CLINICAL PHARMACOLOGY
DDAVP Tablets contain as active substance, desmopressin acetate, a synthetic analogue of the natural hormone arginine vasopressin.
Central Diabetes Insipidus: 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 DDAVP (desmopressin acetate).
The plasma half-life of DDAVP followed a monoexponential time course with t½ values of 1.5 to 2.5 hours which was independent of dose.
The bioavailability of DDAVP oral tablets is about 5% compared to intranasal DDAVP, and about 0.16% compared to intravenous DDAVP. The time to reach maximum plasma DDAVP levels ranged from 0.9 to 1.5 hours following oral or intranasal administration, respectively. Following administration of DDAVP 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 DDAVP 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 DDAVP (DDAVP Nasal Spray and DDAVP 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 DDAVP 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 DDAVP Tablets, no increases in blood pressure in 46 patients receiving DDAVP Tablets for periods of 12 to 44 months were reported.
In one study, the pharmacodynamic characteristics of DDAVP 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 |
|
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) |
|
(SE) = Standard error of the mean
|
|
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 DDAVP 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 |
|
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) |
|
(SD) = Standard Deviation
|
|
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 DDAVP intranasal spray, after one week of self-titration from spray to tablets, patients' diuresis was controlled with 0.1 mg DDAVP Tablets three times a day. Primary Nocturnal Enuresis: Two double-blind, randomized, placebo-controlled studies were conducted in 340 patients with primary nocturnal enuresis. Patients were 5-17 years old, and 72% were males. A total of 329 patients were evaluated for efficacy. Patients were evaluated over a two-week baseline period in which the average number of wet nights was 10 (range 4-14). Patients were then randomized to receive 0.2, 0.4, or 0.6 mg of DDAVP or placebo. The pooled results after two weeks are shown in the following table:
Response to DDAVP and Placebo at Two Weeks of Treatment Mean (SE) Number of Wet Nights/2 Weeks
|
|
Placebo (n = 85) |
0.2 mg/day (n = 79) |
0.4 mg/day (n = 82) |
0.6 mg/day (n = 83) |
|
Baseline
|
10 (0.3) |
11 (0.3) |
10 (0.3) |
10 (0.3) |
Reduction from
Baseline
|
1 (0.3) |
3 (0.4) |
3 (0.4) |
4 (0.4) |
Percent Reduction
from Baseline
|
10%
|
27%
|
30%
|
40%
|
|
p-value vs placebo
|
— |
<0.05
|
<0.05
|
<0.05
|
|
Patients treated with DDAVP Tablets showed a statistically significant reduction in the number of wet nights compared to placebo-treated patients. A greater response was observed with increasing doses up to 0.6 mg.
In a six month, open-label extension study, patients completing the placebo-controlled studies were started on 0.2 mg/day DDAVP, and the dose was progressively increased until the optimal response was achieved (maximum dose 0.6 mg/day). A total of 230 patients were evaluated for efficacy; the average number of wet nights/2 weeks during the untreated baseline period was 10 (range 4-14), and the average duration (SD) of treatment was 4.2 (1.8) months. Twenty-five (25) patients (11%) achieved a complete or near complete response (
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