PROPHYLAXIS OF MIGRAINE
Regular medication to reduce the frequency
and/or severity of attacks is recommended for
moderate-to-severe migraine when 2–3 or more
attacks occur per month. Diverse classes of drugs
are used but none is effective in all cases, and
none abolishes the attacks totally. It may be prudent
to discontinue pophylaxis every 6 months to check
whether its continuation is needed or not. It is
important to avoid the precipitating factor(s).
(i) β-Adrenergic blockers: Propranolol is the
most commonly used drug: reduces frequency as
well as severity of attacks in upto 70% patients.
Effect is generally seen in 4 weeks and is sustained
during prolonged therapy. The starting dose is
40 mg BD, which may be increased upto 160 mg BD if required. The mechanism of action
is not clear; that it is due to β adrenergic blockade
has been questioned. Other nonselective (timolol)
and β1 selective (metoprolol, atenolol) agents are
also effective, but pindolol and others having
intrinsic sympathomimetic action are not useful.
(ii) Tricyclic antidepressants: Many tricyclic
compounds of which amitriptyline (25–50 mg at
bed time) has been most extensively tried, reduce
migraine attacks. It is effective in many patients
but produces more side effects than propranolol.
It is not known whether its 5-HT (and other
monoamine) uptake blocking property is causally
related to the prophylactic effect. The antimigraine
effect is independent of antidepressant property,
but this class of drugs are better suited for patients
who also suffer from depression.
(iii) Calcium channel blockers: Verapamil was
found to reduce migraine attacks, but was judged
inferior to propranolol. Flunarizine is a relatively
weak Ca2+ channel blocker that also inhibits Na+
channels. It is claimed to be as effective as
propranolol, but convincing proof is lacking.
Frequency of attacks is often reduced, but effect on intensity and duration of attacks is less well
documented. It is claimed to be a cerebro-selective
Ca2+ channel blocker; may benefit migraine by
reducing intracellular Ca2+ overload due to brain
hypoxia and other causes. Side effects are sedation,
constipation, dry mouth, hypotension, flushing,
weight gain and rarely extrapyramidal symptoms.
(iv)Anticonvulsants: Valproic acid (400–1200
mg/day) and gabapentin (300–1200 mg/day) have
some prophylactic effect in migraine. The newer
drug topiramate has recently been approved for
migrain prophylaxis. A 50% reduction in the
number of attacks in half of the patients was noted
in 2 randomized trials. Start with topiramate 25
mg OD and gradually increase to 50 mg OD or
BD. Efficacy of anticonvulsants in migraine is
lower than that of β blockers. They are indicated
in patients refractory to other drugs or when
propranolol is contraindicated.
(v) 5-HT antagonists: The prophylactic effect of
methysergide and cyproheptadine is less impressive than β
blockers. They are seldom used now for migraine.
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