findings are evidence for the involvement of a Type I photosensitization in the induction of DNA single-strand breaks by photoactivated AMT.

Extreme resistance to thermally induced DNA backbone breaks in the hyperthermophilic archaeon Pyrococcus furiosus.

Pyrococcus furiosus is a hyperthermophilic archaeon that grows optimally at 100 degrees C. It is not conceivable that these organisms could survive with genomic DNA that was subject to thermal destruction, yet the mechanisms protecting the genomes of this and other hyperthermophiles against such destruction are obscure. We have determined the effect of elevated temperatures up to 110 degrees C on the molecular weight of DNA in intact P. furiosus cells, compared with the effect of elevated temperatures on DNA in the mesothermophilic bacterium Escherichia coli. At 100 degrees C, DNA in P. furiosus cells is about 20 times more resistant to thermal breakage than that in E. coli cells, and six times fewer breaks were found in P. furiosus DNA after exposure to 110 degrees C for 30 min than in E. coli DNA at 95 degrees C. Our hypothesis for this remarkable stability of DNA in a hyperthermophile is that this hyperthermophile possesses DNA-binding proteins that protect against hydrolytic damage, as well as other endogenous protective mechanisms and DNA repair enzyme systems.

The regulatory protein of glucokinase binds to the hepatocyte matrix, but, unlike glucokinase, does not translocate during substrate stimulation.

The kinetic properties of hepatic glucokinase (hexokinase IV) are modulated by binding to a regulatory protein. This study shows that, in hepatocytes incubated with 5 mM glucose as sole carbohydrate substrate, both glucokinase and its regulatory protein bind to the cell matrix by a Mg(2+)-dependent mechanism. After incubation with an elevated [glucose] or with fructose, glucokinase, but not its regulatory protein, translocates from the Mg(2+)-dependent binding site. It is suggested that the regulatory protein acts as a receptor for anchoring glucokinase to the hepatocyte matrix and inhibiting its activity in metabolically quiescent conditions.

Induction of slowly developing alkali-labile sites in human P3 cell DNA by UVA and blue- and green-light photons: action spectrum.

Action spectra (365-520 nm) for the formation of DNA single-strand breaks (SSB) and slowly developing alkali-labile sites (SDALS) in human teratocarcinoma P3 cells in culture were determined. Induction of SDALS results from the absorption of blue- and green-light photons. The spectrum has a broad peak that is maximal between 400 nm to 500 nm and declines sharply above and below these wavelength regions. Negligible yields of SDALS were produced by photons at wavelengths of 365 nm or shorter and at 520 nm or longer, whereas for SSB, the action ioffeases with shorter wavelength throughout the whole spectral range studied. The configuration of the SDALS action spectrum suggests that the primary chromophore, and therefore possibly the photosensitizer, is a mixture of porphyrin and flavin residues.

DNA damage produced by exposure of supercoiled plasmid DNA to high- and low-LET ionizing radiation: effects of hydroxyl radical quenchers.

Production of DNA damage by exposure to ionizing radiation was measured in two in vitro systems. A supercoiled plasmid of 7.3 kbp was isolated and exposed in an aqueous environment to 60Co gamma rays and JANUS 0.85 MeV fission-spectrum neutrons. Dose responses for the production of single-strand breaks (ssbs) and double-strand breaks (dsbs) were computed from the conversion of the supercoil to its relaxed and linear forms. The relative effectiveness (neutrons:gamma-rays) for destruction of genetic transforming activity of M13 viral DNA was 0.23, close to that for ssb production, in contrast with the situation for biological effects such as lethality, mutagenesis and cellular transformation measured in mammalian cells, where RBEs are > 1. The role of hydroxyl (OH) radicals in DNA damage induction by neutrons was investigated by exposure of plasmid in the presence of known quenchers of this species. Of four quenchers tested, all were able to reduce the yields of both ssbs and dsbs. These findings are consistent with a model for ssb and dsb induction by high linear energy transfer radiation that involves OH radical medication.