Salbutamol disposition and dynamics in conscious rabbits: Influence of the route of administration and of the dose

This study assessed the influence of dose and route of administration on salbutamol kinetics and hypokaliemic effect. Salbutamol plasma kinetics were studied in a first group of 6 rabbits who received 60, 800, and 60 g/kg by the intravenous (iv), oral (po), and intratracheal (it) routes, respectively, at 1-week intervals. A second group of 6 rabbits received 120, 2400, and 120 g/kg of salbutamol by the same three routes. Multiple blood samples were withdrawn to assay salbutamol and potassium. Following iv salbutamol (60 g/kg), total plasma clearance was 82±5 ml/min per kg, apparent volume of distribution was 5.0±0.5 l/kg, and terminal half- life was 41±2 min. Similar values were estimated when 120 g/kg of salbutamol was administered iv or was given po or it. The bioavailability of po and it salbutamol was approximately 1 and 20%, respectively. For the first group, the maximal decrease in plasma potassium elicited by salbutamol was 0.80±0.19, 0.48±0.22, and 0.78±0.46 mmol/l, and for the second group, maximal decrement was 1.31±0.37, 0.70±0.24, and 0.84±0.17 mmol/l for the iv, po, and it routes, respectively. Compared to salbutamol peak plasma concentrations, maximal decrease in plasma potassium appeared between 60 and 108 min later for the iv route, 90 and 25 min later for po and it routes, and for this reason, the hypokaliemic effect was not associated to salbutamol plasma concentrations. The hypokaliemic effect was dependent upon the route, e.g., po>it>iv. It is concluded that (i) salbutamol plasma kinetics are first-order independently of the route of administration, and (ii) salbutamol hypokaliemic effect is modulated by the dose and the route of administration.List of abbreviations AUC Area under salbutamol plasma concentration-time curve - cl_INT Salbutamol intrinsic clearance - cl_T Salbutamol total plasma clearance - c_MAX Salbutamol maximal plasma concentration - F Fraction of the dose of salbutamol reaching the systemic circulation - iv Intravenous route of administration - it Intratracheal route of administration - po Oral route of administration - V_area Salbutamol apparent volume of distribution - T ₂ ¹ Salbutamol half-life of the terminal phase - t_MAX Time to observe the maximal decrease in plasma potassium - e_MAX Predicted maximal effect of salbutamol - EC₅₀ Concentration of salbutamol eliciting 50% of e_MAX Supported by the Medical Research Council of Canada (MT-10874). Sylvie Perreault is recipient of a Bourse Formation de troisième cycle des Fonds de la Recherche en Santé du Québec.     

The effect of dose on the disposition of lead in rats after intravenous and oral administration

Single doses of lead acetate were administered to 250- to 350-g rats by both iv (0.5–15 mg Pb/kg) and po (1–100 mg Pb/kg) routes, and blood lead concentrations were measured up to 25 days following dosing. The area under the blood lead concentration vs time curve (AUC) after iv dosing increased in proportion to increases in the dose. Total blood lead clearance and renal lead clearance were not related to the magnitude of the injected dose.After oral dosing, blood lead concentrations (and AUC) did not increase proportionately with dose. After a 1 mg/kg po lead dose, the extent of absorption was estimated at 42%; this decreased to 2% when the dose was increased to 100 mg/kg. Lead concentrations in the blood, kidneys, liver, and brain of both adult and suckling rats recovered 24 hr after various single po doses also indicated that the extent of lead absorption decreased substantially with increasing dose. Blood and kidney lead concentrations in adult rats exposed for 14 days to lead via drinking water also were not proportional to the apparent amount of lead ingested. The results are consistent with published in vitro data which suggested that the mechanism for gastrointestinal absorption of lead is largely capacity-limited in adolescent and adult rats. Because blood lead concentrations were not a linear function of the oral dose in the rat, the relationship between oral dose and toxic effects of lead may not be a simple one. This factor should be considered when safe lead exposure levels in man are to be established via extrapolation of data from high levels of exposure.     

The disposition of [14C]metronidazole in rats following vaginal and oral administration

The absorption, tissue distribution and excretion of [¹⁴C]metronidazole (¹⁴C-MTZ) were compared during the first 4 h after administration of 10 mg kg^?1 of ¹⁴C-MTZ either orally or intravaginally (i.v.g.) to rats. Peak ¹⁴C blood concentrations were reached at 1 h in both groups. Blood samples collected at 0·5, 3 and 4 h had a higher ¹⁴C concentration in orally dosed rats (P <0·05) than in i.v.g.-treated animals. About 3% of the i.v.g. applied dose remained in the vagina at 4 h. After 4 h, the plasma, liver, kidney, brain, lung and uterus concentrations of ¹⁴C were similar in both groups, whereas the blood, skeletal muscle and fat ¹⁴C values were significantly greater in the orally dosed rats. The total recoveries of ¹⁴C in the urine and faeces did not differ (ca 38% over 4 h) between the two groups. These results suggest that the kinetics of metronidazole are similar after the administration of equal amounts of this drug by either route.     

Elimination profile of triamcinolone in urine following oral administration

Triamcinolone (T) is a glucocorticoid commonly used to relieve inflammation and treat arthritis, severe allergies, and asthma; however, it is banned by the World Anti‐Doping Agency in competition for athletes when administered orally, intravenously, intramuscularly, or rectally. The minimum required performance limit (MRPL) for urinary T is 30 ng/mL. However, the data about the urinary excretion of T after oral administration is limited. We investigate the elimination profile and determine whether single‐dose administration of T would cause a positive doping result. Twelve healthy volunteers received a single‐dose of 4‐mg T rally, and urine samples were collected for 24 hours. A validated liquid chromatography–tandem mass spectrometry method was used to determine urinary T levels. Non‐compartmental modeling was used to estimate the pharmacokinetic parameters. All the urinary T concentrations were much higher than the MRPL. The peak urinary T concentration was 3211.4 ± 860.3 ng/mL (mean ± SD), time to peak concentration was 1.7 ± 0.9 hours, and the estimated elimination half‐life was 4.4 ± 2.8 hours. About 27.76% of the consumed dose was eliminated via urine within 24 hours of intake. After a single‐dose oral administration, urinary T concentrations still exceeded the MRPL after 24 hours. This information could be useful for limiting the misuse of T. Athletes should be aware when using T in competition and acquire approval for a therapeutic use exemption prior to use. Moreover, the elimination profile of orally administered T may be crucial information for distinguishing different dosage routes.     

The disposition of [14C]metronidazole in rats following vaginal and oral administration.

The absorption, tissue distribution and excretion of [17C]metronidazole (14C-MTZ) were compared during the first 4 h after administration of 10 mg kg-1 of 14C-MTZ either orally or intravaginally (i.v.g.) to rats. Peak 14C blood concentrations were reached at 1 h in both groups. Blood samples collected at 0.5, 3 and 4 h had a higher 14C concentration in orally dosed rats (P less than 0.05) than in i.v.g.-treated animals. About 3% of the i.v.g. applied dose remained in the vagina at 4 h. After 4 h, the plasma, liver, kidney, brain, lung and uterus concentrations of 14C were similar in both groups, whereas the blood, skeletal muscle and fat 14C values were significantly greater in the orally dosed rats. The total recoveries of 14C in the urine and faeces did not differ (ca 38% over 4 h) between the two groups. These results suggest that the kinetics of metronidazole are similar after the administration of equal amounts of this drug by either route.     

Tissue disposition of the insect repellent DEET and the sunscreen oxybenzone following intravenous and topical administration in rats

The insect repellent N,N‐diethyl‐m‐toluamide (DEET) and sunscreen oxybenzone (OBZ) have been shown to produce synergistic permeation enhancement when applied concurrently in vitro and in vivo. The disposition of both compounds following intravenous administration (2 mg/kg of DEET or OBZ) and topical skin application (100 mg/kg of DEET and 40 mg/kg of OBZ) was determined in male Sprague‐Dawley rats. Pharmacokinetic analysis was also conducted using compartmental and non‐compartmental methods. A two‐compartment model was deemed the best fit for intravenous administration. The DEET and oxybenzone permeated across the skin to accumulate in blood, liver and kidney following topical skin application. Combined use of DEET and oxybenzone accelerated the disappearance of both compounds from the application site, increased their distribution in the liver and significantly decreased the apparent elimination half‐lives of both compounds (p < 0.05). Hepatoma cell studies revealed toxicity from exposure to all treatment concentrations, most notably at 72 h. Although DEET and oxybenzone were capable of mutually enhancing their percutaneous permeation and systemic distribution from topical skin application, there was no evidence of increased hepatotoxic deficits from concurrent application. Copyright © 2011 John Wiley & Sons, Ltd.     

A flip-flop model for nitrofurantoin disposition in the rabbit following oral administration

The influence of route of administration on the absorption of nitrofurantoin and the effect of factors influencing the absorption, such as water volume taken with the drug, change of gastric emptying rate, and effect of particle size, were investigated in rabbits. To clarify the absorption behavior of nitrofurantoin, the Martis-Levy method analogous to the Wagner-Nelson method was used to obtain the absorption kinetics of the drug. Moment analysis was also used to estimate the absorption behavior of the drug.The rate constants of absorption following oral administration of the drug were significantly smaller than those of elimination following intravenous administration. The results of moment analysis (based on a linear approximation) showed that the mean residence time following intravenous administration was much less than the mean absorption time of any oral dosage form. These results clearly show that the pharmacokinetic profile of nitrofurantoin following oral administration is of flip-flop type. Although this result was obtained in the rabbit, the implications of a flip-flop situation for the human case are discussed on the basis of the available published data.     

The relationship between motor effects in rats following acute and chronic haloperidol treatment

Tardive dyskinesia (TD) is a serious and sometimes irreversible side-effect to long-term neuroleptic treatment. In order to find predictors for development of TD, it would be of interest to known whether susceptibility to develop acute side-effects increases the risk of TD development. The study investigated in female Sprague-Dawley rats the relationship between haloperidol-induced acute motor effects, assessed by means of the grid test and the open field test, and the chronic motor effect assessed as vacuous chewing movements (VCM). The doses of haloperidol were 1.2, 2.4 and 4.8 mg/kg IP in the acute experiments and haloperidol decanoate 38 mg/kg per 4 weeks IM in the chronic experiment. The VCM obtained at different timepoints during the 24 weeks of chronic treatment were highly correlated. However, no correlation was found between the motor effects in the acute and the chronic experiments. The study does not indicate any connection between susceptibility to acute side-effects on neuroleptics and later development of TD.     

First-pass elimination of salicylamide in man following oral and rectal administration

In order to study the avoidance of hepatic first-pass elimination following rectal administration, 500 mg of salicylamide (SAM) were given orally and rectally to man. Plasma SAM concentrations were measurable following oral administration, but following rectal administration SAM concentrations were either very low or not detectable. The mean excretion of SAM sulphate (SAMS) and SAM glucuronide (SAMG) in the urine following oral and rectal administration was 71·3 per cent and 45·6 per cent respectively. Increasing the oral and rectal dose (1500 mg of SAM, solution) showed that the mean AUC values were 911 and 144 μg min ml^?l, respectively. The mean urinary excretion of SAMS plus SAMG following oral and rectal administration was 82·0 and 75·6 per cent respectively; the mean plasma elimination half-lives were 31 and 40 min, respectively, while the mean urinary elimination half-lives were 63 and 73 min, respectively.     

Metabolism and disposition of [14C]dibromoacetonitrile in rats and mice following oral and intravenous administration

1. Tissue distribution, metabolism, and disposition of oral (0.2–20?mg/kg) and intravenous (0.2?mg/kg) doses of [2-¹⁴C]dibromoacetonitrile (DBAN) were investigated in male rats and mice.

2. [¹⁴C]DBAN reacts rapidly with rat blood in vitro and binds covalently. Prior depletion of glutathione (GSH) markedly diminished loss of DBAN. Chemical reaction with GSH readily yielded glutathionylacetonitrile.

3. About 90% of the radioactivity from orally administered doses of [¹⁴C]DBAN was absorbed. After intravenous administration, 10% and 20% of the radioactivity was recovered in mouse and rat tissues, respectively, at 72?h. After oral dosing, three to four times less radioactivity was recovered, but radioactivity in stomach was mostly covalently bound.

4. Excretion of radioactivity into urine exceeded that in feces; 9–15% was exhaled as labeled carbon dioxide and 1–3% as volatiles in 72?h.

5. The major urinary metabolites were identified by liquid chromatography-mass spectrometry, and included acetonitrile mercaptoacetate (mouse), acetonitrile mercapturate, and cysteinylacetonitrile.

6. The primary mode of DBAN metabolism is via reaction with GSH, and covalent binding may be due to reaction with tissue sulphydryls.

     

Distribution of nimodipine in brain following intranasal administration in rats

AIM: To determine whether nasally applied nimodipine (NM) could improve its systemic bioavailability and be transported directly from the nasal cavity to the brain. METHODS: NM was administered nasally, intravenously (iv), and orally to male Sprague-Dawley rats. At different times post dose, blood, cerebrospinal fluid (CSF), and brain tissue samples were collected, and the concentrations of NM in the samples were analyzed byHPLC. RESULTS: Oral systemic bioavailability of NM in…     

Characteristics of oral movements in rats during and after chronic haloperidol and fluphenazine administration

Rats were chronically administered either haloperidol (HAL) or fluphenazine (FLU) via depot injections for 8 months, given these same drugs in their drinking water for the next 2 months, and then withdrawn from the drugs. Throughout the experiment the animals were tested repeatedly in an enclosed tube using a computerized device which measured computer-scored movelets (CSMs) and, in the latter half of the experiment, were also scored by a human observer in the tube, as well as in an open cage, for observed oral movements (OMs). In the tube, the animals in both neuroleptic-treated groups showed initial decreases in the number of CSMs and made sluggish CSMs; these effects were generally larger in the FLU animals. After 6 months of chronic neuroleptics, the HAL-treated animals showed increased oral movements, both as reported by the human observer and in CSMs of all amplitudes, and this effect increased upon drug withdrawal. FLU-treated animals showed a more persistent depression of both OMs and CSMs of large amplitudes. However, the behavior most characteristic of both neuroleptic-treated groups was the gradual development of increases in CSMs of the smallest amplitudes measurable.A different pattern was observed in the open cage test, where both neuroleptic groups showed significant increases in vacuous OMs during drug administration which rapidly became attenuated upon drug withdrawal. These results indicate a complex syndrome of oral activity in the drugged animals which changed over time. The measure of oral activity which most clearly showed the time-course for late-onset changes in oral activity was CSMs of the smallest amplitudes.     

Selective antagonism of isolation-induced aggression in mice by diazepam following chronic administration

Benzodiazepines are non-selective (i.e., they only inhibit aggression at doses producing concurrent neuromuscular impairment) antagonists of isolation-induced aggression in mice following acute administration. However, in the present study diazepam was shown to be a selective antagonist of fighting in isolated mice following chronic administration for 5 days. When administered chronically, selective tolerance rapidly developed to the general CNS depression produced by diazepam whereas the antifighting activity was not diminished and, in fact, tended to be enhanced following multiple drug administrations. Thus, the antagonism of fighting in isolated mice by diazepam does not appear to be due solely to general CNS depressant properties.     

Regional homovanillic acid levels and oral movements in rats following chronic haloperidol treatment

Rats with more severe orofacial movements after 51 days of haloperidol administration showed lower levels of the dopamine metabolite homovanillic acid (HVA) in the caudate compared to animals who did not develop significant mouth movements. This effect was not observed in other brain regions sampled. This finding is consistent with the hypothesis that dopaminergic receptor supersensitivity in neostriatal structures plays some role in the development of orofacial movements in rats, in association with chronic neuroleptic administration.     

Amiodarone pharmacokinetics. II. Disposition kinetics following subchronic administration in rats

A 30 mg kg-1 intravenous bolus of 14C-amiodarone (19 microCi kg-1) was given to male Sprague-Dawley rats pretreated with 0 (vehicle), 25 or 100 mg kg-1 day-1 of amiodarone HCl orally for 37-42 days to determine the effects of dose and duration of administration on the disposition kinetics of amiodarone. Serial blood samples and total urine were collected over 48 hours and assayed for 14C-amiodarone by liquid scintillation counting following separation by HPLC. In all three groups, the blood 14C-amiodarone concentration-time curves declined bioexponentially with terminal half-lives (t1/2 beta) ranging from 14-22 hours. No differences in beta, t1/2 beta, or central compartment volume (Vc) were observed between the three groups of rats. In the rats pretreated with 100 mg kg-1 day-1 of amiodarone HCl for 5-6 weeks, amiodarone clearance (CL) and steady state volume of distribution (Vss) were reduced 52 per cent (12.2 to 5.9 ml min-1 kg-1) and 41 per cent (11.73 to 6.97 l kg-1), respectively. At the lower amiodarone daily dose, no changes in CL or Vss were observed. Negligible levels of radioactivity were detected in the urine. Amiodarone accounted for approximately 30-40 per cent of the total radioactivity in each blood specimen. This study demonstrated that CL and Vss were dose-dependent, and that beta, t1/2 beta and Vc were dose-independent. The results further suggested that the disposition kinetics of amiodarone were independent of the duration of drug administration.     

Contribution of the active metabolite, norcocaine, to cocaine's effects after intravenous and oral administration in rats: pharmacodynamics

RATIONALE: Oral cocaine is more effective than IV cocaine by pharmacokinetic and pharmacodynamic analysis. One explanation is involvement of the active metabolite, norcocaine, in cocaine's effects. OBJECTIVES: To evaluate norcocaine's contribution to oral cocaine's effects, norcocaine's effects as a parent compound were determined and compared to those of cocaine using a differential reinforcement of low rate (DRL 45-s) schedule and spontaneous activity (large and small movements) after IV and PO routes of administration. METHODS: The effects of cocaine and norcocaine on DRL performance (shorter-response and reinforcement rates) and spontaneous activity were investigated in 3-h sessions. The changes in effects across time (effect-time profiles) and dose-response curves (DRCs) were constructed to evaluate the duration of action and potency (ED50) of both drugs. RESULTS: Under the DRL 45-s schedule, effect-time profiles showed both drugs via the two routes of administration significantly increasing and decreasing shorter-response rates and reinforcement rates, respectively. However, cocaine produced greater effects on shorterresponse rates than norcocaine, while both drugs produced comparable effects on reinforcement rates. For spontaneous activity, although IV cocaine, PO cocaine, and PO norcocaine dose- and time-dependently increased spontaneous activity, cocaine's effects were more profound than those of norcocaine. Effect-time profiles revealed that the duration of drug action was a function of dose, route, and behavioral paradigm used. According to ED50 values, IV cocaine was more effective than PO cocaine; however, PO cocaine was more effective than IV cocaine as judged by ED50 values corrected for absolute oral bioavailability. CONCLUSIONS: Norcocaine's contribution to oral cocaine's effects on DRL performance is evident. Other mechanism(s), such as a greater acute tolerance to IV cocaine's effects than to PO cocaine's effects, can be excluded.     

Pharmacokinetic studies of meloxicam following oral and transdermal administration in Beagle dogs

Aim： The potential for topical delivery of meloxicam was investigated by examining its pharmacokinetic profiles in plasma and synovial fluid following oral and transdermal administration in Beagle dogs.
Methods： The experiment was a two-period, crossover design using 6 Beagle dogs. Meloxicam tablets were administered orally at a dose of 0.31 mg/kg, and meloxicam gel was administered transdermally at a dose of 1.25 mg/kg. Drug concentrations in plasma and synovial fluid were determined by liquid chromatography-tandem mass spectrometry （LC/MS/MS）. The pharmacokinetic parameters were calculated using the Topfit 2.0 program. Results： The pharmacokinetic results showed that AUC0-t （23.9±8.26 pg·h·mL^-1） in plasma after oral administration was significantly higher than after transdermal delivery （1.00±0.43 pg·h·mL^-1）. In contrast, the ratio of the average concentration in synovial fluid to that in plasma following transdermal administration was higher than that for an oral delivery. The synovial fluid concentration in the treated leg was much higher than that in the untreated leg, whereas the synovial fluid concentration in the untreated leg was similar to the plasma concentration.
Conclusion： The high concentration ratio of synovial fluid to plasma indicates direct penetration of meloxicam following topical administration to the target tissue. This finding is further supported by the differences observed in meloxicam concentrations in synovial fluid in the treated and untreated joints at the same time point. Our results suggest that transdermal delivery of meloxicam is a promising method for decreasing its adverse systemic effects.     

Effects of discontinuous drug administration on the development of dopamine receptor supersensitivity during chronic trifluoperazine or cis-flupenthixol administration to rats

Rats received continuous or discontinuous administration of trifluoperazine or cis-flupenthixol in drinking water for up to 12 months. Continuous and discontinuous trifluoperazine administration had no consistent effect on apomorphine-induced stereotyped behaviour and there was no difference between drug treatments. Continuous and discontinuous cis-flupenthixol administration enhanced apomorphine-induced stereotypy, but there was no difference in the effect of the two drug treatments. Both continuous and discontinuous administration of trifluoperazine increased the number of specific striatal ³H-spiperone binding sites (B _max). Over the period of treatment there was no difference in the effects of the different treatments. Continuous or discontinuous cis-flupenthixol intake did not increase B _max after 6 or 12 months intake. Continuous or discontinuous neuroleptic treatment produced no difference in functional striatal dopamine receptor activity as judged by apomorphine-induced stereotyped behaviour. Ligand binding studies also suggest that the overall change in striatal receptor function is not affected by the use of a discontinuous drug regime.     

Insulin in w/o/w multiple emulsions: Biological activity after oral administration in normal and diabetic rats

Abstract

In this work the biological effects of two w/o/w multiple emulsions composed of the soybean oil (EHS) or medium-chain triglycerides (ETCM), containing insulin, were studied. The release mechanism of insulin from multiple emulsions proposed in our previous in-vitro investigations was confirmed by subcutaneous administration. This mechanism is the swelling-breakdown phenomenon which occurs when the emulsions are diluted under hypo-osmotic condition. The biological effect after oral administration, evaluated in two experimental protocols, single administration in normal and diabetic rats and short-term treatment in diabetic rats, shows that in diabetic rats small amounts of biologically active insulin were absorbed from these emulsions. In these experiments no significant difference between EHS and ETCM was found.