Absorption, Distribution and Excretion
Taking oral hydralazine with food improves the bioavailability of the drug. An intravenous dose of 0.3mg/kg leads to an AUC of 17.5-29.4µM\*min and a 1mg/kg oral dose leads to an AUC of 4.0-30.4µM\*min. The Cmax of oral hydralazine is 0.12-1.31µM depending on the acetylator status of patients.
<10% of hydralazine is recovered in the feces; 65-90% is recovered in the urine.
The volume of distribution is 1.34±0.79L/kg in congestive heart failure patients and 1.98±0.22L/kg in hypertensive patients.
The majority of hydralazine clearance is extrahepatic- 55% for rapid acetylators and 70% for slow acetylators. The average clearance in congestive heart failure patients is 1.77±0.48L/kg/h, while hypertensive patients have an average clearance of 42.7±8.9mL/min/kg.

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Metabolism / Metabolites
Acetylation is a minor metabolic pathway for hydralazine; the major pathway is hydroxylation followed by glucuronidation. There are 5 identified metabolic pathways for hydralazine. Hydralazine can be metabolized to phthalazine or α-ketoglutarate hydrazone. These metabolites can be further converted to phthalazinone or hydralazine can be metabolized directly to phthalazinone. Hydralazine can undergo a reversible converstion to the active hydralazine acetone hydrazone. Hydralazine is spontaneously converted to the active pyruvic acid hydrazone or the pyruvic acid hydrazone tricyclic dehydration product, and these metabolites can convert back and forth between these 2 forms. Hydralazine can be converted to hydrazinophthalazinone, which is further converted to the active acetylhydrazinophthalazinone. The final metabolic process hydralazine can undergo is the conversion to an unnamed hydralazine metabolite, which is further metabolized to 3-methyl-s-triazolophthalazine (MTP). MTP can be metabolized to 9-hydroxy-methyltriazolophthalazine or 3-hydroxy-methyltriazolophthalazine; the latter is converted to triazolophthalazine.
Hydralazine has known human metabolites that include hydralazine N-acetyl.

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Biological Half-Life
Hydralazine has a half life of 2.2-7.8h in rapid acetylators and 2.0-5.8h in slow acetylators. The half life in heart failure patients is 57-241 minutes with an average of 105 minutes and in hypertensive patients is 200 minutes for rapid acetylators and 297 minutes for slow acetylators. Hydralazine is subject to polymorphic acetylation; slow acetylators generally have higher plasma levels of hydralazine and require lower doses to maintain control of pressure. However, other factors, such as acetylation being a minor metabolic pathway for hydralazine, will contribute to differences in elimination rates.

Hepatotoxicity
Serum aminotransferase elevations during hydralazine therapy are considered uncommon. However, hydralazine has been clearly linked to cases of acute liver injury with jaundice as well as a delayed lupus-like syndrome. Two clinical patterns of hepatic injury have been described, associated with either a short (2 to 6 weeks) or long (2 months to more than a year) latency period. The clinically apparent liver injury is usually hepatocellular, although cholestatic forms have also been reported (Case 1). In cases with a short latency period, rash, fever and eosinophilia are common and the onset is typically abrupt and severe, and recovery is rapid. In cases with a longer latency (Case 2), the onset is more typically insidious, liver biopsy may resemble chronic hepatitis and demonstrate fibrosis, and autoantibodies are often present. The late form of hepatitis may also accompany the lupus-like syndrome that occurs with hydralazine, particularly in high doses when given for 6 months or more. Recovery can be prolonged. Autoantibodies to isoforms of the P450 system (CYP 1A2) have been identified in patients with hepatotoxicity due to the structurally related antihypertensive agent dihydralazine (available in Europe, but not the United States) and which is associated with a higher rate of hepatotoxicity than hydralazine.
Likelihood score: A (well established cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Limited milk level and infant serum level data and a long history of use in postpartum mothers indicate that hydralazine is an acceptable antihypertensive in nursing mothers, even those nursing newborns.
◉ Effects in Breastfed Infants
No adverse effects reported in one infant breastfed for 8 weeks.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Hydralazine is 87% protein bound in serum likely to human serum albumin.

[1]. Arce C, Segura-Pacheco B, Perez-Cardenas E, Taja-Chayeb L, Candelaria M, Dueñnas-Gonzalez A. Hydralazine target: from blood vessels to the epigenome. J Transl Med. 2006 Feb 28;4:10.

[2]. Antioxidant activity and inhibitory effects of hydralazine on inducible NOS/COX-2 gene and protein expression in rat peritoneal macrophages. Int Immunopharmacol. 2004 Feb;4(2):163-77.

Hydralazine is the 1-hydrazino derivative of phthalazine; a direct-acting vasodilator that is used as an antihypertensive agent. It has a role as an antihypertensive agent and a vasodilator agent. It is a member of phthalazines, an azaarene, an ortho-fused heteroarene and a member of hydrazines.
Originally developed in the 1950s as a malaria treatment, hydralazine showed antihypertensive ability and was soon repurposed. Hydralazine is a hydrazine derivative vasodilator used alone or as adjunct therapy in the treatment of hypertension and only as adjunct therapy in the treatment of heart failure. Hydralazine is no longer a first line therapy for these indications since the development of newer antihypertensive medications. Hydralazine hydrochloride was FDA approved on 15 January 1953.
Hydralazine is an Arteriolar Vasodilator. The physiologic effect of hydralazine is by means of Arteriolar Vasodilation.
Hydralazine is a commonly used oral antihypertensive agent that acts by inducing peripheral vasodilation. Hydralazine has been linked to several forms of acute liver injury as well as a lupus-like syndrome.
Hydralazine has been reported in Achillea pseudopectinata with data available.
Hydralazine is a phthalazine derivative with antihypertensive effects. Hydralazine exerts its vasodilatory effects through modification of the contractile state of arterial vascular smooth muscle by altering intracellular calcium release, and interfering with smooth muscle cell calcium influx. This agent also causes inhibition of phosphorylation of myosin protein or chelation of trace metals required for smooth muscle contraction, thereby resulting in an increase in heart rate, stroke volume and cardiac output.
A direct-acting vasodilator that is used as an antihypertensive agent.
See also: Hydralazine Hydrochloride (has salt form).

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Drug Indication
Hydralazine is indicated alone or adjunct to standard therapy to treat essential hypertension. A combination product with isosorbide dinitrate is indicated as an adjunct therapy in the treatment of heart failure.

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Mechanism of Action
Hydralazine may interfere with calcium transport in vascular smooth muscle by an unknown mechanism to relax arteriolar smooth muscle and lower blood pressure. The interference with calcium transport may be by preventing influx of calcium into cells, preventing calcium release from intracellular compartments, directly acting on actin and myosin, or a combination of these actions. This decrease in vascular resistance leads to increased heart rate, stroke volume, and cardiac output. Hydralazine also competes with protocollagen prolyl hydroxylase (CPH) for free iron. This competition inhibits CPH mediated hydroxylation of HIF-1α, preventing the degradation of HIF-1α. Induction of HIF-1α and VEGF promote proliferation of endothelial cells and angiogenesis.

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Pharmacodynamics
Hydralazine interferes with calcium transport to relax arteriolar smooth muscle and lower blood pressure. Hydralazine has a short duration of action of 2-6h. This drug has a wide therapeutic window, as patients can tolerate doses of up to 300mg. Patients should be cautioned regarding the risk of developing systemic lupus erythematosus syndrome.

C8H8N4

160.17592

160.075

86-54-4

Hydralazine hydrochloride;304-20-1

3637

Typically exists as solid at room temperature

1.2583 (rough estimate)

276.07°C (rough estimate)

172ºC

1.5872 (estimate)

1.688

2

4

1

12

150

0

N(=C1C2C(=CC=CC=2)C=NN1)N

RPTUSVTUFVMDQK-UHFFFAOYSA-N

InChI=1S/C8H8N4/c9-11-8-7-4-2-1-3-6(7)5-10-12-8/h1-5H,9H2,(H,11,12)

phthalazin-1-ylhydrazine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)