Calcium antagonists and the vestibular system: a critical review of flunarizine as an antivertigo drug

Migraine-associated vertigo: diagnosis and treatment

Migraine-associated vertigo has become a well-recognized disease entity diagnosed based on a clinical history of recurrent vertigo attacks unexplained by other central or peripheral otologic abnormalities, which occurs in the patient with a history of migraine headaches. There is no international agreement on what spectrum of symptoms should be covered under this diagnosis, or what terminology should be used. The headaches and vestibular symptoms of migraine-associated vertigo may not be temporally associated, which often obscures the association. Diagnostic tests usually show nonspecific abnormalities that are also seen in patients with migraine who do not experience vestibular symptoms. Management generally follows the recommended treatment of migraine headaches, and includes dietary and lifestyle modifications and medical treatment with beta blockers, calcium channel blockers, and tricyclic amines. Small case series show that acetazolamide and lamotrigine appear to be more effective for the vertigo attacks than headaches. Vestibular rehabilitation has also been shown to be helpful in several studies. In this review, the epidemiologic and clinical features of the disorder, as well as the current state of knowledge on pathophysiology, diagnostic testing, and treatment are described.

Pharmacological treatment of vertigo

This review discusses the physiology and pharmacological treatment of vertigo and related disorders. Classes of medications useful in the treatment of vertigo include anticholinergics, antihistamines, benzodiazepines, calcium channel antagonists and dopamine receptor antagonists. These medications often have multiple actions. They may modify the intensity of symptoms (e.g. vestibular suppressants) or they may affect the underlying disease process (e.g. calcium channel antagonists in the case of vestibular migraine). Most of these agents, particularly those that are sedating, also have a potential to modulate the rate of compensation for vestibular damage. This consideration has become more relevant in recent years, as vestibular rehabilitation physical therapy is now often recommended in an attempt to promote compensation. Accordingly, therapy of vertigo is optimised when the prescriber has detailed knowledge of the pharmacology of medications being administered as well as the precise actions being sought. There are four broad causes of vertigo, for which specific regimens of drug therapy can be tailored. Otological vertigo includes disorders of the inner ear such as Ménière's disease, vestibular neuritis, benign paroxysmal positional vertigo (BPPV) and bilateral vestibular paresis. In both Ménière's disease and vestibular neuritis, vestibular suppressants such as anticholinergics and benzodiazepines are used. In Ménière's disease, salt restriction and diuretics are used in an attempt to prevent flare-ups. In vestibular neuritis, only brief use of vestibular suppressants is now recommended. Drug treatments are not presently recommended for BPPV and bilateral vestibular paresis, but physical therapy treatment can be very useful in both. Central vertigo includes entities such as vertigo associated with migraine and certain strokes. Prophylactic agents (L-channel calcium channel antagonists, tricyclic antidepressants, beta-blockers) are the mainstay of treatment for migraine-associated vertigo. In individuals with stroke or other structural lesions of the brainstem or cerebellum, an eclectic approach incorporating trials of vestibular suppressants and physical therapy is recommended. Psychogenic vertigo occurs in association with disorders such as panic disorder, anxiety disorder and agoraphobia. Benzodiazepines are the most useful agents here. Undetermined and ill-defined causes of vertigo make up a large remainder of diagnoses. An empirical approach to these patients incorporating trials of medications of general utility, such as benzodiazepines, as well as trials of medication withdrawal when appropriate, physical therapy and psychiatric consultation is suggested.

Drug-induced parkinsonism: cinnarizine and flunarizine are potent uncouplers of the vacuolar H+-ATPase in catecholamine storage vesicles

Cinnarizine (1-diphenylmethyl-4-(3-phenyl-2-propenyl)piperazine) and its di-fluorinated derivative flunarizine inhibit the MgATP-dependent generation of a transmembrane proton electrochemical gradient in chromaffin granule ghosts. The concentrations giving 50% inhibition (IC50) of the MgATP-dependent generation of the pH-gradient were 5.9+/-0.6 microM (n = 6) and 3.0+/-0.3 microM (n = 5) for cinnarizine and flunarizine, respectively. The IC50 values for inhibiting the generation of the membrane potential were even lower, i.e. 0.19+/-0.06 microM (n = 6) and 0.15+/-0.01 microM (n = 4) for cinnarizine and flunarizine, respectively. Cinnarizine (10 microM) also inhibited the energy-dependent vesicular uptake of [14C]-dopamine (50 microM) by 76%, i.e. from 2.1+/-0.9 to 0.5+/-0.6 nmol/mg protein/min (n = 5, P < 0.002). Cinnarizine (10 microM) increased the MgATPase activity of the granule ghosts by 47+/-26% (n = 4) compatible with an uncoupling of the vacuolar H+-ATPase activity. The IC50-values observed for the two compounds are in the same range as their reported therapeutic plasma concentrations in vivo, suggesting that cinnarizine and flunarizine may well inhibit proton pumping and catecholamine uptake in storage vesicles also in vivo. This mechanism of action may contribute to the drug-induced parkinsonism seen as a side-effect of the two drugs.

Drug-induced parkinsonism: a review

The main clinical features, pathophysiology and underlying mechanisms of drug-induced parkinsonism are reviewed. The clinical manifestations of drug-induced parkinsonism are often indistinguishable from idiopathic Parkinson's disease. However, some subtle differences may exist: for example drug-induced parkinsonism is often associated with tardive dyskinesias, bilateral symptoms and the absence of resting tremor, etc. Besides toxins (eg manganese, carbon monoxide or MPTP), many drugs are known to produce parkinsonism: dopamine blocking drugs (true neuroleptics used as antipsychotics: phenothiazines, butyrophenones, thioxanthenes but also sulpiride, "hidden" neuroleptics prescribed as anti-nausea or anti-vomiting drugs (such as metoclopramide and other benzamide derivatives), dopamine depleting drugs (reserpine, tetrabenazine), alpha-methyldopa, calcium channel blockers (flunarizine, cinnarizine, etc). The putative role of other drugs (eg fluoxetine, lithium, amiodarone) as well as the therapeutic management of this side effect are reviewed.