Hospital admissions due to medication misadventure are both costly and frequently avoidable. Quality data reports that medication-related hospital admissions comprise 2% to 4% of all admissions. This rate increases to up to 30% for patients over 75 years of age. The estimated cost of these admissions for 1999-2000 exceeded $400 million. This increased to an estimated $1.2 billion for the year 2011-2012. Although the rate of medication-related admissions remained stable at 2% to 3% of all admissions, the cost of treating each patient increased considerably over that time.

Preventable adverse drug events are responsible for 5.6% of hospital admissions in the general population in Australia. This increases significantly to 30.4% of hospital admissions in elderly patients. The elderly are over-represented in this data, with medication-related hospitalisations increasingly common in this population. A study of Australian veterans reported a medication-related hospitalisation rate of 13.3%. Of these admissions, 20.3% were assessed as being preventable.

There are many factors that contribute to medication-related hospital admissions. Some of these factors, such as drug interactions, dosing, and polypharmacy, can be modified by healthcare professionals. Other factors, such as financial barriers to drug acquisition and poor health literacy, are patient-specific and may be more difficult for healthcare professionals to modify.

Drug interactions:

Drug interactions cause up to 2.8% of hospital admissions. A seven-year study of 909 elderly patients reported that “many hospital admissions of elderly patients for drug toxicity occur after administration of a drug known to cause drug-drug interactions. Many of these interactions could have been avoided.”

This study highlights the often predictable nature of drug interactions. Drug interactions can usually be anticipated based on knowledge of the pharmacology and metabolism of the medications, and upon consultation with the product information and clinical studies. Drug interactions can range from the suspected to the well documented and from the minor to the severe. Some interactions may be so serious that the results can be life-threatening. It is, therefore, vitally important that healthcare professionals are aware of the potential for such drug interactions and modify therapy accordingly.

Excessive dose:

Inappropriate dosing of medications has the potential to cause adverse effects. Dosing above the recommended maximum dose is common for many psychiatric medications. One study demonstrated that polypharmacy and excessive dosing was present in 69% of patients discharged from an acute psychiatric unit. Dosing errors with anticlotting drugs such as warfarin are also common and may result in hospitalisation.

Inappropriate dosing contravenes the quality use of medicines (QUM) and should be avoided. One of the fundamental goals of the National Medicines Policy, QUM aims to improve the safety and effectiveness of medication use in Australia. Dosing above the recommended maximum dose often does not deliver proportionally higher efficacy, yet is associated with considerably higher rates of adverse effects and toxicity.


Polypharmacy is defined as taking more than five medicines. It is one of the “triggers” which will qualify a patient for a home medicines review and is prevalent before, during, and after a hospital stay. Although polypharmacy is associated with adverse clinical outcomes, appropriate combinations of medications have the ability to improve the quality of life and prevent complications. For many patients, taking multiple regular medications will represent the best therapy.

However, polypharmacy is often associated with inappropriate prescribing. One study of older people with cancer found that polypharmacy was present in 57% of patients. It is also common in the general population, with 49% of Australians aged between 65 and 74 years and 66% of people over 75 years taking more than five medications.

Polypharmacy is associated with a range of issues including higher rates of hospitalisation, delirium, falls, frailty, mortality, and functional and cognitive impairment. Compliance is also likely to reduce as the number of daily doses increases. The chance of experiencing a clinically significant drug interaction increases with polypharmacy.

Patient health literacy:

The Australian Commission on Safety and Quality in Health Caredefines health literacy as “how people understand information about health and health care, and how they apply that information to their lives.” Health literacy (HL) is relevant to the quality use of medicines (QUM) as low health literacy will “contribute to poorer health outcomes, increased risk of an adverse event and higher healthcare costs.”

The level of poor health literacy exceeds 33% for people aged over 65 years. Patients with low health literacy ask fewer questions when interacting with a healthcare professional, which has a deleterious impact on their capacity to learn about their health situation and treatment options. Poor health literacy is not limited to under-developed nations. In the United States, approximately 30% of adults lack the capacity to understand and cogently interact with health information. Some US hospitals have implemented pharmacist-driven programs for patients with poor health literacy. One study that has led to the introduction of such programs is the Pharmacist Intervention for Low Literacy in Cardiovascular Disease (PILL-CVD). This study looked at the potential for pharmacist-based interventions to reduce serious medication errors in patients hospitalised with acute coronary syndrome or acute decompensated heart failure. The findings of this study demonstrated that;

Pharmacists considered medication reconciliation, though time-consuming, to be their most important role in improving care transitions, particularly through detection of errors in the admission medication history that required correction. They also identified patients with poor understanding of their medications, who required additional counseling. Providing adherence aids was felt to be highly valuable for patients with low health literacy…”

Transitional care:

Transitional care refers to the transfer of patients from one domain of care to the next sequential domain. For the elderly, those with multiple co-morbidities, and polypharmacy patients, there is a need for precise and timely transfer of patient-related health information between the discharging hospital and the patient’s primary care physician.

Adverse medication-related events and subsequent rehospitalisation are associated with breaks in the transitional care chain. This may occur as a result of the incomplete transfer of information, limited access to essential services, and poor communication and education.

Medication adherence and persistence/compliance:

Medication adherence is defined as the level of patient compliance with a prescriber’s directions regarding the timing, dosage, and frequency of medication ingestion. Persistence refers to whether a patient “stays the course” of a prescribed drug treatment.

Non-adherence and poor adherence result in subtherapeutic levels of prescribed drugs. This lack of patient conformity with prescribed medicines has been reported to be present in almost one in four post-discharge patients. This has the potential to significantly impact on patient quality of life by reducing the efficacy of prescribed treatments and potentially increasing the risk of hospitalisation due to exacerbation of under-treated conditions.

Medication costs:

Medication costs can be considered as a contributing factor to poor overall compliance, understood as encompassing adherence and persistence. The 2012 Australian Bureau of Statistics data reports that 9.2% of patients delayed or failed to have a prescribed medication dispensed due to the cost. It is known that as prescription costs increase, so does non-adherence which may result in poor therapeutic outcomes.

Drug Burden Index (DBI):

The DBI is a mechanism for determining a patient’s exposure to anticholinergic and sedative medications, and the consequent impairment of physical and cognitive capacities. The elderly are particularly susceptible to the central nervous system (CNS) impact of anticholinergic medications. This is associated with an increased risk of falls, confusion, and hospitalisation. Home Medication Reviews have been shown to significantly reduce the DBI score. Further studies are required to quantify the impact this has on the overall quality of life.


Though not discussed here, many other factors can contribute to medication-related hospitalisations. These include patients taking more than twelve doses of medication per day, potential confusion with the use of generic medications, drugs with a narrow safety margin (e.g. warfarin, digoxin, thyroxine), attending a number of different doctors and specialists, and cognitive, eyesight, and language problems.

The next instalment in this series of articles on medication-related hospital admissions will review the rates of reporting of adverse drug events by health care professionals and barriers that impede reporting of these events. The literature that underpins the beneficial impact of hospital-initiated Home Medication Reviews will also be reviewed.


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