generic times: product profiles

MAY 01, 2007
Jim Middleton, BS, RPh

Amlodipine Besylate Tablets

Amlodipine besylate is a calcium channel blocker used for the treatment of hypertension and angina. Under current clinical definitions of hypertension, calcium channel blockers are introduced at stage 2 (systolic pressure of 160 mm Hg or greater or diastolic pressure of 100 mm Hg or greater) generally in combination with a thiazide diuretic. To minimize the risk of orthostatic hypotension, initiation of treatment with 2 antihypertensive agents should be done cautiously among patients with diabetes, the elderly, or patients with autonomic dysfunction.

The release of Mylan Pharmaceuticals' and Greenstone Ltd's amlodipine besylate affords clinicians the opportunity to develop creative genericbased therapies involving calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, and statins—treatments more often associated with brand name combination products. The generic equivalent to Norvasc (Pfizer Inc), amlodipine besylate is available as a single preparation for once-daily administration in 2.5-, 5-, and 10-mg strengths. Mylan Pharmaceuticals is the first and only company to receive FDA approval for its abbreviated new drug application for amlodipine besylate tablets. Simultaneous with Mylan's launch, Greenstone Ltd, Pfizer's generic subsidiary, launched its own authorized generic.

Calcium channel blockers such as amlodipine besylate appear to work well regardless of the ethnicity of the patient, although African Americans respond to calcium channel blockers better than to ACE inhibitors or betablocking drugs. This response to drug categories levels out once a diuretic is added to the therapy.

Recently, amlodipine besylate has been given additional duties in combination preparations. This represents general acceptance of integrated disease states. Although synergy is a concept welcomed in drug therapeutics, it is greeted with less enthusiasm when hypertension and dyslipidemia are involved. These often-coexistent risk factors create damage to the cardiovascular system in excess of expectations for either condition alone.

The unwelcome synergy between hypertension and dyslipidemia can be treated with favorable synergism. Combining amlodipine besylate with atorvastatin creates the branded product known as Caduet. This single-tablet treatment is effective in reducing both blood pressure and lipid levels.

The use of amlodipine besylate in combination products extends to enhanced activity against hypertension. For this hybrid, the ACE inhibitor benazepril is employed.

Rabeprazole Tablets

Proton pump inhibitors (PPIs) and H2-receptor antihistamines are mainstays of treating disorders of the gastrointestinal (GI) tract. Many H2-receptor antihistamines are available generically at a substantial savings to patients, and now varieties of PPIs are following suit.

Rabeprazole is the latest generic PPI to reach the market. Rabeprazole, the generic equivalent of Aciphex (Eisai Co Ltd), is available from Teva Pharmaceuticals as 20-mg tablets.

Most cases of peptic ulcers may occur in the presence of normal acid secretion when nonsteroidal anti-inflammatory drugs or Helicobacter pylori are also present, challenging factors that diminish or disrupt the mucosal defenses present in the GI tract.

In general, PPIs inhibit gastric acid secretion through binding at adenosinetriphosphatase levels, the final common pathway for gastric acid secretion. All examples undergo extensive hepatic metabolism, and all are important factors in eradicating H pylori and treating peptic ulcer disease, gastroesophageal reflux disease, Zollinger-Ellison syndrome, and upper GI bleeding.

Ulcers recur in 50% to 90% of patients within a year when single-agent therapy is employed; this recurrence can be reduced to as low as 10% after a year when amoxicillin or clarithromycin is added to aid in the eradication of H pylori.

The choice of a specific PPI is generally based on cost, formulation, and overall safety profile. Since PPIs require actively secreting proton pumps to be fully effective, dosing should occur 30 minutes before a meal, generally breakfast. If a second dose is required, it should be taken ~10 to 12 hours after this morning dose. Rabeprazole appears unique in its likelihood to have fewer drug interactions with caffeine, diazepam, phenytoin, and warfarin than other PPIs. This is thought to be due to its partially reversible binding to the proton pump process.

Mr. Middleton is an instructor of pharmacology at Kellogg Community College in Battle Creek, Mich.