The U.S. Food and Drug Administration approved in March revisions to safety labeling to advise that use of thioridazine, terfenadine, astemizole, cisapride, pimozide, alosetron, or tizanidine is contraindicated in patients receiving fluvoxamine maleate therapy; use of alfuzosin HCl is contraindicated and use of fluticasone propionate is not recommended in patients receiving ritonavir therapy; and use of somatropin [rDNA origin] injection may be linked to fatalities in children with Prader-Willi syndrome and one or more risk factors.
Tizanidine and Alosetron Contraindicated in Patients Receiving Fluvoxamine Maleate Therapy
The FDA approved in March revisions to the safety labeling for fluvoxamine maleate tablets (made by several manufacturers, formerly marketed as Luvox by Solvay Pharmaceuticals) to advise of contraindications and warnings associated with their use.
Administration of fluvoxamine maleate is contraindicated in patients with a history of hypersensitivity to the active ingredient. In patients receiving fluvoxamine therapy, coadministration of thioridazine, terfenadine, astemizole, cisapride, pimozide, alosetron, or tizanidine is contraindicated.
The FDA notes that fluvoxamine is a potent inhibitor of several cytochrome P (CYP) isoenzymes, including CYP 1A2, whereas tizanidine is a CYP 1A2 substrate. In a drug interaction study of 10 healthy subjects receiving 100 mg of fluvoxamine daily for four days, administration of a single 4-mg dose of tizanidine resulted in significantly increased tizanidine maximal (approximately 12-fold; range, 5- to 32-fold) and mean (33-fold; range, 14- to 103-fold) plasma concentrations, and an almost threefold prolongation of its elimination half-life.
Mean maximal effects of the drug interaction on blood pressure included a 35-mm Hg decrease in systolic blood pressure, a 20-mm Hg decrease in diastolic blood pressure, and a 4 beat per minute decrease in heart rate. Drowsiness was significantly increased and performance on a psychomotor task was significantly impaired.
In another study, fluvoxamine was shown to increase mean plasma concentrations of alosetron by approximately sixfold and prolong its half-life by approximately threefold.
Fluvoxamine maleate tablets are indicated for the treatment of obsessive-compulsive disorder.
Alfuzosin HCl Contraindicated and Fluticasone Propionate Not Recommended in Patients Receiving Ritonavir (Norvir) Therapy
On March 28, the FDA approved revisions to the safety labeling for ritonavir soft gelatin capsules and oral solution (Norvir, made by Abbott Laboratories) to advise of contraindications and warnings associated with their use.
As an alpha1-adrenoreceptor antagonist, alfuzosin HCl is contraindicated for use in patients receiving ritonavir therapy.
In addition, the FDA warns against the use of fluticasone propionate in patients receiving ritonavir therapy, unless the potential benefit to the patient outweighs the risk of systemic corticosteroid effects.
The results of a drug interaction study have shown that fluticasone propionate plasma concentrations are significantly increased by ritonavir, resulting in significantly decreased serum cortisol concentrations. Postmarketing reports of systemic corticosteroid effects in patients receiving ritonavir and inhaled or intranasally administered fluticasone propionate have included Cushing’s syndrome and adrenal suppression.
Ritonavir is indicated for use in combination with other antiretroviral agents for the treatment of HIV infection.
Somatropin (Tev-Tropin) Linked to Fatalities in Children With Prader-Willi Syndrome and Risk Factors
On March 16, the FDA approved revisions to the safety labeling for somatropin [rDNA origin] for injection (Tev-Tropin, made by Savient Pharmaceuticals, Inc.) to advise of contraindications and warnings associated with its use.
Somatropin may only be used in the long-term treatment of pediatric patients with genetically confirmed Prader-Willi syndrome when the diagnosis includes growth hormone deficiency. Within this population, use of the growth hormone is contraindicated in children who are severely obese or have severe respiratory impairment.
The FDA has received reports of fatalities following the initiation of somatropin therapy in pediatric patients with Prader-Willi syndrome and one or more risk factors such as severe obesity, history of upper airway obstruction or sleep apnea, and unidentified respiratory tract infection. The FDA notes that males may confer added risk to those with one or more of these risk factors.
According to the FDA, patients with Prader-Willi syndrome should be evaluated for signs of upper airway obstruction and sleep apnea prior to initiation of somatropin therapy. During treatment, patients should be treated effectively for weight control and monitored for signs of respiratory tract infections with an emphasis on their early diagnosis and aggressive treatment.
Treatment should be interrupted in patients showing signs of upper airway obstruction (including onset of increased snoring) and/or sleep apnea.
Somatropin [rDNA origin] injection is indicated only for the long-term treatment of children who have growth failure due to inadequate secretion of normal endogenous growth hormone.