Intravenous doxapram administration as a potential model of panic attacks in rats

Panic disorder can be categorized into the nonrespiratory or the respiratory subtypes, the latter comprising dyspnea, shortness of breath, chest pain, feelings of suffocation, and paresthesias. Doxapram is an analeptic capable of inducing panic attacks with respiratory symptoms in individuals diagnosed with the disorder; however, its neuroanatomical targets and its effects on experimental animals remain uncharacterized. One of the brain regions proposed to trigger panic attacks is the midbrain periaqueductal gray (PAG). Therefore, in this study, we evaluated the effects of doxapram in Fos (c-Fos) protein expression in the PAG and characterized its cardiorespiratory and behavioral effects on the elevated T maze and in the conditioned place aversion (CPA) paradigms. Doxapram increased Fos expression in different columns of the PAG, increased respiratory frequency, decreased heart rate, and increased arterial pressure when injected via intravenous route. Alprazolam, a panicolytic benzodiazepine, injected via intraperitoneal route, decreased respiratory frequency, whereas URB597, an anandamide hydrolysis inhibitor injected via intraperitoneal route, was ineffective. Doxapram injected via intraperitoneal route induced an anxiogenic-like effect in the elevated T-maze model; however, it failed to induce CPA. This study suggests that the cardiorespiratory and behavioral effects of doxapram in rodents serve as an experimental model that can provide insights into the neurobiology of panic attacks.

Doxapram alleviates low SpO2 induced by the combination of propofol and fentanyl during painless gastrointestinal endoscopy

BACKGROUND

Painless gastrointestinal endoscopy under intravenous propofol anesthesia is widely applied in the clinical scenario. Despite the good sedation and elimination of anxiety that propofol provides, low SpO2 may also result. Doxapram is a respiratory stimulant with a short half-life. The primary aim of this study was to investigate the effects of doxapram on alleviating low SpO2 induced by the combination of propofol and fentanyl during painless gastrointestinal endoscopy.

METHODS

In this prospective study, patients scheduled for painless gastrointestinal endoscopy were randomly assigned to group D or S with 55 patients per group. Initially, both groups received a combination of propofol and fentanyl. Patients in group D received 50 mg doxapram after propofol injection, while patients in group S received an equal volume of saline. Vital signs of the patients, propofol dose, examination duration, and incidences of low SpO2 were recorded.

RESULTS

There were no statistical differences in propofol consumption and examination duration between the two groups. Twenty-six patients in group S experienced low SpO2 versus 10 in group D (P = 0.001). Nineteen patients in group S underwent oxygenation with a face mask in contrast to 8 in group D (P = 0.015). Eighteen patients in group S were treated with jaw lifting compared to 5 in group D (P = 0.002). Four patients in group S underwent assisted respiration compared to 2 in group D (without statistical difference). The average oxygen saturation in group S was significantly lower than that in group D at 1, 2 and 3 min after propofol injection (P < 0.001, P = 0.001 and P = 0.020, respectively). There were no statistical differences in oxygen saturation at other time points. There were no statistical differences in MAP and HR (except for the time point of 1 min after the induction) between the two groups.

CONCLUSIONS

Low dose of doxapram can effectively alleviate low SpO2 in painless gastrointestinal endoscopy with intravenous propofol, without affecting propofol consumption, examination duration, MAP, or HR.

TRAIL REGISTRATION

The study was approved by the Institutional Ethics Committee of Clinical and New Technology of Wuxi People's Hospital on 20th July, 2018 (KYLLH2018029) and registered in the Chinese Clinical Trial Register on 16th August, 2018 (ChiCTR1800017832).

An Impedance-Based Model for the Assessment of Cardiopulmonary Function in Rabbits

Improving the quality of physiologic data collected from research animals is most easily accomplished by collecting as much information as possible from a single subject, thereby reducing animal use and error associated with satellite groups. We investigated the feasibility of using a large-animal implantable telemetry device in New Zealand white rabbits (n = 6). The first task was to develop an implantation technique that yielded calibrated tidal volume (Vt) measurements that were within 10% of those obtained simultaneously from a pneumotachograph, a low-noise electrocardiogram, and stable blood pressure. The second task was to challenge implanted rabbits with the respiratory stimulant doxapram to assess linearity of the calibration across a range of Vt. Of the 3 electrode placements attempted, only one resulted in calibrations consistently below 10% error. Optimal electrode placement resulted in calibrated Vt measurements within 1.7% ± 0.3% of those obtained from a pneumotachograph during normal tidal breathing, 7.3% ± 0.7% of those after saline injection, and 6.0% ± 0.5% of those after doxapram injection. The Vt range was 9 to 15 mL for normal tidal breathing and saline injection and 25 to 30 mL after doxapram injection. Increases in mean arterial pressure of 25.0 ± 6.82 mm Hg and decreases in heart rate of 56.3 ± 6.82 bpm were associated with doxapram injection only. Our findings represent the first time that multiple cardiopulmonary endpoints have been assessed by telemetry in conscious, restrained rabbits. Whether animal position affects calibration accuracy warrants investigation.

Comparative study on effectiveness of doxapram and pethidine for postanaesthetic shivering

INTRODUCTION

Postanaesthetic shivering is a common condition after surgery which needs proper management with pharmacologic agents so as to make postoperative period comfortable to the patient and prevent from the untoward complications that can arise from it. This study was done to compare the effectiveness of Pethidine and Doxapram in the treatment of postanaesthetic shivering.

METHODS

Patients were randomly divided into three groups, ten in each. All received volume of 3 ml as Group I (Doxapram 1.5 mg/kg), Group II (Pethidine 0.35 mg/kg) and Group III (Normal Saline). All patients were observed for 30 minutes after reversal of muscle relaxant and occurrence of shivering within this period was observed, scored and treated. All treated patients were observed for 10 minutes after the test drug was given for control of shivering and any untoward effects.

RESULTS

Pethidine was found more effective than Doxapram in treating postanaesthetic shivering as it was effective in 80% followed by Doxapram in 60% and Normal saline in 20%. Statistically the results between Normal saline and Pethidine was significant as P < 0.05. As statistical significance between Doxapram and Normal Saline was p = 0.16; and between Pethidine and Doxapram was p = 0.62, the difference is statistically not significant.

CONCLUSIONS

Pethidine was found to be more effective compared to Doxapram in treating patients with postoperative shivering.

Dynamic QT/RR relationship of cardiac conduction in premature infants treated with low-dose doxapram hydrochloride

Doxapram hydrochloride, a respiratory stimulant, has several undesirable side effects during high-dose administration, including second-degree atrioventricular (AV) block and QT prolongation. In Japan, this drug is contraindicated for newborn infants. Recent studies, however, have demonstrated the efficacy and safety of doxapram therapy for apnea of prematurity (AOP) using lower doses than those previously tested. As a result, approximately 60% of Japanese neonatologists continue to use this drug. This study used surface ECG recordings to assess the cardiac safety of low-dose doxapram hydrochloride (0.2 mg/kg/h) in fifteen premature very-low-birth-weight infants with idiopathic AOP. Cardiac intervals and number of apnea episodes were compared before and after drug administration. Low-dose doxapram hydrochloride resulted in approximately 90% reduction in the frequency of apnea without side effects. None of the infants developed QT or PR prolongation, arrhythmia, or other conduction disorders. In addition, there was no change in the slope of QT/RR before versus after administration of doxapram hydrochloride. We conclude that low-dose administration of doxapram hydrochloride did not have any undesirable effects on myocardial depolarization and repolarization.

The effect of doxapram on brain imaging in patients with panic disorder

Administration of doxapram hydrochloride, a respiratory stimulant, is experienced by panic disorder patients to be similar to panic attacks but has reduced emotional effect in normal volunteers, thus providing a laboratory model of panic for functional imaging. Six panic patients and seven normal control subjects underwent positron emission tomography with (18)F-deoxyglucose imaging after a single-blinded administration of either doxapram or a placebo saline solution. Saline and doxapram were administered on separate days in counterbalanced order. Patients showed a greater heart rate increase on doxapram relative to saline than controls, indicating differential response. On the saline placebo day, patients had greater prefrontal relative activity than controls. In response to doxapram, patients tended to decrease prefrontal activity more than controls, and increased cingulate gyrus and amygdala activity more than controls. This suggests that panic disorder patients activate frontal inhibitory centers less than controls, a tendency that may lower the threshold for panic.

[Clinical observation of target-controlled remifentanil infusion combined with propofol and doxapram in painless artificial abortion]

OBJECTIVE

To observe the impacts of doxapram on anesthetic efficacy and respiratory and circulatory functions during anesthesia with remifentanil given by target-controlled infusion (TCI) combined with propofol in painless artificial abortion.

METHODS

A total of 120 ASA I women requiring voluntarily painless artificial abortion were randomized into two equal groups. One group was given remifentanil by TCI at 2 ng/ml and propofol 1mg/kg (group I), and the other given remifentanil by TCI, propofol, and doxapram 0.6 mg/kg (group II). The anesthetic efficacy and respiratory and circulatory suppression during anesthesia were observed.

RESULTS

Both of the two groups showed satisfactory anesthetic efficacy with comparable the BIS values (P>0.05). No significant difference was noted in the induction time and awaking time between the two groups (P>0.05), but group I had more serious respiratory and circulatory depression than group II (P<0.05).

CONCLUSION

Doxapram may attenuate respiratory and circulatory depression during anesthesia with remifentanil given by TCI combined with propofol in painless artificial abortion, and provide comparable anesthetic efficacy.

Brain Hemodynamic Effects of Doxapram in Preterm Infants

BACKGROUND

Doxapram is a respiratory stimulant widely used for the treatment of idiopathic apnea of prematurity, although it has been demonstrated that it can induce a transient decrease of cerebral blood flow and that isolated mental delay in infants weighing <1,250 g is associated with the total dosage and duration of doxapram therapy.

OBJECTIVES

To evaluate the effects of doxapram on cerebral hemodynamics in preterm infants using cerebral Doppler ultrasonography and near-infrared spectroscopy.

METHODS

Preterm infants who required treatment with doxapram for apnea of prematurity unresponsive to caffeine were treated with doxapram at an hourly dose of 0.5 mg x kg(-1).h(-1), followed by 1.5 and 2.5 mg x kg(-1).h(-1).

RESULTS

20 preterm infants were studied. Doxapram induced a significant decrease of oxygenated hemoglobin (O(2)Hb) and cerebral intravascular oxygenation (HbD = O(2)Hb - HHb) and an increase of HHb and CtOx concentrations, while cerebral blood volume and cerebral blood flow velocity did not change.

CONCLUSIONS

Doxapram infusion induces the increase of cerebral oxygen consumption and requirement and the contemporary decrease of oxygen delivery probably mediated by a decrease of cerebral blood flow. Caution must be recommended in prescribing this drug for apnea of prematurity.

Doxapram increases corticotropin-releasing factor immunoreactivity and mRNA expression in the rat central nucleus of the amygdala

Doxapram causes panic anxiety in humans. To determine whether doxapram alters corticotropin-releasing factor (CRF) expression in the central nucleus of the amygdala (CeA), paraventricular nucleus of hypothalamus (PVN), or bed nucleus of the stria terminalis (BNST), we used immunohistochemistry to measure CRF peptide in these brain areas after doxapram injection. Doxapram injection significantly increased CRF-like immunoreactivity (CRF-IR) within the CeA, but not in the BNST or PVN, and this increase was significant 2h after injection. In addition, doxapram significantly increased CRF mRNA expression within the CeA, and this was most prominent 30min after injection. These results suggest that doxapram selectively increases CRF expression within the CeA, and that this is mediated by increased CRF gene transcription. This increase in CRF-IR within the CeA might explain the doxapram-induced anxiety reaction.

Doxapram-induced panic attacks and cortisol elevation

Numerous agents with differing biological properties and central nervous system (CNS) effects can induce panic attacks in predisposed individuals. A potential explanation of this finding is that panic disorder patients are more likely to panic than normal control subjects when given a panicogen due to an excessive fear response to somatic arousal. We test this hypothesis by using doxapram, a panicogen with minimal CNS effects, to induce panic in patients and control subjects. Doxapram was given to six subjects with panic disorder with or without agoraphobia and four healthy volunteers. Measures comprised the Acute Panic Inventory, the Borg Exertion scale, the 10-point Anxiety Scale, the 10-point Apprehension Scale, cortisol, prolactin, and MHPG, all obtained at baseline and multiple time points after the doxapram infusion. All panic disorder patients panicked with doxapram, whereas no control subjects had a panic attack. Panic patients had similar levels of breathlessness with doxapram compared with control subjects. Although panic patients had higher levels of anxiety and apprehension, these did not change significantly with doxapram compared with control levels. Doxapram led to similar increases in cortisol and prolactin in both groups, and MHPG was consistently elevated in panic patients, but unaffected by doxapram. These results show that doxapram is a useful panicogen in the study of panic disorder. Since the panic patients and control subjects had similar levels of physiological and psychological arousal, but the panic patients were more likely to have a panic attack, this lends support to the concept of a sensitized fear network in panic disorder patients.

High dose caffeine citrate for extubation of preterm infants: a randomised controlled trial

OBJECTIVE

To compare two dosing regimens for caffeine citrate in the periextubation period for neonates born at less than 30 weeks gestation in terms of successful extubation and adverse effects.

DESIGN

A multicentre, randomised, double blind, clinical trial.

SETTING

Four tertiary neonatal units within Australia.

PATIENTS

Infants born less than 30 weeks gestation ventilated for more than 48 hours.

INTERVENTIONS

Two dosing regimens of caffeine citrate (20 v 5 mg/kg/day) for periextubation management. Treatment started 24 hours before a planned extubation or within six hours of an unplanned extubation.

MAIN OUTCOME MEASURE

Failure to extubate within 48 hours of caffeine loading or reintubation and ventilation or doxapram within seven days of caffeine loading.

RESULTS

A total of 234 neonates were enrolled. A significant reduction in failure to extubate was shown for the 20 mg/kg/day dosing group (15.0% v 29.8%; relative risk 0.51; 95% confidence interval (CI) 0.31 to 0.85; number needed to treat 7 (95% CI 4 to 24)). A significant difference in duration of mechanical ventilation was shown for infants of less than 28 weeks gestation receiving the high dose of caffeine (mean (SD) days 14.4 (11.1) v 22.1 (17.1); p = 0.01). No difference in adverse effects was detected in terms of mortality, major neonatal morbidity, death, or severe disability or general quotient at 12 months.

CONCLUSIONS

This trial shows short term benefits for a 20 mg/kg/day dosing regimen of caffeine citrate for neonates born at less than 30 weeks gestation in the periextubation period, without evidence of harm in the first year of life.

Isolated mental developmental delay in very low birth weight infants: association with prolonged doxapram therapy for apnea

OBJECTIVE

We investigated factors associated with isolated mental delay in infants weighing < 1250 g at birth.

STUDY DESIGN

With a case-control design, matching variables for 40 cases included gestation, birth weight, sex, grade of intraventricular hemorrhage, and socioeconomic status. Case subjects had a mental developmental index < 70, and controls had a mental developmental index > or = 85, according to the Bayley Scales of Infant Development II at 18 months' corrected age.

RESULTS

There were no differences between the case and control subjects for neonatal complications and antenatal or postnatal steroid use. There was a marked difference in the cumulative dosage and duration of doxapram therapy used for apnea of prematurity (total dose 2233 +/- 1927 mg vs 615 +/- 767 mg, P < .001; duration 45.2 +/- 32.5 days vs 19.4 +/- 23.4 days, P < .001 for case subjects and control subjects, respectively). Multivariate analysis did not identify additive predictive variables.

CONCLUSION

Isolated mental delay in infants weighing < 1250 g at birth was associated with the total dosage and duration of doxapram therapy for severe apnea. Although this may be a marker for cerebral dysfunction manifesting as apnea of prematurity, possible adverse effects of doxapram or its preservative, benzyl alcohol, on the developing brain deserve further study.

Low-dose doxapram therapy for idiopathic apnea of prematurity

BACKGROUND

Doxapram is contraindicated for newborn infants in Japan because of its serious side effects. However, because of encouraging results of recent studies regarding the efficacy and safety of therapy for apnea of prematurity (AOP) with lower doses of doxapram than those previously proposed, approximately 60% of Japanese neonatologists continue to use doxapram at small doses. Caution is warranted because the sample sizes of the former studies are inadequate to evaluate doxapram for both its beneficial and harmful effects. Therefore, we conducted the present study in order to investigate the efficacy and harmful events of low-dose doxapram therapy for idiopathic AOP in very low-birth weight (VLBW) infants in a larger population.

METHODS

One hundred and six VLBW infants with idiopathic AOP were treated with doxapram at a dose of 0.2-1.0 mg/kg per h in combination with methylxanthines and the frequency of apnea and secondary outcomes were compared with a group of control infants.

RESULTS

An approximate 80% reduction in the frequency of apnea was found with only minimal side effects following low-dose doxapram. Although there were no significant differences in secondary outcomes between the doxapram-treated and control groups, mortality in doxapram-treated infants was significantly lower than that in control infants.

CONCLUSIONS

Patients with AOP unresponsive to treatment with methylxanthines may benefit from the addition of low-dose doxapram.

Persistent respiratory irregularity in patients with panic disorder

BACKGROUND

Dysregulated respiratory control may play a role in the pathophysiology of panic disorder. This could be due to abnormalities in brain stem respiratory nuclei or to dysregulation at higher brain levels. Results from previous studies using the doxapram model of panic have yielded an unclear picture. A brief cognitive manipulation reduced doxapram-induced hyperventilation in patients, suggesting that higher level inputs can substantially alter their respiratory patterns. However, respiratory abnormalities persisted, including a striking irregularity in breathing patterns.

METHODS

To directly study respiratory irregularity, breath-by-breath records of tidal volume (V(t)) and frequency (f) from previously studied subjects were obtained. Irregularity was quantified using von Neumann's statistic and calculation of "sigh" frequency in 16 patients and 16 matched control subjects. Half of each group received a standard introduction to the study and half received a cognitive intervention designed to reduce anxiety/distress responses to the doxapram injection.

RESULTS

Patients had significantly greater V(t) irregularity relative to control subjects. Neither the cognitive intervention nor doxapram-induced hyperventilation produced significant changes in V(t) irregularity. The V(t) irregularity was attributable to a sighing pattern of breathing that was characteristic of panic patients but not control subjects. Patients also had somewhat elevated f irregularity relative to control subjects.

CONCLUSIONS

The irregular breathing patterns in panic patients appear to be intrinsic and stable, uninfluenced by induced hyperventilation or cognitive manipulation. Further study of V(t) irregularity and sighs are warranted in efforts to localize dysregulated neural circuits in panic to brain stem or midbrain levels.

Effect of doxapram on episodes of apnoea, bradycardia and hypoxaemia in preterm infants

AIM

To study the effect of doxapram on the frequency of apnoea, bradycardia and hypoxaemia.

METHODS

Fifteen infants, median gestational age at birth 27 weeks (range 24-30), age at study 27 days (12-60), with >/=6 episodes of bradycardia or hypoxaemia/6 h despite serum caffeine levels in the therapeutic range, received doxapram either intravenously (0.5-2 mg/kg/h) or orally (2-8 mg/kg every 2 h). Six-hour recordings of pulse oximeter saturation (S(P)O(2)), pulse waveforms, ECG, breathing movements and nasal airflow were performed immediately before as well as 1, 3 and 6 days after onset of treatment. Recordings were analysed for apnoea (>/=4 s), bradycardia (heart rate < 2/3 of baseline) and hypoxaemia (S(P)O(2) </=80%).

RESULTS

There was no difference between enteral and intravenous administration; results are therefore presented for the total group. Doxapram resulted in a significant decrease in the frequency of apnoea [22 (11-27) vs. 14 (7-23)/h, p < 0.01], bradycardia [3 (0-7) vs. 1 (0-3)/h, p < 0.01] and hypoxaemia [8 (0-18) vs. 2 (0- 17)/h, p < 0.01] already after 1 day of treatment, which was sustained throughout the 6-day study period. Side effects included an increase in the proportion of time spent awake [5 (0-24) vs. 12% (3-28), p < 0.01] and in gastric residuals [0% of feeding volume (0-5) vs. 4% (0-19), p < 0.05]. Enteral was switched to intravenous doxapram in 3 of 9 infants because of gastrointestinal side effects.

CONCLUSION

Doxapram substantially reduced the frequency of apnoea, bradycardia and hypoxaemia in these patients with caffeine-resistant apnoea of prematurity. Enteral administration, however, was not tolerated in a significant proportion (33%) of infants.

Low-dose doxapram for treatment of apnoea following early weaning in very low birthweight infants: a randomized, double-blind study

The effects of low-dose doxapram (0.5 mg kg(-1)h(-1)) in combination with caffeine were evaluated on apnoea frequency following weaning from mechanical ventilation, and on blood pressure, in very low birthweight (BW) premature infants. Twenty-nine infants with BW < or=1250 g, gestational age at birth (GA) <34 weeks and postnatal age <5 d, who required minimal respiratory support, were included. Following randomization, they received a loading dose of caffeine citrate and a continuous infusion of doxapram (doxapram, n=14) or placebo (n=15) was started. They were extubated 8 h after starting the infusion, which was continued for 5 d. During this period, weaning was well tolerated in both groups, apnoeas occurred less frequently and there was a greater increase in systolic blood pressure in infants treated with doxapram than in controls. Plasma doxapram levels were also higher than expected. It is therefore suggested that doxapram, even at low doses, should not be used during the first few days of life. Careful monitoring of blood pressure is required if doxapram is used later.

Randomized, controlled, blinded trial of doxapram for extubation of the very low birthweight infant

The objective of the study was to determine whether administering doxapram by infusion to the very low birthweight infant, prior to extubation during the first 3 weeks of life, would increase the incidence of successful extubation. The study patients, 56 infants of less than 1251 g birthweight and less than 30 weeks' gestation, were entered in the first 3 weeks of life when lung disease had started to improve. A randomized blinded trial was performed, with infants receiving 3.5 mg kg(-1) doxapram bolus, followed by an infusion at 1 mg kg(-1) h(-1), or placebo. Weaning from positive pressure ventilation was standardized and extubation occurred after a 12 h trial of an intermittent mandatory ventilation (IMV) rate of 6 breaths min(-1), if PCO2 < 55 mmHg, pH > 7.26, and FiO2 < 0.45. Study drug was continued for 48 h postextubation, and the infants were placed on nasopharyngeal continuous positive airway pressure (CPAP) for 72 h postextubation. Extubation failure within the first 72 h after extubation was objectively defined in terms of acidosis (pH < 7.26), hypercarbia (PCO2 > 55 mmHg), excessive oxygen requirement (FiO2 > 0.8) or frequent apnoea (more than three in 12 h, or more than two requiring face mask IMV in 24 h). No difference was noted in the frequency of successful extubation between the groups. Fifteen infants in each group were successfully extubated before the 10th day of the study. In conclusion, when given in accordance with this protocol doxapram does not increase the likelihood of successful extubation in the very low birthweight infant. Increasing successful extubations in this group of infants will require other strategies.

The minimum effective doses of pethidine and doxapram in the treatment of post-anaesthetic shivering

This study was designed to find the minimum effective doses of doxapram and pethidine to stop post-anaesthetic shivering. Two hundred and twenty healthy patients who shivered following routine surgery were allocated randomly to receive one of 10 doses of doxapram (0.18, 0.23, 0.29, 0.35, 0.41, 0.47, 0.7, 0.93, 1.17 and 1.4 mg.kg-1), one of five doses of pethidine (0.12, 0.18, 0.23, 0.29 and 0.35 mg.kg-1) or saline. Probit analysis demonstrated that the number of patients who stopped shivering with doxapram was independent of the amount of drug given in this dose range. The lowest dose of doxapram (0.18 mg.kg-1) was significantly more effective than placebo (p < 0.01). For pethidine there was a dose-dependent effect on shivering to a maximum of 95% of patients successfully treated with 0.35 mg.kg-1. We conclude that 0.35 mg.kg-1 of pethidine is the minimum dose required to treat post-anaesthetic shivering effectively. We also conclude that 0.18 mg.kg-1 of doxapram is as effective as 1.4 mg.kg-1 in the treatment of post-anaesthetic shivering. Further study is required to find the minimum effective dose of doxapram.

Use of the respiratory stimulant doxapram in southern elephant seals (Mirounga leonina)

The use of doxapram to stimulate breathing was examined in southern elephant seals chemically restrained with ketamine and xylazine. Animals which were breathing spontaneously received doxapram (approximately 0.5, 1, 2, or 4 mg/kg) or saline into the extradural intravertebral vein. Doxapram caused a dose-dependent increase in the depth and rate of respiration which began within one minute, peaked after two minutes and lasted for up to five minutes. A dose of 2 mg/kg appeared to be safe and effective for the stimulation of respiration, while 4 mg/kg caused arousal and shaking. Doxapram (2 mg/kg) was tested on 14 occasions in animals which had developed apnoea during chemical restraint. Doxapram had no effect when administered into the extradural intravertebral vein and appeared to be of more benefit when administered directly into the lungs via an endotracheal tube, but it was not effective in all cases. There was evidence to suggest that the endotracheal tube prevented some of the animals from breathing. The effect of intubation and endotracheal doxapram administration was therefore examined in 19 apnoeic and 31 spontaneously breathing seals. Intubation induced apnoea in animals at low levels of chemical restraint and endotracheal doxapram was unreliable for the stimulation of breathing.

[Oral administration of doxapram in preterm neonates with aminophylline-resistant idiopathic apnea crisis]

Doxapram is an analeptic capable of stimulating both central and periferal areas of the respiratory system. During the last few years, intravenous infusion of doxapram has been carried out, with success, for the treatment of idiopathic apnea in preterm infants otherwise unresponsive to methylxantine. Since doxapram has a tendency to precipitate into various solution containing amino acids and calcium gluconate, oral administration has been suggested. The Authors in this study have seen that in 18 preterm infants suffering from idiopathic apnea unresponsive to amynofillina, an oral administration of doxapram at 12 mg/kg/6h resulted in a complete recovery from apnea spells in 66.7% of cases, while 22.2% gave a partial positive response and only 11.1% a negative result. Furthermore the Authors would like to stress that doxapram showed a good tolerance level when administered orally. In fact, no side effects which were previously reported in other publications were presented in the infants studied.

Use of doxapram hydrochloride injection as an alternative to intubation to treat chronic obstructive pulmonary disease patients with hypercapnia

We report three cases in which doxapram hydrochloride injection was used as an additional method of treating and stabilizing patients with chronic hypercapnia and hypoxia. Patients with such impaired respiratory drives would otherwise require intubation for medical management. In the appropriate setting, the use of doxapram hydrochloride injection has the potential to decrease morbidity and cost and shorten hospitalization as compared with intubation. This treatment also may be a viable option to treat patients for whom intubation is not an option.

In vivo release of glutamate in nucleus tractus solitarii of the rat during hypoxia

1. An attempt has been made to test the hypothesis that, in the caudal part of nucleus tractus solitarii (NTS) where carotid sinus nerve (CSN) afferents project, L-glutamate (Glut) modulates the hypoxic ventilatory response. 2. Unanaesthetized, peripherally chemodenervated (carotid body denervated; CBD) and sham-operated, freely moving rats were used. During peripheral chemoreceptor stimulation by hypoxia (10% O2 for 30 min) or doxapram (Dox) infusion (2 mg kg-1 (30 min)-1), ventilation was recorded and successively, under the same conditions, the extracellular Glut concentration ([Glut]o) in the caudal NTS was measured by in vivo microdialysis. [Glut]o was also measured during hyperoxic hypercapnia (10% CO2-30% O2 for 30 min). 3. Furthermore, the effects on ventilation of exogenous Glut, the NMDA (N-methyl-D-aspartate) receptor antagonist MK-801 or the ionotropic receptor antagonist kynurenate microinjected into the caudal NTS were investigated in sham-operated rats. 4. In sham-operated rats, both ventilation and [Glut]o in NTS were increased during peripheral chemoreceptor stimulation. On the other hand, no increases in either ventilation or Glut release were observed in CBD rats. In spite of ventilatory augmentation during hypercapnia, no response of [Glut]o to hypercapnia was observed in either group. 5. Local Glut application into NTS increased ventilation. Pretreatment with MK-801 or kynurenate reduced the hypoxic ventilatory response. This reduction in ventilation was mainly due to the decrease in tidal volume. 6. These results suggest that hypoxia induced the release of Glut in NTS and that this effect was mediated by arterial chemosensory input.

Doxapram improves pulmonary function after upper abdominal surgery

The effects of doxapram on postoperative pulmonary function were studied in 40 ASA I and II patients randomly allocated to receive either doxapram 1.8 mg.kg-1.h-1 or placebo for 2 h immediately after elective cholecystectomy. The two groups displayed similar reductions of carbon dioxide production at 2 h and 6 h postoperatively, whereas oxygen consumption remained at preoperative levels for 24 h. Minute ventilation was similarly reduced in the two groups at 2 h and 6 h postoperatively, with corresponding increases in PaCO2. PaO2 was similarly and significantly decreased in both groups postoperatively, whereas P(A-a)O2 remained unchanged at 2 h and 6 h in doxapram-treated patients. FRC was reduced postoperatively in both groups, significantly more so in the control group at 6 h. Various indices of intrapulmonary gas distribution, including the functional (nitrogen) dead space, underwent similar changes in the two groups. By contrast, the physiological dead space was reduced in doxapram-treated patients at 2 h, 6 h and 24 h postoperatively, whereas no significant changes were seen in the control group. The ventilatory equivalent for CO2 was significantly lower in the doxapram-treated group, implying higher ventilatory efficiency. Our findings indicate that infusion of doxapram postoperatively attenuates the impairment of pulmonary function postoperatively, chiefly via effects on V'A/Q' ratios. No side effects of doxapram were observed.

Effects of doxapram on hypercapnic response during weaning from mechanical ventilation in COPD patients

Failure of weaning from mechanical ventilation in COPD patients is often related to diaphragmatic fatigue. Whether there is a central respiratory drive fatigue and a reserve of excitability is still debated. The purpose of this study was to analyze the following in 13 COPD patients weaned from mechanical ventilation: (1) ventilatory (VE/PETCO2) and neuromuscular (P0.1/PETCO2) response to hypercapnia; (2) the maximum reserve capacity measured through changes in the VE/PETCO2 and P0.1/PETCO2 slopes after doxapram (DXP) infusion, which, given during the test, allows measurement of the maximum response capacity to overstimulation; and (3) analyze the influence of these changes on the outcome of weaning. The results show a variable P0.1/PETCO2 response and a low VE/PETCO2. DXP infusion does not change the slopes of these relations but increases the end-expiratory volume (delta FRCd); (p less than 0.02). Since there was no change in the VE/PETCO2, P0.1/PETCO2, and delta FRC values with or without DXP, there was no excitability reserve in patients who were successfully weaned. When weaning failed, DXP did not change VE/PETCO2 and P0.1/PETCO2 slope, but delta FRCd was greater the delta FRC (p less than 0.001). The excitability reserve in these patients leads to an increase in end-expiratory volume, probably worsening the diaphragm dysfunction.

Pharmacokinetics and metabolism of intravenous doxapram in horses

The pharmacokinetics and metabolism of doxapram in horses administered intravenous (iv) doses of 0.275, 0.55 and 1.1 mg doxapram/kg bodyweight (bwt) were investigated. Plasma doxapram concentrations decreased rapidly after drug administration and the disappearance of doxapram from plasma was best described by a polyexponential equation. Median values of total body clearance were 10.9, 10.6 and 10.9 ml/min/kg bwt for the three doses and were independent of dose. The steady-state volume of distribution was approximately 1,200 ml/kg bwt and the median biological half-life ranged from 121 to 178 mins. Plasma protein binding of doxapram ranged from 76.0 to 85.4 per cent. The blood:plasma doxapram concentration ratio was approximately 0.8 and the affinity of the red blood cells for doxapram ranged from 2.0 to 2.8 indicating sequestration of doxapram in erythrocytes. Renal clearance of doxapram was a minor route of elimination. Metabolic clearance of doxapram appeared to be a major route of elimination. Four metabolites of doxapram were isolated from urine and were identified. The metabolites were: a) 1-ethyl-4-[(2-hydroxyethyl) amino]ethyl-3,3-diphenyl-2-pyr-rolidinone, b) a glucuronic acid or sulphuric acid conjugate of 1-ethyl-3-(hydroxyphenyl)-4-(2-morpholinoethyl)-3-phenyl-pyrrolidinone, c) 3,3-diphenyl-4-(2-morpholinoethyl)-2-pyrrolidinone and d) 1-(2-hydroxyethyl)-3,3-diphenyl-4-(2-morpholinoethyl)-2-pyr-rolidinon e. The rapid disappearance of doxapram from plasma immediately after iv administration was attributed to redistribution of the drug from plasma to other tissues. The short duration of clinical effect from doxapram may be attributed to redistribution of the drug from plasma and other well-perfused tissues, such as the brain, to less well-perfused tissues such as the skeletal muscles and adipose tissue. Continuous or repeated administration of doxapram could prolong the duration of clinical effect because re-distribution is less important as steady-state conditions are approached.

Doxapram for the initial treatment of idiopathic apnea of prematurity

The ventilatory effects of doxapram in the initial pharmacotherapy for apnea in the newborn were evaluated in 8 premature infants with idiopathic apnea. All received doxapram for 48 h at 0.25 mg/kg/h on the first day and 1 mg/kg/h on the second day. The ventilatory effects and the airway occlusion pressure (p0.1) were measured by means of a face mask, and a pneumotachograph. Compared to the pretreatment period, the mean of the frequency of central apnea greater than or equal to 15 s decreased significantly (p less than 0.01) by 48 and 75% during the first and second day, respectively. Both doses significantly increased inspiratory drive measured by airway occlusion pressure by 20% (p less than 0.05) and 32% (p less than 0.01) on the first and second day of drug treatment, respectively. Minute ventilation, tidal volume and mean respiratory flow significantly increased only with 1 mg/kg/h of doxapram, accompanied by a significant decrease in transcutaneous PCO2. No side effects were noted. Data suggested that doxapram alone at a dose of 1 mg/kg/h is effective for the treatment of neonatal apnea.

Low-dose doxapram for apnea unresponsive to aminophylline in very low birthweight infants

This study was designed to test whether the addition of low-dose (less than or equal to 1.5 mg/kg/h) doxapram may help wean from positive airway pressure very low birthweight (less than or equal to 1250 g) infants with apnea unresponsive to aminophylline. Doxapram infusion was started at 0.1 to 0.5 mg/kg/h and increased as necessary up to a maximum of 1.5 mg/kg/h. Average birthweight (N = 12) was 1026 +/- 170 g (mean +/- SD, range 740 to 1250), gestational age 27.8 +/- 2.6 weeks (range 24 to 34), postnatal age 24.2 +/- 9.4 days (range 13 to 40), central spun hematocrit 44% +/- 4% (range 38% to 48%), and theophylline level 57.1 +/- 7.7 mumol/L. Doxapram therapy resulted in weaning to a head box in 11 of 12 patients; two required a subsequent course after stopping doxapram. Since the only observed toxicity was mild irritability in one patient, we conclude that very low birthweight infants with apnea unresponsive to aminophylline and older than 1 week of age often respond to the addition of low-dose doxapram with only minimal side effects. Since there was a negative correlation between theophylline level and the effective doxapram dose (r = -.64, N = 13, P less than .05), we recommend that treatment with doxapram be considered in the United States only in those infants with a theophylline level greater than or equal to 88.8 mumol/L, in order to limit the cumulative dose of benzyl alcohol administered.

Low-dose doxapram therapy in premature infants and its CSF and serum concentrations

The efficacy of low-dose doxapram therapy (0.2 mg/kg/h) in combination with methylxanthines was evaluated in 20 premature infants with idiopathic apnea unresponsive to methylxanthines alone, and in 13 premature infants with secondary apnea. The serum concentrations of doxapram and, in some infants, the simultaneous cerebrospinal fluid and serum concentrations were measured, and the correlation between cerebrospinal fluid and serum concentrations in the postnatal period was determined. The following results were obtained: 1) In idiopathic apnea of prematurity, low-dose doxapram therapy was as effective as a dose of 1.0-2.5 mg/kg/h and the side effects were few, mild, and reversible. 2) In premature infants over seven days of age, serum concentrations of doxapram were almost stable but were significantly lower than in infants within the first six days of life. 3) The ratio of the cerebrospinal fluid to serum doxapram concentration was 0.48 +/- 0.13 (mean +/- SD). There was a good correlation between cerebrospinal fluid and serum concentrations (r = 0.933, p less than 0.001). The initial doxapram dose can be set as low as 0.2 mg/kg/h in very young premature infants with idiopathic apnea of prematurity unresponsive to methylxanthines.

Reversal of xylazine sedation in dogs

Intramuscular injections of atipamezole (200 micrograms/kg), doxapram (2.5 mg/kg) and saline (0.1 ml/kg) were compared for their ability to reverse xylazine sedation in dogs. Atipamezole effectively reversed the sedative effects and partially reversed the cardiopulmonary effects of xylazine. Doxapram did not arouse the dogs as much as atipamezole, but it shortened the time taken for them to stand although the dogs were still ataxic.

Clinical and physiological responses to prolonged nasogastric administration of doxapram for apnea of prematurity

We hypothesized that enteral doxapram would effectively treat apnea of prematurity without the appearance of major side effects. Of 16 infants, 10 (BW 1,520 +/- 102 g) received doxapram alone and 6 (BW 1,020 +/- 35 g) received doxapram plus theophylline. Apneas decreased from 16.7 +/- 1.9 to 2.1 +/- 0.6 in infants receiving doxapram alone, and from 38.2 +/- 4.4 to 7.9 +/- 2.2 apneas/24 h in those receiving doxapram plus theophylline. This was associated with an increase in alveolar ventilation, a shift of the ventilatory response to CO2 to the left, and no change in the immediate ventilatory response to 100% oxygen. Side effects included premature teeth buds corresponding to the lower central incisors, prevalence of occult blood in stool and necrotizing enterocolitis. The findings suggest that doxapram effectively controls apnea when given enterally, but should be used cautiously because of potentially harmful side effects.

Restored hypoxic pulmonary vasoconstriction by peripheral chemoreceptor agonists in dogs

Hypoxic stimulation of the peripheral chemoreceptors inhibits hypoxic pulmonary vasoconstriction (HPV). On the other hand, almitrine, a peripheral chemoreceptor agonist, has been reported in some studies to enhance HPV. To further explore this apparent contradiction, we investigated the effects of two different low intravenous doses of almitrine on pulmonary arterial pressure (Ppa) versus cardiac index (Q) plots in 32 pentobarbital-anesthetized dogs ventilated alternatively in hyperoxia (FIO2, 0.4) and in hypoxia (FIO2 0.1). HPV, defined as a hypoxia-induced increase in Ppa over the entire range of Q studied, from 2 to 5 L/min/m2, was elicited in 16 dogs. In the first eight of these "responders," almitrine 2 micrograms/kg/min had no vascular effect, and in the other eight, almitrine 4 micrograms/kg/min inhibited HPV. In 16 other dogs, hypoxia did not affect Ppa over the entire range of Q. In these "nonresponders," almitrine 2 micrograms/kg/min (n = 8) as well as 4 micrograms/kg/min (n = 8) restored HPV. To answer the question whether the ability to restore HPV would be specific to almitrine, we administered intravenously the structurally unrelated chemoreceptor agonist doxapram at the dose of 20 micrograms/kg/min to an additional group of eight "nonresponders," and this treatment also restored HPV. Intravenous infusion of the malic acid solution solvent of almitrine had no effect on Ppa/Q plots in a final group of eight "nonresponders". We conclude that low dose almitrine and doxapram restore HPV in dogs with a naturally absent hypoxic pulmonary pressor response, probably by a direct effect at the pulmonary vessels.

Effect of doxapram on postoperative pulmonary complications after upper abdominal surgery in high-risk patients

In a double-blind randomised trial an infusion of doxapram, 2 mg per min for 6 h immediately after surgery and repeated on the first postoperative day, or the same volume of saline, was given to 39 patients who underwent upper abdominal surgery and who were at high risk of postoperative day, or the same volume of saline, was given to 39 patients who underwent upper abdominal surgery and who were at high risk of postoperative pulmonary complications. The patients were assessed pre-operatively and during the first 5 postoperative days by physical examination, spirometry, blood-gas analysis, and chest radiography. Postoperative pulmonary complications were defined as temperature over 38 degrees C for 2 days, abnormal auscultation, pathological radiography, and/or productive cough. Data from 16 patients per group were analysed. Significantly more patients in the placebo group had three criteria of postoperative pulmonary complication compared with the doxapram group (63% vs 19%). The doxapram group also had higher PaO2 postoperatively.

A blinded, randomized, placebo-controlled trial to compare theophylline and doxapram for the treatment of apnea of prematurity

A blinded, randomized, placebo-controlled trial was conducted to evaluate the effectiveness of theophylline and doxapram therapy in 31 infants with significant apnea of prematurity. Of 10 infants, two had a short-term response to placebo, 8 of 10 infants to theophylline, and 7 of 11 infants to doxapram (placebo vs treatment with theophylline or doxapram: p = 0.01). The two infants who initially responded to placebo remained responsive for the duration of the study. Of the eight infants in whom treatment with placebo failed, five were randomly assigned to receive theophylline, for a total of 15 infants treated with theophylline, and two of the eight were randomly assigned to receive doxapram, for a total of 13 infants treated with doxapram; the remaining infant required tracheal intubation. Of the 15 infants randomly assigned to receive theophylline, seven responded for the duration of the study; of the eight infants who did not respond to treatment with theophylline, five responded to doxapram, one responded to a combination of theophylline and doxapram, and two remained resistant to treatment. Of the 13 infants randomly assigned to receive doxapram four responded for the duration of the study; of the nine who did not respond to doxapram, seven responded to theophylline, one responded to a combination of theophylline and doxapram, and one remained resistant to treatment. This study demonstrates that although therapy with theophylline or doxapram is associated with a significant short-term reduction in the incidence of apnea compared with that in placebo-treated infants, the long-term response to treatment is frequently incomplete and is not sustained more than 1 week.

Effects of caffeine and doxapram perfusion on local cerebral glucose utilization in conscious rats

The quantitative autoradiographic 2-[14C]deoxyglucose method was used to measure the effects of a continuous infusion of the respiratory stimulants, caffeine or doxapram, 18 mg/kg per h, on local cerebral glucose utilization in the adult male rat. Local cerebral glucose utilization was measured in 54 cerebral structures from different systems. Caffeine induced widespread increases in energy metabolism, resulting in a significant increase in glucose utilization in 25 structures out of the 54 studied. These increases were distributed within all systems studied, sensory, extrapyramidal motor, limbic and hypothalamic systems. In addition, caffeine induced a non-significant, 10-15%, increase in local cerebral glucose utilization in central respiratory areas. Doxapram infusion did not change the rates of glucose utilization in any of the structures. The rates of local cerebral glucose utilization were significantly lower after doxapram than after caffeine exposure in five cerebral areas, among which were three central respiratory areas. The results confirm the absence of side-effects of doxapram as compared to caffeine when used as respiratory stimulant, especially in neonates. These results also favor a preferentially central action of caffeine on respiratory areas and a more peripheral action of doxapram on chemoreceptors, at least at therapeutic levels.

Effect of oral doxapram on morphine-induced changes in the ventilatory response to carbon dioxide

A double-blind crossover volunteer trial has been carried out to determine if oral doxapram reduces the respiratory depression caused by morphine 0.12 mg kg-1 i.m. Doxapram was given to the subjects 90 min before the morphine and significantly reduced the displacement of the ventilatory response to carbon dioxide caused by the morphine. This occurred despite the fact that the plasma concentrations of doxapram were significantly lower when the subject had been given morphine than when a placebo injection had been administered. Doxapram alone in doses of 300 mg and 600 mg did not alter significantly the respiratory variables measured in this study.

Patient-controlled analgesia with a mixture of pethidine and doxapram hydrochloride. A comparison of the incidence of respiratory dysrhythmias with pethidine alone

Twenty-four patients who underwent elective cholecystectomy received double-blind increments of either pethidine 30 mg or a mixture of pethidine 30 mg and doxapram 45 mg delivered on a patient-controlled basis. A loading dose of doxapram 100 mg or saline was administered. There was no difference in respiratory depression as indicated by respiratory frequency and end tidal carbon dioxide concentration. The incidence of respiratory apnoea was similar in the two groups but apnoea was of shorter duration in patients who received doxapram, although the difference was not significant. Patients who received doxapram assessed overall pain as worse on a linear analogue scale (p less than 0.05) but demanded similar amounts of pethidine. There was no difference in pain on movement.

Serum doxapram and respiratory neuromuscular drive in normal man

To investigate the means by which doxapram affects the control of ventilation, ventilatory function and P0.1 have been related to serum doxapram concentration during a 45-min infusion of doxapram hydrochloride in 7 healthy, conscious subjects under normoxic conditions. Serum doxapram concentrations increased during the infusion: 1.88, 2.48, 3.42, and 3.97 micrograms/ml after 5, 10, 30 and 45 min, respectively. The majority of significant changes in the measurements from the baseline were observed at 30 and 45 min: VE, VT, P0.1, P0.1/end-tidal CO2 tension, VT/Ti and blood pressure were increased, and end-tidal CO2 tension was decreased. No significant changes in Pdimax, Ti/Ttot, VE/P0.1, and P0.1/(VT/Ti) were observed. A correlation was observed between the % increases in P0.1 and VE and doxapram concentration, and between VE and P0.1. The doxapram-induced increase in VE appears to be caused by increased neural drive. It is related to the serum drug concentration in the conscious subject.

Doxapram dosage regimen in apnea of prematurity based on pharmacokinetic data

To 18 premature apneic patients refractory to theophylline, doxapram (0.5-2.5 mg/kg/h) was administered in combination with therapeutic doses of theophylline. Doxapram concentrations in serum were measured 48 h after commencement of the infusion and then in 2-hour intervals during a 6-8 h withdrawal. Total body clearance (dose/Css) of the drug ranged from 0.20 to 0.56 liter/h in 13 patients and 1.14 to 1.75 liter/h in 4 patients suggesting a binomial distribution in the disposition kinetics of the drug. Other pharmacokinetic indices, although variable, did not exhibit binomial distribution. The mean volume of distribution and half-life of doxapram were 7.33 +/- 4.55 liter/kg and 8.17 +/- 4.13 h, respectively. Based on our calculations to accelerate the attainment of a steady-state plasma concentration (Css) of approximately 1.5 mg/l, a loading dose of 5.5 mg/kg and a maintenance dose of 1 mg/kg/h along with serum concentration monitoring are recommended.

Doxapram on blunted respiratory chemosensitivity to hypoxia in hypoxemic, chronic obstructive pulmonary disease

We investigated a possible effect of doxapram (a respiratory stimulant) on the peripheral chemoreceptors in man (8 control subjects, 11 bronchitics, and 4 emphysematous). In addition, we determined whether infusion of doxapram could augment blunted chemosensitivity to hypoxia or hypercapnia seen in both chronic obstructive pulmonary disease (COPD) patients and normal subjects. Doxapram infusion caused a significant increase in delta VE/delta SaO2 (p less than 0.05), as well as delta Po.1/delta SaO2 (p less than 0.05) in control subjects, although the changes in both delta VE/delta PeAco2 (where, PeAco2 = end-tidal Pco2) and delta Po.1/delta PeAco2 did not attain significant level. Control subjects with low baseline delta Po.1/delta SaO2 showed significantly larger changes in both delta Po.1/delta SaO2 and delta VE/SaO2 during doxapram infusion than the patients with chronic bronchitis (0.02 less than p less than 0.05). We conclude that doxapram increases chemosensitivity to hypoxia and slightly increase chemosensitivity to hypercapnia, indicating its primary action being stimulation of peripheral chemoreceptors, and doxapram stimulates chemoreceptors little in patients with chronic bronchitis, whereas blunted hypoxic response in normal subjects could be increased markedly.

Reversal of xylazine-induced sedation in llamas, using doxapram or 4-aminopyridine and yohimbine

For each of 3 separate evaluations, 6 fasted llamas (Lama glama) were sedated with xylazine (1.1 mg/kg of body weight, IV) and then 15 minutes later were given normal saline solution (5.0 ml, IV; control values), doxapram (2.2 mg/kg, IV), or 4-amino-pyridine (0.3 mg/kg, IV) and yohimbine (0.125 mg/kg, IV). After administration of 4-aminopyridine and yohimbine, the llamas stood in a mean of 11 minutes and resumed eating in a mean of 34 minutes; both means were significantly less (P less than 0.05) than control values (46 minutes and 67 minutes, respectively). Doxapram induced muscle fasciculations, and (compared with control values) did not significantly decrease the time to standing (41 minutes) or the time until the animals resumed eating (68 minutes). Yohimbine and 4-aminopyridine in combination rapidly antagonized xylazine-induced sedation in llamas, whereas doxapram was ineffective as an antagonist of xylazine-induced sedation.

Doxapram: cardiopulmonary effects in the horse

The cardiopulmonary effects of 3 dosages of doxapram hydrochloride (0.275 mg/kg, 0.55 mg/kg, and 1.1 mg/kg, IV) were studied in 6 adult horses. Doxapram given IV significantly (P less than 0.05) decreased PaCO2 and increased respiratory rate, cardiac output arterial blood pressures (systolic, mean, and diastolic) arterial pH, and PaO2 at 1 minute after each dose was administered. Heart rate and mean and diastolic pulmonary arterial blood pressure were significantly (P less than 0.05) increased 1 minute after the 2 larger dosages of doxapram were given (0.55 mg/kg and 1.1 mg/kg, IV), but not after the smallest dosage was given. All measurements, except heart rate and cardiac output, had returned to base line by 5 minutes after each dosing. Heart rate remained significantly (P less than 0.05) increased 10 minutes after the 0.55 mg/kg dosage was given and 30 minutes after the 1.1 mg/kg dosage. Cardiac output remained significantly (P less than 0.05) increased at 10 minutes, 5 minutes, and 30 minutes after the 0.275, 0.55, and 1.1 mg/kg dosages, respectively, were given.

Prompt arousal from fentanyl-droperidol-pentobarbital anesthesia in dogs: a preliminary study

Groups of fentanyl-droperidol-pentobarbital-anesthetized dogs (n = 6 dogs/group) were given IV saline solution (control group), graded doses of naloxone (0.01, 0.1, 1.0, 10.0 mg/kg) or fixed doses of 4-aminopyridine (0.5 mg/kg), yohimbine (0.4 mg/kg), or doxapram (5.0 mg/kg) alone or in combination with a fixed dose of naloxone (1.0 mg/kg). The purpose was to determine which drug or drug combination would produce arousal most quickly without producing obvious undesirable side effects. Control group mean arousal time, mean walk time and mean duration of postarousal sedation were 66.1 minutes, 112.4 minutes and 5.6 hours, respectively. Naloxone (1.0 mg/kg) decreased mean arousal time to 10.8 minutes without significantly decreasing mean walk time or mean duration of postarousal sedation. The combination of naloxone + doxapram decreased mean arousal time and mean walk time to 1.0 minute and 57.1 minutes, respectively, without decreasing mean duration of postarousal sedation. In all groups, emergence from anesthesia was smooth. Relapses or undesirable side effects were not observed. Naloxone + doxapram is superior to naloxone alone for arousal of fentanyl-droperidol-pentobarbital-anesthetized dogs.

Physiologic effects of doxapram in idiopathic apnea of prematurity

Twelve premature infants with significant apnea of prematurity while receiving therapeutic doses of aminophylline were given an intravenous infusion of doxapram, 2 or 2.5 mg/kg/hr. The ventilatory effects of the medication were monitored by means of face mask spirometry and airway occlusion studies. Doxapram therapy was associated with significant increases in minute ventilation, tidal volume, mean inspiratory flow, and airway pressure 100 msec after occlusion. Respiratory frequency and the relative duration of inspiration and expiration were unchanged. Paco2 decreased significantly during the infusion. The apnea attack rate, monitored by continuous recording, was significantly reduced after the first 6 hours of therapy. Six hours after starting doxapram, mean arterial blood pressure was significantly elevated, and continued to increase during the 24 hours of therapy. Doxapram is effective in treatment of apnea of prematurity refractory to aminophylline, and appears to act by increasing respiratory center output.