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Felodipine Extended-Release Tablets

Generic and Brand-Name Tablets are Not Equivalent:
Different Coatings Cause Wide Variance in Release Profile

Calcium-Channel Blockers

Felodipine is a calcium-channel blocker. This class of prescription lowers blood pressure by dilating peripheral blood vessels around the heart.

Because of its mode of action, a calcium-channel blocker can also treat the form of dizziness called presyncope.

In Vitro Release of Felodipine from Original Brand and Generic Products

German researcher K. U. Petersen tested the in-vitro release profile of eight different felodipine products. These included seven generic products (labeled A through G) plus the original brand-name available in Germany called Modip. In each case the tablet size was 5mg. By means of UV spectroscopy, samples were assayed to find the concentration of the active ingredient felodipine. The tests were duplicated on six separate tablets within each product group.

Active Ingredient, Total Content: All products examined released at least the total content of the active ingredient declared by the manufacturer (namely 5mg of felodipine).

Release Kinetics: The 6 tablets of brand-name Modip differed from each other only slightly in their release kinetics. However, the generic products showed considerable variability among the 6 tablets tested within each group – with the exception of Generic D (uniform rapid release) and Generic C.

Time Profiles: The brand-name Modip offered the linear controlled-release profile expected from an extended-release product. Among the generics, three different time profiles were distinguished:

  1. Generics A, B, F, and D practically showed immediate release of the active ingredient.
  2. Generics E and G showed some extent of controlled release (however, more than 50% of the total content was released within the first hour).
  3. Generic C displayed controlled-release properties but a more rapid release than the brand-name at all sampling times.

Comparison In Vitro Felodipine Release Rate from the Original versus Generic Product with Controlled Release Coating

After patent protection of an original brand expires, generic copies arrive on the pharmaceutical market. But price reduction, though welcome, is not the only concern. Generic products are developed based on the pharmacological properties of the original brand, and are expected to show the same quality, and almost identical activity, as the original.

This study compared two felodipine controlled-release products commercially available in the Czech Republic – the generic product Presid and the original brand Plendil.  In order to simulate the physiological pH within the gastrointestinal tract, the solubilization tests dissolved felodipine tablets in three media of increasing pH (1.2, 4.5, and 6.5).

Brand-Name Result: The study confirmed a controlled release of felodipine over a period of 24 hours with regard to the original brand-name products Plendil ER 5mg and Plendil ER 10mg.  [ER means extended release]

Generic Result: Release of felodipine from the generic products Presid 5mg and Presid 10mg was finished long before 24 hours was up. The generic tablets released felodipine for a duration between 12 and 18 hours. There was no release at all after 18 hours, which contradicts the 24-hour release period claimed in the manufacturer's information leaflet. In this respect the generic version is not similar to the original brand.

The authors conclude: Since patients take felodipine just once a day in the morning, the generic version – which lasts only 12 to 18 hours – can cause insufficient blood pressure control especially in the critical early morning hours. There is no doubt, it is not rational to use only the 12- or 18-hour acting form of felodipine. A 24-hour blood pressure control is necessary to prevent serious events such as stroke or myocardial infarction.

A Study of the Efficacy of Felodipine Given Once or Twice Daily in the Management of Elderly Hypertensive Patients

These authors focused exclusively on the original brand of felodipine extended-release tablets (no comparison was done with generic felodipine). And still the manufacturer's claim of 24-hour duration could not be substantiated. The effectiveness of brand-name felodipine falls to 75% at the end of each 24-hour period. Conclusion: A twice-daily dose schedule should be an option. The logical foundation of this research study:

In clinical practice, medication given once daily to lower blood pressure (BP) may not adequately control the patient's blood pressure over a full 24 hours because the dose is frequently titrated at the time of peak effect. This over-simplifies human physiology: When treating high blood pressure, the physician selects a medication and measures the patient's BP to judge the dose level. The dose begins small and is raised step-wise (titrated upward) until the patient's BP returns to normal. But those BP measurements are often taken only at the optimum time, when the patient's serum level of the medication is at maximum.

The authors conducted a randomized, double-blind crossover study for treatment of high blood pressure with felodipine at different dose levels and daily schedules. Twenty-three patients aged 65 to 84 participated in the study and received at various stages the doses listed below:

Dose Schedule Studied
a placebo
felodipine 2.5 mg once daily (every 24 hours)
felodipine 2.5 mg twice daily (every 12 hours)
felodipine 5.0 mg once daily (every 24 hours)

The authors measured blood pressure at both the peak time and the trough time. Patients were also outfitted with a 24-hour ambulatory monitor. Method of analysis:

  • A patient took a single tablet of extended-release felodipine, then:
  • The patient's BP was measured between the 3rd and 4th hour post-dose – which is the peak time when the serum level of felodipine was at maximum.
  • The patient's BP was measured between the 23rd and 24th hour post-dose – which is the trough period when the serum level of felodipine fell to its lowest point. It was the point just before the next felodipine dose was due.
  • The trough/peak ratio was calculated as the improvement (fall) in BP during the 23rd and 24th hour post-dose, divided by the improvement in BP during the 3rd and 4th hour post-dose.
Experimental Results
  • The greatest duration of effect occurred when the felodipine dose schedule was 2.5mg twice daily.
  • Felodipine 5mg once daily was also acceptable, but generally maintained only 75% of its effect prior to the next dose.
  • In some patients, felodipine 2.5mg once daily is an adequate regime, but the effect does not persist for 24 hours in all patients. If this dose is chosen, the BP should be measured to assess 24-hour coverage.
Georgena S. Sil
Saskatoon, Canada
Physicist & Technical Writer
Alumnus: University of British Columbia
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