Drug Distribution, Hospital Formulary, TDM & Medication Adherence
This unit covers the operational aspects of hospital pharmacy services. Drug distribution systems (individual prescription, floor stock, and unit dose systems), hospital formulary (definition, contents, preparation, and revision process), therapeutic drug monitoring (need, factors, and Indian scenario), medication adherence (causes of non-adherence and pharmacist intervention), and patient medication history interview (importance and forms used).
Syllabus & Topics
- 1Drug Distribution to Inpatients: Drug distribution system: the method by which medications are delivered from the pharmacy to the patient’s bedside. Goals: (1) Safe and timely delivery. (2) Minimize medication errors. (3) Cost-effective drug use. (4) Accountability of drug usage. Types of systems: (1) Individual Prescription Order System: physician writes individual prescription → sent to pharmacy → pharmacist dispenses for each patient → medication sent to ward. Advantages: pharmacist reviews each order, better inventory control, fewer errors. Disadvantages: slow (delay in medication delivery), more pharmacist workload, may delay emergency medications. (2) Floor Stock System (Ward Stock): bulk quantities of frequently used drugs stocked on each ward/floor. Nurse selects and administers from ward stock. Advantages: immediate availability, fast. Disadvantages: high pilferage risk, storage issues on ward, more medication errors (no pharmacist check), higher drug wastage (expiry), poor inventory control.
- 2Unit Dose Drug Distribution System: UDDDS: most advanced and safest system. Each dose of medication is individually packaged, labeled (drug name, strength, lot, expiry), and dispensed for a specific patient for a specific administration time (typically 24-hour supply). Process: (1) Physician writes order. (2) Pharmacist receives, reviews for DI/contraindications/dose. (3) Pharmacy prepares individual doses in unit dose packages. (4) Filled in patient-specific cassettes/drawers in medication cart. (5) Cart exchanged every 24 hours. (6) Nurse administers from patient’s specific drawer. Advantages: ↓medication errors (pharmacist reviews every order), ↓drug diversion/pilferage, ↑drug accountability, ↓inventory on wards, ↓drug wastage (unused doses returned to pharmacy), accurate charge to patient. Disadvantages: ↑pharmacy workload, requires trained staff, ↑initial investment (packaging equipment, carts). Charging & Labeling: each unit dose labeled with patient name, drug, dose, time. Charges documented per dose → accurate billing.
- 3Dispensing to Ambulatory & Controlled Drugs: Ambulatory patients (outpatients — OPD): prescription brought to OPD pharmacy counter → pharmacist reviews → dispenses → counsels patient on use, side effects, storage. OPD dispensing differences: patient takes medication home → greater counseling need, written instructions, follow-up. Controlled drugs dispensing: (1) Schedule X drugs (narcotics, psychotropic substances): stored in double-locked safe. Separate register maintained (date, patient, prescriber, drug, quantity, balance). (2) Prescription requirements: on Schedule X form, prescriber’s full details, cannot be refilled. (3) In hospital: requisition from ward → authorized by medical officer → dispensed by pharmacist → documented in controlled drug register → ward maintains consumption record → empty ampoules/vials returned. (4) Physical count/audit regularly. (5) Any discrepancy investigated immediately. Governed by NDPS Act, 1985.
- 4Hospital Formulary: Hospital formulary: a continually revised compilation of pharmaceuticals (including important information about their use) reflecting the current clinical judgment of the medical staff. Purpose: guide rational drug use, control drug costs, ensure drug availability. Formulary vs Drug list: Drug list = simple LIST of drugs approved for use in hospital (names only). Hospital formulary = comprehensive document with drug INFORMATION (indications, dosing, side effects, interactions, cost). Contents: (1) General information (hospital policy, pharmacy hours). (2) Drug monographs (alphabetical or therapeutic classification): generic name, brand names, pharmacological class, indications, dosage/route, contraindications, adverse effects, interactions, cost, formulary status. (3) Special sections: antimicrobial guidelines, anticoagulation protocol, TPN guidelines, emergency drug list. (4) Appendices: IV compatibility charts, dose adjustments (renal/hepatic), pregnancy/lactation drug safety.
- 5Hospital Formulary – Preparation & Revision: Preparation: (1) PTC (Pharmacy and Therapeutics Committee) is responsible. (2) Drug selection based on: efficacy (evidence-based), safety profile, cost-effectiveness, availability, therapeutic duplication avoidance. (3) Each drug undergoes formal review (literature evaluation). (4) Categories: formulary (approved — unrestricted), restricted (approved — requires specialist authorization), non-formulary (not approved — exceptional case-by-case). Revision: (1) Continuous process — formulary is a LIVING document. (2) Addition of new drugs: physician request → PTC review → literature evaluation → trial period → permanent addition or rejection. (3) Deletion: if drug withdrawn from market, superior alternative available, safety concerns, or low utilization. (4) Annual comprehensive review recommended. (5) Electronic formulary: online/app-based → real-time updates, drug interaction checking, prescribing decision support.
- 6Therapeutic Drug Monitoring (TDM): TDM: measurement of drug concentrations in blood (usually plasma/serum) to optimize individual patient drug therapy. Need for TDM: required when: (1) Narrow therapeutic index (small difference between therapeutic and toxic concentrations). (2) Poor correlation between dose and plasma level. (3) Wide interpatient variability in pharmacokinetics. (4) Target concentration well-defined. (5) Difficulty in interpreting clinical signs of toxicity vs disease progression. Drugs commonly monitored: Aminoglycosides (gentamicin, amikacin — nephro/ototoxicity), Vancomycin, Phenytoin (nonlinear kinetics), Carbamazepine, Valproic acid, Lithium (narrow TI), Theophylline, Digoxin, Cyclosporine, Tacrolimus, Methotrexate. Factors: (1) Correct sampling time (trough level — just before next dose; peak — 1-2 hours post-dose). (2) Steady state achieved (4-5 half-lives). (3) Patient factors: age, weight, organ function, drug interactions.
- 7TDM – Indian Scenario & Medication Adherence: Indian TDM scenario: (1) Limited availability — only major teaching hospitals and corporate hospitals have TDM facilities. (2) Cost: assays expensive (HPLC, immunoassay). (3) Growing awareness: NABH accreditation encourages TDM for critical drugs. (4) Common monitoring in India: serum creatinine-based dose adjustment (aminoglycosides), phenytoin levels (epilepsy clinics), lithium levels (psychiatry), cyclosporine (transplant centers). Medication adherence (compliance): extent to which a patient’s medication-taking behavior corresponds with prescribed regimen. Causes of non-adherence: (1) Patient factors: forgetfulness, lack of understanding, cultural beliefs, fear of side effects, asymptomatic condition. (2) Drug factors: complex regimen (multiple drugs, multiple times), adverse effects, cost, taste. (3) Healthcare system: poor communication, lack of counseling, long waiting times. Pharmacist’s role: simplify regimen, use pill organizers, provide written instructions, follow-up calls, medication reminders, adherence assessment (pill counts, refill records).
- 8Patient Medication History Interview: Medication history: comprehensive record of all medications a patient is currently taking and has taken in the past. Why needed: (1) Identify potential drug interactions with new therapy. (2) Detect allergies/previous ADRs. (3) Identify medication-related problems (non-adherence, inappropriate use). (4) Ensure continuity of medication at admission/discharge. (5) Medication reconciliation (compare admission meds with in-hospital orders). Interview process: (1) Introduce yourself, explain purpose. (2) Ask about: all prescription drugs, OTC medications, herbal/dietary supplements, drug allergies (type of reaction), previous ADRs. (3) For each drug: name, dose, frequency, duration, reason for use, effectiveness, side effects experienced. (4) Social history: alcohol, smoking, recreational drugs (can affect drug therapy). (5) Document systematically on medication history form. Medication interview forms: standardized forms with sections for each category — demographics, current medications (table format), allergies, OTC use, herbal use, compliance assessment, social history. Should be completed within 24 hours of admission.
Learning Objectives
Exam Prep Questions
Q1. Why is the Unit Dose system considered the safest?
The Unit Dose Drug Distribution System (UDDDS) is safest because: (1) PHARMACIST reviews every prescription before dispensing — catches drug interactions, wrong doses, allergies. (2) Each dose is individually packaged and labeled for a SPECIFIC patient — reduces wrong-drug/wrong-patient errors. (3) Minimal drug handling by nurses — they simply administer from the patient’s cassette rather than selecting from bulk stock. (4) Any unused doses are RETURNED to pharmacy — complete drug accountability. Studies show UDDDS reduces medication errors by up to 80% compared to floor stock systems.
Q2. What is therapeutic drug monitoring and when is it necessary?
TDM is measuring drug levels in the blood to ensure the concentration is within the “therapeutic window” — above the minimum effective concentration (MEC) but below the minimum toxic concentration (MTC). It’s necessary when: (1) The drug has a NARROW therapeutic index (e.g., digoxin: therapeutic 1-2 ng/mL, toxic >2 ng/mL — a small increase can be fatal). (2) The drug shows nonlinear kinetics (e.g., phenytoin — small dose increase → disproportionate level increase). (3) Patient shows unexpected response (no effect at usual dose, or toxicity at normal dose). (4) Organ dysfunction alters drug clearance (renal failure → aminoglycoside accumulation).
Q3. What is medication reconciliation?
Medication reconciliation is the process of comparing the medications a patient is taking at HOME with what is prescribed at each TRANSITION of care (admission, transfer, discharge). Steps: (1) Obtain complete medication history (all drugs from all sources). (2) Compare with admission/transfer/discharge orders. (3) Identify discrepancies (omissions, duplications, doses changed, interactions). (4) Resolve discrepancies with prescriber. (5) Document. This prevents medication errors during transitions — studies show up to 67% of patients have at least one discrepancy. The pharmacist is ideally positioned to lead medication reconciliation.