Signs and symptoms
FHM signs overlap significantly with those of migraine with aura. In short, FHM is typified by migraine with aura associated with hemiparesis, and in FHM1, cerebellar degeneration, which can result in episodic or progressive ataxia. FHM can also present with the same signs as benign familial infantile convulsions and alternating hemiplegia of childhood. Other symptoms are altered consciousness (in fact, some cases seem related to head trauma), gaze-evoked nystagmus, and coma. Aura symptoms, such as numbness and blurring of vision, typically persist for 30–60 minutes, but can last for weeks to months. An attack resembles a stroke, but unlike a stroke, it resolves in time. These signs typically first manifest themselves in the first or second decade of life. Causes
See the equivalent section in the main migraine article. FHM mutations are believed to lead to migraine susceptibility by lowering the threshold for cortical-spreading-depression generation. The FHM1 and FHM3 mutations occur in ion channels expressed in neurons. These mutations may lead to both the hyper- and hypoexcitable neurons that might underlie cortical-spreading-depression. How the mutations seen in FHM2 patients might lead to FHM symptoms is even less clear, as the gene mutated in FHM2 is expressed primarily in astrocytes. One proposal states that the depolarization of astrocytes caused by haploinsufficiency of the ATP1A2 Na+/K+-ATPase causes increased release of compounds such as adenosine from astrocytes. These compounds then interact with neighboring neurons, altering their excitability and leading to cortical-spreading-depression and migraine.
Ibutilide is a Class III antiarrhythmic agent that is indicated for acute cardioconversion of atrial fibrillation and atrial flutter of a recent onset to sinus rhythm. It exerts its antiarrhythmic effect by induction of slow inward sodium current, which prolongs action potential and refractory period (physiology) of myocardial cells. Because of its Class III antiarrhythmic activity, there should not be concomitant administration of Class Ia and Class III agents. Ibutilide is marketed as Corvert by Pfizer. Administration resulted in successful heart rhythm control in 31-44% of patients within 90 minutes, with sustained polymorphic ventricular tachycardia in 0.9-2.5% of patients. It appears to show better results in atrial flutter as compared to atrial fibrillation. Mechanism of action
Ibutilide, like other class III antiarrhythmic drugs, blocks delayed rectified potassium current.It does have action on the slow sodium channel and promotes the influx of sodium through these slow channels. Although potassium current seems to play a role, their interactions are complex and not well understood. Ibutilides unique mechanism works by an activation of a specific inward sodium current, thus producing its therapeutic response in which a prolonged action potential increases myocytes’ cardiac refractoriness in case of atrial fibrillation and flutter. Pharmacokinetics
Absorption
Ibutilide is intravenously administered. It has a high first-pass metabolism, which results in a poor bioavailability when taken orally. Individual pharmacokinetic properties are highly viable during the clinical trial. Distribution
Ibutilide has a relatively large volume of distribution among individual subjects, which is about 11L/kg.