Dose response studies in patients with diabetes insipidus have demonstrated that oral doses of 0.025 mg to 0.4 mg produced clinically significant antidiuretic effects. In most patients, doses of 0.1 mg to 0.2 mg produced optimal antidiuretic effects lasting up to eight hours. With doses of 0.4 mg, antidiuretic effects were observed for up to 12 hours; measurements beyond 12 hours were not recorded. Increasing oral doses produced dose dependent increases in the plasma levels of Desmopressin Acetate Tablets.
The plasma half-life of Desmopressin Acetate Tablets followed a monoexponential time course with t1/2 values of 1.5 to 2.5 hours which was independent of dose.
The bioavailability of Desmopressin Acetate Tablets are about 5% compared to intranasal desmopressin acetate, and about 0.16% compared to intravenous desmopressin acetate. The time to reach maximum plasma desmopressin acetate levels ranged from 0.9 to 1.5 hours following oral or intranasal administration, respectively. Following administration of Desmopressin Acetate Tablets, the onset of antidiuretic effect occurs at around 1 hour, and it reaches a maximum at about 4 to 7 hours based on the measurement of increased urine osmolality.
The use of Desmopressin Acetate Tablets in patients with an established diagnosis will result in a reduction in urinary output with an accompanying increase in urine osmolality. These effects usually will allow resumption of a more normal life style, with a decrease in urinary frequency and nocturia.
There are reports of an occasional change in response to the intranasal formulations of desmopressin acetate (Desmopressin Acetate Nasal Spray and Desmopressin Acetate Rhinal Tube). Usually, the change occurred over a period of time greater than six months. This change may be due to decreased responsiveness, or to shortened duration of effect. There is no evidence that this effect is due to the development of binding antibodies, but may be due to a local inactivation of the peptide. No lessening of effect was observed in the 46 patients who were treated with Desmopressin Acetate Tablets for 12 to 44 months and no serum antibodies to desmopressin were detected.
The change in structure of arginine vasopressin to desmopressin acetate resulted in less vasopressor activity and decreased action on visceral smooth muscle relative to enhanced antidiuretic activity. Consequently, clinically effective antidiuretic doses are usually below the threshold for effects on vascular or visceral smooth muscle. In the four long-term studies of Desmopressin Acetate Tablets, no increases in blood pressure in 46 patients receiving Desmopressin Acetate Tablets for periods of 12 to 44 months were reported.
In one study, the pharmacodynamic characteristics of Desmopressin Acetate Tablets and intranasal formulation were compared during an 8-hour dosing interval at steady state. The doses administered to 36 hydrated (water loaded) healthy male adult volunteers every 8 hours were 0.1, 0.2, 0.4 mg orally and 0.01 mg intranasally by rhinal tube. The results are shown in the following table:
Mean Changes from Baseline (SE) in Pharmacodynamic Parameters in Normal Healthy Adult Volunteers| Treatment | Total Urine Volume in mL | Maximum Urine Osmolality in mOsm/kg |
|---|
| (SE) = Standard error of the mean |
| 0.1 mg PO q8h | -3689.3 (149.6) | 514.8 (21.9) |
| 0.2 mg PO q8h | -4429.9 (149.6) | 686.3 (21.9) |
| 0.4 mg PO q8h | -4998.8 (149.6) | 769.3 (21.9) |
| 0.01 mg IN q8h | -4844.9 (149.6) | 754.1 (21.9) |
With respect to the mean values of total urine volume decrease and maximum urine osmolality increase from baseline, the 90% confidence limits estimated that the 0.4 mg and 0.2 mg oral dose produced between 95% and 110% and 84% to 99% of pharmacodynamic activity, respectively, when compared to the 0.01 mg intranasal dose.
While both the 0.2 mg and 0.4 mg oral doses are considered pharmacodynamically similar to the 0.01 mg intranasal dose, the pharmacodynamic data on an inter-subject basis was highly variable and, therefore, individual dosing is recommended.
In another study in diabetes insipidus patients, the pharmacodynamic characteristics of desmopressin acetate tablets and intranasal formulations were compared over a 12-hour period. Ten fluid-controlled patients under age 18 were administered tablet doses of 0.2 mg and 0.4 mg, and intranasal doses of 0.01 mg and 0.02 mg.
Mean Peak Pharmacodynamic Parameters (SD) in Pediatric and Adolescent Diabetes Insipidus Patients| Treatment | Urine Volume in mL/min | Maximum Urine Osmolality in mOsm/kg |
|---|
| (SE) = Standard error of the mean |
| 0.01 mg IN | 0.3 (0.15) | 717.0 (224.63) |
| 0.02 mg IN | 0.3 (0.25) | 761.8 (298.82) |
| 0.2 mg PO | 0.3 (0.12) | 678.3 (147.91) |
| 0.4 mg PO | 0.2 (0.15) | 787.2 (73.34) |
All four dose formulations (0.01 mg IN, 0.02 mg IN, 0.2 mg PO and 0.4 mg PO) have a similar, pronounced pharmacodynamic effect on urine volume and urine osmolality. At two hours after study drug administration, mean urine volume was 4 mL/min and urine osmolality was >500 mOsm/kg. Mean plasma osmolality remained relatively constant over the time course recorded (0 to 12 hours). A statistical separation from baseline did not occur at any dose or time point. In these patients, the 0.2 mg tablets and the 0.01 mg intranasal spray exhibited similar pharmacodynamic profiles as did the 0.4 mg tablets and the 0.02 mg intranasal spray formulation. In another study of adult diabetes insipidus patients previously controlled on desmopressin acetate intranasal spray, after one week of self-titration from spray to tablets, patients' diuresis was controlled with 0.1 mg desmopressin acetate tablets three times a day.
Desmopressin Acetate Tablets are indicated as antidiuretic replacement therapy in the management of central diabetes insipidus and for the management of the temporary polyuria and polydipsia following head trauma or surgery in the pituitary region. Desmopressin Acetate Tablets are ineffective for the treatment of nephrogenic diabetes insipidus.
Patients were selected for therapy based on the diagnosis by means of the water deprivation test, the hypertonic saline infusion test, and/or response to antidiuretic hormone. Continued response to Desmopressin Acetate Tablets can be monitored by measuring urine volume and osmolality.
Laboratory tests for monitoring the patient with central diabetes insipidus or postsurgical or head trauma-related polyuria and polydipsia include urine volume and osmolality. In some cases, measurements of plasma osmolality may be useful.
Desmopressin Acetate Tablets have been used safely in pediatric patients, age 4 years and older, with diabetes insipidus for periods up to 44 months. In younger pediatric patients the dose must be individually adjusted in order to prevent an excessive decrease in plasma osmolality leading to hyponatremia and possible convulsions; dosing should start at 0.05 mg (1/2 of the 0.1 mg tablet). Use of Desmopressin Acetate Tablets in pediatric patients requires careful fluid intake restrictions to prevent possible hyponatremia and water intoxication. Fluid restriction should be discussed with the patient and/or guardian. (See WARNINGS.)
In long-term clinical studies in which patients with diabetes insipidus were followed for periods up to 44 months of Desmopressin Acetate Tablets therapy, transient increases in AST (SGOT) no higher than 1.5 times the upper limit of normal were occasionally observed. Elevated AST (SGOT) returned to the normal range despite continued use of Desmopressin Acetate Tablets.
The dosage of Desmopressin Acetate Tablets must be determined for each individual patient and adjusted according to the diurnal pattern of response. Response should be estimated by two parameters: adequate duration of sleep and adequate, not excessive, water turnover. Patients previously on intranasal desmopressin acetate therapy should begin tablet therapy twelve hours after the last intranasal dose. During the initial dose titration period, patients should be observed closely and appropriate safety parameters measured to assure adequate response. Patients should be monitored at regular intervals during the course of desmopressin acetate therapy to assure adequate antidiuretic response. Modification in dosage regimen should be implemented as necessary to assure adequate water turnover. Fluid restriction should be observed. (See WARNINGS, PRECAUTIONS, Pediatric Use and Geriatric Use.)