Differences in the metabolism of drugs depending upon their routes of administration

Cardiac Troponin I in Isoproterenol-Induced Cardiac Injury in the Hanover Wistar Rat: Studies on Low Dose Levels and Routes of Administration

The current studies demonstrate the effect of low-dose intraperitoneal (IP) administration of isoprotenerol (ISO) and subcutaneous (SC) versus IP routes of administration of ISO on serum cardiac troponin I (cTnI) levels in female Hanover Wistar rats, providing additional evidence to support acceptance of cTnI as a cardiac biomarker. At 2 hr postdosing with 0-500 μg/kg ISO, mean serum cTnI levels were increased in a dose-related fashion at ≥10 μg/kg with no evidence of cardiac pathology. At 24 h, cTnI concentrations were generally at control levels, but histologic cardiomyocyte injury was evident in a proportion of the animals given ≥10 μg/kg. In a second experiment, rats given SC ISO at 5,000 μg/kg and necropsied at 0, 1, 2, and 4 hr postdosing had higher levels of serum cTnI than animals given the same dose IP.

Inhibitory effects of various beverages on human recombinant sulfotransferase isoforms SULT1A1 and SULT1A3

Sulfotransferase (SULT) 1A1 and SULT1A3 play important roles in the presystemic inactivation of beta(2) agonists in the liver and intestine, respectively. The study aimed to investigate the inhibitory effects of grapefruit juice, orange juice, green tea, black tea and oolong tea and their constituents on the activities of SULT1A1 and SULT1A3. The activities of both SULT1A1 and SULT1A3 were significantly inhibited by all the beverages investigated at a concentration of 10%. The beverage constituents were tested in concentration ranges considered to be physiologically relevant. The grapefruit constituent, quercetin, completely inhibited SULT1A1, while quercetin and naringin both partially inhibited SULT1A3. The orange constituents, tangeretin and nobiletin, also completely inhibited SULT1A1. The tea constituents, (-)-epicatechin gallate and (-)-epigallocatechin gallate, both almost completely inhibited SULT1A1 and SULT1A3. Moreover, the theaflavin and thearubigin fractions of black tea both completely inhibited SULT1A1 and strongly inhibited SULT1A3. The inhibitory action of green tea on SULT1A3 was competitive, while that of black tea and oolong tea was mixed competitive/non-competitive. Mechanism-based inhibition was not observed with any beverage. In conclusion, various beverages, especially teas, inhibit the function of SULT1A3, and therefore may have the potential to increase the bioavailability of orally administered substrates of SULT1A3, such as beta(2) agonists.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Novel delivery systems: oral transmucosal and intranasal transmucosal

During the past 2 decades, anesthesiologists have been provided with a number of new, potent opioid analgesics and sedative/hypnotics, as well as an increased understanding of the pharmacokinetic and pharmacodynamic principles that govern their action and disposition. These developments have suggested that the skin and the buccal and nasal mucous membranes may have use as alternate routes of analgesic and anesthetic drug delivery. A novel transmucosal delivery system for fentanyl has recently been developed by incorporating the drug into a dissolvable matrix on a stick called an "oralete." Oral transmucosal fentanyl citrate has been evaluated as a premedication in the pediatric population and as an analgesicfor acute postoperative and emergency room pain, procedural pain, and breakthrough cancer pain by using fentanyl. Increases in plasma fentanyl and onset of clinical effect are rapid (20-40 min) with this formulation. A potential advantage is the apparent ease of titration to a sedative or analgesic end point. This system may improve premedication, acute postoperative analgesia, and chronic pain therapy in various clinical settings. Delivery of opioids through the nasal mucosa also has been recently investigated. In one study, sufentanil was administered (1.5, 3.0, or 4.5 mu/kg) to 80 children ranging in age from 6 mo to 7yr. Easy separation from parents was achieved in 86% of the children 10 min following administration of the premedication. Unfortunately, 61% of the children cried after drug administration, and side effects included reduced ventilatory compliance (chest-wall rigidity) with higher doses (3.0 and 4.5 microg/kg). Nevertheless, nasal transmucosal drug delivery may have value, especially in frightened or uncooperative children.

Esophageal candidiasis associated with beclomethasone dipropionate aerosol therapy

A 23-year-old woman with asthma developed severe heartburn while using beclomethasone dipropionate. Esophageal candidiasis was diagnosed on endoscopy and confirmed by biopsy. Subsequent studies revealed mild hypogammaglobulinemia and mild impairment of neutrophil candidacidal activity, the significance of which is unknown. Esophageal candidiasis associated with the use of inhaled beclomethasone has not been previously reported.

Extrahepatic sulfation and glucuronidation in the rat in vivo. Determination of the hepatic extraction ratio of harmol and the extrahepatic contribution to harmol conjugation

The phenolic compound, harmol, is metabolized by sulfation and glucuronidation in the rat in vivo. In the present study, various harmol infusion rates into the jugular vein were used to delineate first-order conditions whereby total body clearance was maximal and constant; at low infusion rates the steady state harmol concentration in blood varied proportionally with the infusion rate. At infusion rates of 167 nmole/min and below, the steady state clearance of harmol was 60 ml/min or 200 ml/min/kg. Because this value for total body clearance greatly exceeded the value for hepatic blood flow rate (20 ml/min for a 300 g rat), considerable extrahepatic conjugation of harmol was suggested. At higher harmol infusion rates the total clearance decreased. Since an intraportal infusion of 167 nmole/min to the rat yielded, during steady state, the same arterial harmol blood concentration as a 52 nmole/min jugular infusion, the hepatic extraction ratio of harmol in vivo was 0.7. Extrahepatic clearance, therefore, constituted about 77% of total body clearance (after taking the difference between total body clearance and hepatic clearance). Total sulfation clearance was 52 ml/min, and greatly exceed the value for hepatic clearance (14 ml/min). Extrahepatic clearance for sulfation (at least 38 ml/min) therefore accounted for a major proportion of the sulfation activity. Blood platelets did not seem to contribute to sulfation or glucuronidation in vivo.

Combined oral and nasal beclomethasone diproprionate in children with atopic eczema: a randomised controlled trial

In a double blind, placebo controlled, crossover trial in 26 children with severe atopic eczema those receiving four weeks' treatment with combined oral plus nasal beclomethasone diproprionate improved significantly more than those receiving placebo. No adverse effects were observed, but 24 hour urinary cortisol excretion was slightly reduced. This combination may provide effective treatment in refractory atopic eczema with relatively little of the danger associated with systemic administration of prednisolone and other traditional corticosteroids.

Prodrugs of etilefrine: synthesis and evaluation of 3'-(O-acyl) derivatives

A series of 3'-(O-acyl) derivatives of etilefrine (alpha-[(ethylamino)methyl]-3'-hydroxybenzyl alcohol) was synthesized. Correlations between structure and solubility, pKa value, lipophilicity, and esterase-catalyzed hydrolysis were demonstrated. Of special interest is the 3'-(O-pivaloyl) derivative, which shows, in addition to favorable solubility and improved lipophilicity, marked stability against enzymatic cleavage in blood along with a high rate of hydrolysis in the liver.

Effects of dichlorvos (DDVP) inhalation on the activity of acetylcholinesterase in the bronchial tissue of rats

The experiments presented here deal with the effects of the inhalation of dichlorvos [dimethyl-(2,2 dichlorvinyl)-phosphate, DDVP] vapor on acetylcholinesterase (ACHE) activity in rat bronchial tissue. Exposure to DDVP concentrations of 0.8 and 1.8 micrograms/l for 3 days reduced ACHE activity in the bronchial tissue (62.8 +/- 0.8 and 51.6 +/- 1.6% of the control), but did not elicit any changes in blood ACHE activity (101 +/- 4.5% of the control each). Higher concentrations (4.3 micrograms/l) induced a decline in ACHE activity also in the blood (38.2 +/- 1.1% of the control). In the histochemical preparations used to demonstrate ACHE activity in bronchial tissue (thiolacetic acid method), a staining of the bronchial glands and smooth muscles characteristic of the enzyme activity was strongly reduced after exposure of the animals to even the lowest dose applied (0.2 microgram/l). The question of whether localized inhibition of ACHE in the bronchial tissue might cause increases in airway resistance due to activation of a broncho-bronchial reflex is discussed. This efferent cholinergic mechanism has been found to be at least partly responsible for maintenance of bronchospasm and hypersecretion in chronic obstructive diseases of the respiratory system.

The influences of the route of administration on the metabolism and excretion of bitolterol, a new bronchodilator, in the rat

1. [3H]Bitolterol, an ester prodrug to colterol (N-t-butyl-arterenol), when administered orally, was excreted mostly in the urine; approx. equal amounts of 3H were found in urine and faeces after intraperitoneal or intravenous injection. 2. Half the dose was excreted in the bile following parenteral administration, while only a small amount of radioactivity was found in bile after oral dosage. The biliary-excreted material consisted mainly of glucuronides, for all routes of administration. 3. The glucuronides of colterol and 3-O-methyl-colterol were excreted in urine after oral administration of bitolterol. In addition to the glucuronides, free colterol and 3-O-methyl-colterol were excreted in urine following parenteral administration. 4. A part of bitolterol was hydrolysed to colterol in rat stomach, and bitolterol was more rapidly hydrolysed to colteral with homogenates of intestinal mucosa than with stomach homogenates in vitro.

Effect of route of administration and distribution on drug action

The extent and time course of drug action can be markedly affected by the route of drug administration into the patient as well as the pattern of drug distribution within the patient. Drugs which are rapidly cleared by hepatic processes will show a decreased extent of availability following oral administration due to metabolism of drug on its first pass through the liver. The magnitude of this first pass will depend on the blood flow to the liver and the intrinsic clearing ability of the liver (i.e., the ability of the organ to eliminate the drug independent of the rate at which drug is brought to the organ). Drug distribution in the patient will depend on the blood flow to various sites in the body as well as the partition coefficient of the drug between the blood and the distributive organs. Protein binding both in the plasma and in the tissues will markedly affect this distribution. However, free drug concentrations are generally relieved to be the effective determinant in drug therapy. Often a redistribution due to changes in protein binding will have little effect on the therapeutic efficacy since, although total drug distribution changes, free concentrations in the plasma remain essentially similar.

Paracetamol (acetaminophen) kinetics in patients with Gilber's syndrome

The pahrmacokinetics of paracetamol after intravenous and oral administration has been studied in 6 patients with Gilbert's syndrome, and 6 healthy controls. Paracetamol clearance was significantly less in the patients (255 ml/min SE +/- 23 ml/min) than in the normal subjects (352 ml/min SE +/- 40 ml/min). Moreover, whilst paracetamol concentrations declined monoexponentially in the patients, the decline was biexponential in the controls. No difference in the bioavailability of 500 mg paracetamol given orally was observed between the two groups. The results suggest that not only is paracetamol elimination impaired in Gilbert's syndrome, but that its distribution kinetics are also abnormal. Both these findings could be attributed to a decrease in hepatic glucuronyl transferase activity.

Differences following skin or inhalation exposure in the absorption and excretion kinetics of trichloroethylene and toluene

The concentrations of trichloroethylene in breath and blood and the urinary excretion of its metabolites following 30 minutes' direct immersion of one hand in the liquid, were compared with those obtained after four hours' inhalation exposure to the vapour of 100 ppm, described in a previous paper. The comparison shows that the end-tidal air concentrations during the first two hours of the post-exposure period were about twice as high in the case of skin exposure as in that of inhalation exposure, although the uptake of the solvent through the skin was only about one-third of the inhaled uptake. A kinetic approach suggested that differences in trichloroethylene movement in the body would be a principal cause of this discrepancy. The results of a similar series of experiments using toluene suggested that it is less readily taken up than trichloroethylene through the skin. It was concluded from the present investigation that analyses of not only breath but also of blood or urine are necessary and toluene would rarely be absorbed through the skin in toxic quantities during normal industrial use.

l-Bunolol and propranolol: oral and intravenous beta-adrenoceptor blocking activity in rats compared to dogs and humans

To determine the pharmacological significance of reported differences between species in l-bunolol metabolism, oral and intravenous beta-adrenoceptor blocking activity against an isoproterenol-induced tachycardia was compared in dogs, rats, and humans. Propranolol was similarly studied in rats and dogs. Species differences in intravenous potency were minimal for both compounds in contrast to oral dose studies. Oral to intravenous ratios of doses causing a comparable degree of beta-adrenoceptor blockade after l-bunolol were: rat, 212; dog 4; and human, 5. For propranolol, the oral to intravenous dose ratios were 210 and 32 for the rat and dog, respectively. These pharmacological findings show major differences in the rat compared to dogs and humans and may be explained in part by differences in the urinary excretion patterns of l-bunolol in the various species.

Evaluation of a breath actuated pressurized aerosol

Preliminary investigation suggests that some asthmatic patients find it difficult to synchronize the release of a metered dose from a pressurized aerosol with the correct phase of inspiration. An automatic device has been developed to overcome this problem. Information is presented outlining the physical characteristics of the unit and the methods used to establish its performance in patients. It is suggested that the device may have a place in the management of asthma.

Acrylonitrile biotransformation in rats, mice, and chinese hamsters as influenced by the route of administration and by phenobarbital, SKF 525-A, cysteine, dimercaprol, or thiosulfate

Female wistar rats, conventional albino mice, and Chinese hamsters were given a single dose of acrylonitrile, 0.5 or 0.75 mM/kg body weight. The elimination in the urine of thiocyanate, which is the main metabolite of acrylonitrile, indicated a decreasing proportion of biotransformation after oral (over 20%), intraperitoneal, or subcutaneous (2 to 5%), and intravenous (1%) administration in rats. Oral administration of acrylonitrile in hamsters and mice was also followed by higher biotransformation than intraperitoneal administration. Pretreatment of rats with phenobarbital, SKF 525 A, cysteine, or dimercaprol did not significantly influence elimination of thiocyanate in the urine after the administration of acrylonitrile, but simultaneous administration of thiosulfate significantly increased the metabolized portion of acrylonitrile given intraperitoneally in rats (almost twice) and mice (more than three times). Acrylonitrile was found to be strongly bound in blood. The study confirmed the marked effect of distribution (first-pass metabolic phenomenon) on the metabolic fate of foreign compounds. The strong acrylonitrile binding and cyanoethylation are apparently responsible for the unusually high influence of the different routes of administration on the metabolic fate of acrylonitrile. Acrylonitrile was more effectively metabolized to thiocyanate in mice than in rats after oral, intraperitoneal, and intravenous administration. A greater response of acrylonitrile to thiocyanate metabolism and a larger decrease in its acute toxicity after thiosulfate in mice than in rats indicate possible differences in the mechanism of acrylonitrile toxicity in these animals. Cyanide apparently plays a minor role in the acrylonitrile toxicity in rats, but may play quite an important one in mice.