Journal of Current Research in Scientific Medicine

: 2018  |  Volume : 4  |  Issue : 2  |  Page : 86--93

The incidence and prevalence of adverse drug reactions among medical inpatients in a Nigerian University Teaching Hospital

Peter Ehizokhale Akhideno1, Olumuyiwa John Fasipe2, Ambrose Ohumagho Isah3,  
1 Department of Internal Medicine, Irruar Specialist Teaching Hospital, Irruar, Benin City, Edo State, Nigeria
2 Department of Pharmacology and Therapeutics, University of Medical Sciences, Ondo City, Ondo State, Nigeria
3 Department of Internal Medicine, University of Benin Teaching Hospital, Benin City, Edo State, Nigeria

Correspondence Address:
Olumuyiwa John Fasipe
Department of Pharmacology and Therapeutics, Faculty of Basic Clinical Sciences, University of Medical Sciences, Ondo City, Ondo State


Aim: Evaluating the incidence, prevalence, and pattern of adverse drug reactions (ADRs) with the extent to which they influence cost of healthcare is often informative and useful in patients' management, policymaking and safety considerations. Methods: The patients admitted into the internal medicine wards of a university teaching hospital, South-South Nigeria over a 9-month period from December 2013 to August 2014 were prospectively recruited for the study and followed up till discharge. Results: Five hundred and seven patients were evaluated during the study, out of which 269 (53.1%) of them were males and 238 (46.9%) were females. The mean age of the study population was 48.9 ± 17.8 years (median of 46 years). ADRs had an incidence of 6.5%, while its prevalence rate was 10.1%. The cost of treating ADR was ₦ 161668.00 ($1243.60), equivalent to 1.9% of the total cost of all medications used by patients during admission. The case fatality rate for ADRs was 7.8%, while ADR-related mortality rate was 0.8%. The most frequently affected body systems were the central nervous system and the gastrointestinal system corresponding to insulin use (causing neuroglycopenic symptoms) and nonsteroidal anti-inflammatory drugs (NSAIDs) use (causing NSAID-induced gastroenteritis/GIT bleeding) respectively. Conclusions: The incidence and prevalence of ADRs were clinically significant among these medical inpatients. In this study, ADRs increase patients morbidity, mortality, cost of health care, and duration of hospital stay as it has been shown by previous studies. Insulin caused the highest number of ADRs, suggesting the need for individual diabetic patients to acquire and learn the appropriate regular use of glucometers.

How to cite this article:
Akhideno PE, Fasipe OJ, Isah AO. The incidence and prevalence of adverse drug reactions among medical inpatients in a Nigerian University Teaching Hospital.J Curr Res Sci Med 2018;4:86-93

How to cite this URL:
Akhideno PE, Fasipe OJ, Isah AO. The incidence and prevalence of adverse drug reactions among medical inpatients in a Nigerian University Teaching Hospital. J Curr Res Sci Med [serial online] 2018 [cited 2022 Sep 27 ];4:86-93
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Full Text


Medications are unequivocally very important in patient care. Patient management often requires the use of medications. The use of medicines for patient care is considered to be a major component of patient management in health care settings.[1] Pharmacological interventions do sometimes carry preventable and avoidable medication related problems such as adverse drug reactions (ADRs), drug interactions and consequences of inappropriate medication use.[2] An ADR is defined in this study as a response to a medicine which is noxious and unintended that occurs at doses normally used for therapeutic purposes.[3] ADRs have been known to cause significant morbidity and mortality for centuries being as old as medicine itself.[4]

Despite the extensive study and attention given to ADRs, they still represent a clinical significant problem and burden with high prevalence.[5] In the United States, for example, pharmaceutical sometimes results in ADRs either due to inherent ADRs or from inappropriate medicine use or medication errors. These were noted in over 1.2 million hospital stays or about 3.1% of all hospital stays in the US in 2004.[6] The incidence of serious and fatal ADRs in US hospitals was noted to be extremely high at 6.7% and 0.32% respectively, making these reactions between the fourth and sixth leading causes of death.[7]

In the United Kingdom, the incidence of ADRs among admitted patients was found to be 6.5% and admissions related to ADRs cost the National Health Scheme (NHS) up to £ 466 million annually or 0.62% of annual health budget.[8] Furthermore, at a particular point in time, the equivalent of up to seven 800 bed space hospitals may be occupied by patients with ADRs, amounting to 4% of hospital bed capacity in the UK.[9] The duration of hospital stay is also increased by ADRs.[10] The foregoing data underscores the importance of the economic burden posed by ADRs.

In developing countries including Nigeria, there is minimal information on the in-hospital incidence of ADRs, the culprit medications and the cost of management.[11] This information is useful for health planning and management, budgeting and policy formulation, development of treatment protocols to enable appropriate and optimal patient care.[12]

This study was therefore designed to determine the incidence and prevalence of ADRs among medical in-patients at the University of Benin Teaching Hospital (UBTH), Benin City, Edo State, Nigeria; to highlight the pattern of medications most commonly involved, and to estimate the cost of treating ADRs.


This was a descriptive, prospective study with serial entry points for the patients admitted into the internal medicine wards of UBTH, Benin City, Edo State, South-South Nigeria, over a 9-month period from December 2013 to August 2014. They were all adult medical patients whose ages were above 17 years and were fulfilling the inclusion criteria for recruitment, evaluation, and follow-up. Medications prescribed for the admitted patients were supplied by the hospital pharmacy, or they may occasionally be required to purchase some medications from retail outlets outside the hospital when these drugs are not available in the hospital pharmacy. Patients are generally admitted through the accident and emergency unit where they are reviewed by various cadres of medical doctors until they are transferred to the wards under unit consultants. Some patients are admitted directly from the outpatient clinics into the wards, while a few may be transferred in from other nonmedical wards. The patients are then reviewed daily in the various units and managed till discharge.

The inclusion criteria for evaluation were all the patients admitted to the medical wards after commencing the study provided they granted their informed consents to participate in the study.

The exclusion criteria were as follows:

Patients already admitted before commencing the studyPatients admitted from other wards after initial management for nonmedical condition(s)Patients diagnosed and subsequently managed for nonmedical condition(s) after initial medical diagnosis and managementPatients who did not grant informed consent to participate in the study.

Data information about all the recruited patients were obtained and entered into a data collection form modified from the WHO-INRUD prescribing indicator form.[13] Patients were evaluated with respect to medications used on days 0 (admission day), 1, 3, 7, 10, 14, 21, and weekly thereafter till day of discharge or death. An encounter was regarded as a patient studied on admission on such specified days. An initial sociodemographic data stating age, sex, religion, and occupation among others was obtained at admission. Thereafter, the records of all prescribed medications including the dates, route, doses, and frequencies were all noted for these in-patients during admission. The reviews and changes made in patients' medications between the days of evaluation were also noted to enable the estimation of number of drugs taken during admission and their costs.

Information concerning ADR occurrence and its nature was sought from attending physicians, patients, their relatives, and nursing staff. Charts and case notes were screened for records of ADRs. Clinical evaluation and assessment of laboratory results were also carried out. Repeated admission of the same patient was regarded as two separate admissions when separated by an interval of at least 1 month, otherwise such an admission was considered as a single admission and the interval excluded from the duration of hospital stay.[14]

The cost of medicines was estimated from unit cost of medicines obtained from the hospital pharmacy price list. The costs of the occasional medicines not available in the hospital pharmacy were also estimated using the same price list for uniformity as well, because the cost differences were not often remarkable.

The WHO definition of ADRs was used in the study: “any noxious and unintended response to a drug that occurs at doses used in humans for the prophylaxis, diagnosis or therapy of disease.”[15] ADRs were classified as mild (laboratory abnormality or symptoms not requiring treatment), moderate (laboratory abnormality or symptoms requiring treatment/admission to hospital or resulting in non-permanent disability), severe (laboratory abnormality or symptoms that were life threatening or resulted in permanent disability), and fatal (any ADR that resulted in patient's death regardless and irrespective of the initial severity grading assessment).[13],[14],[16] Causality of ADR was assessed using the WHO causality criteria[17] as well as the Naranjo algorithm,[18] while the ADRs were classified according to the System/Organ Class.[19]

Data collected were encoded and analyzed using the Statistical Package for the Social Sciences (SPSS) version 17 (released 2008; SPSS Inc., Chicago, IL, USA). Results were expressed as mean ± standard deviation or percentage values where necessary. The t-test and Chi-square test were used to compare means and proportions, respectively. The level of statistical significance was set at P < 0.05.

Ethical clearance was obtained from the UBTH Ethical Research Committee before commencing this study. The Ethical Clearance/Protocol Research Number issued for the study was ADM/E.22 A/VOL. VII/104. In addition, verbal informed consent was obtained from each of the patients whose medical records were used, while medical records for those who did not grant their informed consent were excluded from the study. Consent was sought from patient's relative where patient had impaired level of consciousness. Participants' confidentiality was respected and maintained by ensuring that no unauthorized person had access to the information on the data information sheets, that no information can be traced to the subjects (as coding system was used for the data information sheets instead of writing the patients' names on them) and no unauthorized use of information was made.


A total of 507 admitted patients were evaluated during this study. 269 (53.1%) were males, while 238 (46.9%) were females. The mean age for all patients was 48.9 ± 17.8 years (median = 46 years; range = 17–89 years). Though the mean age for females (49.5 ± 17.7 years) was higher than that of the males (48.3 ± 17.9 years), the difference was not statistically significant (t = −0.771, df = 505, P = 0.44). [Table 1] shows the age and sex distribution of the patients. [Table 1] reveals that those patients under 45 years of age were the most predominant with a frequency of 236 patients (46.5%), followed by those within the age group of 45–64 years with a frequency of 146 patients (28.8%). The elderly age groups (65 years and above) constitute 125 (24.7%) of the admitted patients.{Table 1}

[Table 2] shows the details of the medications causing ADRs. The most common drugs causing ADRs in order of frequency were insulin in 14 (27.5%), NSAIDs in 10 (19.6%), antihypertensives in 8 (15.7%), and antimalarials in 5 (9.8%). In addition, herbal medicines and antibacterials caused ADRs in 4 (7.8%) and 3 (5.9%) patients, respectively. The rest of the medications involved in ADRs are shown in [Table 2]. Furthermore, four fatal ADRs were observed during the study; in which herbal medicines caused two deaths, sulphadoxine/pyrimethamine combination (Maloxine®) caused one death, and iron dextran caused one death.{Table 2}

[Table 3] shows the summary for duration of hospital stay by different categories of patients. The mean duration of stay by all patients was 11.9 ± 11.3 days (median = 9 days). Females had a mean duration stay of 12.9 ± 12.3 days (median = 10 days) and stayed significantly longer than males who stayed a mean duration of 10.9 ± 10.2 days with a median of 7 days (t = −1.985, df = 505, P = 0.048). The young age group (that is those <45 years old), stayed a mean duration of 11.3 ± 9.3 days (median = 9 days), while the middle age group had a mean duration stay of 11.7 ± 9.7 (median = 10 days). The elderly age group (65 years and above) had a mean duration stay of 13.0 ± 15.7 days (median = 8 days), and appeared to have stayed longer than patients below 65 years of age (that is the young and middle age groups). However, this was not found to be statistically significant (t = −1.299, df = 505, P = 0.195).{Table 3}

Patients admitted solely because of an ADR (ADR out) had a significantly shorter duration of stay with a mean duration stay of 6.1 ± 3.7 days (median duration stay of 7 days) when compared to those without ADRs whose mean duration of stay was 11.6 ± 11.0 days (median duration stay of 8 days), and this was found to be statistically significant (t = 2.110, df = 472, P = 0.035). Those patients who developed ADRs during admission (ADR in) had a mean duration of stay of 18.3 ± 14.8 (median = 15 days). This was significantly longer than the duration of stay for patients without ADRs (t = −3.398, df = 487, P = 0.001) and also significantly longer than the duration for those who were admitted solely because of ADRs (t = 3.432, df = 49, P = 0.001).

[Figure 1] shows the frequency distribution pattern for patients experiencing ADRs versus their precipitant culprit drugs. Insulin caused ADRs in most number of patients (14, 27.5%). NSAIDs were next in frequency of causation with 10 (19.6%), followed by antihypertensives in 8 (15.7%). Antimalarials, herbal medicines, and antibacterials caused ADRs in 5 (9.8%), 4 (7.8%) and 3 (5.9%) patients respectively. The rest of the medications involved in ADRs are shown in [Figure 1].{Figure 1}

The systems/organs involved in ADRs are shown in [Figure 2]. The most frequently involved body system was the central nervous system (neurological) in 169 patients (33.3%). This was followed by the gastrointestinal system in 110 patients (21.6%), the skin (dermatological) in 89 patients (17.6%) and cardiovascular system in 40 patients (7.8%). The endocrine, respiratory and renal systems were equally affected in 20 patients (3.9%) each. In this study, it was observed that ADRs often affected multiple systems in a patient.{Figure 2}

The causality rating for the observed ADRs were assessed using both the WHO rating and the Naranjo algorithm as shown in [Table 4]. Using the WHO rating, certain cases were 10 (19.6%), probable cases were 17 (33.3%) and possible cases were 24 (47.1%). Using the Naranjo algorithm, definite cases were 9 (17.6%), probable cases were 19 (37.3%) and possible cases were 23 (45.1%).{Table 4}

An evaluation of some known risk factors for ADRs considered gender, age, number of medications used and number of comorbidities. Gender was not found to be a statistically significant risk factor for ADRs in this study (Chi-square = 0.371, P = 0.542). Age was found to be a statistically significant risk factor as the elderly age group (age ≥65 years) were more at risk compared to those patients <65 years (Chi-square = 10.152, P = 0.001). Number of medications used was also a significant risk factor for developing ADRs (Chi-square = 13.174, P = 0.018). Number of comorbidities was also found to be strongly associated with ADRs (Chi-square = 21.962, P < 0.001) [Table 5]. The association of ADRs with the number of medications being used by the patients or the association of ADRs with the number of patients' comorbidities was estimated by excluding patients who were admitted for ADR (patients who developed ADRs prior to admission).{Table 5}

ADRs were classified as mild (laboratory abnormality or symptoms not requiring treatment), moderate (laboratory abnormality or symptoms requiring treatment /admission to hospital or resulting in non-permanent disability), severe (laboratory abnormality or symptoms that were life threatening or resulted in permanent disability), and fatal (any ADR that resulted in patient's death regardless and irrespective of the initial severity grading assessment).[13],[14],[16] Most ADRs were mild and moderate in 21 (41.2%) cases and 24 (47.1%) cases, respectively. Severe ADRs occurred in 2 (3.9%) cases, while four (7.8%) cases were fatal ADRs.

[Table 6] shows that the number of patients admitted solely because of ADRs (ADR out) were 18, which accounts for 3.6% of admissions, while those that experienced ADRs during admission (ADR in) were 33 (6.5%). The total number of patients who had ADRs was 51, giving an ADR prevalence of 10.1% and an incidence of 6.5%. The case fatality rate for ADRs was 7.8% (4/51), while the ADR-related mortality rate was 0.8% (4/507).{Table 6}

The percentage of total cost of all in-patients' medications spent on treating ADRs was 1.9%. The cost of treating ADRs per patient with ADRs was N 3169.96 ± N 6348.77 ($24.38±$48.84), while the mean ADRs treatment cost per admitted patient was N 318.87 ($2.45). As at the time of this study, the currency exchange rate at the international market was $1.00 US dollar equivalent to about N 130.00 Nigerian Naira.


This study was designed to evaluate the incidence and prevalence of ADRs among medical inpatients in a Nigerian University Teaching Hospital, and to further highlight the pattern of medications most frequently causing ADRs in this clinical practice setting. ADRs occurring during admission (incidence) was observed in 6.5% of admitted patients, while 3.6% of the patients were admitted due to an ADR. The prevalence of 10.1%, is similar to the ADR prevalence obtained in some European studies ranging from 6.6% to 11%.[20] A meta-analysis in the United States by Lazarou et al. obtained an incidence of 6.7% for serious ADR among in-patients. The incidence and prevalence values observed in this study thus appears to be consistent with values in previous studies done in Switzerland, France, and the UK.[21]

The ADR-related mortality rate of 0.8% was somewhat between values obtained in a UK study (0.15%) and to that obtained in a Swiss study (1.4%).[22] The lower rate observed in the UK study can be attributed to the fact that the study looked at ADRs causing admissions only. The Swiss study showed a higher mortality, but also looked at both ADRs causing admission and that occurring during admission.[22]

Patients experiencing ADR during hospitalization (ADR in) stayed significantly longer than those without ADRs (median stay of 15 days versus 8 days respectively). ADRs have been found to prolong duration of hospital stay in several studies.[23] The median length of stay obtained for patients with ADR in and those without ADR (15 days and 8 days respectively) is similar to results obtained in an in-patient study by Davies et al. (14.5 days and 8 days respectively). Patients admitted solely because of ADRs (ADR out) had a statistically significant shorter duration of hospital stay (median = 7 days) than those patients without ADR that stayed a median duration of 8 days and also much shorter than those patients that developed ADR during hospitalization (median duration of 15 days). The finding of shorter duration of hospital stay for patients with ADR causing admission (occurring outside the hospital) compared to those without ADR and those with ADR occurring during admission has been noted in a French study. This shorter duration of hospital stay is related to the fact that there is a shorter diagnostic time for ADRs, in effect a shorter time was spent looking for the cause of morbidity since this was obvious from initial clinical evaluation,[24] especially as most of the ADRs were mild (41.2%) or moderate (47.1%). Furthermore their clinical management was essentially observational care and measures such as stopping or adjusting drug dosage.[25] However, a few of the patients required more intense treatment with prolonged stay.

Gender was not found to be a statistically significant risk factor associated with ADR in this study. This finding here differs from what has been observed in other several studies.[26] The association of gender and ADRs like other aspects of ADRs is not well characterized among Nigerians and may differ. Some other known risk factors for ADR however were found to be significantly associated with adverse drug reactions in this study. These were age (elderly),[27] number of medications (polypharmacy)[28] and number of co-morbidities.[29]

The most commonly affected system by ADRs was the central nervous system, probably because two out of the first three topmost implicated classes of medications causing ADRs manifest with symptoms referable to the central nervous system.[30] For example insulin leads to impaired consciousness due to hypoglycaemia, while antihypertensives manifest mainly with postural dizziness and headache due to postural hypotension and increased intracranial pressure respectively. The next most common system involved was the gastrointestinal system,[31] and this may be related to the fact that NSAIDs[32] which constituted the second most common class of medications involved in ADRs usually manifest with problems referable to the gastrointestinal system. In fact, the systems largely affected followed the pattern of medications causing ADRs.[33] Fattinger et al. found the gastrointestinal and the hematological systems as the first and second most commonly affected respectively among inpatients. The pattern of morbidity and thus medication used differ in both settings, therefore the pattern of ADRs will be different.[34]

Mild and moderate ADRs were far more frequent (41.2% and 47.1% respectively) when compared to severe and fatal cases. This pattern is similar to findings in other studies.[35]

The two methods used to ascertain causality rate for ADRs caused by a suspected drug, the WHO and Naranjo algorithms, showed similar causality ratings, strengthening the ascribed causality ranking.[36]

The average cost of medications for treating ADRs among in-patients was N 3169.96 ($24.38 or £ 12). Arulmani et al. in India obtained an average cost of £ 6 which was lower. The cost of medications may differ being cheaper in India that is a large manufacturer and exporter of drugs to other countries including Nigeria.[37] The percentage cost of all in-patients' medications spent on treating ADRs (1.9%) suggests that ADRs cost a lot to the health care system as shown in previous studies.[38] It is noteworthy that this study considered only the cost of drug therapy. Costs of bed space, investigations, meals and other miscellaneous costs were not evaluated.


The incidence of ADRs in this Nigerian University Tertiary Teaching Hospital (patients developing ADRs during admission) was 6.5%, while the overall prevalence for ADRs was 10.1%. These findings are consistent to some extent with several other studies done worldwide. This study provides a profiling of the ADRs among medical in-patients as well as the cost of medications for treating them in such settings. More proactive large scale studies are required to further characterize the burden of drug related problems in Nigeria and sub-Saharan West Africa at large.


The authors of this research work want to specially acknowledge and thank the Almighty God for granting us wisdom and understanding to prepare this research work for publication.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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