Table 1.

Summary of the main and subcategories of the Pharmaceutical Society of Singapore (PSS) Intermediate and Long-Term Care (ILTC) Pharmacists Workgroup Drug-Related Problem (DRP) Classification System.

No.	Main Categories	Subcategories	Remarks
1	Indication	(a) Drug use without indication	Patient is taking a drug without a valid medical indication
		(b) Untreated indication	Patient has medical problem that requires drug therapy but is not receiving medication for that indication Examples: • Conditions where patients are in need of prophylaxis or premedications but are not receiving them • Combination therapy required for synergistic effect but only one drug is used, e.g., antibiotics, chemotherapy
		(c) Therapeutic duplication	Inappropriate duplication of therapeutic group or active ingredients
2	Improper drug selection	(a) Contraindication	Patient has contraindications to the drug prescribed
		(b) More cost-effective drug available	Similarly effective alternative is available at a cheaper price
3	Dosage	(a) Drug dose is too low	Dosage regimen is not individualized for a specific patient, taking into consideration the appropriate drug, disease, and patient-specific information Examples: • Dosage regimen adjustment for patients with renal/hepatic impairment • Dose adjustment when switching between formulations, e.g., phenytoin tablets and syrup, controlled release to immediate release formulation
		(b) Drug dose is too high
		(c) Dosage regimen not frequent enough
		(d) Dosage regimen too frequent
4	Duration	(a) Duration of treatment too short	Patient is prescribed a drug for a duration that is clinically inappropriate
		(b) Duration of treatment too long
5	Drug form	(a) Inappropriate formulation/drug form	Formulation/drug form is not individualized to patient, e.g., sustained release medication given to patient with nasogastric tube
		(b) Inappropriate change in brand	Different preparations of the same drug may not be bioequivalent. For drugs that have a narrow therapeutic window, switch in brands can affect clinical outcomes, e.g., levothyroxine
6	Adverse drug reaction	(a) ADR (nonallergic)	Consistent with pharmacologic actions of the drug, occur commonly, are usually dose dependent, and are fairly predictable
		(b) ADR (allergic)	Allergic or idiosyncratic reactions that are independent of drug pharmacology. Rare, not dose related, and cannot be predicted. (To be differentiated from wrong drug used where patient has been experiencing allergic reactions for a period of time versus ADR, where patient is taking medication for first time and experiences allergic reaction)
7	Drug interaction	(a) Drug–drug interaction	E.g., Clarithromycin and simvastatin
		(b) Drug–food interaction	E.g., Dairy products and levothyroxine
		(c) Drug–lab interaction	E.g., Anaemia and HbA1c results
		(d) Drug–disease interaction	Clinically significant interaction between patient’s pre-existing medical conditions and drug prescribed
8	Others	(a) Lab monitoring	• Lack of routine lab monitoring, which is required for adjustment of drug dose, monitoring of side effects etc., e.g., random blood glucose, HbA1C, LFTs, lipid Panel, renal panel • Lab monitoring not performed at an interval that is clinically appropriate
		(b) RMR—related	E.g., illegibility, ambiguity, clarification of drug order, incomplete information, and lack of doctor’s signature at RMR, lack of nurses’ signature to sign on/off medication, lack of nurses’ signature to indicate medications served, inappropriate use of legends
		(c) Expired medication/inappropriate storage	• Patient given expired medication or medication that have not been stored properly • Patient misses dose as a result of expired or inappropriately stored medication
		(d) Nonavailability of medication	• Patient or family unable to afford medication, thus drug not made available • Drug prescribed is not available in Singapore or exemption medication or unable to be supplied to the institution • Inability to get the medication in time
		(e) Others—please state reason	Any unique/additional cases of DRPs that do not fall under any of the categories above • Please kindly specify the reason for putting it in this category and/or describe the DRP