CLINICAL PHARMACOLOGY
Diazoxide administered orally produces a prompt
dose-related increase in blood glucose level, due primarily to an inhibition of
insulin release from the pancreas, and also to an extrapancreatic effect.
The hyperglycemic effect begins within an hour and
generally lasts no more than eight hours in the presence of normal renal function.
PROGLYCEM® decreases the excretion of sodium
and water, resulting in fluid retention which may be clinically significant.
The hypotensive effect of diazoxide on blood pressure is
usually not marked with the oral preparation. This contrasts with the
intravenous preparation of diazoxide (see ADVERSE REACTIONS).
Other pharmacologic actions of PROGLYCEM® include
increased pulse rate; increased serum uric acid levels due to decreased
excretion; increased serum levels of free fatty acids' decreased chloride
excretion; decreased para-aminohippuric acid; (PAH) clearance with no
appreciable effect on glomerular filtration rate.
The concomitant administration of a benzothiazide
diuretic may intensify the hyperglycemic and hyperuricemic effects of PROGLYCEM®.
In the presence of hypokalemia, hyperglycemic effects are also potentiated.
PROGLYCEM®-induced hyperglycemia is reversed
by the administration of insulin or tolbutamide. The inhibition of insulin
release by PROGLYCEM® is antagonized by alphaadrenergic blocking
agents.
PROGLYCEM® is extensively bound (more than
90%) to serum proteins, and is excreted in the kidneys. The plasma half-life
following I.V. administration is 28 ± 8.3 hours. Limited data on oral
administration revealed a half-life of 24 and 36 hours in two adults. In four
children aged four months to six years, the plasma half-life varied from 9.5 to
24 hours on long-term oral administration. The half-life may be prolonged following
overdosage, and in patients with impaired renal function.
Animal Pharmacology And/Or Toxicology
Oral diazoxide in the mouse, rat, rabbit, dog, pig, and
monkey produces a rapid and transient rise in blood glucose levels. In dogs,
increased blood glucose is accompanied by increased free fatty acids, lactate,
and pyruvate in the serum. In mice, a marked decrease in liver glycogen and an
increase in the blood urea nitrogen level occur.
In acute toxicity studies the LD50 for oral diazoxide
suspension is > 5000 mg/kg in the rat, > 522 mg/kg in the neonatal rat,
between 1900 and 2572 mg/kg in the mouse, and 219 mg/kg in the guinea pig.
Although the oral LD50 was not determined in the dog, a dosage of up to 500
mg/kg was well tolerated.
In subacute oral toxicity studies, diazoxide at 400 mg/kg
in the rat produced growth retardation, edema, increases in liver and kidney
weights, and adrenal hypertrophy. Daily dosages up to 1080 mg/kg for three
months produced hyperglycemia, an increase in liver weight and an increase in
mortality. In dogs given oral diazoxide at approximately 40 mg/kg/day for one
month, no biologically significant gross or microscopic abnormalities were
observed. Cataracts, attributed to markedly disturbed carbohydrate metabolism,
have been observed in a few dogs given repeated daily doses of oral or intravenous
diazoxide. The lenticular changes resembled those which occur experimentally in
animals with increased blood glucose levels. In chronic toxicity studies, rats
given a daily dose of 200 mg/kg diazoxide for 52 weeks had a decrease in weight
gain and an increase in heart, liver, adrenal and thyroid weights. Mortality in
drug-treated and control groups was not different. Dogs treated with diazoxide
at dosages of 50, l00, and 200 mg/kg/day for 82 weeks had higher blood glucose
levels than controls. Mild bone marrow stimulation and increased pancreas
weights were evident in the drug-treated dogs; several developed inguinal
hernias, one had a testicular seminoma, and another had a mass near the penis.
Two females had inguinal mammary swellings. The etiology of these changes was
not established. There was no difference in mortality between drug-treated and
control groups. In a second chronic oral toxicity study, dogs given milled
diazoxide at 50, l00, and 200 mg/kg/day had anorexia and sever weight loss,
causing death in a few. Hematologic, biochemical, and histologic examination
did not indicate any cause of death other than inanition. After one year of
treatment, there is no evidence of herniation or tissue swelling in any of the
dogs.
When diazoxide was administered at high dosages
concomitantly with either chlorothiazide to rats or trichlormethiazide to dogs,
increased toxicity was observed. In rats, the combination was nephrotoxic;
epithelial hyperplasia was observed in the collecting tubules. In dogs, a
diabetic syndrome was produced which resulted in ketosis and death. Neither of
the drugs given alone produced these effects.
Although the data are inconclusive, reproduction and
teratology studies in several species of animals indicate that diazoxide, when
administered during the critical period of embryo formation, may interfere with
normal fetal development, possibly through altered glucose metabolism.
Parturition was occasionally prolonged in animals treated at term. Intravenous
administration of diazoxide to pregnant sheep, goats, and swine produced in the
fetus an appreciable increase in blood glucose level and degeneration of the
beta cells of the Islets of Langerhans. The reversibility of these effects was
not studied.