Prescriptions with potentially hazardous/contraindicated drug combinations presented to community pharmacies

Focal points

Prescribing errors and other problems reported by community pharmacists

INTRODUCTION

Prevention of medication errors is a priority for health services worldwide. Pharmacists routinely screen prescriptions for potential problems, including prescribing errors. This study describes prescribing problems reported by community pharmacists and discusses them from an error prevention perspective.

METHOD

For one month, nine community pharmacists documented prescribing problems, interventions made, and the proximal causes of the problems. The results were presented to local GPs and pharmacists at a meeting and feedback was invited.

RESULTS

For 32 403 items dispensed, pharmacists reported 196 prescribing problems (0.6%). The reporting rates ranged from 0.2%-1.9% between pharmacists and were inversely correlated to dispensing volume. Prescriptions containing incomplete or incorrect information accounted for two-thirds of the problems. Lack of information on the prescriptions and transcribing/typing errors were the most frequently cited proximal causes. A few pitfalls of computerized prescribing were observed.

CONCLUSION

Although rates of prescribing problems reported were relatively low, community pharmacists and patients remain important safeguards. This study identified potential causes of prescribing errors, and illustrated areas which could be improved in the design of computerized prescribing systems, and the communication and sharing of information between GPs and pharmacists.

Incidence and possible causes of prescribing potentially hazardous/contraindicated drug combinations in general practice

BACKGROUND

Preventing the use of medications where there is the potential for serious drug-drug interactions or drug-disease interactions (contraindications) is essential to ensure patient safety. Previous studies have looked at the incidence of prescribing contraindicated drug combinations, but little is known about the underlying reasons for the co-prescribing events. The objectives of this study were to estimate the incidence of prescribing contraindicated drug combinations in general practice and to explore the clinical context, possible causes and potential systems failures leading to their occurrence.

METHODS

A list of contraindicated drug combinations was compiled according to established references. A search of computerised patient medication records was performed, followed by detailed chart review and assessment. The patient records from four general practices in an area of England were searched for a period of 1 year (1 June 1999-31 May 2000) to identify contraindicated drug combinations. All patients registered with the four participating practices during the study period were included (estimated n = 37 940). Medical records of the cases identified by the computer search were reviewed in detail and relevant information was extracted. Each case was then independently assessed by a pharmacist and a physician who judged whether the co-prescribing was justified and whether it was associated with an adverse drug event. Proximal causes and potential systems failures were suggested for each co-prescribing event.

MAIN OUTCOME MEASURES AND RESULTS

Fourteen patients with potential drug-drug interactions and 50 patients with potential drug-disease interactions were identified. Overall, these represent an incidence of 1.9 per 1000 patient-years (95% CI 1.5, 2.3) or 4.3 per 1000 patients being concurrently prescribed > or =2 drugs per year (95% CI 3.2, 5.4). 62 cases involving 63 co-prescribing events were reviewed. Two-thirds of these events involved medications that were initiated by hospital doctors. Awareness of the potential drug-drug or drug-disease interactions was documented in one-third of the events at the time of initial co-prescribing. Within the study period, the co-prescribing was judged to be not justified in 44 events (70%). Potential drug-drug interactions possibly resulted in two adverse drug events. The majority of contraindicated co-prescribing related to drug-disease interactions involved the use of propranolol or timolol eye drops for patients receiving bronchodilators and the use of amiodarone for patients receiving levothyroxine sodium.

CONCLUSION

The prescribing of contraindicated drug combinations was relatively rare in this study. Multiple possible causes and systems failures were identified and could be used to develop strategies for the prevention of prescribing errors involving contraindicated drug combinations in primary care.

Heterogeneity of beta-adrenoceptors in guinea-pig brain: radioligand binding and cyclic nucleotide generation

In this report, we have examined the radioligand binding and second messenger signalling characteristics of beta-adrenoceptors in the guinea-pig brain. [125I]-Iodocyanopindolol ([125I]ICYP)-labelled sites in the cerebellum and cerebral cortex were of similar densities (Bmax 34 and 24 fmol x mg(-1)) and affinities (K(D) 20 and 55 pM), respectively. Analysis of competition for [125I]ICYP binding in the cerebellum was compatible with the presence of a beta2-adrenoceptor. In this tissue, isoprenaline evoked a cyclic AMP stimulation, and also potentiated cyclic GMP accumulations evoked in the presence of a nitric oxide donor, consistent with mediation via a beta2-adrenoceptor. The [125I]ICYP binding profile in the cerebral cortex did not comply with those previously described for beta-adrenoceptor subtypes, and isoprenaline failed to alter significantly cyclic AMP accumulation in the cerebral cortex, hippocampus, or neostriatum, even in the presence of forskolin or a phosphodiesterase inhibitor. Isoprenaline was also without effect on cyclic GMP accumulation or phosphoinositide turnover in the cerebral cortex. These results suggest that the guinea-pig cerebellum expresses a functional beta2-adrenoceptor coupled to cyclic AMP generation, and potentiation of cyclic GMP accumulation. However, the guinea-pig cerebral cortex displays binding sites that exhibit beta-adrenoceptor-like pharmacology but fail to show functional coupling to cyclic AMP, cyclic GMP, or phosphoinositide signalling systems.

Coupling of metabotropic glutamate receptors to phosphoinositide mobilisation and inhibition of cyclic AMP generation in the guinea-pig cerebellum

1. The effects of metabotropic glutamate receptor (mGluR) agonists on cyclic nucleotide and phosphoinositide turnover were investigated in adult guinea-pig cerebellar slices by use of radioactive precursors. 2.L-Glutamate, 1-aminocyclopentane-1S,3R-dicarboxylate (1S,3R-ACPD) and RS-3,5-dihydroxyphenylglycine (DHPG) evoked concentration-dependent increases in the accumulation of [3H]-inositol phosphates with pEC50 values of 2.98 +/- 0.02, 4.45 +/- 0.06 and 4.47 +/- 0.07, respectively. Maximal responses to these agents were 43 +/- 8, 52 +/- 12 and 84 +/- 11% of the response to 1 mM histamine, respectively. 3. The phosphoinositide response to 1S,3R-ACPD was antagonized in the presence of (+)-alpha-methyl-4-carboxyphenylglycine, with a calculated pKi value of 3.55 +/- 0.03. 4. Forskolin-stimulated accumulation of [3H]-cyclic AMP was not significantly altered in the presence of 10 microM DCG-IV or 300 microM 1S,3R-ACPD. Similarly, 300 microM 1S,3R-ACPD failed to alter isoprenaline-(1 microM) or 2-chloroadenosine (2-CA, 30 microM)-stimulated accumulation of [3H]-cyclic AMP. 5. Forskolin-stimulated accumulation of [3H]-cyclic AMP was concentration-dependently inhibited in the presence of L-glutamate and L-serine-O-phosphate (L-SOP) with pIC50 values of 2.91 +/- 0.17 and 2.86 +/- 0.04 with maximal inhibitions of 47 +/- 2 and 92 +/- 3%, respectively. L-2-Amino-4-phosphonobuty-rate (L-AP4) inhibited the forskolin response without saturating, evoking an inhibition of 71 +/- 7% at 3 mM. 6. 2-CA-evoked accumulation of [3H]-cyclic AMP was also inhibited by L-glutamate and L-SOP with pIC50 values of 2.71 +/- 0.03 and 2.72 +/- 0.08 and maximal inhibitions of 51 +/- 5 and 99 +/- 0%, respectively. L-AP4 inhibited the 2-CA response without saturating, evoking an inhibition of 68 +/- 1% at 3 mM. 7. Isoprenaline-evoked accumulation of [3H]-cyclic AMP was inhibited by L-glutamate and L-SOP with pIC50 values of 3.21 +/- 0.01 and 2.96 +/- 0.08 and maximal inhibitions of 88 +/- 2 and 93 +/- 3%, respectively. 8. These results suggest that the guinea-pig cerebellum expresses Group I and Group III mGluRs coupled to phosphoinositide turnover and inhibition of cyclic AMP generation, respectively.