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The problem with generic atypical antipsychotics

From Mrs C. L. Feetam, MRPharmS


Optimum adherence to medicines is a fragile commodity in mental illness. Poor adherence is a major cause of relapse in schizophrenia and a significant challenge to the effective treatment of bipolar disorder. The availability of generic atypical antipsychotics will indeed reduce the drugs bill but at what cost to patient care and long-term outcomes (PJ, 28 April 2012, p512)?

Oral dosage forms of atypical antipsychotics differ in name, appearance and packaging. Such differences can cause anxiety, confusion and misperceptions in some patients, as well as reduced confidence in the treatment. A study that looked into these issues reported that 73 per cent of 106 patients interviewed said they would be unlikely to take a generic product if it were substituted for their usual branded atypical antipsychotic.1

What is of greater concern, however, is the possibility of significant variations in bioequivalence between different generic formulations. The standard bioequivalence study is a two-way crossover trial in 18 to 60 healthy volunteers. Single dose test and reference products are administered to the fasting subjects and plasma levels of the drug and its metabolites are measured over time. The ratios of test-reference mean values for the key parameters, maximum concentration (Cmax) and area under the curve (AUC) must be within 90 per cent confidence limits of 80 per cent to 125 per cent. If one of the ratios is close to the upper or lower limit it is unlikely that the confidence intervals will be within the specified range. However, if one generic product is substituted for another generic product, the range of difference can clearly still be large.2

Some clinicians have expressed concern about the speed of dissolution of some branded orodispersible formulations and there have already been anecdotal reports of relapse following a switch to generic quetiapine. A patient may well receive a different generic product each month if community pharmacists source the cheapest available. Varying bioequivalence coupled with inconsistent adherence could well precipitate a relapse, the cost of which will far outweigh any savings made on the medicine’s acquisition cost.

Perhaps one solution might be the consistent prescribing of particular generic atypical antipsychotics by name for individual patients, coupled with a full explanation and reassurance, so that they can get used to any change in appearance, steady state is achieved and maintained and the risk of relapse minimised.


Celia Feetam

Postgraduate Tutor in Psychiatric Pharmacy,
Aston University


References

1    Roman B. Patients’ attitudes towards generic substitution of oral atypical antipsychotics: a questionnaire-based survey in a hypothetical pharmacy setting. CNS Drugs 2009;23:693–701.

2    Meyer MC. United States Food and Drug Administration requirements for approval of generic drug products. Journal of Clinical Psychiatry 2001;62(suppl 5):4–9.

Citation: The Pharmaceutical Journal URI: 11102156

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