Stability of phenoxybenzamine hydrochloride in various vehicles

The stability of phenoxybenzamine hydrochloride in various oral liquids was studied. Phenoxybenzamine hydrochloride powder or capsules were combined with various vehicles to prepare 10-mL formulations with a drug concentration of 2 mg/mL and a 20-mL stock solution containing 10 mg/mL. All formulations were prepared in triplicate and stored at 4 degrees C. A 1.0-mL sample of each of the 2-mg/mL formulations was withdrawn on days 0, 1, 2, 3, and 4, and samples of selected formulations were taken on days 7 and 10. Samples of the stock solution were withdrawn on days 0, 2, 4, 7, 10, 14, and 30. All samples were analyzed by high-performance liquid chromatography. Phenoxybenzamine hydrochloride 2 mg/mL was stable for a longer time in 1% propylene glycol, 0.15% citric acid, and water than in a similar vehicle in which syrup was used in place of water. The concentrations of the drug in both the 10-mg/mL stock solution and stock solutions diluted to 2 mg/mL were > 90% of the initial drug concentration for 30 days. Phenoxybenzamine hydrochloride 2 mg/mL in 1% propylene glycol and 0.15% citric acid in distilled water was stable for 7 days at 4 degrees C. A stock solution of phenoxybenzamine hydrochloride 10 mg/mL in propylene glycol was stable for 30 days at 4 degrees C and, after dilution with 66.7% sucrose in distilled water to a concentration of 2 mg/mL, for up to one hour at 4 degrees C.

Alpha-adrenoceptor reserve in the canine cephalic vein

In the canine cephalic vein, the pD2 for the selective alpha 1-agonist, phenylephrine, was 6.08 +/- 0.08 (n = 14) and that for the selective alpha 2-agonist, UK-14,304, was 8.32 +/- 0.06 (n = 10). The pA2 values for the antagonism exerted by the selective alpha 1-antagonist, prazosin, against phenylephrine and UK-14,304 were 7.74 +/- 0.05 (n = 14) and 6.28 +/- 0.03 (n = 8), respectively, while those for the antagonism exerted by the selective alpha 2-antagonist, yohimbine, against phenylephrine and UK-14,304 were 7.40 +/- 0.02 (n = 14) and 8.93 +/- 0.05 (n = 14), respectively. Furthermore, the concentration-response curve for UK-14,304 was typically biphasic, the first phase being antagonized by yohimbine and the second phase by prazosin and phenoxybenzamine. These results show that there are postsynaptic alpha 1- and alpha 2-adrenoceptors in the canine cephalic vein. In such a preparation, only one concentration of phenoxybenzamine (1 nM) shifted the concentration-response curves for noradrenaline, adrenaline and isoprenaline to the right without reducing the maximum. However, at the concentrations tested, phenoxybenzamine did not shift the concentration-response curve for phenylephrine to the right without depressing its maximum. It is concluded that: (1) the canine cephalic vein is a suitable preparation to study postsynaptic alpha 1- and alpha 2-adrenoceptors; (2) according to the original definition of 'spare receptors', there is no alpha 1-adrenoceptor reserve in canine cephalic vein; (3) UK-14,304 is a partial agonist at alpha 1-adrenoceptors.

13C-NMR spectra of alpha-adrenergic blocking agents

The natural abundance 13C-NMR spectra of five alpha-adrenergic blocking agents, tolazoline, dibenamine, azapetine, phenoxybenzamine, and phentolamine, are reported. The chemical shifts of various carbon resonances were assigned on the basis of chemical shift theory, multiplicities observed in single-frequency off-resonance-decoupled spectra, relaxation times, and comparisons with the chemical shifts of model compounds.

Insulin secretion studied in the perfused rat pancreas. II. Effect of glucose, glucagon, 3'5' adenosine monophosphate, theophylline, imidazole and phenoxybenzamine; their interaction with diazoxide

This communication reports studies dealing with the action of glucagon, theophylline, cyclic adenosine monophosphate (3′5′.AMP) and phenoxybenzamine on insulin secretion, and their possible interaction with glucose and diazoxide.

Diazoxide inhibited both phases of insulin secretion produced by glucose. This blocking action was suppressed when the alpha-blocking phenoxybenzamine was present.

Glucagon produced a uniform pattern of insulin secretion when perfused alone. A one-minute pulse of 3′5′.AMP produced a sharp peak of insulin secretion. Neither glucagon nor 3′5′.AMP effects were inhibited by diazoxide.

Theophylline did not increase the basal insulin-secretion. However, when perfused together with glucose, theophylline stimulated additional insulin secretion, significantly higher than that produced by glucose alone.

When combinations of glucagon plus glucose, 3′5′.AMP plus glucose and theophylline plus glucose, were perfused, diazoxide blocked the secretion of insulin stimulated by glucose, but not that produced by glucagon, 3′5′.AMP or theophylline. This suggests that glucagon, 3′5′.AMP and theophylline stimulate insulin secretion by actingon mechanismsdifferent from the ones stimulated by glucose