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PubMed2004

Influence of methanol on the enantioresolution of antihistamines with carboxymethyl-beta-cyclodextrin in capillary electrophoresis.

According to the model of Wren and Rowe, the separation between two enantiomers in capillary electrophoresis (CE) decreases if an organic modifier is added to the run buffer containing a neutral cyclodextrin (CD) in a concentration below its optimal value in a solvent-free system. In previous work, however, it was observed that the addition of methanol to the background electrolyte (BGE) containing not charged carboxymethyl-beta-CD in a concentration below its optimal value, increased the enantioresolution of dimetindene maleate. The enantioresolution decreased when other organic modifiers (ethanol, isopropanol or acetonitrile) were added and/or when other neutral (beta-CD, hydroxypropyl-beta-CD) or chargeable (carboxyethyl-beta- and succinyl-beta-CD) CDs were used. In this CE study further attempts are made to elucidate the observed phenomena through investigating other basic drugs. The effect of organic modifier and CD concentration on the enantioseparation was studied by means of central composite designs. It is shown that obtaining this increase in enantioresolution depends upon the type of CD, the type of organic modifier, and the structure of the analytes. It was also observed that small differences in the structure of the analytes or the CD could have an influence on the enantioresolution. The addition of methanol also resulted in different effects on the resolution of closely related analytes.

Dimethindene↗
PubMed1997

Administration of H1 and H2 antagonists for chemoprophylaxis: a double-blind, placebo-controlled study in healthy volunteers.

A double-blind, placebo-controlled trial was performed to establish the duration of action of antihistamines and their ability to attenuate the adverse affects associated with histamine release. Thirty volunteers were assigned randomly to receive either placebo or a combination of the H1 blocker dimetindene maleate (0.1 mg/kg) and the H2 blocker cimetidine (5 mg/kg). A bolus dose of histamine (450 ng/kg) was given 15 minutes after antihistamine or placebo treatment and repeated after 2, 4, and 6 hours. Cardiovascular variables, plasma histamine levels, cutaneous manifestations, and objective and subjective signs and symptoms associated with histamine release were determined before and after each histamine injection. Although many of the signs of histamine release, including erythema and metallic taste, could be attenuated effectively for 6 hours with antihistamine treatment, the protection against histamine-induced flush and headache diminished after 2 hours. Statistically significant protection against histamine-mediated tachycardia persisted for only 2 hours. Antihistamine treatment significantly reduced the increase in plasma histamine levels after the first histamine injection but did not alter the levels after subsequent histamine injections. The currently recommended administration regimen for prophylaxis with antihistamines is insufficient to prevent histamine-mediated side effects, and additional doses may be required after 4 hours to achieve appropriate chemoprophylaxis.

Adult↗
PubMed1991

Controlled clinical trials and cross-sectional studies with plasma histamine measurements and histamine receptor antagonists: solving the problem of preoperative H1- + H2-prophylaxis by asking new questions?

The problem of a preoperative histamine H1- + H2 - prophylaxis was tackled by a group of new studies including randomized controlled clinical trials and cross-sectional studies with plasma histamine measurements and administration of H1- + H2 - antagonists to a control group. The first study demonstrated serial histamine release in the induction of anaesthesia up to 4 times in a single patient. Basal plasma histamine levels in resting subjects fell below 100 pg/ml during the time necessary for preparation of the surgical patient. Hence, spikes of elevated plasma histamine concentrations corresponded to histamine release. Although this histamine release very often was less than 1 ng/ml plasma histamine, it created systemic reactions after atracurium. The cut-off point of 1 ng/ml for such anaphylactoid reactions does no longer exist, also lower plasma levels are of patho-physiological significance. The clinical signs of histamine release in the induction of anaesthesia vary from drug to drug. Sometimes tachycardia and hypertension produce the highest likelihood ratio, sometimes tachy- and bradycardia, but no changes in blood pressure as in the case of atracurium. It is concluded that the reasons why histamine release in anaesthesia and surgery is so much underreported and under-estimated include the present paradigms about plasma histamine levels and the "classical picture" of histamine release. Both are no longer valid and need a re-assessment.

Adolescent↗
PubMed1991

Importance of histamine for seizure susceptibility.

The influence of drugs affecting the turnover of histamine in brain and histamine antagonists on pentetrazole seizure threshold in mice was studied. A rise in histamine brain concentration as well as treatment with central acting H1-, but not H2- and H3-antagonists led to an increase of the convulsive threshold. It is therefore concluded that histamine has a certain anticonvulsant effect which is mediated through H1-receptors.

Animals↗
PubMed1990

Time course of the effect of intravenous dimetindene maleate.

In order to evaluate the time course of its effects, dimetindene maleate has been investigated in a histamine provocation model in man. Eight healthy male volunteers were treated i.v. with 4 mg dimetindene maleate or sodium chloride solution in a double blind, cross over study. Intracutaneous histamine injections were given at -1, 2, 5, 14, 17, 20, 23, 26, and 29 h following drug administration and the areas of flares and wheals were measured after 5, 10, 20, and 30 min. There was strong inhibition of the development both of flares and wheals, which was more pronounced for the former. Baseline adjusted areas under the curve differed significantly following drug and placebo treatment. The maximum effect was observed at 2 h. The mean residence time of the inhibitory effect was calculated to be approximately 13 h compared to the mean residence time of dimetindene in blood of approximately 5 h, which indicates a non-linear relationship between blood level and effect.

Adult↗
PubMed1986

Electrophysiological characterization of histamine receptor subtypes in mammalian heart preparations.

Histamine-induced electrophysiological effects have been investigated in guinea-pig left atria, papillary muscles and rabbit AV-nodal preparations by means of intracellular recording of action potentials, slow responses in the presence of 27 mmol/l (K+)o and voltage clamp experiments. Differentiation of the H-receptor subtypes was performed by the use of the H2-selective agonists dimaprit and impromidine and the H1- and H2-selective antagonists dimetindene and cimetidine, respectively. The following results were obtained: Histamine and the H2-agonists dimaprit and impromidine show similar actions on electrophysiological parameters of ventricular myocardium. Histamine at concentrations less than 1 mumol/l leads to a small increase in APD30 and APD90, but to a marked decrease at concentrations greater than or equal to 1 mumol/l, whereas Vmax, resting potential and amplitude remain nearly unchanged. The effects on ADP are completely blocked by cimetidine and not changed by dimetindene. Changes in action potential may be explained by an increased in slow inward current and outward currents as shown by voltage clamp experiments. In left atria histamine increases APD30 and APD90, whereas there is only a minor increase in amplitude with no changes in Vmax and resting potential. These effects are completely reversed by the H1-antagonist dimetindene but not by cimetidine. IBMX decreases APD90 and does not potentiate the action of histamine. Vmax of slow responses is increased in left atria by stimulation of H1-receptors and in papillary muscles by stimulation of H2-receptors. The results suggest that stimulation of atrial H1-receptors directly causes an increase in Ca-channel conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1982

Prophylaxis of anaphylactoid reactions to a polypeptidal plasma substitute by H1- plus H2-receptor antagonists: synopsis of three randomized controlled trials.

To demonstrate the efficacy of a premedication with H1- + H2-receptor antagonists against histamine-release responses in anaesthesia and surgery 3 randomized controlled trials were conducted in patients, volunteers and experimental animals (dogs). Cutaneous anaphylactoid reactions following infusion of polygeline (Haemaccel) in orthopedic patients were successfully abolished by premedication with 0.1 mg/kg dimethpyrindene (Fenistil) and 5 mg/kg cimetidine (Tagamet). Chlorpheniramine (Piriton) was also useful, but dimethpyrindene was more effective in the doses recommended and used. Side-effects of the premedication were not observed when the 2 drugs were slowly administered (2 min each). Systemic anaphylactoid reactions following infusion of polygeline were completely prevented in volunteers by the same premedication (0.1 mg/kg dimethpyrindene and 10 mg/kg cimetidine). Life-threatening reactions could not be tested in human subjects, but were elicited in experimental animals (dogs). In this species which resembles man in its sensitivity against histamine, in plasma histamine levels and in response to polygeline life-threatening reactions were prevented or in especially severe cases diminished to such an extent by the premedication with H1- + H2-blockers that this premedication was finally judged to be very effective against histamine-release responses of any grade of severity. To confirm this clinically very important hypothesis more clinical trials in patients at risk for anaphylactoid reactions to drugs are urgently needed.

Adult↗