From the Guidelines
The equivalent oral (PO) dose of hydralazine for 10 mg administered intravenously (IV) is approximately 50 mg, based on a 1:5 ratio due to significant first-pass metabolism. When converting from IV to oral hydralazine, this ratio is used because oral hydralazine has a bioavailability of about 20-30% due to first-pass metabolism, as noted in general pharmacological principles 1. This means that only about one-fifth of an oral dose reaches the systemic circulation compared to the same IV dose. Therefore, to achieve the same therapeutic effect as 10 mg IV hydralazine, a patient would need to take 50 mg orally.
- Key points to consider when making this conversion include:
- Monitoring the patient's blood pressure response to ensure the oral dose is providing an adequate antihypertensive effect.
- Being aware that individual variations in metabolism can affect the exact equivalence.
- Noting the difference in onset of action between IV and oral hydralazine, with IV hydralazine acting within 5-20 minutes and oral hydralazine taking 30-60 minutes to begin working, as generally understood in clinical practice 1.
- The provided evidence tables, such as Table 18 and Table 19, offer detailed information on various antihypertensive drugs, including their usual dose ranges and comments on their use 1. However, the specific conversion ratio for hydralazine from IV to PO is not directly stated in these tables but is based on pharmacokinetic principles.
- It's crucial to consult the most recent and highest quality studies for specific guidance on drug conversions and to always prioritize patient safety and monitoring when switching between different routes of administration.
From the Research
Hydralazine Equivalent Doses
- The equivalent oral (PO) dose of hydralazine for 10 mg administered intravenously (IV) is not directly stated in the provided studies.
- However, study 2 mentions that oral hydralazine doses of 50 or 75 mg were used to treat chronic refractory heart failure, and study 3 evaluated hemodynamic responses to different doses of hydralazine, including 50,75, and 100 mg.
- Study 4 investigated the effect of oral hydralazine, 300 mg per day, on blood pressure in hypertensive patients, but does not provide a direct comparison to IV doses.
- Based on the available information, it can be inferred that the oral dose of hydralazine is typically higher than the IV dose, but the exact equivalent dose for 10 mg IV is not specified in the provided studies 5, 6, 2, 3, 4.
Dosage Considerations
- The dosage of hydralazine needed to induce hemodynamic improvement in patients with severe heart failure is variable and requires individualization, as stated in study 3.
- Study 4 suggests that a daily dose of 300 mg of hydralazine can be effective in treating hypertension, but the optimal dosing regimen may depend on various factors, including patient response and renal function.