Plasma and tissue distribution of bismuth in normal and cirrhotic rats

The effect of liver disease on total body handling of bismuth was studied in normal and cirrhotic rats to test the hypothesis that hepatic function can be a significant determinant of heavy metal handling. Excretion and tissue distribution of bismuth were investigated in animals administered bismuth subcitrate by the intramuscular route for 70 d. Plasma bismuth in control rats reached an apparent steady state of 31.89 +/- 4.15 micrograms l-1 (mean +/- standard error of mean, n = 12) by day 28-35. The plasma profile in cirrhotic rats resembled that of controls until day 42 after which bismuth concentrations became significantly elevated. At day 70 of dosing the mean plasma bismuth concentration was 63.68 +/- 9.68 micrograms l-1 (n = 11) in cirrhotic rats compared with 32.68 +/- 4.24 micrograms l-1 (n = 12) in control rats (p < 0.05). Total urinary excretion of cirrhotic animals closely paralleled that of controls; however, urinary bismuth clearance was significantly reduced beyond 42 d, as was faecal excretion. Bismuth tissue distribution was analysed in a randomly selected sub-set of control and cirrhotic animals. There was a significantly higher concentration of bismuth in the liver, bone, spleen, lungs and heart of the cirrhotic rats, with no change in the kidney. There was minimal accumulation of bismuth in the central nervous system of either normal or cirrhotic animals. Bismuth accumulation in cirrhotic rats suggests that patients with cirrhosis could be at risk from similar accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of brain injury related to mathematical modelling and epidemiological data

Measurements of the frequency response of head impact points on the exterior and the interior of a car were used to characterize the dynamic behavior of the object that was struck. These points were then arranged in a hierarchy of increasing stiffness. Thirty-two cases in which the distribution of injury to the brain had been recorded were grouped according to the stiffness of the object struck and by the location of the impact on the head. The distribution of the brain lesions were determined for each class of stiffness and location of impact. Three probable mechanisms of brain injury were distinguished: relative motion between the brain and the skull, local bone deformation, and intracerebral stresses. Each mechanism was related to a range of stiffness and natural frequency of the structure impacted. These theories of brain injury mechanisms are consistent with observed epidemiological data and with conclusions drawn from mathematical modelling.

Staining of amyloid precursor protein to study axonal damage in mild head injury

The most common definition of cerebral concussion is that of a transient loss of neurological function without macroscopic or microscopic abnormality in the brain. However, some patients have persistent symptoms and subtle neuropsychological deficits, particularly affecting memory. We have studied five patients aged 59-89 years who sustained mild concussive head injury and died of other causes (2-99 days post-injury). Immunostaining with an antibody to amyloid precursor protein, a marker of fast axonal transport, showed multifocal axonal injury in all five. All had axonal damage in the fornices, which are important in memory function.

A method of estimating linear and angular accelerations in head impacts to pedestrians

In order to investigate the relationship between impact to the head and brain injury, we have developed a method, using information obtained from reconstruction of the collisions, of estimating the peak linear and angular accelerations of the head for pedestrian impacts on a vehicle. This information includes the location of the impact on the head, the impact velocity of the head, and the stiffness of the struck surface. In developing the method we assumed that the velocity of the head on striking the vehicle was the same as the velocity of the vehicle itself, that the force vector was normal to the surface of the skull, that the force-deflection curve characterising the combined response of the impacted surfaces was linear, and that the kinetic energy of the head immediately prior to impact was converted into strain energy in deforming the head and the vehicle structure. Only the loading phase of the impact was considered, there was no assumption of an elastic unloading phase. Using cadavers, the validity of these assumptions and hence the usefulness of the method were tested by comparing the estimates of peak linear acceleration with the results of 18 pedestrian-vehicle impact reconstructions. On average, the method underestimated the experimental values by about 15%, with a range of +/- 35%. The results from the application of this method are currently being used to study the relationship between the magnitude and direction of the impact to the head and the distribution and severity of the brain injury resulting from actual collisions.

Age, sex, and blood alcohol concentration of killed and injured drivers, riders, and passengers

The relationships between type of road user, sex, age, and blood alcohol concentration (BAC) were examined among 1,389 adult vehicle occupants and motorcyclists fatally injured in crashes within South Australia from 1985 to 1992, inclusive, and among 1,573 adult vehicle occupants and motorcyclists admitted to a Level-1 trauma centre from August 1985 to July 1987. The relationships between BAC and both day of week of crash and the number of vehicles involved were determined among fatalities, whereas among admissions, duration of hospitalization and type of unit to which the casualty was admitted were also examined. BACs of .08 g/100 mL or higher were found in 38% of killed and 30% of injured drivers, 37% and 27% of passengers, and 35% and 22% of male motorcycle riders. Alcohol involvement was almost nonexistent among the elderly. The finding that the proportion of injured motorcyclists was similar to that of drivers is consistent with motorcyclists' increased risk of injury even in relatively minor crashes. Male motorcycle riders were found to be significantly younger than male drivers. They were also significantly less likely to have been drinking and, if they had been drinking, their mean BAC was significantly lower. The results are also consistent with the well-established observations that alcohol involvement is greater in single-vehicle crashes and in crashes occurring on weekends. Average duration of hospitalization was not found to differ between types of road user or between those with a BAC above and below .08 g/100 mL.

Absence of toxicity in patients with malignant otitis externa following long-term treatment with high dosage tobramycin

An in-vitro model of aminoglycoside dosing was used to demonstrate that the bactericidal activity of tobramycin against Pseudomonas aeruginosa is directly related to the peak concentration of the drug. In addition, six patients who were being treated for malignant otitis externa with long-term, high dosage tobramycin were monitored for oto- and nephro-toxicity; the only adverse effects were transient increases in the serum creatinine concentration in two patients.

Bactericidal effect of gentamicin trough concentration provides a rationale for administration of bolus doses and maintenance of trough levels

An in-vitro study was made of the influence of trough gentamicin concentrations (Cmin) on the bactericidal effect of gentamicin against Escherichia coli NCTC 10418. Lag phase bacterial cells were exposed in vitro to gentamicin concentration versus time profiles which modelled profiles in patients up to 30 min after either an 80 mg iv bolus over 1 min or a 30 min infusion. The gentamicin was removed 30 min post-dose and the cultures were reconstituted in broth containing a constant trough gentamicin concentration in the range of 0-3 mg/L. Bacterial cfu counts and gentamicin concentrations were measured before and during antibiotic exposure. It was found that antibacterial activity was not determined by AUC, but rather there was a threshold trough concentration producing a bactericidal effect which differed between bolus and infusion profiles. With the bolus profile trough concentrations required for a bactericidal effect were 0.5-1.0 mg/L, while with the infusion profile generating an identical post-distribution peak concentration, trough concentrations required for a sustained bactericidal effect were 2.5-3.0 mg/L. These findings favour bolus iv gentamicin dosing over infusion dosing, provided appropriate attention is paid to any potential toxicity associated with high peak concentrations. Trough data indicate the likely need to maintain critical trough concentrations by choice of appropriate intervals between doses.

Brain injury patterns in fatally injured pedestrians

To study the relationship between the severity of impact to the head and the severity and distribution of injury to the brain in fatally injured pedestrians, events in vehicle-pedestrian collisions were reconstructed to determine the peak linear and angular acceleration sustained by the pedestrians' heads. The nature and distribution of injuries to the brain were determined by neuropathologic examination of coronal sections of the brain. Study of 13 cases with occipital impacts and 18 with lateral impacts showed that the brain appeared to be more susceptible to injury from lateral impacts. The frontal and temporal regions appeared to be more susceptible to injury at low accelerations in occipital impacts, providing an explanation for "coup" and "contrecoup" injuries. For occipital impacts, a positive relationship was found between linear acceleration and the extent of injury to the brain, suggesting that there was a threshold for observable and concussive brain injury at about 1500 m/s2 peak linear acceleration. These findings are important for the development of measures for preventing brain injuries.

Bactericidal effect of gentamicin peak concentration provides a rationale for administration of bolus doses

A study was made of the influence of peak gentamicin concentration (Cmax) independent of the area under the antibiotic concentration-time curve (AUC) on the bactericidal effect of gentamicin against Escherichia coli NCTC 10418. Bacteria in the lag phase were exposed to in-vitro gentamicin concentration-time profiles which modelled complete profiles determined in vivo in patients after an intravenous bolus (1 min) or infusion (30 min) regimen. An additional in-vitro profile reflected antibiotic removal 30 min after bolus dosing. Bacterial viable cell counts and gentamicin concentrations were measured before and during antibiotic exposure. Both Cmax and AUC were shown to be factors determining antibacterial activity; however Cmax independently represented some 35% of total exposure effect. These findings indicate grounds for preferring bolus intravenous gentamicin dosing with appropriate attention to potential toxicity.

Kill kinetics and regrowth patterns of Escherichia coli exposed to gentamicin concentration-time profiles simulating in vivo bolus and infusion dosing

The relative influence of peak concentration (Cmax) versus the area under the antibiotic concentration-time curve (AUC) on the bactericidal effect of gentamicin against Escherichia coli NCTC 10418 was studied. Bacteria in the lag phase were exposed to an in vitro gentamicin concentration series which mirrored the concentrations determined in patients after 80-mg intravenous bolus (1 min) and 80-mg intravenous infusion (30 min) doses. Bacterial viable cell counts and gentamicin concentrations were measured before and during antibiotic exposure. Both the Cmax and AUC were shown to be factors determining antibacterial activity; however, the Cmax was an independent determinant of effect. These findings indicate that bolus intravenous dosing with gentamicin could maximize bactericidal activity. Increased efficacy could result at any given daily antibiotic dose if delivered via bolus with long intervals (12 to 24 h) between doses if appropriate precautions to avoid toxicity are taken.

Prospective audit of an aminoglycoside consultative service in a general hospital

OBJECTIVE

To investigate the impact of the introduction of a consultative service on the use, efficiency of dosing and clinical toxicology of the aminoglycoside antibiotics, gentamicin and tobramycin, in a general hospital.

METHODS

Two audits were conducted six months and 18 months after the introduction of the consultative service. The audits reviewed the use of drug assay services, the adequacy of drug administration (as measured by serum antibiotic concentrations), indications for prescription, adverse outcomes (by noting markers of nephrotoxicity) and the antibiotic sensitivity of Gram-negative pathogens. The results were compared with the results of an audit conducted before the consultative service was instituted.

RESULTS

There was a significant (P < 0.001 by chi 2 test) increase in the use of assays, with drug assays performed in 67% (first audit) and 77% (second audit) of aminoglycoside courses compared with 48.2% in the pre-intervention audit. Sample timing was greatly improved, with more than 70% of the samples collected at the appropriate times. Assay wastage in terms of uninterpretable assay results decreased significantly (P < 0.001) from 42.9% of total assays to 6.3% at the first audit and 3.8% at the second audit. The percentage of assay results in the desirable range increased significantly (P < 0.001) from 39.1% to 71.9% (first audit) and 75.4% (second audit). Pharmacokinetic recommendations were made in 39.1% and 64% of all aminoglycoside courses during the first and second audits respectively, with clinician acceptance of dosage recommendations at 83.1% and 82.8% respectively. For aminoglycoside courses prescribed for therapeutic reasons, 97.9% (first audit, n = 325) and 98.6% (second audit, n = 280) of indications for use were judged as clinically appropriate. The incidence of suspected aminoglycoside-induced nephrotoxicity was reduced from 8.9% of patients to 1.6% (first audit, P < 0.001) and 2.4% (second audit). Bacterial sensitivity audits showed that the great majority of clinical isolates of target organisms (n = 3523, Year 1 and n = 3385, Year 2) were sensitive to gentamicin (92.2% and 91.5% respectively) and tobramycin (98.1% and 98.8% respectively); these aminoglycosides exceeded all alternative agents in effectiveness, including first and third generation cephalosporins.

CONCLUSIONS

The overall results indicate that introduction of the consultative service had a positive impact on the effective use of aminoglycosides, with a marked decrease in clinical toxicity. These influences were shown to persist for at least 18 months. The availability of reliable predictive techniques to reduce toxicity allows active promotion of aminoglycosides as the agents of choice on grounds of efficacy and economy.

Human factors in rural road crashes

An in-depth study of 79 vehicle crashes on rural roads in an area of about 100 km radius around Adelaide examined sociodemographic and psychophysiological characteristics of the drivers and riders involved. In many respects this sample of crashes was similar to a much larger number of police-reported crashes in the same area but included: relatively more crashes with severe or fatal injuries; more crashes on divided roads, on sealed roads and on curves; and more crashes involving trucks. Alcohol and lack of seat belt use were shown to be major problems in these rural crashes. The drivers and riders most strongly associated with these particular problems were males, in blue collar occupations and with limited education; they tended to be aged 30 years or more in the case of alcohol abuse, and were likely to be under 30 years in the case of restraint misuse. The attitudes of these drivers and riders, and other characteristics likely to have contributed to their involvement in a crash, are discussed. There is a need to develop specific and effective countermeasures to reduce drink-driving and increase seat belt wearing in rural areas.

Pharmacoeconomic consequences of measurement and modification of hospital drug use

Patterns of drug usage affect hospital-based delivery of healthcare in a variety of ways. Adverse reactions to drugs (ADR) precipitate some 5% of admissions and prejudice the care of some 20% of patients who are in hospital, while inadequate drug therapy prejudices outcomes and prolongs hospital stay. Conversely, appropriate application of drugs can promote recovery and increase the quality of care. Well documented examples include prevention of deep vein thrombosis and postoperative wound infections. Accordingly, optimisation of drug use represents a major quality assurance issue in addition to determining cost-efficiency of healthcare delivery. Drug utilisation review (DUR) requires all elements of the quality assurance process. In practice, therapeutically meaningful and cost-efficient exercises can only be mounted if there is knowledge of the linkage between patterns of drug use and clinical outcomes. These processes of measurement are currently rate-limiting in quality assurance. There are various ways that hospital drug usage can be measured. These range from readily available and relatively cheap quantitative methods to methods requiring the availability of expert staff. There is a sequence of methods involving increasing costs and increasing resource demands yielding increasing detail of information obtained. This sequence commences with pharmacy purchases, followed by pharmacy issues to particular clinical areas, prescription or treatment sheet survey, clinical record review, and finally the reports of trained investigators working in the clinical area. The simpler methods can provide useful information and an efficient basis for choosing and planning definitive studies. Once a category of drug use is appropriately targeted for intervention, drug use can be modified by planned intervention with improvement in clinical outcomes and reduced economic costs in many instances. The intervention strategies to modify drug usage may be classed as re-educative, persuasive, facilitative and power strategies. Other models for implementing behavioural change have been considered, including the impact of trained investigators and the use of online computer prescribing with interactive software with appropriate guidelines. The challenge is to achieve sustained change when interventions are implemented. Cost-efficient quality assurance of drug use is possible with modest resources if outcome-orientated activities are prioritised.

Head injuries in infants and children: measures to reduce mortality and morbidity in road accidents

In the 6-year period from 1983 to 1988, 12 infants (less than 24 months of age) and 103 children (2 to 14 years of age) were killed in road crashes in South Australia. This represents an annual incidence of 6.4 deaths per 100,000 children at risk. At least 4 other children were killed in off-road vehicle-related accidents. Of these deaths, approximately half were car passengers, one third pedestrians, and one sixth pedal cyclists. Most of these infants and children died at the accident site or soon after, but 26 of them survived long enough to be admitted to hospitals with neurosurgical units and an audit of these patients suggests that there were at least 3 preventable deaths. However, autopsies of 78 patients show that the great majority of these deaths resulted from devastating brain and/or trunk visceral injuries. Better emergency care and the use of neurosurgical retrieval teams may save some lives. But more lives might be saved by the use of appropriate restraints for infants and children in cars, by reducing the exposure of child pedestrians and cyclists to road traffic, and by mandatory use of helmets by child cyclists. Off-road vehicular accidents are not as a rule included in road crash statistics; the practice of giving small motorcycles to young children has created a new category of vehicular accidents sometimes causing severe head injury.

Pharmacokinetic interaction between verapamil and metoprolol in the dog. Stereochemical aspects

The effect of verapamil co-administration on the hepatic first-pass clearance of metoprolol was investigated in dogs. Plasma concentration-time course of metoprolol enantiomers and urinary recovery of oxidative metabolites were determined after a single iv (0.51 mg/kg) and an oral (1.37 mg/kg) dose of deuterium-labeled pseudoracemic metoprolol, with or without concomitant administration of racemic verapamil (3 mg/kg). Verapamil inhibited both the systemic and oral clearance of metoprolol by about 50-70%. The first-pass effect of metoprolol was completely abolished after co-administration of verapamil, reflecting a marked alteration in the degree of hepatic extraction of metoprolol from intermediate to low. The hepatic clearance of metoprolol was slightly (S)-enantioselective (R/S ratio = 0.89 +/- 0.04) in control dogs. Inhibition of hepatic clearance of metoprolol by verapamil was selective towards (S)-metoprolol, such that the enantioselectivity in hepatic clearance toward (S)-metoprolol disappeared following verapamil co-administration (R/S ratio = 1.01 +/- 0.05). Urinary metabolite profiles indicated that O-demethylation and N-dealkylation were the major pathways of oxidative metabolism in the dog. alpha-Hydroxymetoprolol was a minor metabolite in urine. N-Dealkylation showed a strong preference for (S)-metoprolol, whereas O-demethylation and alpha-hydroxylation exhibited a modest selectivity toward (R)-metoprolol; hence, the slight (S)-enantioselectivity in the overall hepatic clearance. Comparison of metoprolol metabolite formation clearances in the absence or presence of verapamil co-administration showed that all three oxidative pathways were inhibited by 60-80%. The greater inhibition of hepatic clearance observed with (S)-metoprolol as compared to (R)-metoprolol was attributed to a significant (S)-enantioselective inhibition in the O-demethylation of metoprolol by verapamil.

Dosage adjustment and clinical outcomes of long-term use of high-dose tobramycin in adult cystic fibrosis patients

A two-phase study was undertaken designed to investigate the impact of computer-aided drug monitoring on tobramycin concentrations and clinical outcomes in adult patients with cystic fibrosis. In phase one, a baseline (historical control) study of drug use patterns was performed. During the second phase, patients admitted for intravenous treatment with tobramycin for acute exacerbations of pseudomonal pulmonary infections were randomly allocated to one of two schedules. Group A patients had tobramycin dosage regimens decided by clinicians based on pre-existing protocols using serum tobramycin assay data determined three times weekly. Group B patients had dosage regimens determined by a computerized pharmacokinetic predictive program using both population-based pharmacokinetic parameter estimation and fitting of serum concentration-time data using Bayesian regression. The agreed therapeutic target was a peak serum tobramycin concentration of 8-10 mg/L and a trough concentration of 1-2 mg/L. There was a major difference between the two groups comparing the number of paired trough and peak concentrations within the target concentration ranges (group A-14%; group B-34.7%, chi 2 test, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

A new method of breath testing the general driving population

The efficacy of drinking-driving countermeasures can be assessed in several ways, including reported changes in attitudes and behavioral intent as well as changes in crash rates. However, few studies have examined the changes in actual drinking-driving behavior. A method of surveying the blood alcohol concentrations (BACs) of drivers, without either police intervention or disruption to traffic flow, was developed in South Australia. This method, which has been used successfully to test approximately 50,000 drivers, is described in detail.