Low Drug Levels Research Articles

Serum phenobarbital and barbital concentrations in rats on a limited food regimen

Serum barbiturate levels were tracked for several hours in food deprived rats given 40, 60 or 80 mg/kg (SC) of either phenobarbital or barbital. All 3 phenobarbital doses produced peak serum drug levels at 1.5 hr postinjection. Serum barbital concentrations peaked 3 hr after both 60 and 80 mg/kg barbital doses while the 40 mg/kg dose produced a stable low drug level throughout the 4 postinjection hours. For both barbiturates administered, 40 mg/kg doses produced lower serum drug levels than either 60 or 80 mg/kg. The differences in serum drug concentrations between the latter two dose levels were inconsistent over time.

Adriamycin resistance and radiation response

Mammalian cells (V79) in culture developed resistance to Adriamycin during continuous exposure to low levels of drug. This resistance was accompanied by change in X-ray survival properties which, in turn depended upon the isolation of subpopulations from resistant sub lines. These changes in X-ray survival properties were characterized by reduced D Q values and a decrease in the D 0. However, these changes were not observed together in the same cell sub line. Adriamycin-resistant cells did not appear to be radiation damage repair deficient. Other phenotypic changes (cell morphology, DNA content and chromosome number) suggested mutational events coincident with the development of Adriamycin resistance.

Lymphocytotoxicity and immunosuppression by organotin compounds. Suppression of graft-versus-host reactivity, blast transformation, and E-rosette formation by Di-n-butyltindichloride and Di-n-Octyltindichloride

Di-n-butyltindichloride (DBTC) and di-n-octyltindichloride (DOTC) represent a new group of organometallic compounds with antilymphocytic properties. In rats they induce lymphocyte depletion in thymus and thymus-dependent areas of spleen and peripheral lymph nodes without signs of myelotoxicity or a generalized toxicity. The number and viability of cells isolated from thymus and peripheral lymphoid organs was severely decreased, whereas the number and viability of bone marrow cells was not reduced. Immunosuppressive properties of DBTC and DOTC are indicated, in this study, by a severe decrease of the graft-versus-host response and the response to the T-cell mitogens phytohemagglutinin and concanavalin A. The T-cell selectivity of these compounds is discussed. In vitro DBTC and DTOC are extremely cytotoxic. Blast transformation of human as well as rat thymocytes was already inhibited at concentrations as low as 0.02 micrograms DBTC (or 0.1 micrograms DOTC) ml medium. Also the E-rosette formation was inhibited at very low drug levels. The similarity of effects upon rat and human lymphocytes suggests that DBTC and DOTC acts in the same manner in rat and man and offers the possibility of a therapeutic use of these compounds.

Cellular DNA damage by the antitumor protein macromomycin and its relationship to cell growth inhibition

Macromomycin, an antitumor protein, after purification inhibited HeLa S 3 cell growth at low nanomolar concentrations. DNA synthesis was inhibited at drug levels that left RNA and protein synthesis unaffected. Incubation of macromomycin with HeLa S 3 cells resulted in a rapid fragmentation of cellular DNA that was detectable at low nanomolar drug levels. Heat denaturation of macromomycin showed that both its ability to inhibit cell growth and to fragment cellular DNA were lost at similar rates.

Experimental mycosis in immunosuppressed rabbits

The influence of immunosuppression on the course of experimental aspergillosis was investigated. Rabbits (2.2--2.5 kg) were divided into four groups. Group one received no drugs and was given 10(6) spores intravenously (IV) or intratracheally (IT) on two occasions one week apart. Weight gain or loss, appearance or disappearance of aspergillus antigen and/or antibody, and detection of aspergillosis at autopsy were followed. Group 2 received weekly injections of cyclophosphamide (70 mg/kg) starting two weeks prior and throughout the experiment. Animals in group three received either 1.14 or 2.25 mg/kg/day methyl prednisolone and group four received 2.28 mg/kg/day methyl prednisolone and 70 mg/kg/week cyclophosphamide. In group one, serum antigen levels were detected within a week of infection followed by antibody (I.D.) levels for three months. All animals grew normally and no infection was detected at autopsy. In group 2, animals survived one but not two challenges and had Ag but no Ab. In group 3, animals survived two challenges at the lower drug level but not the higher. All animals in group 4 succumbed to one challenge.

A Study of the Pharmacodynamics of Oxytetracycline in the Chicken

Oxytetracycline HCl was administered to 24 hr. old and 1 week old chicks at a dosage of 5 mg./kg. The routes of administration were oral and intramuscular and in addition the week old chicks received the drug subcutaneously. The birds were killed in groups of 5, representing each of the routes of administration of the experiment, at the following intervals, 1 hr., 2 hr., 4 hr., 6 hr. and 24 hr. after administration.Oral administration of oxytetracycline results in very low levels of drugs in the tissues of both age groups, but the levels appeared lower and absorption less complete in the 1 week old birds. Intramuscular and subcutaneous administration resulted in higher levels in all the tissues of the birds in both age groups. Kidney and liver samples contained the highest tissue levels of oxytetracycline in all experiments, whereas lung and serum levels were in all cases very low and at some intervals entirely absent.

Metabolism of pentaerythritol trinitrate.

The absorption, excretion, and biotransformation of 14C-labeled pentaerythritol (PE) trinitrate was studied in man. The administration of a single sublingual dose was followed by rapid absorption and extensive biotransformation. Six drug metabolites were identified. Final excretion of the drug and its metabolites was almost totally through the kidney. Low levels of unchanged drug were present in plasma and urine. PE mononitrate was the major drug metabolite in plasma and urine. Glucuronides of PE trinitrate, dinitrate, and mononitrate were identified for the first time in man. PE trinitrate glucuronide appeared in plasma rapidly and about 8% of the dose was excreted in urine. Reversible and irreversible pathways are proposed for the formation of the metabolites. The reconversion of PE trinitrate glucuronide to PE trinitrate is postulated to explain the duration of drug activity and excretion.

Regional Differences in Ocular Concentration of Gentamicin After Subconjunctival and Retrobulbar Injection in the Rabbit

We compared the penetration of radioactive carbon (14C) labeled-gentamicin into ocular tissues and fluids of albino rabbit eyes after subconjunctival (anterior subtenon's) and retrobulbar (posterior subtenon's) injections. In both normal and infected (Staphylococcus aureus endophthalmitis) eyes, higher levels of drug were produced with subconjunctival rather than with retrobullar admininistration in cornea, sclera, choroid and retina (as a unit), and iris; levels in the aqueous and vitreous humors of infected eyes were similar with the two routes of injection. Marked regional variations in the concentrations of gentamicin were noted in cornea, sclera, and choroid-retina after subconjunctival therapy. The pattern of these variations suggests that subconjunctival antibiotic penetrates the eye by direct diffusion. The low levels of drug after retrobulblar injection may be due to systemic absorption through the highly vascular orbital plexus of the rabbit.

Levels of chlorpromazine and its active metabolites in rat brain and the relationship to central monoamine metabolism and prolactin secretion

Chlorpromazine (CPZ), demethylated(nor1)-CPZ, 7-hydroxy(7-OH)-CPZ, and CPZ-nitrogenoxide-(NO) were administered to rats. Levels of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MOPEG) in the brain and prolactin in serum were determined. The HVA increase calculated per nmole unchanged drug in brain was about the same in the CPZ and 7-OH-CPZ groups, but nor1-CPZ was less than 50% as effective in this respect. When CPZ-NO was administered, high amounts of CPZ and nor1-CPZ were formed. The amounts of these products could fully explain the HVA elevation induced by CPZ-NO. The HVA levels were significantly correlated to the amount of the respective drug in the brain. After CPZ and 7-OH-CPZ the levels of unchanged drug in serum were about 3% of the brain level, while the drug serum/brain ratio was significantly lower in the nor1-CPZ-treated group. The prolactin level in serum was raised to about 200% of control 90 min after all drugs were administered. This may be explained by assuming a supramaximal stimulation of the prolactin release mechanism already being achieved at low drug levels in the brain. At 7.5 mg/kg none of the drugs affected the levels of MOPEG or 5-HIAA. After high doses of CPZ the level of MOPEG in the brain was increased.

The gas-liquid chromatograph and the electron capture detection in equine drug testing.

Three gas-liquid chromatographic (G.L.C.) procedures discussed have been designed around the four "esses" of detection tests--speed, sensitivity, simplicity, and specificity. These techniques are admirably applicable to the very low plasma drug levels encountered in blood testing under pre-race conditions. The methods are equally applicable to post-race testing procedures, where both blood and urine samples are tested. Drugs can only rarely be detected by the electron capture detector (E.C.D.) without a prior derivatization step, which conveys to the drug(s) high electron affinity. Because of broad applicability, two derivatizing agents, heptafluorobutyric (HFBA) and pentafluorpropionic (PFPA) anhydrides are employed. The three techniques, allowing broad coverage of various drug classes are: 1) direct derivatization of drugs to form strongly electron capturing amides and esters. 2) reductive fragmentation of drugs with lithium aluminum hydride to form alcohols, with conversion to ester derivatives. 3) oxidative fragmentation of drugs with potassium dichromate to form derivatizable groups, followed by direct derivatization.

Attainment of highly uniform solid drug dispersions employing molecular scale drug entrapment in polymeric latices

AbstractThe uniformity of distribution attainable for an amine drug in solid dispersions prepared using a molecular scale entrapment procedure was investigated. Excellent reproducibility of drug content throughout the entire entrapment product was demonstrated in both flocculated (high drug levels) and deflocculated (low drug levels) systems. Drug content and content uniformity were found to be predictable for deflocculated systems, even at high drug dilution ratios. Milling or particle-size fractionation appeared to have no effect on the distribution of drug throughout the solid dispersion entrapment products. Dry blending was inferior to molecular scale drug entrapment in distributing small quantities of drug uniformly.

Clofibrate-induced alterations in serum protein patterns

Clofibrate when added to the diet at 0.05 to 1.25% (w/w) not only causes an apparently dose-dependent decrease in serum cholesterol of rats but also markedly affects the plasma protein pattern. An increase in albumin is detectable by cellulose acetate strip electrophoresis, acrylamide gel electrophoresis, and by extraction of albumin from plasma. Cellulose acetate strip electrophoresis reveals a decrease in the α 2-globulin fraction, while acrylamide gel electrophoresis indicates that there are manifold changes. Extractable seromucoid concentration declined from 440 mg/100 ml to 150 mg/ml as the dose of clofibrate increased. A concentration decrease in plasma glucose was also observed. Part of the decrement in seromucoid at low drug levels may be related to lessened haptoglobin concentration. The trypsin inhibitory capacity of the plasma was significantly decreased in what appeared to be a dose-dependent fashion. The decrease in seromucoid is consistent with the reduction in bound fraction of ribosomal RNA. Another explanation would appear to be required to explain the rise in albumin.

Cytotoxic effect in vitro and tumour volume reduction in vivo induced by chemotherapeutic agents

By a comparison of in vitro and in vivo effectiveness of cytostatic agents on a transplantable mouse osteosarcoma, a number of drugs were identified for which the in vitro response is not a good prediction for the in vivo response. For a number of such discrepancies, explanations have been identified or tentatively been put forward, namely: 1. (1) absence in vitro of drug metabolizing systems which are effective in vivo. 2. (2) too low tumour drug levels reached by safe drug doses; 3. (3) too short duration of effective drug levels after single dose in vivo. For a number of drugs, unidentified factors cause such discrepancies. However, there is another group of widely used cytostatic agents for which an in vitro test may give a good prediction of overall tumour response and further studies seem to confirm this for other types of tumours.

Mechanism of ethidium bromide inhibition of RNA polymerase

The effect of ethidium bromide on various steps of the reaction catalyzed by Escherichia coli DNA-dependent RNA polymerase is studied. Inhibition caused by low levels (approx. 6 μm) of this DNA-binding drug is a consequence of reducing the rate of RNA chain initiation; the rate of RNA chain growth is unaffected at this concentration. The sensitive step in the initiation process is the formation of stable complexes between RNA polymerase and initiation sites on the DNA. At higher levels (25 μm), ethidium bromide does inhibit the polymerization of those RNA molecules whose initiation has not been blocked.

Effects of methadone-HCl on dorsal root ganglia in organotypic culture

In this study an attempt was made to evaluate comparatively, using methadone, previous reports of habituation and addiction in cultured tissues to narcotics, especially morphine derivatives. Organotypic cultures of dorsal root ganglia from fetal mice were exposed to d- or l-methadone-HCl for periods up to 55 days, in dosages ranging from 2 × 10 −3 m to 10 −6 m. Initial overt toxic response to methadone of three neural elements, viz., neuron somas, myelinated neurites, and satellite cells, was rated on a scale of 0 to +++, on the basis of light-microscopic observation of living cultures. At 10 −4 m or greater concentrations of drug, morphological evidence of toxicity was seen within 24 hr, and a concentration of 10 −3 m was lethal. At 10 −4 m, recovery was observed if the drug was withdrawn after 7 days. Continued exposure to concentrations of 10 −5 m and 10 −6 m permitted indefinite survival, though at a lower rating than that of the controls: the neuronal elements did not return to normal status during exposure periods of 27–44 days. At 10 −6 m, satellite cells were not affected, but neuronal elements continued at a slightly subnormal rating. Cultures maintained at the lower drug levels (10 −5 m, 10 −6 m) did not develop increased tolerance of higher levels, nor did they return to normal condition during the exposure period. d-methadone-HCl was no less toxic than the l-form In this system, during the time period of exposure, neither increased tolerance nor dependence of neural tissue upon methadone was observed.

Combined Treatment with a Dithiosemicarbazonc and Oxytetracycline to Eliminate Anaplasma marginale Infections in Splcnectomizcd Calves

Summary A total of 12 treatment schedules combining Oxytetracycline and an alpha-dithiosemicarbazone were tested in 36 splcnectomizcd calves carrying Anaplasma marginale infectious. Anaplasma infection was eliminated following the administration of 5 or 10 mg./kg. dithiosemicarbazonc combined with 11 mg./kg. Oxytetracycline, and given 3 times at 24 or 48 hr. intervals. Treatments employing lower drug levels, fewer injections, or at greater time intervals failed to eliminate infection. Treated splcnectomizcd calves failing to show evidence of an A. marginale relapsing infection within 62 days were found to be free of infection on the basis of iujectivity trials conducted an average of 87 days after treatment, and by re-inoculation with A. marignale an average of 164 days after treatment.

Pharmacology of gentamicin in man.

Dosage of gentamicin based upon the weight of the patient (1.5-8 mg/kg per day) produced a wide range of concentrations of the drug in serum. In 10% of patients, the level is potentially toxic, but in 30% it is inadequate for therapy. Concentrations of gentamicin in urine are high, in cerebrospinal fluid low, and in bile, pleural, and pericardial fluid one-half to one-fourth that in the serum. Renal insufficiency requires an altered maintenance dosage. Hemodialysis clears gentamicin at a rate equal to 60% of that at which creatinine is cleared. Individual patterns in the response to dose were observed to be accelerated, typical, or dampened, giving brief high, average, or low levels of drug in serum. A significant inverse relation exists between the level of gentamicin in serum and hematocrit. Studies with radioactive gentamicin (100 ztg/ml) showed that 10% was associated with erythrocytes, 30% with plasma proteins, and 60% in solution. The individual dose-responses emphasize the value of monitoring gentamicin levels in serum during treatment. The optimal clinical benefit from treatment of infections caused by organisms sensitive to gentamicin can be obtained only if the dose used provides a therapeutic, but not a toxic, level in the blood. To achieve this goal, it is essential to have information concerning the factors and conditions that influence the concentration of drug in the plasma and the penetration of the drug into various compartments of body fluids. Because gentamicin is not appreciably metabolized or inactivated in the body, the principal determinants of the level in plasma attained with any given dose are the absorption, binding, distribution, and excretion of the drug. The major, if not the exclusive route of elimination of gentamicin from the body is through the kidneys by glomerular fil

In vivo effects of intercalating drugs on the superhelix density of mitochondrial DNA isolated from human and mouse cells in culture

The degree of supercoiling (superhelix density) of closed circular mitochondrial DNA was found to increase three- to fivefold when the intercalating drug ethidium bromide was added to exponentially growing cultures of HeLa cells and to an SV40 virus-transformed line of mouse cells (SV3T3). This structural change was complete within ten hours in cells growing at a normal rate in the presence of 0.1 μg of the drug/ml., and within a shorter time at 1 μg/ml. Mitochondrial DNA synthesis, as indicated by incorporation of [ 32P]orthophosphate and [ 3H]thymidine, is essentially completely inhibited at the higher drug level and is greatly reduced at the lower drug level. The above results demonstrate that mitochondrial DNA is subject to nicking-closing cycles in the presence of the drug. Four acridine derivatives, known to unwind DNA upon binding, have similar in vivo effects on the superhelix density of mitochondrial DNA. The ethidium analogue, propidium di-iodide, has no effect, but appears on the basis of fluorescence microscopy to be excluded from the cells. Actinomycin D also has no effect. Ethidium bromide had no detectable effect on the base composition of mitochondrial DNA as indicated by buoyant density studies in neutral and alkaline cesium chloride. The drug had no effect on the distribution of complex mitochondrial DNA (circular dimers and catenated oligomers) measured with the electron microscope.

Reoccurrence of the microsporidan Perezia pyraustae in the European corn borer, Ostrinia nubilalis, reared on diet containing Fumidil B

Fumidil B suppressed the level of Perezia pyraustae infection in the larvae of the European corn borer, Ostrinia nubilalis, while they were feeding on diet containing the drug. After feeding ceased and the gut was emptied of diet containing Fumidil B, the level of infection again increased. Drug levels of 1000 and 1500 ppm in the meridic diet significantly reduced the mean level of P. pyraustae in the adult stage as compared with lower drug levels of 200 and 500 ppm. The level of infection increased throughout the pupal and adult stages, but during the pupal stage it increased much faster in the female than in the male. The rapid increase in the level of infection in the female is discussed in relation to transovariole transmission to the next generation.

Biochemical properties of anti-inflammatory drugs—III.: Uncoupling of oxidative phosphorylation in a connective tissue (cartilage) and liver mitochondria by salicylate analogues: Relationship of structure to activity

At low drug levels, sodium salicylate and other drugs which uncouple oxidative phosphorylation in liver and muscle mitochondria selectively inhibit (i) the incorporation of inorganic phosphate into organic phosphates and (ii) the incorporation of inorganic sulphate into polysaccharide sulphates by bovine cartilage in vitro, without inhibiting the oxidation of glucose or octanoate by this tissue. Processes (i) and (ii) are also inhibited by respiratory inhibitors (nitrogen atmosphere, cyanide). It is concluded that salicylate will uncouple oxidative phosphorylation in connective tissues, as well as in muscle, kidney, liver etc. The relationship of chemical structure to activity in uncoupling phosphorylation in cartilage and in rat liver mitochondria, was studied for 80 salicylate analogues. The partial structures given in figure 1 were essential for uncoupling activity: within this structural requirement, potency was governed by lipophilic character. The following compounds were notably more active than salicylate in vitro: o.hydroxynaphthoates, phenylsalicylates, 2-mercaptobenzoate and lipophilic N-substituted derivatives of PAS, salicylamide and anthranilic acid. N-Salicyloylanthranilate, 3,5-diiodosalicylate and 5-phenylazosalicylate were the most active drugs in vitro uncovered in this survey. Nitrosalicylates were much less active than the corresponding nitrophenols.