How do I convert a DDAVP (Desmopressin) IV dose of 3 mcg twice daily to nasal and oral forms?

Converting DDAVP IV Dose to Nasal and Oral Forms

For a patient on DDAVP (desmopressin) IV 3 mcg twice daily, convert to oral tablets at 60 mcg twice daily and intranasal spray at 10 mcg twice daily.

Conversion Ratios and Bioavailability

When converting between DDAVP formulations, it's important to understand the different bioavailability of each route:

• IV to Intranasal conversion ratio: 1:3-4

  • IV 3 mcg = Intranasal 10 mcg

• IV to Oral conversion ratio: 1:20

  • IV 3 mcg = Oral 60 mcg

These conversion ratios are based on bioavailability differences between formulations. The FDA label for desmopressin states that when switching from nasal spray to injection, the starting dose is one-tenth of the nasal spray dose 1. Conversely, when switching from injection to nasal spray, multiply by 10.

Specific Dosing Recommendations

IV to Intranasal Conversion

• Current dose: 3 mcg IV twice daily
• Recommended intranasal dose: 10 mcg twice daily
• Available as: Nasal spray (typically 10 mcg per spray)
• Administration: One spray in one nostril twice daily

IV to Oral Conversion

• Current dose: 3 mcg IV twice daily
• Recommended oral dose: 60 mcg twice daily
• Available as: Tablets (typically 100,200, or 400 mcg)
• Administration: Consider using 100 mcg tablets (half tablet twice daily) or adjust to nearest available tablet strength

Evidence for Conversion Ratios

The conversion ratio of approximately 1:20 for IV to oral is supported by multiple studies:

• A retrospective analysis found the mean nasal dosage was 20.4 mcg and mean oral dosage was 417 mcg, giving a dosage ratio of about 20 2
• Pharmacokinetic studies show the bioequivalent intranasal/oral ratio was 1:16 3

For IV to intranasal conversion, the literature supports a ratio of approximately 1:10 when switching from injection to nasal spray 1, 4.

Important Monitoring Considerations

• Serum sodium levels: Monitor closely after conversion to detect hyponatremia
• Urine output: Assess adequacy of antidiuretic effect
• Duration of action: May vary between formulations (8-20 hours for intranasal; variable for oral)

Potential Pitfalls and Caveats

1. Individual variability: There is wide inter-individual variation in dose requirements and dosing intervals 5

2. Water intoxication risk: Excessive water intake while on DDAVP can lead to hyponatremia; instruct patients to limit fluid intake when thirst is not present

3. Bioavailability differences: Oral DDAVP has lower bioavailability (0.08-0.16%) compared to intranasal (3-5%), which is why the oral dose is much higher than the IV dose

4. Absorption issues: Nasal congestion, sinusitis, or improper administration technique can affect intranasal absorption

5. Timing considerations: The onset of action is typically faster with IV (immediate) and intranasal (15-30 minutes) compared to oral (60-90 minutes)

Always titrate the dose based on clinical response after conversion, as individual responses may vary significantly.