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At least 19 recordsLinked to original sources

PubMed1985

Mechanism of nasal absorption of drugs. II: Absorption of L-tyrosine and the effect of structural modification on its absorption.

The nasal absorption of L-tyrosine and the effect of structural modification on that absorption have been studied using an in-situ experimental technique. The extent of nasal absorption of the amino acid was found to be the same at pH values of 4.0 and 7.4 but dependent on concentration in the range of 2.8 X 10(-4)-2.2 X 10(-3) M. O-Acyl-L-tyrosine esters, although possessing higher octanol-water (pH 7.4) partition coefficients, have the same rate of nasal absorption as the parent amino acid. N-Acetyl-L-tyrosine, on the other hand, was found to have both partition coefficient and nasal absorption rate similar to those of L-tyrosine. Esterification of the carboxyl moiety of L-tyrosine results in derivatives that hydrolyze in the in-situ perfusion medium generating the original amino acid. The rate of nasal absorption of these derivatives was, therefore, determined from an overall disappearance rate which accounted for the rate of hydrolysis to L-tyrosine. These carboxylic esters were absorbed 4 to 10 times faster than L-tyrosine. Although the carboxylic esters of L-tyrosine possess higher octanol-water partition coefficients than the parent amino acid, the differences in the rates of nasal absorption could not be attributed solely to partition coefficient. The enhancement in the rate of absorption observed for these esters was attributed instead to the absence of the negative charge on the carboxylate moiety. It is a result of this negative charge that the rates of nasal absorption of L-tyrosine, O-acyl-L-tyrosine esters and N-acetyl-L-tyrosine are similar, despite significant differences in their partition coefficients.

Absorption↗

PubMed1986

Enhancing effect of absorption promoters on percutaneous absorption of a model dye (6-carboxyfluorescein) as a poorly absorbable drug. III. Histological study after addition of various absorption promoters in rats.

We have studied the effect of various absorption promoters on the percutaneous absorption dynamics of 6-carboxyfluorescein (CF) which is a poorly absorbable drug. The absorption of CF was determined by fluorescence photographic image since CF emits a strong light yellow fluorescence. The co-administration of sodium dodecylsulfate (SDS) and 2-mercaptoethanol (MER), the pretreatment with calcium thioglycolate and the co-administration of Azone (AZ) and surfactant (HCO-60) were used to promote the absorption of CF. We have also studied the injury of skin tissue by the absorption promoters. The fluorescence photographic image of rat skin, after the co-administration of SDS and MER and after the co-administration of AZ and HCO-60 were similar to the image with the stratum corneum removed from the skin. These absorption promoters did not affect the histological nature of the rat skin tissue and the recovery experiment showed no injurious effect by these absorption promoters to the skin tissue.

Animals↗

PubMed1979

Dietary heme iron absorption. A discussion of possible mechanisms for the absorption-promoting effect of meat and for the regulation of iron absorption.

Two main findings are reported. 1) The absorption of heme iron from a composite meal was very little if at all influenced by the subject's iron status at doses in the usual physiological range, but at high doses of heme iron there was a strong correlation with the subject's iron status. A hypothesis is presented to explain the regulation of iron absorption, so as to account for the impact of the subject's iron status, which is always evident with non-heme iron absorption but occurred only at high doses with heme iron. 2) Meat enhanced the absorption of heme iron. A probable explantation for the influence of meat on the separate absorbing mechanisms is that meat may stimulate the digestion of food, so that iron in either form is more efficiently released and made available for absorption.

Absorption↗

PubMed1985

Enhancing effect of absorption promoters on percutaneous absorption of a model dye (6-carboxyfluorescein) as poorly absorbable drugs. II. Study on the absorption promoting effect of azone.

The percutaneous absorption of drugs was investigated in rats by measuring plasma levels, using mainly 6-carboxyfluorescein (CF) as a model of poorly absorbable drugs. Azone (AZ), a new useful promoter for the percutaneous absorption of drugs, was used instead of dimethylsulfoxide. We have examined the effects of the solubilized state and concentration of AZ on the percutaneous absorption of CF. AZ was dissolved with the aid of surface-active agents, beta-cyclodextrin (CD) or dimethyl-beta-cyclodextrin (DMCD). When AZ (2 v/v%) was dissolved completely by a surface-active agent (HCO-60: polyoxyethylene hardened castor oil derivative), plasma CF levels showed the highest value. Plasma CF levels following the administration of CF with AZ which formed a complex with CD or DMCD were scarcely increased as compared to that of CF alone. In the case of fluorescin (FL), which has a higher partition coefficient than CF, the percutaneous absorption of FL was more enhanced by the addition of AZ than in the case of CF.

Adjuvants, Pharmaceutic↗

PubMed1992

[Mucus models for investigation of intestinal absorption mechanisms. 4. Comparison of mucus models with absorption models in vivo and in situ for prediction of intestinal drug absorption].

Intestinal absorption with an in vitro model using pig intestinal mucus was examined by means of in vivo and in situ experiments in the rat. With 10 compounds of different structure, in vitro, in situ, and in vivo models were tested. The in vitro model in the present form can only simulate the first step of intestinal absorption, namely diffusion through the mucus layer. Indeed, we found that one function of the intestinal mucus can be described being a molecular sieve with a molecular mass (MM) cut off within the range of about 600 to 700 [g/mol]. Absorption of substances with higher molecular mass remains at a low level. With the mucus model prediction of intestinal absorption of hydrophilic substances with MM < 600 to 700 [g/mol] will be possible, if the mass transport in the mucus layer is rate limiting. Independent of polarity, it is also valid for substances of MM > 600 to 700 [g/mol]. Estimation however, is not valid for lipophilic substances and MM < 600 to 700 [g/mol], when mass transport from the mucus to the adjacent compartments is rate limiting. Further optimization of the mucus model for a more extensive application seems possible and reasonable with respect to saving in vivo experiments with animals.

Animals↗

PubMed1979

GI absorption of beta-lactam antibiotics. III: Kinetic evidence for in situ absorption of ionized species of monobasic penicillins and cefazolin from the rat small intestine and structure-absorption rate relationships.

Absorption rates of monobasic beta-lactam antibiotics were measured as a function of lumen solution pH between 4 and 9 by utilizing the rat intestinal recirculating method in situ. Between pH 6.5 and 9, the absorption rate constants of ionized antibiotics were almost identical; but, at pH 4, the unionized species were highly absorbed, depending on their lipophilicity through the GI membrane lipoidal barrier. The structure-absorption rate relationship was established with the unstirred layer model.

Animals↗

PubMed1976

Magnesium absorption in the human small intestine. Results in normal subjects, patients with chronic renal disease, and patients with absorptive hypercalciuria.

Magnesium absorption was studied in the normal human jejunum and ileum by in vivo intestinal perfusion, using test solutions containing from 0 to 20 mM Mg (as MgCl2). As luminal Mg concentration was increased, the rate of absorption in the jejunum rose progressively with a tendency towards saturation at the higher concentrations. The kinetics and rates of Mg absorption in the ileum were comparable to those in the jejunum, with the exception that at higher luminal concentrations the ileal absorptive process was fully saturated. Using test solutions containing various combinations of Ca and Mg, we found that Ca had little or no influence on Mg absorption, even through Mg depressed Ca absorption to a modest extent. Patients with end-stage renal disease, who had a reduced rate of Ca absorption (presumably due to deficiency of 1,25-dihydroxycholecalciferol) were found to have a severe depression of Mg absorption. On the other hand, patients with absorptive hypercalciuria and nephrolithiasis, who had an increased rate of Ca absorption, were found to absorb Mg normally. These results suggest that Mg absorption in the human is mediated by a transport process different from that which facilitates Ca absorption, and that normal Mg absorption may be dependent on vitamin D. Our results do not establish whether or not the normal intestine can absorb Mg against an electrochemical gradient.

Adult↗

PubMed1990

Duration of absorption-enhancing effect of sodium octanoate, sodium hexanoate or glyceryl-1-monooctanoate on rectal absorption of gentamicin in rabbits.

The duration of the absorption-enhancing effect of sodium octanoate (C8), sodium hexanoate (C6) and glyceryl-l-monooctanoate (MO) on the rectal absorption of gentamicin (GM) using the hollow-type suppository was investigated in rabbits. To evaluate the duration of the absorption-enhancing effect by pretreatment (treatment of absorption enhancer before GM administration), suppository I containing each absorption enhancer in the cavity was administered into the rectum. Then suppository II containing GM in the cavity was administered at predetermined times (0.33, 2, 6 and 24 h) after the administration of suppository I. Plasma GM levels obtained by the pretreatment with absorption enhancer were compared with those obtained by the simultaneous administration of GM with absorption enhancer. The AUC and Cmax of GM significantly decreased with the pretreatment of C8 (6 and 24 h), C6 (2 and 6 h) or MO (6 and 24 h) before rectal GM administration, as compared with the simultaneous administration of GM with C8, C6 or MO. A marked decrease in the absorption-enhancing effect of C8, C6 and MO on rectal GM absorption was observed by the prolongation of the period between the pretreatment of each absorption enhancer and GM administration. The duration of the absorption-enhancing effect of C6 was shorter than that of C8, whereas this duration of MO was similar to that of C8. The effect of these absorption enhancers disappeared 24 h after the pretreatment. These results suggested that the lowering of the membrane transport barrier function recovered about one day after the administration of C8 or MO.

Administration, Rectal↗

PubMed1975

Effect of surfactants on absorption through membranes III: effects of dioctyl sodium sulfosuccinate and poloxalene on absorption of a poorly absorbable drug, phenolsulfonphthalein, in rats.

The influence of dioctyl sodium sulfosuccinate and poloxalene on the GI absorption of phenolsulfonphthalein in the rat was studied. Urinary excretion data after oral administration of the drug to intact rats and loss of the drug from the whole small intestine as a loop were both utilized to assess the effect of the surfactants on absorption. Dioctyl sodium sulfosuccinate markedly increased the absorption of the drug, and the extent was dependent on the surfactant concentration. Maximum effect was observed at the reported ED50 in rats, of the surfactant as a fecal softener. The mechanism responsible for absorption enhancement seems to be an alteration of the permeability of the intestinal membrane. Micellar complexation between the drug and the surfactant resulted in a lesser increase in absorption at the higher surfactant concentrations. Poloxalene did not increase drug absorption, but higher concentrations caused a decrease in absorption due to micellar entrapments of the drug molecules. The influence of dioctyl sodium sulfosuccinate on the peritoneal absorption of the drug was also investigated. Lower doses of the surfactant increased absorption of the drug by altering the membrane permeability. Higher doses decreased absorption due to unavailability of the drug molecules entrapped in the micelles.

Animals↗

PubMed1987

Pharmacokinetic analysis of concentration data of drugs with irregular absorption profiles using multi-fraction absorption models.

Nonlinear regression analysis of plasma drug concentration data with irregular or stepwise absorption profiles was studied using multi-fraction absorption models in which drugs in the gastrointestinal tract were assumed to be divided into several fractions each with its respective lag time and absorption rate constant. Plasma allopurinol concentration data, with two-phase absorption profiles in dogs after oral administration, were found to be satisfactorily fitted using a two-fraction absorption model. Plasma sulfisoxazole concentration data in humans were also successfully analyzed using a two-fraction absorption model. Plasma and urinary concentrations of pindolol in humans after oral administration of sustained-release preparations were fitted to two- or three-fraction absorption models. The pharmacokinetic absorption behavior of a sustained-release preparation of diltiazem hydrochloride was studied using a multi-fraction absorption model. Pharmacokinetic parameters derived from these models and those from the discontinuous absorption model were compared.

Allopurinol↗

PubMed1975

'Sufficient' absorption--a quantitative method to replace 'exhaustive' absorption.

At present, the only guideline for removal of undesired reactivities from an antiserum is that no activity against the cross-reacting (undesired) antigens should remain after exhaustive absorption. Since this guideline sets no upper limit on the amount of undesired antigens required for an exhaustive absorption, waste of possibly precious material and of time in performing multiple sequential absorptions can result. To minimize the quantity of antigen and of experimental work required for an absorption, a quantitative approach is suggested: the antiserum is test-absorbed with various amounts of the undesired antigens, and antibody activity still present against these antigens is then tested. The results can be plotted as a curve by use of Reif's modification of the Von Krogh equation. Thus, the exact amount of undersired antigens sufficient to remove all detectable reactivity against these antigens can be determined. The procedure is termed 'sufficient' rather than 'exhaustive' absorption, to stress that only detectable amounts (rather than every last trace) of undesirable antibodies have been removed. The nomenclat re 'exhaustive absorption' gives no indication that any practical attempt to achieve it can hardly escape having the same limitations as 'sufficient absorption'; it is therefore suggested that the misleading non-quantitative nomenclature 'exhaustive absorption' be eliminated from immunological terminology. 'Sufficient absorption' has been applied to the absorption of undesired (blood group) antibodies from rabbit antisera to CEA.

ABO Blood-Group System↗

PubMed1985

Intestinal absorption of oestrone, oestrone glucuronide and oestrone sulphate in the rat in situ--I. Importance of hydrolytic enzymes on conjugate absorption.

The biliary excretion of steroid after administration of [3H]oestrone ([3H]E1), [3H]oestrone glucuronide ([3H]E1G) and [3H]oestrone sulphate ([3H]E1S) into the hepatic portal vein of anaesthetized rats was very rapid with more than 70% of E1S and greater than 80% of E1 and E1G excreted in the first 30 min. There was a lag period in the biliary excretion of E1S, this was less apparent with E1 and absent with E1G. Biliary excretion accurately reflects the amount of steroid in the portal circulation and was therefore used as an assessment of absorption from the gastrointestinal (GI) tract. Absorption (as judged by excretion in bile) was least after administration of each steroid into the stomach. The extent of absorption correlated well with the lipophilicity of the steroids as shown by their relative partition coefficients between n-octanol and pH 6.5 phosphate-buffered saline (E1 greater than or equal to E1S greater than or equal to E1G). There was no significant difference in excretion profile when the steroids were given into the caecum (at 5 h, E1, 46.3 +/- 9.1%; E1G, 42.2 +/- 14.5%; E1S, 39.9 +/- 7.1%). The similarity, despite marked differences in physicochemical properties, suggested conjugate hydrolysis to the parent steroid. In contrast, after administration into the small intestine, excretion of E1 was very rapid and was maximal at 1 h (72.5 +/- 8.0%); E1G showed a near-linear excretion rate (1 h, 14.4 +/- 3.0%; 5 h, 80.0 +/- 11.7%), whereas in comparison E1S excretion was low (1 h, 12.1 +/- 2.4%; 5 h, 36.9 +/- 2.7%). The involvement of hydrolytic enzymes in conjugate absorption was assessed. Ampicillin pretreatment (200 mg/kg/day for 2 days) reduced the absorption of E1G from both the proximal and distal small intestine (by approximately 50%) but had no effect on the absorption of E1S. There was, therefore, evidence that quantitative absorption of E1G requires prior hydrolysis (by mammalian and/or microbial enzymes) but intact absorption of E1S from this region of the tract was implicated. Ampicillin pretreatment reduced the absorption of both conjugates (greater with E1S) from the caecum; hydrolysis clearly precedes absorption from the caecum. The above findings were supported by an in vitro study which showed that ampicillin pretreatment abolished the hydrolysis of E1S by caecal contents but only partially reduced the hydrolysis of E1G. The presence of mammalian glucuronidase enzyme may account for this difference.

Ampicillin↗

PubMed1975

Regional differences in oxalate absorption by rat intestine: evidence for excessive absorption by the colon in steatorrhoea.

Clinical studies suggest that steatorrhoea can be associated with excessive absorption of dietary oxalate. We examined the influence of bile salts, Ca++, and long-chain fatty acid on the absorption of oxalate and water by rat intestine in vivo. Absorption was measured under steady-state conditions during single-pass infusions. Each intestinal segment served as its own control. In jejunum, 10 mM taurocholate, the principal salt in rat bile, depressed absorption of oxalate and water. Absorption was not depressed further by Ca++ or linoleic acid. In ileum, 10 mM taurocholate did not inhibit absorption. Linoleic acid, 2 mM, depressed absorption of both oxalate and water. In colon 10 mM taurocholate decreased absorption. Net water transport was depressed further when linoleic acid was added to the infusion, but oxalate absorption was enhanced. Ca++ negated these effects of linoleic acid. It is concluded that long-chain fatty acids may enhance the absorption of oxalate from the rat colon. This observation may be relevant to understanding hyperoxaluria in patients with steatorrhoea.

Animals↗

PubMed1991

Enhanced rectal and nasal absorption of human epidermal growth factor by combined use of the absorption promoter and the synthetic polymer in rats.

Previously, the presence of sodium carboxymethylcellulose (CMC Na) in addition to an absorption promoter, sodium caprate (C10 Na), in the dosing solution was found to be necessary for the enhancement of the rectal absorption of human epidermal growth factor (hEGF). In the present study, other synthetic polymers and absorption promoters were examined for their ability to enhance the rectal and nasal absorption of hEGF in rats. The effect of polymers in combined use with 100 mM C10 Na on the rectal absorption of hEGF was in the following order: 1% methylcellulose 1% hydroxypropylmethylcellulose 0.1% polyacrylic acid 1% CMC Na. Other absorption promoters such as N-lauroyl-alanine (C12-A) and dihydroxy-bile salts also enhanced the rectal absorption of hEGF in combined use with CMC Na. In order to confirm the increased rectal absorption of hEGF, the disappearance of hEGF from the rectal loop was examined. When hEGF in a 1% CMC Na solution (200 ug/kg) was administered in the rectal loop, the disappearance percent of hEGF during 60 min was 13.9% of the dose, although hEGF was not detected in the plasma. The presence of promoters such as 10 mM C10 Na or 15 mM C12-A in 1% CMC Na increased the disappearance percent to about 50% in a dosing range of hEGF from 100 to 500 ug/kg. On the other hand, a markedly enhanced nasal absorption of hEGF by 100 mM C10 Na was observed even in the absence of any polymer in a dising solution. However, addition of CMC Na into the dosing solution accelerated the rate of nasal absorption of hEGF in early phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗

PubMedDate not supplied

Absorption of iothalamate after oral administration and absorption enhancement by amino acids in dogs and rats.

The oral absorption of iothalamate and the effect of amino acids on its absorption were studied in 6 dogs and 6 rats using a simple HPLC assay. The results showed that iothalamate was absorbed in dogs, averaging 9.9, 8.5, and 10.0 per cent following the administration of 40 and 100 mg kg-1 of iothalamic acid capsules and 50 mg kg-1 of sodium iothalamate solution, respectively. The absorption from the capsule was slower and more sustained than that from the solution. In rats, the absorption appeared to be dose-independent (averaging about 4.2 per cent) in the dose range of 20-800 mg kg-1. The low bioavailability obtained was mainly due to the high polarity of iothalamate molecules as suggested by the GI recovery and in vitro partition studies. Among several amino acids tested as possible ion-pair formers, only homoarginine hydrochloride increased the partition of iothalamate into chloroform layer. However, both homoarginine hydrochloride and arginine hydrochloride at the amino acid/iothalamate molar ratio of 25 were found to significantly enhance (about 70 per cent) the iothalamate absorption in dogs. The in situ rat small intestinal loop study indicated that the absorption-enhancing effect of arginine was sodium dependent. At the sodium chloride concentration of 0.09 M, no significant increase in the absorption was observed, while at the concentration of 0.3 M or higher, a marked increase (about twofold) was obtained in both upper and lower intestine. Thus, the mechanism of the amino acids in facilitating the iothalamate absorption may be more closely related to the active amino acid transport system rather than the possible increase in lipophilicity of the ion-pair formed. The potential use of such naturally occurring, relatively non-toxic amino acids for increasing the GI absorption of water-soluble weak acids or bases through ion-pair formation remains to be fully investigated.

Administration, Oral↗

PubMed1977

GI drug absorption in rats exposed to cobalt-60 gamma-radiation II: in vivo rate of absorption.

The rate of absorption of sulfanilamide, bretylium tosylate, sulfisoxazole acetyl, and riboflavin was studied in rats exposed to 850 rad of cobalt-60 gamma-radiation either 1 or 5 days before oral drug administration. Polyethylene glycol 4000 was administered with sulfanilamide; its distribution along the GI tract indicated that the gastric emptying rate was reduced threefold at 1 day postirradiation but returned to normal at 5 days postirradiation; the small intestinal transit rate was not detectably altered by irradiation. At 1 day postirradiation, there was a marked decrease in the absorption rate of sulfanilamide, a smaller, although significant, decrease in the absorption rate of sulfisoxazole acetyl and bretylium, and an increase in the absorption rate of riboflavin. At 5 days postirradiation, the drug absorption rate was normal. The changes in the absorption rate of the drugs were due to a radiation-induced reduction in the gastric emptying rate; the permeability of the GI epithelium did not appear to be affected by radiation. The results indicate that, immediately following irradiation, a marked reduction in the gastric emptying rate causes a pronounced reduction in the absorption rate of rapidly absorbed drugs, a less pronounced reduction in the absorption rate of drugs that are absorbed slowly because of slow dissolution or slow diffusion across the GI epithelium, and an increase in the absorption rate of drugs that are absorbed by a saturable mechanism provided the mechanism is not impaired by irradiation.

Animals↗

PubMed1985

Mechanism of nasal absorption of drugs I: Physicochemical parameters influencing the rate of in situ nasal absorption of drugs in rats.

The effect of rate of perfusion, volume, pH of the perfusate, and partition coefficient of the drug on the rate of in situ nasal absorption in rats was examined. The studies showed that the rate constant for the nasal absorption of phenobarbital was independent of the rate of perfusion above a value of 2 mL/min. The nasal absorption of benzoic acid was found to depend on the pH of the perfusate with the benzoate anion being absorbed at a rate one-fourth of that of benzoic acid. The effect of lipid solubility on the extent of nasal absorption was studied using a series of barbiturates. The rate and extent of absorption was found to be dependent on the chloroform-water partition coefficient of the barbiturate. The effect of the volume of the perfusate on the absorption rate constant of phenobarbital, phenol red, tyrosine, and propranolol was studied. The data obtained showed that a linear relationship existed between the rate constants of absorption and the reciprocal of the volume of the perfusate. Using this in situ relationship it was possible to predict in vivo absorption rate constants for propranolol and L-tyrosine when volumes of 0.1 mL were administered. The calculated values for these compounds were found to be close to those determined in in vivo experiments. This indicates that the in situ technique can be used to predict in vivo absorption rate constants.

Absorption↗

PubMed1978

Arachidonic acid intestinal absorption: mechanism of transport and influence of luminal factors of absorption in vitro.

The mechanism and characteristics of intestinal absorption of arachidonic acid were studied in vitro using everted intestinal sacs of the rat. Arachidonic acid absorption was studied at concentrations of 5 micron to 8.36 mM. The plot of absorption rate vs. concentration fitted best to a rectangular hyperbola at low micron concentrations and to a straight linear relationship in the mM range of concentrations. Metabolic inhibitors and uncouplers did not change absorption in either range of concentrations. The absorption of arachidonic acid increased with thinning of the unstirred water-layer, decrease in the pH, or the substitution of sodium taurocholate by Pluronic F 68 OR Tween 80. Absorption decreased following the equimolar additions of oleic, linoleic, and linolenic acids. Absorption rate did not change when the taurocholate concentration was varied from 5-15 mM or following the additions of butyric or glutamic acids, leucine, lysine, or dextrose. It was concluded that arachidonic acid is absorbed by a concentration-dependent dual mechanism of transport which is not energy dependent. At the low micron range of concentrations, facilitated diffusion is predominant, while at mM concentrations, simple diffusion is the dominant mechanism of absorption. Changes in the intestinal fluid composition, flow rate, and pH can modify the rate of absorption of arachidonic acid.

Animals↗