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Biomedical subjects

M Rowland

Publications and source records attributed to M Rowland.

At least 145 records · Page 8Linked to original sources
PubMed1990

Flight activity of insecticide resistant and susceptible Anopheles stephensi mosquitoes in actograph chambers lined with malathion, gamma HCH or dieldrin.

The activity and resting behaviour of resistant and susceptible Anopheles stephensi Liston were recorded in acoustic actograph chambers lined with residual deposits of malathion, dieldrin or gamma HCH. In gamma HCH-treated flight chambers, SS and RS mosquitoes became active only after picking up lethal doses of insecticide, which explains why few SS and RS mosquitoes survive release into gamma HCH-treated experimental huts. Similar results were obtained in flight chambers treated with dieldrin; however, more mosquitoes would be expected to survive dieldrin under field conditions because resistance to this insecticide is greater than to gamma HCH. Mosquitoes in contact with malathion showed a three-phase activity pattern: an initial active phase, an inactive phase, and hyper-activity/convulsions. Initial activity or irritability was especially pronounced in SS and RS but absent in RR mosquitoes. Whether or not irritability would protect RS mosquitoes from malathion would probably depend on the ratio of sprayed to unsprayed surfaces in treated huts.

Animals↗
PubMed1990

Clinical pharmacokinetics of teicoplanin.

Teicoplanin is a recently introduced glycopeptide antibiotic for the treatment of a variety of aerobic and anaerobic Gram-positive infections. It is a mixture of 5 closely related components, of similar polarity and biological activity, and 1 or more polar hydrolysis products. Teicoplanin is rapidly and extensively absorbed from muscle and the peritoneal cavity but very poorly absorbed from the gastrointestinal tract. Following intravenous administration, the disposition kinetics are best described by a tri-exponential equation, and the majority of drug is excreted unchanged, by glomerular filtration. In patients with normal renal function, the half-lives of the first, second and terminal phases are 35 minutes, 10 hours and 87 hours, respectively. The initial volume of distribution is 0.089 L/kg, the volume of distribution at steady-state is 0.86 L/kg, clearance is 0.0114 L/h/kg and renal clearance is 0.0083 L/h/kg. Teicoplanin is highly bound in plasma to albumin (fraction unbound = 0.1) and in tissues. The pharmacokinetics are linear over a wide dose range (2 to 26 mg/kg). The minor differences in the pharmacokinetics of the components of teicoplanin can be accounted for by differences in lipophilicity. The events following multiple dosing are predicted from single dose data; renal clearance decreases in patients with renal insufficiency in a predictable manner. Negligible drug is lost during haemodialysis. As expected, clearance per kilogram is higher in children than in adults, and lower in the elderly, associated with a decrease in glomerular filtration rate with advancing years. Tissue distribution data are limited. Concentrations, relative to those in plasma, are high in lung and bone tissue and low in fat. Animal data show high concentrations in most tissues, and particularly high in liver and kidneys. Teicoplanin penetrates slowly and poorly into cerebrospinal fluid, but relatively rapidly and effectively in synovial and pleural fluids and in soft tissue. The manufacturer's recommended intravenous or intramuscular dosage regimens rapidly achieve and maintain adequate plasma concentrations of teicoplanin; the dosing interval is usually 1 day. The maintenance dosing rate, but not the loading dose (if needed), must be reduced in patients with poor renal function and in the elderly. For those patients on continuous ambulatory peritoneal dialysis, the peritoneal cavity offers a convenient alternative route of drug administration.

Absorption↗
PubMed1989

Binding of sulfonamides to carbonic anhydrase: influence on distribution within blood and on pharmacokinetics.

Four new aromatic sulfonamides were synthesized and purified by standard techniques. Two were unsubstituted, primary sulfonamides and two possessed substituents on the sulfonamide nitrogen. The affinity of the inhibitors for the enzyme carbonic anhydrase was determined in terms of the inhibitory potency, which was found to be dependent on the presence of an unsubstituted sulfonamide group. Binding studies were performed in erythrocyte suspensions using a range of concentrations and the unbound, extracellular concentrations were determined by high-performance liquid chromatographic (HPLC) assay. The dissociation constant of binding and the total binding capacity of the erythrocytes were estimated by nonlinear regression using a two-site binding model. The affinity of the compounds for erythrocytes reflected their inhibitory potency against the enzyme. Binding to plasma proteins was more dependent on lipophilicity and pKa and was stronger for the substituted sulfonamides. Pharmacokinetic studies in rats showed that the unsubstituted sulfonamides with a high affinity for carbonic anhydrase in erythrocytes have longer half-lives and lower clearance values than the substituted sulfonamides which were more strongly bound to plasma proteins. However, comparison of unbound clearance values showed that the variations in molecular structure, which produced differences in carbonic anhydrase binding and in distribution, also produced variations in susceptibility to elimination processes.

Animals↗
PubMed1989

Route of administration and sex differences in the pharmacokinetics of aspirin, administered as its lysine salt.

One thousand milligrams of aspirin, as its lysine salt was administered intravenously, orally, and intramuscularly to nine male and nine female young healthy adult volunteers. After intravenous injection mean (+/- SD) values of clearance, steady-state volume of distribution, and terminal half-life were 12.2 +/- 2.2 ml/min/kg, 0.219 +/- 0.042 liter/kg, and 15.4 +/- 2.5 min, respectively, with no differences between males and females. Following administration aspirin was absorbed more quickly in females than in males (mean absorption times of 16.4 and 21.3 min, respectively although the bioavailability, 54%, was the same in both groups. In contrast, following intramuscular administration, aspirin was absorbed more slowly in females than males (mean absorption time of 97 and 53 min, respectively) but again the bioavailability, 89%, was the same in both groups. The data suggest that in the female the intramuscular injection is going into fat. Salicylic acid concentration-time profiles showed a less pronounced sex difference and were comparable among the routes of administration.

Absorption↗
PubMed1989

Pharmacokinetics of cyclosporin: influence of rate-duration profile of an intravenous infusion in renal transplant patients.

1. The pharmacokinetics of cyclosporin were studied in six renal transplant patients, following intravenous administration of 5 mg kg-1 infused over 3, 6 and 24 h. 2. Plasma, separated at 37 degrees C, was analysed for cyclosporin by h.p.l.c. 3. The data were described by a biexponential disposition model. 4. None of the disposition parameters (clearance, initial volume of distribution, half-lives) changed with the duration of infusion.

Adult↗
PubMed1989

Cimetidine-nicoumalone interaction in man: stereochemical considerations.

1. The cimetidine-nicoumalone interaction was studied in five subjects who received a single 10 mg oral dose of racemic nicoumalone alone and 3 days into an oral regimen of cimetidine of 200 mg three times daily and 400 mg at night. 2. The concentrations of R(+)- and S(-)-nicoumalone in plasma were measured using a stereospecific h.p.l.c assay; augmentation of prothrombin time was used as a measure of response. 3. Cimetidine increased the rate (but not extent) of absorption of both R(+)- and S(-)-nicoumalone, and reduced the clearance of R(+)-nicoumalone but not that of the S(-)-enantiomer. 4. Cimetidine increased the anticoagulant response produced by nicoumalone in some but not all subjects, despite a consistent effect on the pharmacokinetics of the oral anti-coagulant. 5. Cimetidine appears to produce its effect by stereoselectively inhibiting the elimination of R(+)-nicoumalone.

Acenocoumarol↗
PubMed1989

Cyclosporin-erythromycin interaction in renal transplant patients.

1. The interaction between cyclosporin (CyA) and erythromycin was studied in renal transplant patients following oral and intravenous administration of CyA. 2. Blood and plasma CyA concentrations and blood concentrations of metabolite 17 were measured by h.p.l.c. 3. Erythromycin produced almost a two-fold increase in bioavailability, from 36% to 60%; with a small (13%) decrease in clearance of CyA. 4. The metabolite 17 data further support the postulate that erythromycin increases the absorption of CyA rather than inhibits its metabolism, as generally believed.

Administration, Oral↗
PubMed1989

Rate and extent of absorption of clonidine from a transdermal therapeutic system.

The in-vivo performance of a clonidine transdermal therapeutic system (TTS 3.5 cm2, 2.5 mg) was assessed in 12 healthy normal volunteers. Particular attention was paid to the rate and extent of absorption of clonidine from the TTS dosage form by reference to a 2 h i.v. infusion of clonidine. The absolute bioavailability of clonidine from the TTS dosage form was found to be approximately 60% with clonidine being released from the TTS at a relatively reproducible and consistent rate of 4.32 micrograms h-1 over a 7-day period.

Absorption↗
PubMed1988

Relationship between lipophilicity and tubular reabsorption for a series of 5-alkyl-5-ethylbarbituric acids in the isolated perfused rat kidney preparation.

The renal clearances of a homologous series of six 5-substituted barbituric acids, of varying lipophilicity, were examined using a recirculating isolated perfused rat kidney preparation. Renal clearance was found to decrease with increasing lipophilicity. The renal clearance of the individual compounds was shown to be dependent on urine flow, with the dependence increasing with increasing lipophilicity. A simple physiologically based model of tubular reabsorption, evoking nonequilibrium permeability considerations, is used to explain this influence of urine flow on renal clearance. The relationship between clearance and tubular permeability was examined with the purpose of integrating lipophilicity into the model.

Animals↗
PubMed1988

Cyclosporin: pharmacokinetics and detailed studies of plasma and erythrocyte binding during intravenous and oral administration.

On the basis that unbound concentration better correlates with response than total plasma or blood concentration, the inter- and intra-subject variability in the distribution of cyclosporin within blood and to plasma components was studied in renal transplant patients. Pharmacokinetic aspects were also studied. Blood samples were analysed from patients who received the drug both by a 72-h i.v. infusion and orally (7 mg.kg-1 twice daily). Steady-state was reached within 18 h of starting the i.v. infusion; the plasma data were best fitted by a biexponential equation with half-times of 0.13-1.02 h and 4.3-13.9 h, associated with the two phases. The mean plasma clearance was 700 ml/min. Concentrations during the infusions measured by RIA and HPLC were comparable. Oral profiles showed rapid and extensive absorption. The peak plasma concentrations were 1460-1880 micrograms.l-1 and occurred 2-4 h after dosing, with bioavailability estimates of 41-113%. Concentrations measured by RIA were higher than by HPLC. Blood-to-plasma concentration ratio measurements of cyclosporin at 37 degrees C decreased with increasing plasma concentration and increased with haematocrit. Fraction unbound, measured by ultra-centrifugation, was in the range 0.042-0.122 with an average of 0.068, and varied little in some patients but showed systematic changes with time in others. Cyclosporin binding was found to be related not only to the triglyceride but, more particularly, to the cholesterol-related lipoproteins in plasma. Monitoring cholesterol may be helpful in identifying patients with extremes in binding or with widely varying binding.

Administration, Oral↗
PubMed1988

Models of hepatic elimination: comparison of stochastic models to describe residence time distributions and to predict the influence of drug distribution, enzyme heterogeneity, and systemic recycling on hepatic elimination.

The residence time distribution of noneliminated solutes in the liver can be represented by a variety of stochastic models. The dispersion model (closed and mixed boundary conditions), gamma distribution, log normal distribution and normal distribution models were used to describe output concentration-time profiles after bolus injections into the liver of labeled erythrocytes and albumin. The dispersion model and log normal distribution model provide the best representation of the data and give similar estimates of relative dispersion and availability for varying hepatocellular enzyme activity. The availability of solutes eliminated from the liver by first-order kinetics is determined by the residence time distribution of the solute in the liver and not on events occurring in the liver when a uniform enzyme distribution is assumed. Both enzyme heterogeneity (axial or transverse) and hepatocyte permeability may affect solute availability. A more complex model accounting for enzyme distribution and the micromixing of solute within the liver is required for solutes undergoing saturable kinetics.

Biological Transport↗
PubMed1988

Bioavailability assessment and pharmacologic response: impact of first-pass loss when both drug and metabolites are active.

Many drugs with low oral bioavailability due to substantial first-pass hepatic loss form pharmacologically active metabolites. In such cases, the pharmacologic activity after oral administration is greater than anticipated from bioavailability data, based on chemical assay of drug alone. This paper explores the use and meaning of pharmacologic data to assess bioavailability under these circumstances. Two steady-state concepts are introduced: a metabolite-to-drug intravenous delivery rate potency ratio and an effective bioavailability, defined as the ratio of intravenous-to-oral delivery rates of drug required to produce the same response. Using a combined pharmacokinetic-pharmacodynamic model, the impact of various factors on the effective bioavailability and on its estimation, using the intravenous-to-oral dose ratio required to produce the same area under the response time curve after acute administration, are explored. It is proposed that attention be centered more on comparison of rates of administration, or doses, that produce equal responses than on bioavailability per se.

Biological Availability↗
PubMed1988

Changes in the spontaneous flight activity of the mosquito Anopheles stephensi by parasitization with the rodent malaria Plasmodium yoelii.

An acoustic actograph was used to monitor for 17 days after infection the spontaneous flight activity of the mosquito Anopheles stephensi parasitized with the rodent malaria Plasmodium yoelii. Activity fell to approximately two-thirds of control levels at about day 10 post-infection--when oocysts were reaching maximum size and starting to rupture (mean number of oocysts = 92)--and thereafter remained at this reduced level. The circadian activity pattern was not affected by the parasitism.

Animals↗
PubMed1988

Saturable binding of cyclosporin A to erythrocytes: estimation of binding parameters in renal transplant patients and implications for bioavailability assessment.

Cyclosporin (CyA) exhibits saturable binding to erythrocytes. A one-site binding model was fitted to data from renal transplant patients receiving CyA therapy. The average maximum binding capacity is 2560 micrograms CyA/liter of packed erythrocytes; the unbound CyA concentration associated with 50% saturation of the binding site is 67 micrograms/liter. Analysis indicates that whole-blood CyA measurement to monitor drug therapy should be viewed cautiously, particularly when the hematocrit varies considerably. The error in estimating absolute bioavailability at steady state from whole-blood measurements, resulting as a consequence of the saturable binding, has been explored. Although extrapolation to the therapeutic situation, which involves transient drug administration, is difficult, errors of up to 25% are anticipated. When an accurate estimate of bioavailability is required, analysis based on plasma data is proposed. For bioequivalence testing, both blood and plasma CyA data are equally acceptable.

Binding, Competitive↗
PubMed1988

The racemic metoprolol H2-antagonist interaction.

The effects of concomitant administration of cimetidine and ranitidine on the pharmacokinetics and pharmacodynamics of multiple-dose metoprolol were investigated in 12 normal, healthy male volunteers. The pharmacokinetics of metoprolol were assessed in terms of racemic metoprolol and the individual (R)- and (S)-enantiomers with a stereoselective assay. Ranitidine had no effect on the pharmacodynamics or pharmacokinetics of metoprolol. Although not affecting the pharmacodynamics of metoprolol, cimetidine did produce an increase in the bioavailability of metoprolol through inhibition of enzymes responsible for the first-pass elimination of the beta-blocker. The effect was stereoselective, with the major effect being on the less pharmacologically active (R)-enantiomer.

Adult↗
PubMed1988

A study to assess the anticholinergic activity of rolipram in healthy elderly volunteers.

Rolipram is an antidepressant with a novel mechanism of action: enhanced noradrenaline (first messenger) synthesis and release, and inhibition of cAMP (second messenger) breakdown. This study was aimed at objectively assessing potential anticholinergic effects of rolipram in healthy elderly volunteers by measurement of saliva production and pupil size. Eight male volunteers between 67 and 77 years of age first received in a randomized manner either a single dose of 50 mg amitriptyline or a placebo control. After a minimum washout period of seven days, they then received a multiple dosing regimen of a) 0.75 mg and b) 1.5 mg rolipram given every eight hours over a 5-day period with a two day washout between a) and b). Whereas no changes at all in pupil size could be observed, amitripyline significantly reduced salivary flow. Rolipram however had no effect on saliva production after either single or repeated administration of 0.75 or 1.5 mg. The results are discussed in connection with pharmacokinetic parameters obtained in the study.

Aged↗
PubMed1988

Stereospecific assay of nicoumalone: application to pharmacokinetic studies in man.

1. A stereospecific h.p.l.c. assay of nicoumalone in plasma has been developed. 2. The assay was applied to a study in which 20 mg racemic nicoumalone was given orally to three volunteers and blood samples taken for 168 h. 3. The mean pharmacokinetic parameters of the individual enantiomers were: clearance/bioavailability 1.28 1 h-1, R-enantiomer; 17.5 1 h-1, S-enantiomer: volume of distribution/bioavailability 12.5 1, R-enantiomer; 22.6 1, S-enantiomer: terminal half-life 6.8 h, R-enantiomer; 0.91 h, S-enantiomer. 4. The data are consistent with a substantial first-pass hepatic loss of S-nicoumalone.

Acenocoumarol↗