Why should optometry become involved in the hospital setting?

Our nation's hospitals are no longer the private domain of the medical physician. Other "independent" health care providers are justified in applying for clinical privileges. The expanding scope of practice has served to make optometrists more aware of their rights to practice in the hospital environment. Recent changes in the guidelines of the Joint Commission for Accreditation in Health Care Organizations (JCAHO) has further reinforced the concept that no independent health care providers should be denied clinical privileges based solely on the fact that an applicant is not an "MD."

Gas chromatographic-mass spectroscopic characterisation of the psychotomimetic indolealkylamines and their in vivo metabolites.

The use of liquid chromatography with on-line fluorescence detection has formed the basis for the separation, characterisation and quantitation of a number of metabolites of the psychotomimetic indolealkylamines N,N-dimethyltryptamine and 5-methoxy-N,N-dimethyltryptamine formed both in vitro and in vivo. Verification of the identity of metabolites has previously been facilitated by the combined use of a number of analytical techniques including multidimensional liquid chromatography and stop-flow spectroscopic analysis. We now describe the combination of liquid chromatography with gas chromatography-mass spectrometry for the unequivocal verification of a number of structurally characteristic metabolites of the psychotomimetic indolealkylamines.

Study of metabolism of psychotomimetic indolealkylamines by rat tissue extracts using liquid chromatography.

The use of a series of liquid chromatographic techniques involving cation-exchange, reverse-phase and normal-phase chromatography has permitted the separation and characterisation of a number of metabolites of the psychotomimetic indolealkylamines N,N-dimethyltryptamine and 5-methoxy-N,N-dimethyltryptamine which were isolated following incubation of these compounds with rat tissue extracts. In liver, kidney and brain tissue extracts the routes of metabolism identified included oxidative deamination, N-demethylation, O-demethylation and N-oxidation. The quantitative significance of individual routes of metabolism in these tissues was assessed using N,N-dimethyltryptamine as a substrate.

In vivo metabolism of 5-methoxy-N,N-dimethyltryptamine and N,N-dimethyltryptamine in the rat.

Following intraperitoneal administration, 5-methoxy-N,N-dimethyltryptamine and N,N-dimethyltryptamine are subject to both a very rapid uptake into, and clearance from, all tissues examined. The current studies in vivo confirm previous in vitro observations that the routes involved in the metabolism of these compounds include oxidative deamination, N-demethylation, O-demethylation, and N-oxidation. The analysis of metabolic profiles in various tissues led to the identification of the N-oxides as major metabolites. The successful inhibition and redirection of metabolism away from the indole acids towards the parent compounds and their structurally unique metabolites were demonstrated in animals pretreated with iproniazid.

Evaluation of infusion regimens for thiopentone as a primary anaesthetic agent.

Several multi-stage infusion regimens and a computer controlled exponentially decreasing infusion regimen were evaluated in twelve patients undergoing head and neck surgery or neurosurgery. Thiopentone dosage was based on the mean of pharmacokinetic parameter values from the literature and adjusted for each patient's lean body mass in order to rapidly achieve a predetermined plasma thiopentone concentration of 15 or 20 micrograms/ml in the period following the initial bolus dose to induce anaesthesia. Anaesthesia was satisfactory in all cases. Plasma thiopentone concentrations were maintained between 10-20 micrograms/ml during infusion in the five patients who received either a four or five stage infusion and in the six patients who received the exponential infusion, but not in the single patient who received a two-stage infusion. The mean recovery time was 111 min. The plasma concentrations of total and unbound thiopentone at awakening showed little intersubject variability, despite considerable differences in total dose and duration of infusion, suggesting the absence of acute tolerance to the drug. Plasma clearance of total thiopentone correlated strongly with calculated lean body mass and to a lesser extent with total body weight suggesting that lean body mass, in particular, should be an accurate predictor of thiopentone maintenance dose requirements. This study shows that it is feasible to use thiopentone as a primary anaesthetic agent during surgery by administering the drug either as an exponentially decreasing infusion or as an infusion comprising 4 or 5 stepwise decreasing rates.

Aortocaval compression and plasma concentrations of thiopentone at caesarean section.

The venous plasma concentration-time profiles of thiopentone were measured simultaneously over the first 30-40 min after induction of anaesthesia, in blood obtained from an arm vein and a vein in the foot, in nine healthy full-term women undergoing Caesarean section. Patients were tilted laterally to the left by from 8 to 18 degrees during the procedure. In all but two of the patients, the profiles from the arm and foot were virtually identical, suggesting that aortocaval compression was absent or insignificant. Therefore, the large intersubject variability in volume of distribution of thiopentone at Caesarean section is unlikely to be the result of aortocaval compression.

The ion-pair extraction, purification, and liquid chromatographic analysis of indolealkylamines in human urine.

A highly efficient ion-pair extraction technique for the isolation of tryptamine, 5-hydroxytryptamine, and their mono- and N,N-dimethylated derivatives from aqueous media is described. The technique has been used to isolate nanogram quantities of both N, N-dimethyltryptamine and 5-hydroxy-N, N-dimethyltryptamine from large volumes of urine. A rapid and efficient normal-phase liquid chromatographic procedure has also been developed for the subsequent purification of indolealkylamines isolated from urine. The methods described have been used in the measurement of the urinary excretion of 5-hydroxy-N, N-dimethyltryptamine. Analyses were performed by liquid chromatography using a cation-exchange column with online fluorescence detection. Further characterization was achieved by stop-flow spectroscopic analysis of the LC eluant.

Urinary excretion of placentally transferred thiopentone by the human neonate.

The urinary excretion of thiopentone and its metabolite, pentobarbitone, was studied in 7 neonates whose mothers-had received thiopentone. During the urine collection period (range 39.3-63.8 h), a mean of 26.4 micrograms thiopentone was recovered, representing only a mean of 0.0066% of the maternal dose. This suggests that the elimination of thiopentone by the neonate occurs mainly by metabolism. The metabolite pentobarbitone could not be detected. Mean elimination half-life of thiopentone, calculated from sigma-minus plots, was 8.04 h which is similar to the value reported previously in adults. This contrasts with other barbiturates which show much longer half-lives in neonates than in adults.

High-performance liquid chromatographic determination of clomiphene using post-column on-line photolysis and fluorescence detection.

A method has been developed for the extraction and quantitation of the ovulatory stimulant drug clomiphene from plasma. The cis- and trans-isomers were separated by normal-phase chromatography using chloroform-methanol as the mobile phase. After eluting from the column, the clomiphene was passed through a PTFE photolysis coil irradiated by a powerful UV lamp, resulting in conversion of the isomers to highly fluorescent species. The derivatised material was then detected using a fluorescence spectrometer. Use of this method enables a substantial improvement of sensitivity over UV detection and has permitted the measurement of plasma clomiphene levels in patients receiving clomiphene therapy.

Pharmacokinetics and plasma binding of thiopental. II: Studies at cesarean section.

This study was undertaken to investigate the effect of pregnancy on the disposition of thiopental and to determine the major factors which influence the placental transfer of the drug to the fetus. Maternal venous (MV) and umbilical venous (UV) and arterial (UA) blood samples were collected at delivery from 11 pregnant women at term who received thiopental for induction of anesthesia for elective cesarian section. A detailed study of the pharmacokinetics of thiopental was carried out in 7 of these subjects and blood samples were collected for 80 to 100 hours following thiopental administration. A transient rise in thiopental plasma concentration was observed at delivery. Mean values of pharmacokinetic parameters (plus or minus SD) were: initial distribution volume (V1) 17.31 (plus or minus 8.5), apparent volume of distribution (Vdbeta) 564 1 (plus or minus 343), volume of distribution at steady state (Vss) 2881 (plus or minus 180), systemic plasma clearance (Clp) 0.286 l/min (plus or minus 0.156), rate of change of volume of distribution at zero time (RVd0) 1.03 l/min (plus or minus 0.36) and elimination half-life (t1/2) 26.1 h (plus or minus 12.6). Comparison of these data with our previously reported data in nonpregnant surgical patients shows that Vdbeta, Vss, T1/2 are significantly greater at cesarian section (P less than 0.05) and that systemic plasma clearance shows a similar trend. UA and UV values at delivery were similar within individuals. There was no correlation between the ratio UV/MV at delivery and the dosing-delivery interval (delta t), or between UV and the administered dose or delta t. There were good correlations between UV (corrected for dose) and the reciprocals of V1, Vdbeta, Vss, and plasma clearance of thiopental. This demonstrates that differences in maternal distribution and elimination characteristics of thiopental may be more important determinants of intersubject differences in fetal drug exposure than differences in dose or delta t.

Pharmacokinetics and plasma binding of thiopental. I: Studies in surgical patients.

The pharmacokinetics and plasma protein binding of thiopental were investigated in 5 female patients who received a bolus intravenous dose of the drug for induction of anesthesia for gynecologic surgery. Blood samples were collected for 3 to 4 days after the dose. Plasma protein binding determinations were also carried out by ultrafiltration and equilibrium dialysis on samples from a panel of healthy volunteers. Plasma concentrations of thiopental were determined by reverse-phase, high-performance liquid chromatography. The coefficient of variation of the method was 2.8 per cent (n equals 10). In healthy volunteers, the plasma protein binding of thiopental was concentration dependent. Percentage bound ranged from 96.7 (n equals 4, SD equals 0.8) at 150 micrograms/ml. Therefore, saturation of binding sites on rapid administration of the drug may occur, exposing vital organs to unexpectedly high concentrations of free drug. Values of the fraction of thiopental bound in plasma obtained from the surgical patients during the hour following drug administration were similar to values obtained in healthy volunteers at comparable concentrations. Mean pharmacokinetic parameters obtained for thiopental in the surgical patients were as follows: initial distribution volume 13.81 (SD equals 9.4), apparent volume of distribution 233 1 (SD equals 98), volume of distribution at steady state 97.51 (SD equals 40), elimination half-life 11.5 h (SD equals 1.0) and systemic plasma clearance 0.150 l/min (SD equals 0.063). None of these parameters correlated with body weight. Values reported by other workers vary from ours and this variation may be explained by the much shorter duration of blood collection used in those studies.

High performance liquid chromatographic determination of phenothiazine residues in sheep tissues.

A high performance liquid chromatographic (HPLC) technique is described for the determination of residue levels of the anthelmintic drug phenothiazine in sheep tissues. Phenothiazine was administered to sheep which were slaughtered after withholding periods of 24, 48, and 72 h. Residues of phenothiazine were then extracted from tissue samples by homogenization in methanol. The HPLC analysis of the extracts involved separation on a 10 micrometer silica column using a mobile phase of 0.3% n-propanol in cyclohexane. The lower limit of detection by ultraviolet absorption at 254 nm was 0.05 ppm.