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Evaluation of polyvinyl alcohol hydrogel as a sustained-release vehicle for rectal administration of indomethacin.

In order to evaluate an indomethacin polyvinyl alcohol (PVA) hydrogel for rectal administration, the in vitro release characteristics of indomethacin from the hydrogel and indomethacin plasma concentrations after rectal administration were examined. The PVA hydrogel containing indomethacin was prepared by a low-temperature crystallization method. The release of indomethacin from the PVA hydrogel agreed with the Fickian diffusion model for 10 hr. Rectal administration of indomethacin hydrogels to rats yielded high indomethacin plasma concentrations, without producing a sharp peak, and a sustained-release effect. In dogs, the indomethacin hydrogel produced a similar sustained-release effect; however, the indomethacin plasma concentration was relatively low compared with that of an indomethacin suppository.

Administration, Rectal↗

Pharmacokinetics of zidovudine after rectal administration in human immunodeficiency virus-infected patients.

We evaluated the pharmacokinetics of rectally administered zidovudine (ZDV) in 10 human immunodeficiency virus-infected adults. After rectal administration of an aqueous ZDV solution (250 mg of ZDV), mean peak ZDV levels were 1.3 +/- 0.7 micromol/liter (mean +/- standard deviation) versus 5.0 +/- 2.2 micromol/liter (P < 0.0001) after oral intake of a 250-mg ZDV capsule. The half-life at beta phase was 87.8 +/- 39.6 min for rectally administered ZDV versus 55.8 +/- 20.1 min (P = 0.035) for orally administered ZDV. The mean area under the concentration-time curve from 0 min to infinity was 232 +/- 181 micromol/liter x min after rectal administration versus 362 +/- 110 micromol/liter x min after oral intake. Although the two routes were not bioequivalent, ZDV was absorbed considerably after rectal administration, with a pharmacokinetic profile resembling that of a sustained-release device.

Administration, Oral↗

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 micrograms min ml-1, 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.

Administration, Oral↗

Pharmacokinetics and relative bioavailability of vinylbital in man after oral and rectal administration.

A sensitive and specific method for the quantitative determination of 5-vinyl-5-(1-methylbutyl)-barbituric acid (vinylbital) in plasma was developed, by using gas chromatography with alkali flame ionization detection. The method is suitable for measuring vinylbital plasma levels in man after administration of therapeutic doses. The pharmacokinetics and relative bioavailability of vinylbital after oral and rectal administration were studied in man. Tablets (Bykonox) containing 150 mg vinylbital, were used for the oral experiments and suppositories (Suppoptanox, polyethylene glycol base) containing 200 mg vinylbital, were used for rectal administration. Six volunteers participated in a cross-over way in the study. Vinylbital plasma concentrations were determined at regular intervals after drug administration. Absorption and elimination of vinylbital appeared to occur according to a single first-order process and the plasma concentrations were fitted by computer according to the equation intrinsic to the one-compartment open model after oral or rectal administration. The lag time was shorter for the suppository than for the tablet, whereas the absorption rate was faster for the tablet (mean absorption half-life 0.24 h compared with 0.64 h for the suppository). The elimination half-life of vinylbital varied from 17.6 to 33.5 h, with a mean value of 23.5 h for oral administration and 23.8 h for rectal administration. The half-lives were not considerably different on the two occasions for the individual volunteers. The average bioavailability of vinylbital for the suppository, relative to the tablet, was approximately 93%. Three volunteers collected their urine during 3--4 days after administration of a tablet. Unchanged vinylbital was determined and approximately 1.6% of the administered dose was excreted as unchanged drug. Some preliminary experiments of repetive vinylbital administration showed that self-induction of metabolism did not occur.

Administration, Oral↗

Failure of absorption of gabapentin after rectal administration.

PURPOSE: We wished to determine the extent of absorption of gabapentin (GBP) after rectal administration to children on maintenance therapy. METHODS: Two children scheduled for extensive surgery received GBP rectally and orally. A pharmacokinetic profile was derived after each route of administration. RESULTS: Serum GBP levels after rectal administration decreased at a rate similar to their rate of decrease after oral administration. However, GBP concentrations were much lower after rectal administration; therefore, we concluded that the aqueous solution was poorly absorbed rectally. The GBP half-life (t1/2) for the 2 children after oral doses were 4.2 and 4.8 h. CONCLUSIONS: Rectal administration of GBP is not satisfactory when oral administration is interrupted. When oral GBP therapy is temporarily discontinued, clinicians should consider administration of alternative antiepileptic drugs (AEDs) that can be administered parenterally or rectally.

Acetates↗

Increased bioavailability of tacrolimus after rectal administration in rats.

The oral bioavailability of tacrolimus is low and varies considerably in humans due to first-pass metabolism by cytochrome P450 (CYP) 3A4 and the active efflux mediated by P-glycoprotein. This study was undertaken to elucidate the usefulness of rectal administration of tacrolimus as an alternative route to improve its bioavailability. Tacrolimus powder was suspended in a suppository base (witepsol H-15) and the tacrolimus suppository was inserted into the anus of the rats. For comparison, tacrolimus was suspended in 0.5% sodium methylcellulose solution and administered orally to rats. The dose of tacrolimus was fixed to 2 mg/kg. Blood samples were collected periodically up to 24 h after dosing, and tacrolimus concentrations were assayed by microparticle enzyme immunoassay. The whole blood concentrations of tacrolimus after rectal administration were much greater than those after oral administration. The C(max) and AUC(0-24 h) values after rectal administration were 3.9- and 6.9-fold greater than those after oral administration, respectively. These results clearly suggest a possibility that rectal administration of tacrolimus is capable of improving its bioavailability and cutting the costs of tacrolimus treatment.

Administration, Oral↗

[Animal and clinical studies on rectal administration of a mixed solution of ibuprofen and diazepam].

OBJECTIVE: Seizure is a common emergency in children with complicated pathogeny. Seizures are usually caused by complicated etiology and fever and febrile seizure are the commonest causes. Repeated and permanent seizures can damage the brain. So it is important to take active and effective measures to control seizure and high fever. Because most seizures and fever take place at home or out of hospital and it is difficult to administer drugs intravenously, it is important to explore an easy, safe, quick and effective way to control and prevent both seizure and fever. The present study aimed to explore the efficacy and safety of rectal administration of mixed ibuprofen and diazepam (IBU-DZP) solution. METHODS: (1) Animal study on the pharmacokinetics in rabbits and pharmacodynamics in rats after rectal administration with the mixed solution and on the irritability of the mixed solution to rectum. (2) Clinical study: Pharmacokinetics of the mixed solution in children after rectal administration were investigated. RESULTS: (1) Animal study: IBU and DZP were both rapidly absorbed from rectum with a peak blood level of (11.7 +/- 1.2) min and (9.4 +/- 2.7) min in rabbits, respectively. The mixed solution could effectively prevent the severity of seizures induced by pentetrazole and significantly suppressed fever induced by yeast. There were no remarkable pathological changes in rectal tissues after repeated rectal administration of the mixed solution. (2) Clinical study: IBU and DZP rapidly reached their peak blood levels at about 30 min and 15 min respectively after rectal administration to the children. The peak values were (57.8 +/- 7.9) mg/L and (450.1 +/- 158.7) microg/L, respectively. In fact, both of them reached levels that were much higher than their therapeutic levels in serum just at 5 min after administration, their blood levels were (41.4 +/- 5.5) mg/L and (321.8 +/- 53.9) microg/L, respectively. CONCLUSIONS: IBU-DZP mixed solution administered rectally is an easy, safe, quick and effective way to control and prevent both seizure and fever.

Administration, Rectal↗

Lack of absorption of didanosine after rectal administration in human immunodeficiency virus-infected patients.

The feasibility of rectal administration of didanosine (DDI) was studied in six human immunodeficiency virus-infected patients. After oral intake of a DDI solution (100 mg/m2 of body surface area) combined with an antacid (Maalox), pharmacokinetic parametric values were in accordance with previously published data; the mean +/- standard deviation for terminal half-life was 59.5 +/- 15.0 min, that for peak concentration was 5.2 +/- 3.9 mumol/liter, and that for the area under the time-concentration curve (AUC) was 494 +/- 412 min.mumol/liter. After rectal administration of a similarly prepared DDI solution (100 mg/m2 of body surface area), plasma DDI levels were below the detection limit (0.1 mumol/liter) at all time points in five of the six patients, and in the remaining patient the AUC after rectal application was only 5% of that after oral administration. We conclude that oral administration of DDI cannot be easily replaced by rectal application.

Administration, Rectal↗

Design of polyvinyl alcohol hydrogel as a controlled-release vehicle for rectal administration of dl-propranolol-HCl and atenolol.

Preparations of beta-blockers, propranolol-HCl and atenolol, in poly(vinyl alcohol) (PVA) hydrogel were designed for the therapeutic treatment of hypertension by transrectal delivery. In vitro release characteristics and plasma drug concentration profiles after rectal administration in rats and dogs were examined. The PVA hydrogels containing beta-blockers were prepared by a low-temperature crystallization method. The release of beta-blockers from hydrogel preparations was consistent with Fickian diffusion (Higuchi model); the drug release versus the square root of release time profile gave a straight line over 60% of the total release process. The release of beta-blockers from hydrogel preparations increased at higher concentrations of PVA in the hydrogel preparations and was not affected by the pH of hydrogel preparations. Plasma concentrations of beta-blockers after rectal administration of hydrogels were higher than those after administration of suppositories (Witepsol H-15) in rats and dogs. The drug plasma concentrations increased at higher concentrations of PVA in hydrogel preparations. In the case of propranolol, which is a hepatic high-clearance drug, area under the blood concentration curve, 0-8 h after rectal administration of a hydrogel preparation (20% w/w PVA, pH 7.0) was 2.16 times and 5.26 times higher than those obtained with Witepsol H-15 suppository and oral administration, respectively. Rectal administration with PVA hydrogels is a favorable route for a hepatic high-clearance drug such as propranolol.

Animals↗

[Effects of rectal administration of an ampicillin suppository (KS-R1) on cecal microflora and cecal weight in mice].

KS-R1 is a new rectal preparation of ampicillin (ABPC) sodium. Changes of cecal microflora, changes of cecal weight and ABPC concentrations in the cecum after rectal administration of KS-R1 to mice were compared with those after oral and subcutaneous administration of ABPC. When KS-R1 was administered to mice by 25.0 mg/kg 3 times a day for 10 days continuously, a little changes were observed in the number of Enterobacteriaceae, Staphylococcus and Lactobacillus in the cecum. However, at the fifth day after completing the rectal administrations, normal level of microflora was gained. This change of microflora closely resemble those in case when ABPC sodium was administered subcutaneously. On the other hand, when ABPC was administered orally, changes of microflora were large, i.e. the number of Enterobacteriaceae and Streptococcus increased remarkably, the number of Fusobacterium increased and the number of Staphylococcus and Bacteroides decreased. Recovery of normal level of microflora was late. The cecal weight did not show changes but the increase observed in the case when ABPC was orally administered. This increase was due to the increase of moisture in the cecum. The concentrations of ABPC in the cecum when administered by 25.0 mg/kg were in the order of oral administration greater than rectal administration (KS-R1) greater than subcutaneous administration. The highest concentrations were respectively 219.6, 54.1 and 5.1 micrograms/g. Changes of microflora in the cecum was great in proportion to the concentrations of ABPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

[Comparison of salicylazosulfapyridine bioavailability following oral and rectal administration in patients with ulcerative colitis].

Salicylazosulfapyridine--a drug commonly used in the ulcerative colitis--is effective following both oral and rectal administration. Pharmacokinetics of the drug given per rectum (in the form of suppositories) has not been investigated so far. The present study aims at comparing bioavailability of salicylazosulfapyridine following oral and rectal administration to patients with the ulcerative colitis and healthy volunteers. It was found, that following rectal administration the drug is not so readily absorbed as in oral dosage form. No sulfapyridine and 5-aminosalicylic acid have been detected in blood serum, when the drug was given in the form of rectal suppositories. Clinical stage of the disease did not affect absorption of both unchanged drug and its metabolites. Due to the fact, that the drug is active locally, rectal suppositories seem a therapeutical alternative in patients only with lesions localized in the rectum.

Administration, Oral↗

Clinical pharmacokinetics of ketobemidone. Its bioavailability after rectal administration.

The pharmacokinetic constants and rectal bioavailability of the narcotic analgesic ketobemidone were determined in six male patients after surgery. Plasma concentrations were measured following intravenous administration of Ketogin 2 ml, containing ketobemidone chloride 10 mg, and a spasmolytic compound N,N-dimethyl-3,3-diphenyl-1-methylallylamine chloride 50 mg, and following rectal administration of one suppository of Ketogin, containing ketobemidone chloride 10 mg and the spasmolytic component 50 mg. Following intravenous administration, the disposition of ketobemidone followed a biexponential pattern with a fast distribution phase and a slower elimination phase: the plasma half-life (t1/2) was 2.42 +/- 0.41 h (m +/- SD). After rectal administration, the disposition of ketobemidone fitted a one-compartment model. The elimination half-life was 3.27 +/- 0.32 h. The mean rectal bioavailability for ketobemidone was 44% +/- 9%. The pharmacokinetic constants of the spasmolytic component, N,N-dimethyl-3,3-diphenyl-1-methylallylamine, were also determined in five of the patients, both after intravenous and after rectal administration. The plasma half-life was 3.07 +/- 0.53 h and 3.79 +/- 1.14 h, respectively. The rectal bioavailability was estimated to be 33% +/- 14%.

Adult↗

Brain, liver and spleen detection of liposomes after rectal administration.

Bangham-type liposomes, undergoing freeze-thawing cycles, were detected electron microscopically in the brain, liver and spleen of experimental animals 24 h after rectal administration. This novel approach has several important advantages over intravenous, intraperitoneal and other usual means of administration of liposome drug-entrapped treatment and diagnostics for human application. The location of the liposomes in the brain after rectal administration shows that the brain-blood barrier can be overcome successfully by this method. Moreover, the risk of embolism and hypersensitivity, strict control of sterility and some other undesirable effects can be avoided. The possible role of rectal administration in the development of liposome drug-entrapped treatment and diagnostics is discussed.

Administration, Rectal↗

Ketamine and norketamine plasma concentrations after i.v., nasal and rectal administration in children.

It has been suggested that nasal administration of ketamine may be used to induce anaesthesia in paediatric patients. We have examined the pharmacokinetics of ketamine and norketamine after nasal administration compared with rectal and i.v. administration in young children. During halothane anaesthesia, 32 children, aged 2-9 yr, weight 10-30 kg, were allocated randomly to receive ketamine 3 mg kg-1 nasally (group IN3) or ketamine 9 mg kg-1 nasally (group IN9); ketamine 9 mg kg-1 rectally (group IR9); or ketamine 3 mg kg-1 i.v. (group IV3). Venous blood samples were obtained before and up to 360 min after administration of ketamine. Plasma concentrations of ketamine and norketamine were measured by gas liquid chromatography. Statistical comparisons were performed using ANOVA and the Kruskall-Wallis test, with P < 0.05 as significant. Mean plasma concentrations of ketamine peaked at 496 ng ml-1 in group IN3 within 20 min, 2104 ng ml-1 in group IN9 within 21 min, and 632 ng ml-1 in group IR9 within 42 min. Plasma concentrations of norketamine peaked at approximately 120 min after nasal ketamine, but appeared more rapidly after rectal administration of ketamine and were always higher than ketamine concentrations in the same situation. Calculated bioavailability was 0.50 in groups IN3 and IN9 and 0.25 in group IR9. We conclude that nasal administration of low doses of ketamine produced plasma concentrations associated with analgesia, but using high doses via the nasal route produced high plasma concentrations of ketamine similar to those that induce anaesthesia. However, the large volume of ketamine required was partly swallowed and led to an unacceptable variability of effect that precludes this route for induction of anaesthesia.

Administration, Intranasal↗

The effect of rectal administration of insulin on the short-term treatment of alloxan-diabetic dogs.

Six alloxan-diabetic dogs with fasting plasma glucose levels above 200 mg/100 mL were treated with rectal administration of insulin suppositories twice a day for 6--9 days. The effectiveness was compared with that of subcutaneous insulin injections. In three diabetic dogs with fasting plasma glucose levels below 300 mg/100 mL, both insulin suppository at a dose of 20 U (2.3 U/kg) and subcutaneous insulin at a dose of 0.2 U/kg showed a similar effect in reducing fasting glucose levels and daily urinary glucose amounts. In dogs with higher fasting glucose levels, 0.5 U of subcutaneous insulin/kg is less effective in reducing fasting glucose than 50 U (5.2 U/kg) suppositories, in spite of the same effects on daily urinary glucose output. Postprandial glucose responses were significantly lessened with rectal administration of insulin suppositories. The integrated area of increase in peripheral insulin concentration after subcutaneous infection of 0.2 or 0.5 U insulin/kg was significantly greater than that after rectal administration of an insulin suppository (2.3 or 5.2 U/kg, respectively). These results indicate that diabetes could be controlled by the daily rectal administration of an insulin suppository instead of the conventional subcutaneous injection.

Animals↗

Biopharmaceutical evaluation of ketoprofen following intravenous, oral, and rectal administration in dogs.

The influence of the hydrophilicity of three suppository bases on the rectal absorption of ketoprofen was studied. Absorption characteristics of ketoprofen were compared after intravenous, oral, and rectal administrations of 100 mg of drug given in a crossover design to five dogs. Rectal formulations included an aqueous solution and three suppository formulations. After oral dosing, ketoprofen was rapidly absorbed (time of maximum concentration, tmax: 0.83 +/- 0.61 h), and a comparison with the intravenous solution indicated a complete bioavailability of 0.90 +/- 0.10. After rectal administration, the rate of absorption, as evaluated with tmax and mean absorption time, was always slower than after oral dosing. A high variability was observed in the plasma concentrations obtained with suppository formulations; bioavailability values were approximately 20% lower than those from the oral solutions. No statistical difference in bioavailability and peak concentrations between the three suppository formulations was observed. Time of peak concentrations, mean absorption times, and fractions of the dose absorbed 6 h post administration did not show a difference in rate of ketoprofen absorption from the three suppository formulations. This study did not reveal a relationship between rate and extent of ketoprofen rectal absorption and the hydrophilicity of the suppository bases tested.

Administration, Oral↗

Pharmacokinetics of hydromorphone after intravenous, peroral and rectal administration to human subjects.

The pharmacokinetic properties of hydromorphone in healthy young male subjects were studied after i.v., peroral, and rectal administration. After i.v. administration the following pharmacokinetic parameters were found: elimination half-life 2.36 +/- 0.5 h, hepatic extraction ratio 0.51, apparent volume of distribution 2.9 +/- 1.3 L kg-1 and volume of central compartment 0.23 +/- 0.2 L kg-1. The absolute bioavailability after peroral administration was 50.7 +/- 29.8 per cent, and that after rectal administration was 33 +/- 22 per cent.

Administration, Oral↗

Bioavailability of ketoprofen in horses after rectal administration.

Six healthy mares ranging in age from 6 to 12 years and weighing from 415 to 540 kg were used to determine the rectal bioavailability of ketoprofen. For the rectal administration, three different formulations, each containing 1 g of ketoprofen, were administered in a fatty and a hydrophilic suppository base and as a liquid suspension. An average elimination half-life of 1.3 h (+/-1.2) was found. The average value for the total plasma clearance (ClT) was 131.9mL/ min.kg (range 95-183.5). The volume of distribution Vd(area) was 255 mL/kg and the mean residence time (MRT) value was 0.47 h. After rectal administration, the mean maximal plasma ketoprofen concentrations were 1.6(+/-0.8), 1.1(+/-0.7) and 1.6(+/-0.2) micrograms/mL for the fatty suppository, the hydrophilic suppository and the liquid suspension respectively. The absolute bioavailability of ketoprofen in horses after rectal administration of the three formulations was relatively low, with a large interindividual variability (24.5 +/- 9.5%, 28.7 +/- 18% and 31.3 +/- 6.8% for the fatty suppository, the hydrophilic suppository and the liquid suspension respectively). These values were not significantly different (P = 0.05; Friedman test). Despite the low rectal bioavailability obtained in this study, there was some evidence for the clinical effectiveness of the rectal formulations.

Administration, Rectal↗