Intravenous diazoxide therapy in hypertensive crisis

Screening for Efficacious Anticonvulsants and Neuroprotectants in Delayed Treatment Models of Organophosphate-induced Status Epilepticus

Organophosphorus (OP) compounds are deadly chemicals that exert their intoxicating effects through the irreversible inhibition of acetylcholinesterase (AChE). In addition to an excess of peripheral ailments, OP intoxication induces status epilepticus (SE) which if left untreated may lead to permanent brain damage or death. Benzodiazepines are typically the primary therapies for OP-induced SE, but these drugs lose efficacy as treatment time is delayed. The CounterACT Neurotherapeutic Screening (CNS) Program was therefore established by the National Institutes of Health (NIH) to discover novel treatments that may be administered adjunctively with the currently approved medical countermeasures for OP-induced SE in a delayed treatment scenario. The CNS program utilizes in vivo EEG recordings and Fluoro-JadeB (FJB) histopathology in two established rat models of OP-induced SE, soman (GD) and diisopropylfluorophosphate (DFP), to evaluate the anticonvulsant and neuroprotectant efficacy of novel adjunct therapies when administered at 20 or 60 min after the induction of OP-induced SE. Here we report the results of multiple compounds that have previously shown anticonvulsant or neuroprotectant efficacy in other models of epilepsy or trauma. Drugs tested were ganaxolone, diazoxide, bumetanide, propylparaben, citicoline, MDL-28170, and chloroquine. EEG analysis revealed that ganaxolone demonstrated the most robust anticonvulsant activity, whereas all other drugs failed to attenuate ictal activity in both models of OP-induced SE. FJB staining demonstrated that none of the tested drugs had widespread neuroprotective abilities. Overall these data suggest that neurosteroids may represent the most promising anticonvulsant option for OP-induced SE out of the seven unique mechanisms tested here. Additionally, these results suggest that drugs that provide significant neuroprotection from OP-induced SE without some degree of anticonvulsant activity are elusive, which further highlights the necessity to continue screening novel adjunct treatments through the CNS program.

Opening of ATP-sensitive potassium channels causes migraine attacks: a new target for the treatment of migraine

Migraine is one of the most disabling and prevalent of all disorders. To improve understanding of migraine mechanisms and to suggest a new therapeutic target, we investigated whether opening of ATP-sensitive potassium channels (KATP) would cause migraine attacks. In this randomized, double-blind, placebo-controlled, crossover study, 16 patients aged 18–49 years with one to five migraine attacks a month were randomly allocated to receive an infusion of 0.05 mg/min KATP channel opener levcromakalim and placebo on two different days (ClinicalTrials.gov number, NCT03228355). The primary endpoints were the difference in incidence of migraine attacks, headaches and the difference in area under the curve (AUC) for headache intensity scores (0–12 h) and for middle cerebral artery blood flow velocity (0–2 h) between levcromakalim and placebo. Between 24 May 2017 and 23 November 2017, 16 patients randomly received levcromakalim and placebo on two different days. Sixteen patients (100%) developed migraine attacks after levcromakalim compared with one patient (6%) after placebo (P = 0.0001); the difference of incidence is 94% [95% confidence interval (CI) 78–100%]. The incidence of headache over the 12 h observation period was higher but not significant after levcromakalim (n = 16) than after placebo (n = 7) (P = 0.016) (95% CI 16–71%). The AUC for headache intensity was significantly larger after levcromakalim compared to placebo (AUC0–12h, P < 0.0001). There was no change in mean middle cerebral artery blood flow velocity after levcromakalim compared to placebo (AUC0–2hP = 0.46). Opening of KATP channels caused migraine attacks in all patients. This suggests a crucial role of these channels in migraine pathophysiology and that KATP channel blockers could be potential targets for novel drugs for migraine.

Effect of diazoxide-induced hypotension on cerebral blood flow in hypertensive rats

The effect on cerebral blood flow of acute diazoxide-induced hypotension was studied in rats with renal and spontaneous hypertension. Diazoxide (5 mg/kg, i.v. bolus), caused arterial pressure to fall rapidly to that of normotensive rats, i.e. c. 75 mmHg. There was a concomitant fall in cerebral blood flow of about 35% (P less than 0.01) in renal hypertensive rats and 25% (P less than 0.05) in spontaneously hypertensive rats; the greater fall in flow in the former corresponded to a greater drop in pressure. Flow remained at these reduced levels during a 2 h observation period. Histological examination revealed small areas of ischaemic damage in the brains of five of the twelve animals. In control hypertensive rats not given diazoxide, cerebral blood flow and blood pressure were stable during a 2 1/2 h period and there was no evidence of ischaemic damage to the brains. The diazoxide-induced reduction in cerebral blood flow was interpreted as being secondary to a blood pressure fall to below the lower limit of cerebral blood flow autoregulation. No evidence was found of direct effects on the cerebral circulation such as seen with ganglionic blockers, alpha-blockers and cerebral vasodilators.

Beneficial hemodynamic effects of intravenous diazoxide in refractory congestive heart failure

Despite the growing popularity of vasodilator therapy for acute and chronic congestive heart failure (CHF), no single agent has been uniformly effective and well tolerated. Therefore, we investigated the acute hemodynamic response to diazoxide, a potent and long-acting arteriolar dilator, in nine patients with severe CHF refractory to conventional treatment and, in seven of nine, other vasodilators. Diazoxide was administered intravenously in successive 300 mg infusions, each over 10 minutes, until a satisfactory response in cardiac and output occurred or a fall in arterial blood pressure or increase in heart rate was noted. The mean dose of diazoxide was 670 mg (range 450 to 900 mg). Systemic vascular resistance fell immediately, by a maximum of 44%. Arterial pressure was not changed significantly, but cardiac and stroke volume indices rose by 64% and 49%, respectively, from 2.0 +/- 0.5 to 3.3 +/- 0.6 L/min/m2 and from 24 +/- 10 to 36 +/- 9 ml/m2 (each p less than 0.001). Pulmonary capillary wedge pressure declined more gradually, by a mean of 8 mm at 4 and 6 hours after drug infusion. This hemodynamic improvement was sustained for a mean of 9.7 hours (range 6 to 12 hours). Our findings indicate that intravenous diazoxide may be useful in the management of acute heart failure and that a trial of oral diazoxide in chronic normotensive CHF is warranted.

Efficacy of slow infusion of diazoxide in the treatment of severe hypertension without organ hypoperfusion

Diazoxide, as usually given in a single bolus, may cause precipitous falls in blood pressure (BP) with resultant tissue hypoperfusion. To examine the efficacy and safety of slow infusion, we treated 18 patients with mean initial BP of 220/143 mm Hg by two regimens: group A (nine patients) received 15 mg/minute; group B (nine patients) received 30 mg/minute. The goal of therapy, diastolic BP of 100 to 105 mm Hg, was reached in 16 of the 18 with no immediate drug-related side effects. Infusion time was 38.1 minutes in group A and 20.7 minutes in group B. Slow intravenous infusion of diazoxide appears to be safe and effective treatment for severe hypertension and should replace the rapid bolus technique.

In vivo and In vitro studies on the cerebrovascular dilatation induced by diazoxide in normotensive and renal hypertensive goats

We studied the in vivo and in vitro effects of diazoxide on the cerebral circulation of 8 normotensive (mean arterial pressure = 100 mm Hg) and 5 renal hypertensive (mean arterial pressure = 146 mm Hg) goats. Injections of diazoxide (0.3-27 mg) into the internal maxillary artery of unanesthetized goats produced dose-dependent increases in cerebral blood flow (electromagnetic flowmeter), this effect being significantly higher in hypertensive goats. Intravenous injection of 5 mg/kg of diazoxide into normotensive goats increased cerebral blood flow 40 ml/min/100 g and mean arterial pressure dropped 22 mm Hg whereas in hypertensive goats cerebral blood flow was unchanged and mean arterial pressure decreased 50 mm Hg. The increase in heart rate due to intravenous diazoxide was similar in normotensive and hypertensive goats (35 beats/min). Cumulative applications of diazoxide (10(-5) to 10(-3)M) on isolated middle cerebral arteries produced dilatory responses both under resting conditions and after previous tonic contraction by serotonin. This relaxation was significantly greater in arterial segments from hypertensive goats. The results indicate that diazoxide exerts powerful dilatatory effects on cerebral vessels, both in vivo and in vitro, and that these effects are particularly evident in hypertensive animals.

[Comparison of oral diazoxide and minoxidil in refractory hypertension]

The efficacy and side effects of two potent vasodilatators, namely diazoxide and minoxidil given orally, were compared in 11 patients who had hypertension refractory to conventional drug treatment. The latter included diuretics, betablockers and/or sympatholytics, and either dihydralazine or prazosin. In a crossover approach, dihydralazine and prazosin were withdrawn and replaced by diazoxide or minoxidil. In nine patients the diazoxide phase preceded the minoxidil treatment, while in two it followed minoxidil treatment. Before introduction of the more potent vasodilators blood pressure averaged 181/107 mm Hg in the supine and 161/103 mm Hg in the upright position. Both, oral diazoxide (median dose 400 mg/d( and minoxidil (medium dose 17.5 mg/d) produced similar decreases (p < 0.02) in mean arterial pressure (-15%) in the supine and (-11 vs. -12%) in the upright position. They caused a comparable tendency for sodium retention and weight gain which could be satisfactorily controlled with increased diuretic therapy, except in one patient. Hypertrichosis occurred with both drugs, but tended to be somewhat milder with diazoxide. Electrocardiograms remained generally unchanged. Plasma glucose levels were increased during diazoxide treatment in six patients necessitating interruption of this therapy in four patients. It is concluded that the antihypertensive potency and most side effect of orally administered diazoxide are comparable to those of minoxidil, except for diazoxide-related hyperglycemia which may limit the use of this substance.

Analysis of cerebrovascular action of diazoxide in conscious goats

The effects of diazoxide on cerebral blood flow were evaluated in unanesthetized goats under control conditions and after selective blockade of adrenergic or cholinergic receptors in cerebral vessels. Injections of diazoxide (1-27 mg) into the internal maxillary artery produced dose-dependent increases in cerebral blood flow, an increase of 90% occurring with the highest dose. Administration of phentolamine, propranolol, or atropine into the internal maxillary artery did not modify the cerebrovascular response to diazoxide. In reserpine-treated animals the cerebral effects of diazoxide were also unchanged. Intravenous injections of diazoxide (150-400 mg) produced sustained hypotension and tachycardia whereas cerebral blood flow was maintained within normal values or increased slightly. The normal cerebral vasoconstriction obtained with injections of norepinephrine directly into the internal maxillary artery was unaffected during the diazoxide induced-hypotension. These findings show that diazoxide exerts a powerful vasodilatory effect on cerebral vessels through mechanisms other than blockade of alpha-adrenergic receptors or inhibition of adrenergic activity. The results also indicate that activation of beta-adrenergic or atropine-sensitive vascular receptors in the cerebral response to diazoxide is negligible.

Individual titration of diazoxide dosage in the treatment of severe hypertension

Diazoxide, 300 mg as a single bolus injection, is widely used to treat severe hypertension. Although usually effective, this standard dosage may decrease the blood pressure too much, inducing hypotensive problems. In this study 32 patients with a diastolic blood pressure above 125 mm Hg were treated with smaller bolus injections, 105 or 150 mg, which were repeated every 5 minutes as needed to reduce the diastolic pressure to 110 mm Hg or less. Seven patients of the 32 patients needed only one injection of 150 mg; only one patient needed more than three injections. This individual titration with mini-bolus injections of diazoxide was effective and did not induce hypotension or other side effects.