Pharmacology

Pharmacodynamics. 5-HT receptors are all G-protein coupled receptors except for 5-HT3, which is a ligand-gated ion channel. The receptors that have been found to be involved in migraine are 5-HT1B, 5-HT1D, and 5-HT1F receptors. 5-HT1B receptors are found in meningeal arteries. The 5-HT1D receptors are located primarily in the trigeminal nerve in the central nervous system; they are also found in vascular smooth muscles. The amino acids contributing to the binding of ligands to the receptor are aspartic acid, phenylalanine, serine, threonine, tryptophan, and tyrosine.

Effect on migraine. Triptans are specific and selective agonists for the 5-HT1 receptors. The rate of brain serotonin (5-HT) synthesis increases during migraine attacks, and triptans exert a negative feedback regulation of brain serotonin synthesis along with modulation of pain pathways. Sumatriptan binds to 5-HT1D receptors; zolmitriptan, rizatriptan, naratriptan, almotriptan, and frovatriptan binds to 5-HT1B/1D; and eletriptan binds to 5-HT1B/1D/1F receptors. Triptans have no significant activity at 5-HT2 or 5-HT3 receptors or at dopamine, gamma-aminobutyric acid, or adrenoreceptors. The beneficial effect of triptans in patients with migraine is related to their multiple mechanisms of action at sites implicated in the pathophysiology of migraine. Although the exact mechanism of action of triptans on migraine is not fully understood, the explanations offered include:

	• Vasoconstriction of painfully dilated cerebral vessels without affecting cerebral circulation.
	• Inhibition of nociceptive neurotransmission.
	• Inhibition of the release of vasoactive peptides by trigeminal nerves.
	• Sumatriptan has direct scavenging activity on free radicals and nitric oxide, but it inhibits the nitric oxide response by inhibiting trigeminal activation and CGRP release.
	• Neither peripheral nor central trigeminovascular neurons are directly inhibited by triptans, but the action appears to be exerted through presynaptic 5HT1 receptors in the dorsal horn to block synaptic transmission between axon terminals of the peripheral trigeminovascular neurons and cell bodies of their central counterparts.

Effect on nonmigrainous pain. 5-HT receptors are not localized to afferents in the head but are found throughout the body, suggesting that the triptans should be able to relieve nonmigrainous pain. Although triptans have been shown to be effective in various noncranial, nonmigrainous pain states if given early after onset, the effect is much less pronounced than that on migraine. The ability of the triptans to regulate inflammatory pain is affected by the expression and localization of the 5-HT receptor, which is upregulated in persistent injury and pain. Thus, these results suggest that triptans can provide treatment of prolonged or chronic pain. Advantages of using triptans as analgesics are:

	• Triptans are nonaddictive and less susceptible to substance abuse, unlike other analgesics such as morphine.
	• Triptans may potentiate the analgesic effects when used in combination with other analgesics.
	• Such combination therapy may allow lower doses of drugs to be effective, reduce tolerance in long-term efficacy, and increase the therapeutic index.

Pharmacokinetics. The pharmacokinetics of oral triptans is shown in Table 1.

Table 1. Pharmacokinetics of Oral Triptans

Triptan	Bio-availability	Renal clearance (mL/min-1)	Protein binding	tmax (h)	Excretion
Sumatriptan	14%	260	10%-21%	2-2.5	Urine (57%) Feces (38%)
Zolmitriptan	40%	193	25%	2	Urine (65%) Feces (30%)
Naratriptan	63%-74%	220	28%-31%	2-3	Urine
Rizatriptan	47%	414	14%	1.3	Urine
Almotriptan	69%	----	35%	1.4-3.8	Urine (40%) Feces (13%)
Eletriptan	50%	597	85%	1-2	Urine (40%)
Frovatriptan	24%-30%	132-216	20%-30%	2-4%	----

After absorption, triptans are extensively metabolized to an inactive indoleacetic acid analog that is excreted mainly in the urine. Pharmacokinetics varies according to the method of delivery. A linear relationship is observed between total applied current and sumatriptan delivery to reach therapeutic blood levels following transdermal delivery by an iontophoresis patch, which uses an electrical current to propel sumatriptan across intact skin into underlying tissue.

Relatively short tmax and good bioavailability are associated with rapid onset of action. Ability to cross the blood-brain barrier and relatively long terminal elimination half-life may result in a lower incidence of headache recurrence. Sumatriptan and rizatriptan undergo first-pass hepatic metabolism and result in lower bioavailability.

Formulations and methods of delivery of triptans. The delivery system of triptans plays an important role in the onset of action. Subcutaneous injection is the fastest way to control rapidly progressing migraine attacks. The sumatriptan nasal spray provides faster onset of action than the tablets, but it is not suitable for all patients because of bad taste and lack of consistency of response.

The drawbacks of triptans for the treatment of migraine are: (1) low oral bioavailability and (2) low concentration of active metabolites. Improved formulations and methods of delivery would be beneficial. Currently available routes of administration of triptans include subcutaneous (sumatriptan), nasal spray (sumatriptan and zolmitriptan), rectal (sumatriptan), rapidly dissolving wafer (rizatriptan and zolmitriptan), and oral tablets (all).

Pharmacogenetics and pharmacogenomics. Pharmacogenomics may help in rationalizing triptan administration according to characterization of an individual’s genomic profile. An observational study shows that serotonin transporter gene polymorphism STin2 VNTR confers an increased risk of inconsistent response to triptans in migraine patients (18). Although some genetic factors influence drug response, prediction of therapy response with adequate predictive power requires a systematic approach to genetic association studies due to complexity of the field (06). Risk of inconsistent response to triptans has been identified for a genetic risk score model based on two known risk alleles for migraine without aura, suggesting its potential usefulness in predicting headache response to triptan therapy (03).

Clinical trials

Clinical trials on triptans can be located by searching the U.S. National Institute of Health’s ClinicalTrials.gov web site. A search for all trials on triptans for migraine shows 179 studies as of October 2021: https://clinicaltrials.gov. The number retrieved used the term for class of drugs is higher than that that for individual triptans; for example, the search for sumatriptan reveals 101 studies: https://clinicaltrials.gov/. Selected triptans in clinical trials are shown in Table 2. Most of these are already approved, and the studies are in phase IV for additional indications of variants of migraine or special methods of delivery.

Table 2. Marketed Triptans with Additional Clinical Trials and Outcome

Drug	Indication/method of delivery	Phase/status
Almotriptan	Safety of oral almotriptan for the treatment of migraine in adolescents	Phase IV
Eletriptan	Efficacy of early intervention on mild versus moderate to severe pain intensity of migraine	Marketed
Eletriptan	Follow-up of patients treated for menstrual migraine	Phase IV
Frovatriptan	Long-acting triptan for prophylaxis of menstrually associated migraine	Phase III completed
Frovatriptan	Prevention of fasting-induced migraine	Completed
Naratriptan	Psychotic personality disorder	Phase IV
Rizatriptan	Early treatment of acute migraine	Phase III completed
Rizatriptan	Acute migraine in patients with unilateral autonomic symptoms	Phase IV
Rizatriptan	Distinction between pharmacological effects, placebo effects, and their interactions in relief of symptoms of acute migraine	Phase IV
Rizatriptan + acetaminophen	Efficacy of combination for treatment of acute migraine	Phase IV
Sumatriptan	5HT1 agonist, needle-free injection	Phase II completed
Sumatriptan	Iontophoretic transdermal delivery	Phase III completed
Sumatriptan	Sumatriptan Succinate Injection Kit for the treatment of migraine or cluster headache attack	Phase III completed
Sumatriptan	Sumatriptan iontophoretic transdermal patch (NP-101) for the treatment of migraine	Phase III completed
Sumatriptan + naproxen	Migraine with or without aura, cluster headache	Completed
Sumatriptan + naproxen	Migraine not responding to eletriptan	Completed
Zolmitriptan	Nasal spray for treatment of acute migraine	Approved

In comparative clinical trials, oral triptans outperform oral ergotamine mostly because of the extremely low oral bioavailability of ergotamine; compared with nonsteroidal antiinflammatory drugs (NSAIDs), triptans are not, in most cases, superior to aspirin. In a systematic review of controlled clinical trials of comparative efficacy of drugs for migraine, standard dose triptans were associated with better outcomes than ergots, and most triptans were associated with equal or better outcomes than NSAIDs, aspirin, or acetaminophen (02). Use of triptans in combination with aspirin or acetaminophen, or using alternative methods of administration such as injections, may result in slightly better relief of pain than standard dose triptan tablets.

Results of the TEMPO clinical trial, a multicenter, phase 2 study conducted in neurologic practice, showed that early triptan intake after headache onset may help improve the efficacy of acute migraine treatments (08).

Expert opinion on some phase 2 clinical trials of triptans shows that data from 5-HT1B/1D receptor agonist (sumatriptan TDS), 5-HT1D receptor agonist (PNU-142633), 5-HT1F receptor agonists (LY334370, lasmiditan), and a combined 5-HT1B/1D receptor agonist with nNOS inhibition (NOX-188) provided encouraging results for sumatriptan TDS (transdermal system) and lasmiditan, disappointing results for PNU-142633, and promising findings for NOX-188 (01). The 5-HT1F receptor agonist lasmiditan, which acts through nonvasoconstrictive mechanisms, is a safe and effective therapy for acute migraine therapy, even for those with cardiovascular risk factors. A phase 3 trial of lasmiditan has been completed and results indicate that lasmiditan is an effective treatment option for patients refractory to current acute migraine medications or who have cardiovascular risk factors (13).

Indications

Triptans are indicated for the treatment of migraine headaches.

Off-label uses

Triptans are under investigation for migraine variants, and special methods of administration are also being studied. Triptans seem to be safe and effective treatment for most hemiplegic migraine patients. Investigational uses include those for non-migraine headaches and other conditions:

	• High-altitude headache.
	• Post-dural puncture headache.
	• Post-electroconvulsive therapy headache.
	• Headache in professional sports.
	• Headache of subarachnoid hemorrhage.
	• Trigeminal neuralgia.
	• Prevention of acute mountain sickness.
	• Acute posttraumatic headache.
	• Acute cluster headaches. A systemic review of controlled clinical trials showed that zolmitriptan and sumatriptan are effective in the acute treatment of cluster headaches.
	• Prevention of airplane headache. Triptans administered half an hour before flight can prevent airplane headaches in subjects with a history of such headaches during flights.

Contraindications

Contraindications for triptan therapy are:

	• Patients with coronary artery disease or hypertension.
	• Patients with hemiplegic or basilar artery migraine.
	• Patients receiving ergot compounds. Triptans should not be given intravenously within 24 hours of administration of an ergot compound.
	• Patients who have demonstrated hypersensitivity to any triptan.
	• Severe hepatic or renal failure.

Goals and duration of treatment

Apart from selection of a triptan, a suitable dosage should also be considered for an acute attack. Like some other anti-migraine drugs, the dose-response curve for efficacy of most triptans is flat, and increasing the dose often increases adverse effects, but triptans still have the most favorable efficacy-tolerability profile (07). Clinical studies show that most patients who fail to obtain adequate alleviation of symptoms with one triptan may be successfully treated with a different triptan. The seven available triptans show more similarities than differences in action. Almotriptan 12.5 mg is as effective as sumatriptan 100 mg and zolmitriptan 2.5 mg. A comparative study showed that the extent of initial pain relief obtained with frovatriptan is like that with rizatriptan in treatment of migraine, but duration of action is longer because of its longer terminal half-life (17). None of the available triptans produce an effective response in every migraine attack, and prolonged use of triptans may produce an increase in the migraine frequency and headache. In a study of the option of using an oral triptan other than sumatriptan and subsequently using an injectable sumatriptan to treat a given attack of migraine gave a high rate of patient satisfaction (15). Due to the availability of multiple formulations of triptans, including oral, intranasal, and injectable forms, subcutaneous injection with a favorable pharmacokinetic profile can be used in acute migraine as an alternative to oral therapy (05). Some patients may be resistant to triptans, and alternative drugs may be considered for relief of migraine headache.

Individualization of use of triptans for migraine. With several triptans now available, it may be possible to match individual patient needs with the specific characteristics of the individual triptans to optimize therapeutic benefit. Pharmacogenetics provides the possibility of tailoring the therapeutic approach to individual patients to maximize treatment efficacy while minimizing the potential for unwanted side effects. Genetic profiling of predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. The development of the International Hap Map project could provide a powerful tool for identification of the candidate genes in this complex disease, and pharmacogenomics research could be the promise for individualized treatments and prevention of adverse drug response. Pharmacogenomics will likely provide a strong scientific basis for optimizing triptan therapy according to a patient's genetic constitution.

Dosing

Doses, formulations, and duration of action of triptans are shown in Table 3.

Table 3. Doses, Formulations, and Duration of Action of Triptans

Drug	Formulations	Doses (mg)	Maximum daily dose (mg)	Onset of action (min)	Duration of action
Sumatriptan	Tablets Nasal spray Subcutaneous injection Suppositories	25, 50, 100 5, 20 6 25	300 40 12 50	30-60 15-30 10-15 30-60	Short
Zolmitriptan	Tablets Orally disintegrating tablets Nasal spray	2.5, 5 2.5, 5 2.5, 5	10 10 10	45 - 10-15	Short
Naratriptan	Tablets	1, 2.5	5	60-180	Long
Rizatriptan	Tablets Orally disintegrating tablets	5, 10 5, 10	30 30	30-120 -	Short
Almotriptan	Tablets	25, 12.5	25	60-180	Short
Eletriptan	Tablets	20, 40	80	<60	-
Frovatriptan	Tablets	2.5	7.5	60-120	Long

Special considerations

Extreme caution should be exercised with use of triptans in cerebral ischemic disorders, such as that due to vasospasm following ruptured intracranial aneurysms.

Pediatric. Safety in children has not been established. Although the use of triptans in children and adolescents is mostly “off-label,” there are more positive efficacy data for sumatriptan and zolmitriptan nasal sprays as well as rizatriptan and almotriptan tablets than for the other triptans.

Geriatric. No information is available about the safety of use of triptans in patients over the age of 65 years because they were excluded from clinical trials.

Pregnancy. Triptans fall into category C of the United States Food and Drug Administration regarding safety of use during pregnancy. Animal reproduction studies have shown an adverse effect on the fetus, and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks. All triptans, except for sumatriptan, are contraindicated in pregnancy and breastfeeding.

Sumatriptan is secreted in human milk, and caution should be exercised when administering it to nursing mothers.

Anesthesia. No special precautions are required for patients on triptans.

Interactions

Triptans are compatible with most of the commonly used drugs, including those used for the treatment of headaches. Concomitant use of triptans and SSRIs or selective serotonin/norepinephrine reuptake inhibitors can lead to serotonin syndrome. An alert by the United States Food and Drug Administration in 2016 warned of the risk of serotonin syndrome from using opioids concomitantly with 5-hydroxytryptamine receptor agonists (triptans) or serotonergic antidepressants: selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). During a period of approximately 2 years prior to the FDA warning use of these combinations was common in the United States. Of 7,672,193 visits for patients diagnosed with migraine, 16.3% included opioid prescribing, and 2.0% included co-prescribed opioid-triptan (12). Studies on the risk of serotonin syndrome associated with these co-prescriptions are needed. Interactions may also occur with the following categories of drugs:

• Ergot-containing compounds may lead to additional vasoconstrictor effect (14). • Monoamine oxidase inhibitors • Calcium channel-blocking antagonists • Beta blockers

Adverse effects

Triptans are generally well tolerated with minor adverse effects. Those reported include the following:

	• Chest pain due to myocardial ischemia because coronary arteries also express 5-HT1B receptors whose activation by triptans would produce coronary vasoconstriction. • Reversible cerebral arterial vasospasm and cerebral infarction
	• Triptan-overuse headache is a type of rebound headache, which can occur with the use of triptans for more than 10 days per month.

Management. The management of adverse effects is according to the event. The important factors are the prevention of adverse effects and their differentiation from complications of migraine.

Lack of efficacy of triptan therapy for migraine. Triptans are the first-line therapy for migraine. However, in approximately 30% to 40% of migraine patients, use of triptans for acute treatment is associated with lack of efficacy or tolerability. The most common applied measures of efficacy were headache pain freedom and pain relief at 2 hours. Some studies assessed efficacy of switching or optimizing treatment in patients with historical insufficient efficacy or tolerability by reverting to previous triptan treatment and demonstrated varying levels of success. Factors associated with increased risk or lack of efficacy of triptan included severe baseline headache severity, photophobia, phonophobia, nausea, and depression (09).

Lack of compliance. In a 25-year review of triptan use in Denmark, a country with free medical care and low medication costs, compliance rates of triptan were low, likely due to disappointing efficacy or unpleasant side effects rather than economic considerations (04). There was poor implementation of clinical guidelines and high rates of treatment discontinuance.

Current development in triptans is focused on new methods of administration and formulations, triptan combination therapies, treatment in menstrually related migraines, and novel serotonin receptor subtype agonists (10).

Triptanophobia. This term is used for excessive and unjustified concern about potential risks of triptans. A case control study was conducted to evaluate causes and consequences of the nonuse of triptans in chronic migraine sufferers by comparing triptan users with triptan naive patients for the presence of contraindications, frequency of vascular risk factors, and differences in management prior to the referral to a headache clinic (11). The study concluded that triptans were not used by three quarters of chronic migraine patients, which was not justified by tolerability, contraindications, or risk factors.

Future of triptan therapy for migraine. Future trends include development of triptans with the following desirable properties for treatment of acute migraine:

	• It should be more efficacious than currently available drugs.
	• It should be tolerated better.
	• The recurrence rate should be low.
	• It should have a prophylactic role as well.
	• It should provide improved patient choice.

Comparison of triptans with new antimigraine drugs. New therapeutic classes of migraine-specific treatment have been developed, including 5-hydroxytryptamine1F receptor agonists (lasmiditan) and calcitonin gene-related peptide antagonists (rimegepant and ubrogepant). A comparison of randomized clinical trials showed that (19):

	• Most of the included treatments were associated with reduced pain at 2 hours compared with placebo.
	• Most triptans were associated with higher odds ratios for pain freedom at 2 hours.
	• The comparisons between lasmiditan, rimegepant, and ubrogepant were not statistically significant for either pain freedom or pain relief at 2 hours.
	• Lasmiditan was associated with the highest risk of any adverse events.
	• Certain triptans (rizatriptan, sumatriptan, and zolmitriptan) were associated with a higher risk of adverse events than the calcitonin gene-related peptide antagonists.
	• The review concluded that lack of cardiovascular risks for these new classes of migraine-specific treatments may offer an alternative to triptans.

Because migraineurs have an increased cardiovascular risk, antimigraine drugs devoid of vascular side effects are being developed. Like most of the triptans, ditans, selective 5-HT1F receptor agonists, activate trigeminal 5-HT1F receptors, which are part of the triptans' antimigraine action. One of the ditans, lasmiditan, does not constrict human coronary arteries and was effective for the acute treatment of migraine in phase 3 clinical trials (16). Although its exact site of action is still unknown, lasmiditan has a high lipophilicity, indicating a direct action on the central descending antinociceptive pathways.