Methazolamide Plus Aminophylline Abrogates Hypoxia-Mediated Endurance Exercise Impairment

The Impact of Acetazolamide and Methazolamide on Exercise Performance in Normoxia and Hypoxia

Doherty, Connor J., Jou-Chung Chang, Benjamin P. Thompson, Erik R. Swenson, Glen E. Foster, and Paolo B. Dominelli. The impact of acetazolamide and methazolamide on exercise performance in normoxia and hypoxia. High Alt Med Biol. 24:7-18, 2023.-Carbonic anhydrase (CA) inhibitors are commonly prescribed for acute mountain sickness (AMS). In this review, we sought to examine how two CA inhibitors, acetazolamide (AZ) and methazolamide (MZ), affect exercise performance in normoxia and hypoxia. First, we briefly describe the role of CA inhibition in facilitating the increase in ventilation and arterial oxygenation in preventing and treating AMS. Next, we detail how AZ affects exercise performance in normoxia and hypoxia and this is followed by a discussion on MZ. We emphasize that the overarching focus of the review is how the two drugs potentially affect exercise performance, rather than their ability to prevent/treat AMS per se, their interrelationship will be discussed. Overall, we suggest that AZ hinders exercise performance in normoxia, but may be beneficial in hypoxia. Based upon head-to-head studies of AZ and MZ in humans on diaphragmatic and locomotor strength in normoxia, MZ may be a better CA inhibitor when exercise performance is crucial at high altitude.

Effects of theophylline and theobromine on exercise performance and implications for competition sport: A systematic review

A systematic review was undertaken to evaluate studies on the effects of theophylline and theobromine on exercise performance in normal (healthy) subjects. Theophylline was found to have been studied on eight occasions and theobromine on one, the number of subjects per study ranging from seven to 15. In two exercise investigations, theophylline was superior to placebo at a p < 0.05 level and no different in four including one that was conducted in artificial hypoxia. In a treadmill time trial over 3 km, theobromine was superior to placebo and equal to caffeine, at the <0.05 level. In strength studies, theophylline increased wrist strength in one and showed a slight but not statistically significant increase in limb strength in four of the seven subjects in the other. Theophylline caused adverse effects in six participants. There were no adverse effects in the theobromine investigation. Although the studies showed contradicting results and/or insufficient data to draw solid conclusions, it appears both drugs have potential to enhance performance and could be considered for inclusion on the WADA banned list.

Methazolamide in high-altitude illnesses

As a carbonic anhydrase inhibitor and a methylated lipophilic analogue of acetazolamide, Methazolamide has higher lipid solubility, less plasma protein binding and renal excretion, and fewer side effects, compared to acetazolamide. Methazolamide can increase systemic metabolic acidosis and sequentially improve ventilation and oxygenation level. The increased oxygenation level leads to reduced reactive oxygen species (ROS) production, relived cerebral edema, mitigated hypoxic pulmonary vasoconstriction, abrogated hypoxic fatigue, and decreased excessive erythrocytosis. In addition to the effect as a carbonic anhydrase inhibitor, methazolamide directly activates the transcription factor anti-oxidative nuclear factor-related factor 2 (Nrf2) and inhibits interleukin-1β (IL-1β) release. These pharmacological functions of methazolamide are beneficial for the prevention and treatment of high-altitude illnesses. Besides, methazolamide causes less fatigue side effects than acetazolamide does. It is also worth noting that several studies suggested that a lower dose of methazolamide has similar prophylaxis and treatment efficacy in acute mountain sickness (AMS) to a higher dose of acetazolamide. Given methazolamide's advantages over acetazolamide, methazolamide may thus represent an alternative for acetazolamide when taken for high-altitude illnesses prophylaxis and treatment. However, more in-depth clinical trials are needed to fully evaluate this efficacy of methazolamide.

Interventions for preventing high altitude illness: Part 3. Miscellaneous and non-pharmacological interventions

BACKGROUND

High altitude illness (HAI) is a term used to describe a group of mainly cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 metres (˜ 8200 feet). Acute mountain sickness (AMS), high altitude cerebral oedema (HACE), and high altitude pulmonary oedema (HAPE) are reported as potential medical problems associated with high altitude ascent. In this, the third of a series of three reviews about preventive strategies for HAI, we assessed the effectiveness of miscellaneous and non-pharmacological interventions.

OBJECTIVES

To assess the clinical effectiveness and adverse events of miscellaneous and non-pharmacological interventions for preventing acute HAI in people who are at risk of developing high altitude illness in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS and the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) in January 2019. We adapted the MEDLINE strategy for searching the other databases. We used a combination of thesaurus-based and free-text search terms. We scanned the reference lists and citations of included trials and any relevant systematic reviews that we identified for further references to additional trials.

SELECTION CRITERIA

We included randomized controlled trials conducted in any setting where non-pharmacological and miscellaneous interventions were employed to prevent acute HAI, including preacclimatization measures and the administration of non-pharmacological supplements. We included trials involving participants who are at risk of developing high altitude illness (AMS or HACE, or HAPE, or both). We included participants with, and without, a history of high altitude illness. We applied no age or gender restrictions. We included trials where the relevant intervention was administered before the beginning of ascent.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures employed by Cochrane.

MAIN RESULTS

We included 20 studies (1406 participants, 21 references) in this review. Thirty studies (14 ongoing, and 16 pending classification (awaiting)) will be considered in future versions of this suite of three reviews as appropriate. We report the results for the primary outcome of this review (risk of AMS) by each group of assessed interventions.Group 1. Preacclimatization and other measures based on pressureUse of simulated altitude or remote ischaemic preconditioning (RIPC) might not improve the risk of AMS on subsequent exposure to altitude, but this effect is uncertain (simulated altitude: risk ratio (RR) 1.18, 95% confidence interval (CI) 0.82 to 1.71; I² = 0%; 3 trials, 140 participants; low-quality evidence. RIPC: RR 3.0, 95% CI 0.69 to 13.12; 1 trial, 40 participants; low-quality evidence). We found evidence of improvement of this risk using positive end-expiratory pressure (PEEP), but this information was derived from a cross-over trial with a limited number of participants (OR 3.67, 95% CI 1.38 to 9.76; 1 trial, 8 participants; low-quality evidence). We found scarcity of evidence about the risk of adverse events for these interventions.Group 2. Supplements and vitaminsSupplementation of antioxidants, medroxyprogesterone, iron or Rhodiola crenulata might not improve the risk of AMS on exposure to high altitude, but this effect is uncertain (antioxidants: RR 0.58, 95% CI 0.32 to 1.03; 1 trial, 18 participants; low-quality evidence. Medroxyprogesterone: RR 0.71, 95% CI 0.48 to 1.05; I² = 0%; 2 trials, 32 participants; low-quality evidence. Iron: RR 0.65, 95% CI 0.38 to 1.11; I² = 0%; 2 trials, 65 participants; low-quality evidence. R crenulata: RR 1.00, 95% CI 0.78 to 1.29; 1 trial, 125 participants; low-quality evidence). We found evidence of improvement of this risk with the administration of erythropoietin, but this information was extracted from a trial with issues related to risk of bias and imprecision (RR 0.41, 95% CI 0.20 to 0.84; 1 trial, 39 participants; very low-quality evidence). Regarding administration of ginkgo biloba, we did not perform a pooled estimation of RR for AMS due to considerable heterogeneity between the included studies (I² = 65%). RR estimates from the individual studies were conflicting (from 0.05 to 1.03; low-quality evidence). We found scarcity of evidence about the risk of adverse events for these interventions.Group 3. Other comparisonsWe found heterogeneous evidence regarding the risk of AMS when ginkgo biloba was compared with acetazolamide (I² = 63%). RR estimates from the individual studies were conflicting (estimations from 0.11 (95% CI 0.01 to 1.86) to 2.97 (95% CI 1.70 to 5.21); low-quality evidence). We found evidence of improvement when ginkgo biloba was administered along with acetazolamide, but this information was derived from a single trial with issues associated to risk of bias (compared to ginkgo biloba alone: RR 0.43, 95% CI 0.26 to 0.71; 1 trial, 311 participants; low-quality evidence). Administration of medroxyprogesterone plus acetazolamide did not improve the risk of AMS when compared to administration of medroxyprogesterone or acetazolamide alone (RR 1.33, 95% CI 0.50 to 3.55; 1 trial, 12 participants; low-quality evidence). We found scarcity of evidence about the risk of adverse events for these interventions.

AUTHORS' CONCLUSIONS

This Cochrane Review is the final in a series of three providing relevant information to clinicians, and other interested parties, on how to prevent high altitude illness. The assessment of non-pharmacological and miscellaneous interventions suggests that there is heterogeneous and even contradictory evidence related to the effectiveness of these prophylactic strategies. Safety of these interventions remains as an unclear issue due to lack of assessment. Overall, the evidence is limited due to its quality (low to very low), the relative paucity of that evidence and the number of studies pending classification for the three reviews belonging to this series (30 studies either awaiting classification or ongoing). Additional studies, especially those comparing with pharmacological alternatives (such as acetazolamide) are required, in order to establish or refute the strategies evaluated in this review.

Interventions for preventing high altitude illness: Part 2. Less commonly-used drugs

BACKGROUND

High altitude illness (HAI) is a term used to describe a group of mainly cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 metres (˜ 8200 feet). Acute mountain sickness (AMS), high altitude cerebral oedema (HACE) and high altitude pulmonary oedema (HAPE) are reported as potential medical problems associated with high altitude ascent. In this second review, in a series of three about preventive strategies for HAI, we assessed the effectiveness of five of the less commonly used classes of pharmacological interventions.

OBJECTIVES

To assess the clinical effectiveness and adverse events of five of the less commonly used pharmacological interventions for preventing acute HAI in participants who are at risk of developing high altitude illness in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS and the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) in May 2017. We adapted the MEDLINE strategy for searching the other databases. We used a combination of thesaurus-based and free-text search terms. We scanned the reference lists and citations of included trials and any relevant systematic reviews that we identified for further references to additional trials.

SELECTION CRITERIA

We included randomized controlled trials conducted in any setting where one of five classes of drugs was employed to prevent acute HAI: selective 5-hydroxytryptamine(1) receptor agonists; N-methyl-D-aspartate (NMDA) antagonist; endothelin-1 antagonist; anticonvulsant drugs; and spironolactone. We included trials involving participants who are at risk of developing high altitude illness (AMS or HACE, or HAPE, or both). We included participants with and without a history of high altitude illness. We applied no age or gender restrictions. We included trials where the relevant medication was administered before the beginning of ascent. We excluded trials using these drugs during ascent or after ascent.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures employed by Cochrane.

MAIN RESULTS

We included eight studies (334 participants, 9 references) in this review. Twelve studies are ongoing and will be considered in future versions of this review as appropriate. We have been unable to obtain full-text versions of a further 12 studies and have designated them as 'awaiting classification'. Four studies were at a low risk of bias for randomization; two at a low risk of bias for allocation concealment. Four studies were at a low risk of bias for blinding of participants and personnel. We considered three studies at a low risk of bias for blinding of outcome assessors. We considered most studies at a high risk of selective reporting bias.We report results for the following four main comparisons.Sumatriptan versus placebo (1 parallel study; 102 participants)Data on sumatriptan showed a reduction of the risk of AMS when compared with a placebo (risk ratio (RR) = 0.43, CI 95% 0.21 to 0.84; 1 study, 102 participants; low quality of evidence). The one included study did not report events of HAPE, HACE or adverse events related to administrations of sumatriptan.Magnesium citrate versus placebo (1 parallel study; 70 participants)The estimated RR for AMS, comparing magnesium citrate tablets versus placebo, was 1.09 (95% CI 0.55 to 2.13; 1 study; 70 participants; low quality of evidence). In addition, the estimated RR for loose stools was 3.25 (95% CI 1.17 to 8.99; 1 study; 70 participants; low quality of evidence). The one included study did not report events of HAPE or HACE.Spironolactone versus placebo (2 parallel studies; 205 participants)Pooled estimation of RR for AMS was not performed due to considerable heterogeneity between the included studies (I² = 72%). RR from individual studies was 0.40 (95% CI 0.12 to 1.31) and 1.44 (95% CI 0.79 to 2.01; very low quality of evidence). No events of HAPE or HACE were reported. Adverse events were not evaluated.Acetazolamide versus spironolactone (1 parallel study; 232 participants)Data on acetazolamide compared with spironolactone showed a reduction of the risk of AMS with the administration of acetazolamide (RR = 0.36, 95% CI 0.18 to 0.70; 232 participants; low quality of evidence). No events of HAPE or HACE were reported. Adverse events were not evaluated.

AUTHORS' CONCLUSIONS

This Cochrane Review is the second in a series of three providing relevant information to clinicians and other interested parties on how to prevent high altitude illness. The assessment of five of the less commonly used classes of drugs suggests that there is a scarcity of evidence related to these interventions. Clinical benefits and harms related to potential interventions such as sumatriptan are still unclear. Overall, the evidence is limited due to the low number of studies identified (for most of the comparison only one study was identified); limitations in the quality of the evidence (moderate to low); and the number of studies pending classification (24 studies awaiting classification or ongoing). We lack the large and methodologically sound studies required to establish or refute the efficacy and safety of most of the pharmacological agents evaluated in this review.

Safety and Ergogenic Properties of Combined Aminophylline and Ambrisentan in Hypoxia

We hypothesized that concomitant pharmacological inhibition of the endothelin and adenosine pathway is safe and improves exercise performance in hypoxic humans, via a mechanism that does not involve augmentation of blood oxygenation. To test this hypothesis, we established safety and drug interactions for aminophylline (500 mg) plus ambrisentan (5 mg) in normoxic volunteers. Subsequently, a placebo-controlled study was employed to test the combination in healthy resting and exercising volunteers at simulated altitude (4,267 m). No serious adverse events occurred. Drug interaction was minimal or absent. Aminophylline alleviated hypoxia-induced headaches. Aminophylline, ambrisentan, and their combination all significantly (P < 0.05 vs. placebo) improved submaximal hypoxic exercise performance (19.5, 20.6, and 19.1% >placebo). Single-dose ambrisentan increased blood oxygenation in resting, hypoxic subjects. We conclude that combined aminophylline and ambrisentan offer promise to safely increase exercise capacity in hypoxemic humans without relying on increasing blood oxygen availability.

Interventions for preventing high altitude illness: Part 1. Commonly-used classes of drugs

BACKGROUND

High altitude illness (HAI) is a term used to describe a group of cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 metres (8202 feet). Acute hypoxia, acute mountain sickness (AMS), high altitude cerebral oedema (HACE) and high altitude pulmonary oedema (HAPE) are reported as potential medical problems associated with high altitude. In this review, the first in a series of three about preventive strategies for HAI, we assess the effectiveness of six of the most recommended classes of pharmacological interventions.

OBJECTIVES

To assess the clinical effectiveness and adverse events of commonly-used pharmacological interventions for preventing acute HAI.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), Embase (OVID), LILACS and trial registries in January 2017. We adapted the MEDLINE strategy for searching the other databases. We used a combination of thesaurus-based and free-text terms to search.

SELECTION CRITERIA

We included randomized-controlled and cross-over trials conducted in any setting where commonly-used classes of drugs were used to prevent acute HAI.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane.

MAIN RESULTS

We included 64 studies (78 references) and 4547 participants in this review, and classified 12 additional studies as ongoing. A further 12 studies await classification, as we were unable to obtain the full texts. Most of the studies were conducted in high altitude mountain areas, while the rest used low pressure (hypobaric) chambers to simulate altitude exposure. Twenty-four trials provided the intervention between three and five days prior to the ascent, and 23 trials, between one and two days beforehand. Most of the included studies reached a final altitude of between 4001 and 5000 metres above sea level. Risks of bias were unclear for several domains, and a considerable number of studies did not report adverse events of the evaluated interventions. We found 26 comparisons, 15 of them comparing commonly-used drugs versus placebo. We report results for the three most important comparisons: Acetazolamide versus placebo (28 parallel studies; 2345 participants)The risk of AMS was reduced with acetazolamide (risk ratio (RR) 0.47, 95% confidence interval (CI) 0.39 to 0.56; I² = 0%; 16 studies; 2301 participants; moderate quality of evidence). No events of HAPE were reported and only one event of HACE (RR 0.32, 95% CI 0.01 to 7.48; 6 parallel studies; 1126 participants; moderate quality of evidence). Few studies reported side effects for this comparison, and they showed an increase in the risk of paraesthesia with the intake of acetazolamide (RR 5.53, 95% CI 2.81 to 10.88, I² = 60%; 5 studies, 789 participants; low quality of evidence). Budenoside versus placebo (2 parallel studies; 132 participants)Data on budenoside showed a reduction in the incidence of AMS compared with placebo (RR 0.37, 95% CI 0.23 to 0.61; I² = 0%; 2 studies, 132 participants; low quality of evidence). Studies included did not report events of HAPE or HACE, and they did not find side effects (low quality of evidence). Dexamethasone versus placebo (7 parallel studies; 205 participants)For dexamethasone, the data did not show benefits at any dosage (RR 0.60, 95% CI 0.36 to 1.00; I2 = 39%; 4 trials, 176 participants; low quality of evidence). Included studies did not report events of HAPE or HACE, and we rated the evidence about adverse events as of very low quality.

AUTHORS' CONCLUSIONS

Our assessment of the most commonly-used pharmacological interventions suggests that acetazolamide is an effective pharmacological agent to prevent acute HAI in dosages of 250 to 750 mg/day. This information is based on evidence of moderate quality. Acetazolamide is associated with an increased risk of paraesthesia, although there are few reports about other adverse events from the available evidence. The clinical benefits and harms of other pharmacological interventions such as ibuprofen, budenoside and dexamethasone are unclear. Large multicentre studies are needed for most of the pharmacological agents evaluated in this review, to evaluate their effectiveness and safety.

The novel combination of theophylline and bambuterol as a potential treatment of hypoxemia in humans

Hypoxemia can be life-threatening, both acutely and chronically. Because hypoxemia causes vascular dysregulation that further restricts oxygen availability to tissue, it can be pharmacologically addressed. We hypothesized that theophylline can be safely combined with the β2-adrenergic vasodilator bambuterol to improve oxygen availability in hypoxemic patients. Ergogenicity and hemodynamic effects of bambuterol and theophylline were measured in rats under hypobaric and normobaric hypoxia (12% O₂). Feasibility in humans was assessed using randomized, double-blind testing of the influence of combined slow-release theophylline (300 mg) and bambuterol (20 mg) on adverse events (AEs), plasma K⁺, pulse, blood pressure, and drug interaction. Both drugs and their combination significantly improved hypoxic endurance in rats. In humans, common AEs were low K⁺ (<3.5 mmol/L; bambuterol: 12, theophylline: 4, combination: 13 episodes) and tremors (10, 0, 14 episodes). No exacerbation or serious AE occurred when drugs were combined. A drop in plasma K⁺ coincided with peak bambuterol plasma concentrations. Bambuterol increased heart rate by approximately 13 bpm. Drug interaction was present but small. We report promise, feasibility, and relative safety of combined theophylline and bambuterol as a treatment of hypoxemia in humans. Cardiac safety and blood K⁺ will be important safety endpoints when testing these drugs in hypoxemic subjects.