Table 2.

Characteristics of excluded studies.

Title	Authors	Year	Country	Aim	Methods	Findings	Reason for Exclusion
The traditional method of oral as-needed pain medication delivery compared to an oral patient-controlled analgesia device following total knee arthroplasty [33]	Lambert, T.L., Cata, D.M.	2014	USA	To compare postoperative pain control afforded by usual care—PRN oral pain medication—with the new oral patient-controlled analgesia device.	Quantitative, survey of thirty patients in each group.	The device offered a significant improvement: less pain, less interference with general activity, mood, sleep and appetite during the first 2 post-operative days and 24 h before discharge.	Survey
As required versus fixed schedule analgesic administration for postoperative pain in children [34]	Hobson, A., Wiffen, P.J., Conlon, J.A.	2015	UK	To assess the efficacy of PRN versus fixed schedule analgesia administration for the management of postoperative pain in children under the age of 16 years.	Systematic review, three RCTs of 246 children aged lower than 16 years.	No conclusions were drawn, due to limited evidence.	Systematic review
Patient controlled opioid analgesia versus non-patient controlled opioid analgesia for postoperative pain [35]	McNicol, E.D., Ferguson, M.C., Hudcova, J.	2015	USA	To assess efficiency and safety of PCA in comparison with non-patient controlled analgesia of PRN for relieving postoperative pain.	Meta-analysis, 1725 participants in the PCA group and 1687 participants in the non-patient controlled group.	PCA was associated with significantly: lower pain scores on visual analogue scales (VAS), greater satisfaction with opioids, higher consumption of opioids and higher incidence of pruritus.	Meta-analysis
Patient controlled opioid analgesia versus conventional opioid analgesia for postoperative pain [36]	Hudcova, J., McNicol, E., Quah, C., Lau, J., Carr, D.B.	2006	USA	To investigate the efficiency of PCA in comparison with conventional analgesia for controlling postoperative pain.	Meta-analysis, 2023 participants in the PCA group and 1838 participants in the non-patient controlled control group.	PCA afforded better pain control and patient satisfaction than conventional opioid analgesia.	Meta-analysis
The effects of as-needed nalmefene on patient-reported outcomes and quality of life in relation to a reduction in alcohol consumption in alcohol-dependent patients [37]	François, C., Rahhali, N., Chalem, Y., Sørensen, P., Luquiens, A., Aubin, H.J.	2015	France	To evaluate the effect of as-needed nalmefene vs. placebo on health-related quality of life (HRQoL) in patients with alcohol dependence.	Quantitative, post hoc subgroup analysis of 2 RCTs with 667 patients.	The majority of patients with as-needed nalmefene had significant improvements in HRQoL drinking behaviour and total alcohol consumption.	All arms received a preparation PRN. Comparisons were between nalmefene and placebo.
Systematic review of the predisposing, enabling and reinforcing factors which influence nursing administration of opioids in the postoperative period [38]	Yin, H.H., Tse, M.M., Wong, F.K.	2015	China	To describe factors affecting nurses’ decision-making related to PRN administration of opioid analgesics for postoperative pain.	Systematic review of 39 qualitative and quantitative studies.	Nurses’ knowledge of pain management and opioid analgesia was the main perceived barrier to administration of effective pain relief.	Systematic review
A randomized clinical trial of the efficacy of a self-care intervention to improve cancer pain management [39]	Rustøen, T., Valeberg, B.T., Kolstad, E., Wist, E., Paul, S., Miaskowski, C.	2014	Norway	To assess the efficacy of the PRO-SELF Pain Control Program on pain control and opioid intake in comparison with usual care among out-patients with bony metastases.	Quantitative, a clinical trial of self-care, 87 participants in the PRO-SELF group and 92 participants in the control group.	Both groups reported significant reductions in pain intensity scores and in hours per day in pain. Total opioid consumption increased over time in both groups.	No focus on PRN.
Post-operative pain: the impact of prescribing patterns on nurses’ administration of analgesia [40]	Simons, J., Moseley, L.	2008	UK	To measure the difference between prescribed analgesia and administered analgesia in children during the first 24 h after surgery.	Quantitative, a retrospective chart review of 175 children.	Less paracetamol was administered when prescription was on a PRN basis.	Retrospective cohort
Pro re nata (as needed) medication in nursing homes: the longer you stay, the more you get? [41]	Dörks, M., Schmiemann, G., Hoffmann, F.	2016	Germany	To examine predictors of PRN administration in nursing homes.	Quantitative, cross-sectional review of medicines charts of 852 residents in 21 homes.	Most (74.9%) residents were treated with at least one PRN medication. Acetaminophen (paracetamol) was the drug most commonly administered PRN, prescribed to 33.9% residents. PRN prescription was predicted by duration of residence and polypharmacy.	A cross sectional chart review
Pain medication in German nursing homes: a whole lot of metamizole [42]	Hoffmann, F., Schmiemann, G.	2016	Germany	To assess the use of analgesics, particularly metamizole (not available in UK) in nursing homes.	Quantitative, cross-sectional review of medicines charts of 852 residents in 21 homes.	More than half the residents received at least one analgesic. The most frequently prescribed medications were metamizole and paracetamol, the latter as PRN. The proportion of residents receiving metamizole increased with age. Patient safety concerns were raised by the authors.	A cross sectional, retrospective, chart review
Examining trends in the administration of “as needed” medications to inpatients with behavioural and psychological symptoms of dementia [43]	Neumann, R.D., Faris, P., Klassen, R.	2015	Canada	To identify trends in the administration of PRN medications to inpatients with dementia.	Quantitative, retrospective review of medicines charts, 170 inpatients with dementia in neurology wards.	Younger patients received more PRN prescriptions. PRN prescriptions were more common following evening shift change or during weekends. Where patients were receiving regularly scheduled medication from the same drug class, there was a risk of double dosing, exceeding dosage guidelines.	Retrospective chart review
Effect of hospice nonprofessional caregiver barriers to pain management on adherence to analgesic administration recommendations and patient outcomes [44]	Mayahara, M., Foreman, M.D., Wilbur, J., Paice, J.A, Fogg, L.F.	2015	USA	To assess hospice nonprofessional caregivers’ adherence to analgesic administrations and patient outcomes.	Quantitative, a short-term longitudinal correlational study of 46 patient–caregiver dyads.	Higher caregiver adherence to PRN analgesic regimens was associated with lower patient pain intensity and higher patient quality of life.	A longitudinal study
Behavioural and psychological symptoms of dementia: how long does every behaviour last and are particular behaviours associated with PRN antipsychotic agent use? [45]	Voyer, P., McCusker, J., Cole, M.G., Monette, J., Champoux, N., Ciampi, A., Belzile, E., Richard, H.	2014	USA	To assess the course of behavioural and psychological symptoms of dementia (BPSD) over a period of 6 months.	Quantitative, a secondary analysis of a prospective observational cohort study of 146 nursing home residents from 7 homes.	PRN administration of antipsychotic medication was associated with nocturnal BPSD and requesting help unnecessarily. Within 3 months, most BPSD were resolved by usual care and use of PRN antipsychotic medication was not associated with behaviours that put the residents or their caregivers at risk.	Prospective cohort
PRN prescribing in psychiatric inpatients: potential for pharmacokinetic drug interactions [46]	Davies, S.J., Lennard, M.S., Ghahramani, P., Pratt, P., Robertson, A., Potokar, J.	2007	UK	To assess the prevalence of PRN regimens and the potential interactions involving PRN medications in mental health wards.	Quantitative, a cross-sectional survey of prescription charts of 323 inpatients.	In 2089, 48% of prescription items were on a PRN basis. One fifth of patients were prescribed drug combinations interacting via CYP2D6 or CYP3A4, with potential for clinical harm. This included one or more drugs prescribed on a PRN basis.	A cross-sectional review of medicines charts
Administration of PRN medications and use of non-pharmacologic interventions in acute geropsychiatric settings: implications for practice [24]	Lindsey, P.L., Buckwalter, K.C.	2012	USA	To evaluate the effect of PRN psychotropic medications and non-pharmacological interventions to manage psychological symptoms in older adults.	Quantitative, a retrospective chart audit of 108 medical records for patients ≥ 55 years or older admitted to two inpatient geropsychiatric units over a 3-month period.	Insufficient documentation was found regarding PRN administrations and non-pharmacological interventions to identify the best clinical practice.	A retrospective chart audit and review
Nurses’ opinions on appropriate administration of PRN range opioid analgesic orders for acute pain [23]	Gordon, D.B., Pellino, T.A., Higgins, G.A., Pasero, C., Murphy-Ende, K.	2008	USA	To investigate nurses’ opinions of the appropriate implementation of dose-range orders.	Quantitative, online survey of 602 nurses in a medical centre.	Nurses who attended pain management courses were more likely to respond appropriately to questions on patient management than those who did not.	A cross-sectional survey
A study of the prescription and administration of sedative PRN medication to older adults at a secure hospital [16]	Haw, C., Wolstencroft, L.	2014	UK	To investigate the risks of polypharmacy, high dose medications and adverse drug reactions to sedative PRN medications.	Quantitative, review of patients’ records of 92 older adults and 242 working age patients.	Lorazepam was the most commonly administered PRN drug and violence was the most common reason for administrating it. Documentation of adverse drug reactions and patient outcomes was considered suboptimal. Older people received less PRN medication and lower doses.	A retrospective record review
Pro re nata medication for psychiatric inpatients: time to act [21]	Hilton, M.F., Whiteford, H.A.	2008	Australia	To evaluate PRN administration of psychotropic medications in term of mental health policies, professional ethics and PRN administration protocols.	Literature review	Development of best practice guidelines is an essential need for the use of PRN administration.	Literature review