Pharmacodynamics and pharmacokinetics of isosorbide in man

Live Imaging of the Dehydration Effect of Isosorbide on the Normal and Hydropic Guinea Pig Cochleae Using Optical Coherence Tomography

OBJECTIVE

To investigate the isosorbide-induced dehydration effect on the endolymphatic space by intratympanic administration of isosorbide.

BACKGROUND

Isosorbide, an osmotic diuretic, is used orally as a typical conservative therapy for Menière's disease (MD) in Japan. The dehydration effect occurs 6 hours after isosorbide ingestion. Intratympanic administration of isosorbide resolves endolymphatic hydrops faster than oral ingestion. In addition, the dehydration effect has never been shown directly. Therefore, we investigated the dehydration effect of intratympanic administration of isosorbide on endolymphatic hydrops using optical coherence tomography.

METHODS

We used eight Hartley guinea pigs, divided into normal and hydrops groups. In the hydrops group, the animals underwent endolymphatic sac obliteration to create endolymphatic hydrops. We obtained midmodiolar section images of the cochleae using optical coherence tomography. Then, 50 to 70% isosorbide was sequentially administered intratympanically for 5 minutes, and the apical turn of the cochlea was observed. The relative midmodiolar cross-sectional area of the scala media was calculated for quantitative assessment of the endolymphatic space.

RESULTS

In the normal group, 50% isosorbide had a slight but significant dehydration effect on the scala media; at 55 to 70%, Reissner's membrane became flat. In the hydrops group, 50% isosorbide slightly reduced endolymphatic hydrops; 65% flattened Reissner's membrane, and 70% slightly concaved it toward the basilar membrane.

CONCLUSION

The results suggest that we could select the concentration of isosorbide according to the stage or severity of MD and relief from acute attack. Intratympanic administration of isosorbide may be a promising treatment for patients with MD.

Isosorbide-Induced Decompression Effect on the Scala Media: Participation of Plasma Osmolality and Plasma Arginine Vasopressin

OBJECTIVE

The correlation between the isosorbide-induced decompression effect on the endolymphatic space and plasma osmolality (p-OSM) or plasma arginine vasopressin (p-AVP) was investigated on comparing two different dosages of isosorbide (2.8 and 1.4 g/kg) to elucidate why the decompression effect is delayed with a large dose of isosorbide.

MATERIALS AND METHODS

Two experiments were performed using 80 guinea pigs. Experiment 1 was designed to morphologically investigate the sequential influence of the oral intake of 1.4- and 2.8-g/kg doses of isosorbide on the endolymphatic volume. The animals used were 50 guinea pigs (control: 10, experimental: 40). All animals underwent surgical obliteration of the endolymphatic sac of the left ear. One month after the surgery, control animals were sacrificed 3 hours after the intake of distilled water, and experimental animals were sacrificed 3 and 6 hours after the isosorbide intake. All of the left temporal bone served for the quantitative assessment of changes in the endolymphatic space, and the cross-sectional area of the scala media was measured from the mid-modiolar sections of the cochlea.Experiment 2 was designed to investigate changes in p-OSM and p-AVP levels 3 hours after the oral intake of isosorbide. Animals used were 15 guinea pigs (control: 5, experimental: 10). The control group received the oral administration of distilled water (4 ml/kg), and the experimental animals were subdivided into two groups consisting of 10 animals each by the dosage of isosorbide (1.4 or 2.8 g/kg). All animals were sacrificed for the measurement of p-OSM and p-AVP concentrations 3 hours after the intake of water or 70% isosorbide solution.

RESULTS

Morphologically, an isosorbide-induced decompression effect was noted in animals with both 1.4- and 2.8-g/kg doses of isosorbide. According to the regression analysis, however, the volumetric decrease of the endolymphatic space was more evident in cases with the small dose (1.4 g/kg) 3 hours after the intake (analysis of covariance [ANCOVA], p < 0.001). Six hours after, the decompression effect was significantly greater in cases with the large dose (2.8 g/kg) (ANCOVA, p < 0.001).Isosorbide intake caused a rise in p-OSM levels dose-dependently. The Cochran-Cox test revealed that the differences in the mean values among control and isosorbide groups were significant (p < 0.01). Regarding the p-AVP level, a significant increase was evident in cases with the large dose (2.8 g/kg) (p < 0.01, Cochran-Cox test), and not in cases with the small dose (1.4 g/kg).

CONCLUSION

An isosorbide-induced decompression effect of the endolymphatic space was evident in spite of two different dosages of isosorbide (2.8 and 1.4 g/kg). Three hours after the isosorbide intake, however, the decompression effect was more marked in the group with the small dose (1.4 g/kg). Since significant rises in p-OSM and p-AVP were evident in the group with the large dose, this early rise of p-AVP due to dehydration seems to be the major reason for the delayed decompression effect in cases with a large isosorbide intake.

History of the synthesis and pharmacology of isosorbide dinitrate

A major research program in the University of Maryland School of Medicine, Department of Pharmacology, in the 1930s was the preparation of a large number of sugar alcohols and their anhydrides as substitute carbohydrates for diabetic diets. As an outgrowth of this work, many of these polyols were converted to their nitrate esters and investigated for their vasodilating properties. The organic nitrates that were synthesized were examined for their potency, duration of action, and possible therapeutic use. It was demonstrated that, contrary to prior belief, the depressor and vasodilating action was exhibited by their own molecular structure and not through hydrolysis and reduction to nitrite. The search for the finer mechanism(s) of action on the vascular musculature showed that these nitrated polyols and their anhydrides inhibited arterial adenosine triphosphatase, although this enzyme inhibition did not correlate with pharmacologic activity. Today the mechanism of action of these drugs is not clearly understood at the cellular level. The 1,4:3,6-dianhydrosorbitol 2,5-dinitrate (isosorbide dinitrate) was synthesized, studied, and reported in 1940. It appeared to be a useful drug because blood levels of the unhydrolyzed ester were found to persist for long periods of time. Subsequent clinical studies in the 1960s demonstrated its prophylactic value in angina pectoris and its prolonged action as a therapeutic asset. In 1967 the mononitrate was shown to be formed in vivo when the dinitrate was administered orally and has been studied as the possible pharmacodynamically active moiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis and microbiological stability of an isosorbide 50% mixture

Isosorbide mixture containing 50% w/v isosorbide and 5% w/v sorbitol is used in the treatment of hydrocephalus. The G.L.C. analysis of the mixture is described and its antimicrobial properties investigated. Results for the determination of lead in the mixture are given and the significance of the levels discussed with relevance to the treatment of infants.

Gallium nitrate (NSC-15200) induced toxicity in the rat: a pharmacologic, histopathologic and microanalytical investigation

Administration of gallium nitrate to rats resulted in the formation of renal precipitates which occluded tubular lumina. When analyzed with a combination of scanning electron microscopy and x-ray energy spectrometry, these precipitates were found to contain gallium complexed with calcium and phosphate. Injection of gallium nitrate also resulted in hypercalciuria, although serum calcium levels remained unaltered. Administration of an osmotic diuretic, isosorbide, prior to gallium treatment resulted in the formation of fewer renal precipitates and histopathologic changes than in the nondiuresed animals. Diuresis did not alter gallium serum pharmacokinetics, the 24 hour cumulative renal excretion of gallium or the extent of the drug-induced hypercalciuria. However, isosorbide pretreatment significantly reduced the urinary concentrations of both gallium and calcium. The data presented indicate that diuresis reduces the severity of gallium-induced renal lithiasis and subsequent renal accumulation of gallium by diluting the urinary concentration of gallium and calcium thereby lowering the incidence of interaction of these two elements within the kidney tubule.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.