Effects of two isometheptene enantiomers in isolated human blood vessels and rat middle meningeal artery - potential antimigraine efficacy

Background

Racemic isometheptene [(RS)-isometheptene] is an antimigraine drug that due to its cardiovascular side-effects was separated into its enantiomers, (R)- and (S)-isometheptene. This study set out to characterize the contribution of each enantiomer to its vasoactive profile. Moreover, rat neurogenic dural vasodilatation was used to explore their antimigraine mechanism of action.

Methods

Human blood vessel segments (middle meningeal artery, proximal and distal coronary arteries, and saphenous vein) were mounted in organ baths and concentration response curves to isometheptene were constructed. Calcitonin gene-related peptide (CGRP)-induced neurogenic dural vasodilation was elicited in the presence of the enantiomers using a rat closed cranial window model.

Results

The isometheptene enantiomers did not induce any significant contraction in human blood vessels, except in the middle meningeal artery, when they were administered at the highest concentration (100 μM). Interestingly in rats, (S)-isometheptene induced more pronounced vasopressor responses than (R)-isometheptene. However, none of these compounds affected the CGRP-induced vasodilator responses.

Conclusion

The isometheptene enantiomers displayed a relatively safe peripheral vascular profile, as they failed to constrict the human coronary artery. These compounds do not appear to modulate neurogenic dural CGRP release, therefore, their antimigraine site of action remains to be determined.

Pharmacological analysis of the increases in heart rate and diastolic blood pressure produced by (S)-isometheptene and (R)-isometheptene in pithed rats

Background

Isometheptene is a sympathomimetic drug effective in acute migraine treatment. It is composed of two enantiomers with diverse pharmacological properties. This study investigated in pithed rats the cardiovascular effects of (S)- isometheptene and (R)-isometheptene, and the pharmacological profile of the more potent enantiomer.

Methods

The effects of i.v. bolus injections (0.03, 0.1, 0.3, 1 and 3 mg/kg) of isometheptene racemate, (S)-isometheptene or (R)-isometheptene on heart rate and blood pressure were analyzed in control experiments. The enantiomer producing more pronounced tachycardic and/or vasopressor responses was further analyzed in rats receiving i.v. injections of prazosin (0.1 mg/kg), rauwolscine (0.3 mg/kg), propranolol (1 mg/kg) or intraperitoneal reserpine (5 mg/kg, -24 h).

Results

Compared to (R)-isometheptene, (S)-isometheptene produced greater vasopressor responses, whilst both compounds equipotently increased heart rate. The tachycardic responses to (S)-isometheptene were abolished after propranolol, but remained unaffected by the other antagonists. In contrast, the vasopressor responses to (S)-isometheptene were practically abolished after prazosin. Interestingly, after reserpine, the tachycardic responses to (S)-isometheptene were abolished, whereas its vasopressor responses were attenuated and subsequently abolished by prazosin.

Conclusions

The different cardiovascular effects of the isometheptene enantiomers are probably due to differences in their mechanism of action, namely: (i) a mixed sympathomimetic action for (S)-isometheptene (a tyramine-like action and a direct stimulation of α₁-adrenoceptors); and (ii) exclusively a tyramine like action for (R)-isometheptene. Thus, (R)-isometheptene may represent a superior therapeutic benefit as an antimigraine agent.

Paracetamol (acetaminophen) for acute treatment of episodic tension-type headache in adults

BACKGROUND

Tension-type headache (TTH) affects about 1 person in 5 worldwide. It is divided into infrequent episodic TTH (fewer than one headache per month), frequent episodic TTH (two to 14 headaches per month), and chronic TTH (15 headache days a month or more). Paracetamol (acetaminophen) is one of a number of analgesics suggested for acute treatment of headaches in frequent episodic TTH.

OBJECTIVES

To assess the efficacy and safety of paracetamol for the acute treatment of frequent episodic TTH in adults.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (CRSO), MEDLINE, EMBASE, and the Oxford Pain Relief Database to October 2015, and also reference lists of relevant published studies and reviews. We sought unpublished studies by asking personal contacts and searching online clinical trial registers and manufacturers' websites.

SELECTION CRITERIA

We included randomised, double-blind, placebo-controlled studies (parallel-group or cross-over) using oral paracetamol for symptomatic relief of an acute episode of TTH. Studies had to be prospective, with participants aged 18 years or over, and include at least 10 participants per treatment arm.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion and extracted data. We used the numbers of participants achieving each outcome to calculate the risk ratio (RR) and number needed to treat for one additional beneficial outcome (NNT) or one additional harmful outcome (NNH) for oral paracetamol compared to placebo or an active intervention for a range of outcomes, predominantly those recommended by the International Headache Society (IHS).We assessed the evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) and created 'Summary of findings' tables.

MAIN RESULTS

We included 23 studies, all of which enrolled adults with frequent episodic TTH. Twelve studies used the IHS diagnostic criteria or similar, six used the older classification of the Ad Hoc Committee, and five did not describe specific diagnostic criteria but generally excluded participants with migraines. Participants had moderate or severe pain at the start of treatment. While 8079 people with TTH participated in these studies, the numbers available for any analysis were lower than this because outcomes were inconsistently reported and because many participants received active comparators.None of the included studies were at low risk of bias across all domains considered, although for most studies and domains this was likely to be due to inadequate reporting rather than poor methods. We judged five studies to be at high risk of bias for incomplete outcome reporting, and seven due to small size.For the IHS preferred outcome of being pain free at two hours the NNT for paracetamol 1000 mg compared with placebo was 22 (95% confidence interval (CI) 15 to 40) in eight studies (5890 participants; high quality evidence), with no significant difference from placebo at one hour. The NNT was 10 (7.9 to 14) for pain-free or mild pain at two hours in five studies (5238 participants; high quality evidence). The use of rescue medication was lower with paracetamol 1000 mg than with placebo, with an NNTp to prevent an event of 7.8 (6.0 to 11) in six studies (1856 participants; moderate quality evidence). On limited data, the efficacy of paracetamol 500 mg to 650 mg was not superior to placebo, and paracetamol 1000 mg was not different from either ketoprofen 25 mg or ibuprofen 400 mg (low quality evidence).Adverse events were not different between paracetamol 1000 mg and placebo (RR 1.1 (0.94 to 1.3); 5605 participants; 11 studies; high quality evidence). Studies reported no serious adverse events.The quality of the evidence using GRADE comparing paracetamol 1000 mg with placebo was moderate to high. Where evidence was downgraded it was because a minority of studies reported the outcome. For comparisons of paracetamol 500 mg to 650 mg with placebo, and of paracetamol 1000 mg with active comparators, we downgraded the evidence to low quality or very low quality because of the small number of studies and events.

AUTHORS' CONCLUSIONS

Paracetamol 1000 mg provided a small benefit in terms of being pain free at two hours for people with frequent episodic TTH who have an acute headache of moderate or severe intensity.

Synergistic effect of the L-tryptophan and kynurenic acid with dipyrone or paracetamol in mice

PURPOSE

Our great interest in this work was study the synergism between l-tryptophan and dipyrone or paracetamol as well as the interaction of kynurenic acid (l-tryptophan metabolite) and these analgesics agents utilizing a robust methodology.

METHODS

We performed the writhing test induced by acetic acid in mice to evaluate the antinociceptive effect of the treatments isolated and combined (p.o. and i.p.). Dose-response curves were constructed and the values of ED50 for treatment alone and combined were statistically compared. In addition, isobolographic analysis was performed and the experimental values were compared with the theoretical values for simple additive effect.

RESULTS

The combined treatment with l-tryptophan and dipyrone or paracetamol reduced significantly the ED50 of these analgesics when compared to the isolated treatments. l-tryptophan alone has no antinociceptive effect. l-Tryptophan increases the central amount of 5-HT and the synergism with dipyrone is antagonized by the 5-HT depletion. The kyna has an antinociceptive dose-related effect and a synergistic interaction with dipyrone and paracetamol verified by isobolographic analyses and confirmed by experimental values of ED50 of combined treatments were statistically lower than theoretical calculated values for simple additive effect. Melatonin antagonist receptor attenuates the antinociceptive synergism between l-tryptophan and dipyrone.

CONCLUSION

Our results demonstrate that the increased 5-HT amount on the central nervous system is not per se capable to induce antinociception. The l-tryptophan interacts synergistically with dipyrone and paracetamol both orally and by i.p. route. This effect is dependent on the biotransformation of l-tryptophan to 5-HT and involves kynurenic acid and melatonin receptors.