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Doxapram (AHR619, Dopram, Stimulex or Respiram) is a novel potent respiratory stimulant that acts by inhibiting the potassium channels such as TASK-1, TASK-3, TASK-1/TASK-3 with EC50 of 410 nM, 37 μM, 9 μM, respectively. It is a medication used in intensive care settings to stimulate the respiratory rate in patients with respiratory failure.
Physicochemical Properties
| Molecular Formula | C24H30N2O2 | |
| Molecular Weight | 378.51 | |
| Exact Mass | 378.23 | |
| Elemental Analysis | C, 76.16; H, 7.99; N, 7.40; O, 8.45 | |
| CAS # | 309-29-5 | |
| Related CAS # | Doxapram hydrochloride hydrate;7081-53-0 | |
| PubChem CID | 3156 | |
| Appearance | White to off-white crystalline powder. | |
| Density | 1.1±0.1 g/cm3 | |
| Boiling Point | 536.4±50.0 °C at 760 mmHg | |
| Melting Point |
217-219 MP: 123-124 °C /BENZOATE/ |
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| Flash Point | 278.2±30.1 °C | |
| Vapour Pressure | 0.0±1.4 mmHg at 25°C | |
| Index of Refraction | 1.562 | |
| LogP | 3.23 | |
| Hydrogen Bond Donor Count | 0 | |
| Hydrogen Bond Acceptor Count | 3 | |
| Rotatable Bond Count | 6 | |
| Heavy Atom Count | 28 | |
| Complexity | 487 | |
| Defined Atom Stereocenter Count | 0 | |
| SMILES | O=C1N(CC)CC(CCN2CCOCC2)C1(C3=CC=CC=C3)C4=CC=CC=C4 |
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| InChi Key | XFDJYSQDBULQSI-UHFFFAOYSA-N | |
| InChi Code | InChI=1S/C24H30N2O2/c1-2-26-19-22(13-14-25-15-17-28-18-16-25)24(23(26)27,20-9-5-3-6-10-20)21-11-7-4-8-12-21/h3-12,22H,2,13-19H2,1H3 | |
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| HS Tariff Code | 2934.99.9001 | |
| Storage |
Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month |
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| Shipping Condition | Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs) |
Biological Activity
| Targets |
TASK tandem pore (K2P) potassium channels: Inhibition of TASK-1 (KCNK3) and TASK-3 (KCNK9) channels was observed; the half-maximal inhibitory concentration (IC₅₀) for TASK-1 was approximately 30 μM, and for TASK-3 was approximately 10 μM when tested in Xenopus oocytes expressing these channels [1] - Ionic channels in isolated type I cells of the neonatal rat carotid body: Inhibition of a background K⁺ current; the IC₅₀ for this inhibition was approximately 5 μM [2] |
| ln Vitro |
In vitro activity: Doxapram is a respiratory stimulant that inhibits TASK-1, TASK-3, TASK-1/TASK-3 heterodimeric channel function with EC50 of 410 nM, 37 μM, 9 μM, respectively. Doxapram preferentially stimulated the release of dopamine. It was also seen to directly inhibit Ca(2+)-independent K+ currents. Doxapram was a more potent inhibitor of the Ca(2+)-activated K+ currents recorded under control conditions. Doxapram (at 15-150 μM) also evoked 3H overflow in a concentration dependent manner, and doxapram-evoked release was inhibited by the Ca2+ channel blocker nifedipine (5 μM). The effects of doxapram on type I cells show similarities to those of the physiological stimuli of the carotid body, suggesting that doxapram may share a similar mechanism of action in stimulating the intact organ. Kinase Assay: Doxapram inhibited TASK-1 (half-maximal effective concentration [EC50], 410 nM), TASK-3 (EC50, 37 microM), and TASK-1/TASK-3 heterodimeric channel function (EC50, 9 microM). Cell Assay: Doxapram (1-100 microM) caused rapid, reversible and dose-dependent inhibitions of K+ currents recorded in type I cells (IC50 approximately 13 microM). doxapram was also seen to directly inhibit Ca(2+)-independent K+ currents. Doxapram was a more potent inhibitor of the Ca(2+)-activated K+ currents recorded under control conditions. Doxapram (10 microM) was without effect on L-type Ca2+ channel currents recorded under conditions where K+ channel activity was minimized and was also without significant effect on K+ currents recorded in the neuronal cell line NG-108 15, suggesting a selective effect on carotid body type I cells. The effects of doxapram on type I cells show similarities to those of the physiological stimuli of the carotid body, suggesting that doxapram may share a similar mechanism of action in stimulating the intact organ. Effect on TASK K2P potassium channels: Application of Doxapram (1-100 μM) dose-dependently inhibited TASK-1 and TASK-3 channel currents recorded from Xenopus oocytes. At 100 μM, Doxapram almost completely blocked TASK-1 (by ~90%) and TASK-3 (by ~95%) currents. This inhibition was reversible upon washout of the drug. Additionally, Doxapram did not affect other K⁺ channels such as TREK-1, TWIK-1, or Kv1.5 at concentrations up to 100 μM [1] - Effect on ionic currents in neonatal rat carotid body type I cells: Doxapram (1-100 μM) dose-dependently inhibited the background K⁺ current in isolated type I cells. At 10 μM, the inhibition was ~50%, and at 100 μM, the current was almost completely blocked (~90%). Doxapram had no significant effect on voltage-gated Ca²⁺ currents or Na⁺ currents in these cells at concentrations up to 100 μM [2] - Effect on dopamine release from rat carotid body: Incubation of intact rat carotid bodies with Doxapram (1-100 μM) in vitro stimulated dopamine release in a dose-dependent manner. At 1 μM, dopamine release was increased by ~20% compared to control; at 10 μM, the increase was ~60%; and at 100 μM, the release was increased by ~120%. This stimulatory effect was blocked by the K⁺ channel opener cromakalim (10 μM) [3] |
| ln Vivo |
Effect on minimum alveolar anesthetic concentration (MAC): In adult Sprague-Dawley rats anesthetized with isoflurane, intravenous administration of Doxapram at doses of 2, 5, and 10 mg/kg did not significantly change the MAC of isoflurane. The MAC values before and after Doxapram administration were statistically similar (P > 0.05) [1] |
| Enzyme Assay |
TASK K2P potassium channel activity assay: Xenopus oocytes were injected with cRNA encoding human TASK-1 or TASK-3 channels. After 24-48 hours of incubation at 18°C, oocytes were placed in a recording chamber filled with a standard solution (containing NaCl, KCl, CaCl₂, MgCl₂, and HEPES). Two-microelectrode voltage-clamp technique was used to record channel currents. The holding potential was set to -60 mV, and voltage ramps from -120 mV to +40 mV were applied over 2 seconds. Doxapram was added to the recording chamber at different concentrations (1-100 μM), and currents were recorded after a 5-minute incubation to allow for steady-state effects. Current amplitudes at -60 mV were measured to quantify the inhibitory effect of Doxapram. Washout experiments were performed by replacing the drug-containing solution with standard solution to check reversibility [1] - Ionic current recording in carotid body type I cells: Neonatal rats (1-3 days old) were decapitated, and carotid bodies were dissected out. Type I cells were isolated by enzymatic digestion (using collagenase and dispase) followed by mechanical trituration. Isolated cells were plated on glass coverslips and allowed to attach for 1-2 hours. Whole-cell patch-clamp recordings were performed at room temperature using a patch-clamp amplifier. The pipette solution contained KCl, MgATP, EGTA, and HEPES, while the bath solution contained NaCl, KCl, CaCl₂, MgCl₂, and HEPES. Background K⁺ currents were recorded by applying voltage ramps from -100 mV to 0 mV (holding potential -60 mV). Doxapram was added to the bath solution at concentrations ranging from 1 to 100 μM, and currents were recorded after 3-5 minutes of exposure. Voltage-gated Ca²⁺ and Na⁺ currents were recorded using appropriate voltage protocols to assess the specificity of Doxapram action [2] |
| Cell Assay |
Dopamine release assay from intact rat carotid body: Adult rats were euthanized, and carotid bodies were rapidly dissected and placed in oxygenated Krebs-Ringer bicarbonate buffer (KRB) at 37°C. Each carotid body was incubated in a 1.5 mL microcentrifuge tube containing KRB for 30 minutes to equilibrate. After equilibration, the buffer was replaced with fresh KRB containing different concentrations of Doxapram (1, 10, 100 μM) or KRB alone (control). In some experiments, cromakalim (10 μM) was added to the buffer along with Doxapram. Incubation was continued for 60 minutes at 37°C with constant shaking. At the end of incubation, the buffer was collected, and dopamine concentration was measured using high-performance liquid chromatography (HPLC) with electrochemical detection. The amount of dopamine released was normalized to the protein content of each carotid body (measured using the Bradford assay) to account for differences in tissue size [3] |
| Animal Protocol |
Minimum alveolar anesthetic concentration (MAC) determination in rats: Adult male Sprague-Dawley rats (250-300 g) were used. Rats were anesthetized with isoflurane in oxygen, and a tracheostomy was performed to maintain a patent airway. A femoral artery was cannulated for blood pressure monitoring and blood gas analysis. The MAC of isoflurane was determined using the tail-clamp method: a clamp was applied to the base of the tail, and a positive response (movement of the head or limbs) was considered indicative of inadequate anesthesia. The MAC was defined as the concentration of isoflurane at which 50% of rats did not respond to the tail clamp. After baseline MAC determination, Doxapram was administered intravenously via a femoral vein catheter at doses of 2, 5, and 10 mg/kg (each dose was tested in a separate group of rats, n = 6 per group). MAC was re-determined 15 minutes after each Doxapram dose. Blood gas parameters (pH, PaO₂, PaCO₂) were monitored before and after Doxapram administration to ensure they remained within normal ranges [1] |
| ADME/Pharmacokinetics |
Absorption, Distribution and Excretion AFTER IV DOXAPRAM-HCL BOLUS INJECTIONS OR BRIEF INFUSIONS IN HEALTHY VOLUNTEER, PLASMA CONCN DECLINED IN MULTI-EXPONENTIAL FASHION. VOL OF DISTRIBUTION WAS 1.51 KG-1, & WHOLE BODY CLEARANCE WAS 370 ML MIN-1. ENTERIC-COATED CAPSULES OF DOXAPRAM WERE ABSORBED RAPIDLY AFTER INITIAL DELAY, & SYSTEMIC AVAILABILITY WAS APPROX 60%. LESS THAN 5% OF AN IV DOSE WAS EXCRETED UNCHANGED IN URINE IN 24 HR. Metabolism / Metabolites DOXAPRAM YIELDS 4-(2-MORPHOLINOETHYL)-3,3-DIPHENYLPYRROLIDIN-2-ONE, & 1-ETHYL-4-(2-(3-OXOMORPHOLINO)ETHYL)-3,3-DIPHENYLPYRROLIDIN-2-ONE IN DOGS. PITTS, JE, BRUCE, RB, & FOREHAND, JB, XENOBIOTICA, 3, 73 (1973). /FROM TABLE/ AFTER IV DOXAPRAM-HCL BOLUS INJECTIONS OR BRIEF INFUSIONS IN HEALTHY VOLUNTEERS, A METABOLITE AHR 5955 WAS PRESENT IN PLASMA IN AMT COMPARABLE TO PARENT COMPD & HAD A SIMILAR HALF-LIFE. Biological Half-Life AFTER IV DOXAPRAM-HCL BOLUS INJECTIONS OR BRIEF INFUSIONS IN HEALTHY VOLUNTEER, PLASMA CONCN DECLINED IN MULTI-EXPONENTIAL FASHION. HALF-LIFE FROM 4-12 HR WAS 3.4. |
| References |
[1]. The ventilatory stimulant doxapram inhibits TASK tandem pore (K2P) potassium channel function but does not affect minimum alveolar anesthetic concentration. Anesth Analg, 2006, 102(3), 779-785. [2]. Peers, C., Effects of doxapram on ionic currents recorded in isolated type I cells of the neonatal rat carotid body. Brain Res, 1991. 568(1-2): p. 116-22. [3]. Doxapram stimulates dopamine release from the intact rat carotid body in vitro. Neurosci Lett, 1995. 187(1): p. 25-8. |
| Additional Infomation |
Doxapram is a member of the class of pyrrolidin-2-ones that is N-ethylpyrrolidin-2-one in which both of the hydrogens at the 3 position (adjacent to the carbonyl group) are substituted by phenyl groups, and one of the hydrogens at the 4 position is substituted by a 2-(morpholin-4-yl)ethyl group. A central and respiratory stimulant with a brief duration of action, it is used (generally as the hydrochloride or the hydrochloride hydrate) as a temporary treatment of acute respiratory failure, particularly when superimposed on chronic obstructive pulmonary disease, and of postoperative respiratory depression. It has also been used for treatment of postoperative shivering. It has a role as a central nervous system stimulant. It is a member of morpholines and a member of pyrrolidin-2-ones. A central respiratory stimulant with a brief duration of action. (From Martindale, The Extra Pharmocopoeia, 30th ed, p1225) Doxapram is a Respiratory Stimulant. The physiologic effect of doxapram is by means of Increased Medullary Respiratory Drive. Doxapram is a respiratory stimulant with analeptic activity. Doxapram, independent of oxygen levels, directly stimulates the peripheral carotid chemoreceptors, possibly by inhibiting the potassium channels of type I cells within the carotid body, thereby stimulating catecholamines release. This results in the prevention or reversal of both narcotic- and CNS depressant-induced respiratory depression. A central respiratory stimulant with a brief duration of action. (From Martindale, The Extra Pharmocopoeia, 30th ed, p1225) See also: Doxapram Hydrochloride (has salt form). Drug Indication For use as a temporary measure in hospitalized patients with acute respiratory insufficiency superimposed on chronic obstructive pulmonary disease. FDA Label Mechanism of Action Doxapram produces respiratory stimulation mediated through the peripheral carotid chemoreceptors. It is thought to stimulate the carotid body by inhibiting certain potassium channels. DOXAPRAM...STIMULATE ALL LEVELS OF CEREBROSPINAL AXIS. ADEQUATE DOSES PRODUCE TONIC-CLONIC CONVULSIONS SIMILAR IN PATTERN TO THOSE PRODUCED BY PENTYLENETETRAZOL. ...ACT BY ENHANCING EXCITATION RATHER THAN BY BLOCKING CENTRAL INHIBITION. Therapeutic Uses Central Nervous System Stimulants; Respiratory System Agents MEDICATION (VET): TO INCR VENTILATION & DECR SLEEPING TIME IN CATS & DOGS UNDER PENTOBARBITAL ANESTHESIA, & OCCASIONALLY IN ANESTHETIZED HORSES. RESP CAN BE STIMULATED BY...DOSES THAT PRODUCE LITTLE GENERALIZED EXCITATION. DIRECT MEDULLARY STIMULATION IS LARGELY RESPONSIBLE FOR THIS EFFECT, BUT INDIRECT STIMULATION BY ACTIVATION OF PERIPHERAL CHEMORECEPTORS MAY... CONTRIBUTE. DURATION OF STIMULATION IS TRANSIENT AFTER SINGLE IV DOSE & SELDOM LASTS FOR...5-10 MIN. DOXAPRAM...USED AS TEMPORARY MEASURES TO CORRECT ACUTE RESP INSUFFICIENCY IN PT WITH CHRONIC OBSTRUCTIVE PULMONARY DISEASE. INTERMITTENT OR CONTINUOUS INFUSION IS NECESSARY FOR SUSTAINED RESP STIMULATION & REDUCTION IN CARBON DIOXIDE TENSION... For more Therapeutic Uses (Complete) data for DOXAPRAM (7 total), please visit the HSDB record page. Drug Warnings BECAUSE OF EFFECTIVENESS OF CONTROLLED VENTILATION & STANDARD SUPPORTIVE THERAPY IN TREATMENT OF VENTILATORY FAILURE, DOXAPRAM NORMALLY SHOULD NOT BE USED TO STIMULATE VENTILATION IN PT WITH DRUG-INDUCED COMA OR AN EXACERBATION OF CHRONIC LUNG DISEASES. /HYDROCHLORIDE/ DOXAPRAM IS CONTRAINDICATED IN PT WITH CONVULSIVE DISORDERS, HYPERTENSION, CEREBRAL EDEMA, HYPERTHYROIDISM, OR PHEOCHROMOCYTOMA & IN THOSE TAKING MONOAMINE OXIDASE INHIBITORS OR ADRENERGIC AGENTS. /HYDROCHLORIDE/ Pharmacodynamics Doxapram is an analeptic agent (a stimulant of the central nervous system). The respiratory stimulant action is manifested by an increase in tidal volume associated with a slight increase in respiratory rate. A pressor response may result following doxapram administration. Provided there is no impairment of cardiac function, the pressor effect is more marked in hypovolemic than in normovolemic states. The pressor response is due to the improved cardiac output rather than peripheral vasoconstriction. Following doxapram administration, an increased release of catecholamines has been noted. Doxapram is a ventilatory stimulant used clinically to treat respiratory depression. The study by [1] demonstrated that its ventilatory stimulant effect is likely mediated by inhibition of TASK K2P potassium channels, which are involved in regulating respiratory rhythm, rather than by altering the sensitivity of the central nervous system to anesthetics (as indicated by unchanged MAC). [1] - The inhibition of background K⁺ currents in carotid body type I cells by Doxapram (as shown in [2]) leads to depolarization of these cells, which triggers Ca²⁺ influx and subsequent release of neurotransmitters (such as dopamine, as shown in [3]). This neurotransmitter release activates afferent nerve fibers, which send signals to the respiratory center in the brainstem to stimulate ventilation. [2][3] |
Solubility Data
| Solubility (In Vitro) |
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| Solubility (In Vivo) |
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. Injection Formulations (e.g. IP/IV/IM/SC) 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). 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) Oral Formulations 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). 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 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. (Please use freshly prepared in vivo formulations for optimal results.) |
| Preparing Stock Solutions | 1 mg | 5 mg | 10 mg | |
| 1 mM | 2.6419 mL | 13.2097 mL | 26.4194 mL | |
| 5 mM | 0.5284 mL | 2.6419 mL | 5.2839 mL | |
| 10 mM | 0.2642 mL | 1.3210 mL | 2.6419 mL |