Selective prescribing of spasmolytics.

BACKGROUND: Daily clinical practice often differs largely from the clinical trial setting, so extrapolation of outcomes from trial data, such as safety, effectiveness, and economic outcomes, can be deceptive. Prescribers may intend to treat a selected group of patients with new drugs; this practice could result in significant bias in assessing outcomes of these agents during their use in daily clinical practice.
OBJECTIVE: To evaluate what type of patient received tolterodine compared with the spasmolytic drugs previously marketed (oxybutynin, flavoxate, emepronium).
DESIGN: An observational, follow-up study.
SETTING: Eighteen collaborating community pharmacies. PATIENTS: Aged > or = 18 years, noninstitutionalized; initial therapy with tolterodine, oxybutynin, flavoxate, or emepronium.
RESULTS: Tolterodine was often used as a second-line and even as a third-line treatment, and was prescribed to a "polluted" population in terms of concomitant psychotropic medication. Tolterodine users were 7.5 times more likely to have received another spasmolytic drug (RR 7.5, 95% CI 4.8 to 11.9). In addition, these patients more frequently used antiparkinsonian drugs (RR 4.1, 95% CI 1.6 to 10.4) as well as antipsychotic drugs (RR 2.9, 95% CI 1.4 to 6.2). There was a small difference in concomitant use of antidepressants and benzodiazepines between patients receiving tolterodine versus those taking other spasmolytic drugs.
CONCLUSIONS: Tolterodine is prescribed for a population differing from that receiving previously marketed spasmolytic drugs. Selective prescribing should recognized when evaluating new drugs in daily clinical practice. Policy makers, such as pharmacy and therapeutics committees, should consider this aspect in their formulary decisions since selective prescribing can lead to unjustified conclusions about a drug's therapeutic effects (e.g., efficacy, safety, cost-effectiveness).