Calculates IV-to-oral conversions and opioid equianalgesic dosing. Use when converting medication routes, calculating equianalgesic doses, or transitioning IV to oral therapy.
Calculates IV-to-oral conversions and opioid equianalgesic dosing for safe medication route transitions.
Intravenous-to-oral (IV-to-PO) conversion is one of the most impactful pharmacist interventions in the inpatient setting. IV medications cost 2-5 times more than their oral equivalents, require nursing time for administration, carry catheter-related infection risk, and may prolong hospital stay. Studies demonstrate that systematic IV-to-PO conversion programs reduce IV antibiotic days by 20-40%, decrease length of stay, and save institutions hundreds of thousands of dollars annually.
However, incorrect conversion carries serious risk. Not all drugs have 1:1 bioavailability (e.g., oral morphine is only 30% bioavailable compared to IV), and some medications require different doses by different routes (e.g., metoprolol IV:PO ratio is 1:2.5). Opioid equianalgesic dosing errors are a leading cause of preventable overdose deaths in hospitals—the ISMP has issued multiple alerts about fatal errors in opioid conversions, particularly involving methadone and fentanyl patches. Pharmacists must apply pharmacokinetic principles, bioavailability data, and conservative dosing strategies (including safety reductions) when converting routes.
The patient must meet ALL of the following for IV-to-PO conversion:
Drugs NOT appropriate for simple IV-to-PO conversion:
High Bioavailability (≥80%) — 1:1 Dose Conversion:
| Drug | IV Dose | PO Dose | Oral Bioavailability |
|---|---|---|---|
| Fluoroquinolones (levofloxacin, moxifloxacin) | 500 mg IV | 500 mg PO | ~99% |
| Metronidazole | 500 mg IV | 500 mg PO | ~100% |
| Fluconazole | 400 mg IV | 400 mg PO | ~90% |
| Linezolid | 600 mg IV | 600 mg PO | ~100% |
| TMP-SMX | 5 mg/kg IV q6h | 1 DS tab PO q12h (equivalent) | ~95% |
| Clindamycin | 600 mg IV q8h | 300-450 mg PO q6-8h | ~90% |
| Doxycycline | 100 mg IV q12h | 100 mg PO q12h | ~93% |
| Voriconazole | 4 mg/kg IV q12h | 200 mg PO q12h | ~96% |
Moderate Bioavailability — Dose Adjustment Required:
| Drug | IV Dose | PO Dose | Conversion Notes |
|---|---|---|---|
| Pantoprazole | 40 mg IV q12-24h | 40 mg PO daily | PO adequate for most non-ICU indications |
| Metoprolol | 5 mg IV | 12.5-25 mg PO | IV:PO ratio ~1:2.5 |
| Labetalol | 20 mg IV | 100-200 mg PO | ~25% bioavailability |
| Furosemide | 40 mg IV | 80 mg PO | ~50% oral bioavailability |
| Diazepam | 5 mg IV | 5 mg PO | ~100% but different onset |
| Hydralazine | 10 mg IV | 25-50 mg PO | Variable first-pass metabolism |
Equianalgesic Dose Table (approximate equivalence to morphine 10 mg IV):
| Opioid | IV/IM Dose | PO Dose | Conversion Factor (to PO morphine) |
|---|---|---|---|
| Morphine | 10 mg | 30 mg | 1.0 (reference) |
| Hydromorphone | 1.5 mg | 4 mg | PO: 4 mg = 30 mg PO morphine |
| Oxycodone | N/A (no IV in US) | 20 mg | PO: 20 mg = 30 mg PO morphine |
| Hydrocodone | N/A | 30 mg | PO: 30 mg = 30 mg PO morphine |
| Fentanyl | 100 mcg | N/A (transdermal/buccal) | See fentanyl patch conversion |
| Methadone | Variable | Variable | NON-LINEAR — use AMDG conversion |
Critical safety rules for opioid conversion:
Methadone conversion (AMDG Guidelines): Methadone has a non-linear equianalgesic ratio that increases with higher morphine doses:
| Daily Oral Morphine Equivalent | Morphine:Methadone Ratio |
|---|---|
| <60 mg | 4:1 |
| 60-200 mg | 8:1 |
| 200-500 mg | 10:1 |
| 500-1000 mg | 12:1 |
| >1000 mg | 15-20:1 |
Fentanyl transdermal patch conversion: Fentanyl 25 mcg/h patch ≈ 60-90 mg oral morphine/day (use conservative end)