Clinical drug interactions in outpatients of a university hospital in Thailand.

BACKGROUND: A clinical event is likely to occur in patients receiving a pair of drugs, that have the potential to cause an interaction. The occurrence of a clinical drug-drug interaction in outpatients of university hospitals in Thailand is unknown. PURPOSE: To investigate the occurrence of a clinical event associated with drug-drug interactions in outpatients at a Thai university hospital. METHODS: A case-control study was established. The case was a sample group, randomly selected from a 1-year sample of outpatient prescriptions containing 'significance-1' potential drug-drug interactions, whereas the control was from the same year but with no potential drug interactions. Medical records of the cases and the controls were reviewed for an adverse event (AE) using a newly developed review form. The odds ratio of occurrence of the AE between the cases and the controls was determined. The AE was assessed for its possibility of being caused from a drug-drug interaction. RESULTS: The most common specific AE in both the cases and the controls was cough. An unplanned revisit to outpatient department or emergency room was found to be the most common general AE. The odds ratio of the occurrence of an AE in the cases, compared with the controls, was 1.495 (95% CI: 0.917-2.438). The possibility that the AEs resulted from drug interactions in the case group was nine 'probable' patients and 15 'possible' patients, whereas that in the control group was eight 'possible' patients. The most common interacting drug pair was isoniazid-rifampin with an increase in serum hepatic enzymes as the corresponding AE. CONCLUSIONS: Despite outpatients receiving drug pairs with a high potential for adverse interactions, the rate of occurrence of clinical drug interaction events was low.

Pharmacoepidemiologic study of potential drug interactions in outpatients of a university hospital in Thailand.

BACKGROUND: Drug-drug interaction is a potential cause of adverse drug reactions. The incidence of such drug interactions in university hospitals in Thailand is unknown. PURPOSE: To estimate the rate of potential drug-drug interactions in outpatients of a typical Thai university hospital, and to identify risk factors for such interactions in Thai patients. METHODS: One-year outpatients' prescription data were retrieved from the hospital computer records. Potential drug interactions were identified using the existing drug-interaction database system. Potential interactions within a specific prescription and involving drugs prescribed 1-, 3- and 7-day earlier were searched for. Possible associations between occurrence of an interaction and a patient's age and gender and the number of items on the prescription were explored. RESULTS: The overall rate of potential drug interactions was 27.9% with a maximal value of 57.8% at the Department of Psychiatry. The rate of the most potentially significant interactions was 2.6%, being the highest in the Department of Medicine (6.0%), with isoniazid vs. rifampin as the most common interacting combination. The rate increased with the patient's age and prescription size (P=0.000). The odd's ratio of having at least one potential drug interaction was 1.8 (64.2%) when age increased by 20 years (P=0.000) and 2.8 (165.7%) when another drug was added (P=0.000). The rate of potential drug interactions was the same for both genders. The rate of potential drug interactions detected across prescriptions was higher than within prescriptions and was dependent on the time interval between prescriptions. CONCLUSIONS: Potential drug interactions were common in our sample of patients. The rate of such interactions increased with the number of drugs prescribed and the patient's age.

Polypharmacy among older men in South Wales.

OBJECTIVE: To describe the pattern of polypharmacy (PP) among older men and to relate medication use to personal, social and medical information. METHODS: Information on medication use, both prescribed and 'over the counter' (OTC), was collected from 1906 men, aged 56-75 years, observed on up to four occasions since 1979 in a community survey the Caerphilly prospective study. On each visit, a variety of questionnaires regarding personal, social and medical factors were completed, and a brief medical examination was conducted. Medication use was related to some of the questionnaire information and biological measurements collected in order to identify factors associated with PP. RESULTS: A quarter of the men (475/1906) reported using three or more prescription-only medicines (PoMs), with 9% (163) using five or more (major PP). PP was related to increasing age, lower social class, not being in employment, smoking and obesity (high body mass index). Men with a medical history, especially of high blood pressure, angina, heart attack, or hospital admission in the last 5 years, comprised a large proportion of those on major PP. Higher levels of PoM use by this group had been apparent over the previous 14 years. Men on PP reported lower levels of self-rated health and higher rates of non-PoM use. Cardiovascular and, to a lesser extent, central nervous and respiratory system drugs were the main medicines used by men on major PP. CONCLUSIONS: PP is common among men aged 56-75 years in Caerphilly, South Wales. It is related to many personal, social and medical factors, and associated with lower self-rated health status and greater use of non-PoMs. Cardiovascular medicines are the main contributor to major PP. Those on PP require regular review and, where possible, PP should be reduced as it has many potential adverse effects.