myparkinsons.co.uk

Be Aware-Generic Brands

The effective control of Parkinson’s disease requires
that we are staBilised on usually a combination of medicines taken at set times which optimises symptom control. This usually requires a degree oftrial and error with the medications prescribed and the times of the day when
they are taken.

Once an individual patient with Parkinson’s is stabilised on a particular
medicine or a combination of medicines, it is important that they get the
same medicine dispensed on each occasion. Fear of loss of control of
symptoms is a source of great anxiety for patients with Parkinson’s. Patients
may experience symptoms of ‘freezing’ or dyskinesia, the former may occur
if blood levels of medication fall two low and the latter may occur if blood
levels are too high. Each patient therefore needs to have confidence in the
medicines dispensed, and if different generic medicines are dispensed on
different occasions they may well become anxious as to whether the medicine
will control their symptoms as well as the branded medicines they are used to.

A crucial element in the proposal for generic substitution from the Department
of Health is that the prescriber should have the means when writing the
prescription to specify that if a brand name is written that is what should be
dispensed. It is proposed that the prescriber can do this by means of ticking a
box for ‘no substitution’ somewhere on the FP 10 form.

Whilst this may seem reasonable, the question is will doctors always
remember to ‘tick the box’ for patients with Parkinson’s who are being
prescribed a combination of branded medicines like Sinemet CR + Requip?
The answer is almost certainly no. This would be particularly likely to occur
when a doctor is signing a large batch of repeat prescriptions, and may well
not take the time with each prescription to properly evaluate whether generic
substitution is right for a particular patient before signing the prescription.

Generic substitution can lead to more than one switch
in generic medicines.
Generic medicines always have a different
size, shape, colour and packaging from each
other, and to branded medicine
Therefore, a patient could receive a different
medication, with a different appearance with every prescription

. In a European study, one in three
patients who had experienced a generic
substitution had to become accustomed to a
different colour or shape medication

Bioavailability and formulation issues
Generic medicines have the same active
ingredient as the branded medicine.
However, they are not always identical to
the branded medicine
. The amount of drug
that finally reaches the site of action is
known as the ‘bioavailability’. The
bioavailability is very important, because
this will determine how effective the
medicine will be. Too little drug reaching
the target could lead to less effective
treatment, but too much could increase side
effects. The bioavailability can vary between
branded and generic medicines, and
between different generic medicines, with
the same amount of active ingredient. This
is because the formulation and excipients
(other ingredients included in the medicine)
affect the absorption and metabolism of the
drug.
Branded medicines undergo a rigorous
process of clinical trials assessing safety and
effectiveness before they are approved for
human use. However, generic medicines can
be approved on the basis of
pharmacokinetic studies carried out on a
minimal number of healthy volunteers,
where they are shown to be ‘bioequivalent’
to the branded medicine. This means that
the rate and extent of their bioavailability
lies within ‘acceptable predefined limits’
compared with the original branded
medicine. For a generic medicine to be
considered bioequivalent, the European
Medicines Agency (EMEA) requires the
measures of bioavailability (area under the
curve and Cmax) to be within 0.8 and 1.25 of
the original medicine’s values.26, 27

Thus, the relative bioavailability of the generic
medicine can lie anywhere between 80%
and 125% of the original medicine’s values.
Bearing in mind that patients can be
switched between different branded products

Patients with certain conditions requiring
carefully balanced combinations of
medications would also be
disproportionately affected by medicine
substitutions. For example, people with
Parkinson’s disease often take a
combination of medications, which must be
taken at the correct time for them to avoid
worsening of their symptoms. Patients
with Parkinson’s disease could be
understandably concerned about apparent
changes in their medication. In addition,
changes in formulation type could affect
symptom control

July 16, 2014 - Posted by Chris | Generics