Different studies conducted in several parts of Nigeria have investigated antihypertensive drugs prescribing

Different studies conducted in several parts of Nigeria have investigated antihypertensive drugs prescribing, utilization patterns and adherence to standard treatment guidelines10-19. These studies focused on describing the most prescribed and utilized antihypertensive medications for management of hypertension and adherence to standard guidelines in non-health insurance settings. To our knowledge, no study has assessed antihypertensive drug utilization among insured patients in Nigeria. Therefore, the objectives of this study were to evaluate antihypertensive prescription and utilization patterns, to assess adherence to NHIS standard treatment guideline for hypertension, and to evaluate age and gender based disparities in antihypertensive drugs consumption.
METHODS
SETTING
This study was carried out in the NHIS pharmacy unit of the University of Nigeria Teaching Hospital (UNTH), Enugu. UNTH is a tertiary health facility of about 500 bed capacity with personnel made up of professionals and non–professionals. It serves as the Teaching Hospital for the Faculty of Medicine of the University of Nigeria. The department of pharmaceutical services is a service arm of the tertiary hospital. It provides pharmaceutical services to both the in-patients and out-patients. There is a dedicated pharmacy that attends to the drugs or drug related needs of only patients registered under the NHIS. NHIS dispensing pharmacy outlet opens to patients throughout the workdays but the peak hours for out-patients transactions is from 10.00 am to 1.00 pm. All NHIS essential medicines are accessed from this dispensing pharmacy outlet except injections, creams, ophthalmic drugs, ear preparations, and surgical items which are accessed from other dispensing pharmacy outlets under NHIS coverage. Prescriptions filled at the NHIS dispensing pharmacy outlet are also stored and kept for a minimum period of one year in the pharmacy before disposal. As at time of this study, the average number of prescriptions dispensed per day was 50. Four (4) pharmacists, two (2) intern Pharmacists, one (1) pharmacy technician, one (1) pharmacy assistant, and one (1) clerk were working in this pharmacy unit.
STUDY DESIGN AND SAMPLE SIZE
Following ethical approval from the Research and Ethics Committee of the studied hospital, this descriptive, cross-sectional, retrospective study was conducted. Four hundred and fifty seven (457) prescription sheets (that contained at least an antihypertensive drug) issued to different NHIS out-patients that attended the health facility between January and December 2013 were systematically selected for this study.
DATA COLLECTION
The data for this study were collected from the NHIS out-patient’s prescription sheets of twelve months period of 2013.The following information including patient age in years, gender, number of antihypertensive medicines prescribed, antihypertensive drug name, therapeutic class, route of administration, dosage form, strength, dose, frequency of administration, and duration of treatment were abstracted from the sampled prescription sheets, while DDDs were abstracted from WHO Collaborating Centre for Drug Statistics list of DDD20 into the pretested data collection forms. Abstracted information were subsequently keyed into Microsoft excel spread sheet and Statistical Package for Social Sciences (SPSS) version 20 for windows, coded for analysis.
DATA MANAGEMENT
Patients’ ages were categorized into 4 groups (20-34years, 35-49years, 50-64years, and ? 65years). Antihypertensive drugs were classified based on Anatomic Therapeutic Chemical (ATC)/Defined Daily Dose (DDD) methodology proposed by World Health Organization20. Drug groups with these ATC codes were analyzed: CO3 (diuretics)- diuretics included diuretics, and diuretic-diuretic combinations; CO7 (B-Blockers- BBs and BB fixed dose combinations), the BBs also included carvedilol (alpha and beta-blockers); CO8 (Calcium Channel Blockers- CCBs); CO9 (Angiotensin Converting Enzyme Inhibitors- ACEIs, ACEIs fixed dose combinations, ARBs- Angiotensin Receptor Blockers, and ARBs fixed dose combinations); and CO2 (Centrally Acting Agents- CAA and Peripheral Vasodilators- PVD). The number of antihypertensive drugs taken by a single patient was determined based on a total count of active components in each prescription taken by a patient, with multiple counts given to different medication class. Monotherapy was defined as treatment with a single antihypertensive drug, and polytherapy as treatment with ?2 agents. Patients treated with both a thiazide diuretic and a loop diuretic was categorized under polytherapy treatment. Patients treated with a thiazide plus the potassium sparing diuretic (amiloride) were categorized as receiving monotherapy, as amiloride was considered to have minimal or no BP-lowering contribution when prescribed in low doses with thiazide agent. Antihypertensive drug utilization was expressed in the utilization indicators as number/volume of DDD, DU90% (the number of drugs accounting for 90% of drug use), and DDD/TPD. DDD is the assumed average daily maintenance dose for the main indication of a drug in adult. All antihypertensive pharmaceutical products that had a DDD, as assigned by the WHO Collaborating Centre for Drug Statistics20 were identified, and the numbers of DDDs was calculated. The numbers of DDDs for all antihypertensive drugs were aggregated and utilization was calculated for antihypertensive drugs by antihypertensive therapeutic category and for individual antihypertensive drugs. The number of individual antihypertensive drugs that accounted for 90% of the total volume of DDDs (the area under the curve) was calculated and presented only. Quality of prescribing was determined by index of adherence to NHIS Standard Treatment Guideline21,22. Index of Adherence to standard treatment guideline for hypertension therapy was calculated from the volume of DDD of antihypertensive drug prescribed according to the guideline divided by total volume of DDD of all the antihypertensive drugs in the DU90% segment, expressed in percentage in accordance with Bergman et al, 1998 23. DDD/TPD for individual antihypertensive drugs was calculated with the formula below:
Total amount of drug used during the study period (mg, units) X 1000
DDD (mg, units) x Study duration x Total sample size

STATISTICAL ANALYSIS
Data entry was double checked for consistency before the commencement of analysis. Statistical analyses were conducted with both Microsoft excel 2007 and Statistical Package for Social Sciences (SPSS) version 20 for windows. Descriptive analyses were performed and results presented as frequencies, percentages, mean or mean (standard deviation), and median. Pearson chi square test (?2) was used to analyze differences in proportions, and the independent student t test (t-test) was used to compare the antihypertensive drugs consumption of the 2 groups. Statistical significance was set at p < 0.05.

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