4.1 Non-Sterile Compounding & Beyond-Use Dating (NAPRA Standards)

4.1 Non-Sterile Compounding & Beyond-Use Dating (NAPRA Standards)

Pharmaceutical compounding represents a core professional competency for Canadian pharmacists. When commercial drug products are unavailable, unsuitable for a patient's clinical needs (e.g., pediatric dosing requirements, severe excipient allergies, dysphagia), or discontinued, pharmacy professionals formulate customized therapeutic preparations. In Canada, pharmacy compounding is regulated by provincial and territorial pharmacy regulatory authorities (PRAs) operating under national standards established by the National Association of Pharmacy Regulatory Authorities (NAPRA), specifically the Model Standards for Pharmacy Compounding of Non-Sterile Preparations.

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Regulatory Framework: Compounding vs. Manufacturing

A critical distinction on entry-to-practice examinations is the legal boundary separating pharmacy compounding from commercial pharmaceutical manufacturing under Health Canada's Policy on Manufacturing and Compounding Drug Products in Canada (POL-0051):

• Compounding: Occurs within a bona fide patient-pharmacist-prescriber relationship, triggered by a specific prescription or an anticipated historical prescription demand in limited quantities. Compounded preparations do not possess a Drug Identification Number (DIN) and cannot be distributed commercially for wholesale resale.
• Manufacturing: Involves the large-scale mass production of standardized drug products for broad commercial distribution. Manufacturing falls exclusively under federal jurisdiction (Food and Drugs Act, Good Manufacturing Practices [GMP], and Health Canada Establishment Licensing).

Patient-Specific Need / Prescription ---> Pharmacy Compounding (Provincial Regulatory Authority / NAPRA)
Mass Distribution / Resale Without Prescriptions ---> Commercial Manufacturing (Health Canada / GMP / DIN)

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NAPRA Non-Sterile Compounding Risk Levels: A, B, and C

NAPRA's Model Standards for Pharmacy Compounding of Non-Sterile Preparations (2018) set three levels of requirements. The pharmacist chooses the level through a documented risk assessment that weighs the complexity of the preparation, the hazard classification of each ingredient (NIOSH list, WHMIS safety data sheet), the quantity, how often it is compounded, and the physical form (powders aerosolize; creams do not). NAPRA's decision tree routes occasional small quantities of lower-risk hazardous drugs to Level A or B, and Group 1 drugs to Level C:

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Beyond-Use Dating (BUD) Standards

The Beyond-Use Date (BUD) is the date or time after which a compounded preparation must not be used, administered, or stored. Unlike a manufacturer's expiration date—which is determined through extensive real-time and accelerated stability testing in final commercial packaging—a BUD is assigned conservatively by the compounding professional based on chemical stability, physical degradation risks, and microbial vulnerability.

Default Maximum BUDs (NAPRA / USP <795> Framework)

In the absence of published, stability-indicating analytical studies or official pharmacopoeial monographs, compounders must strictly observe the following conservative default BUD parameters:

                                  NON-STERILE COMPOUNDED PREPARATION
                                                 │
               ┌─────────────────────────────────┴─────────────────────────────────┐
               ▼                                                                   ▼
     AQUEOUS FORMULATION                                                NON-AQUEOUS FORMULATION
               │                                                                   │
     ┌─────────┴─────────┐                                                         ▼
     ▼                   ▼                                                   MAXIMUM 6 MONTHS
ORAL LIQUID       TOPICAL / MUCOSAL                                         (180 Days) or earliest
MAX 14 DAYS          MAX 30 DAYS                                              API expiry date
(Refrigerated:       (Controlled Room Temp:                                 (Room Temp: 20°C–25°C)
 2°C–8°C)             20°C–25°C)                                             

1. Water-Containing Oral Formulations:

   • Maximum BUD: 14 days
   • Storage Requirement: Controlled refrigerated storage ($2^\circ\text{C}$ to $8^\circ\text{C}$)
   • Rationale: Water acts as a catalyst for chemical hydrolysis and provides a fertile medium for bacterial and fungal proliferation. Refrigeration significantly slows hydrolytic reaction kinetics and microbial growth.
   • Examples: Compounded pediatric oral suspensions (e.g., omeprazole oral suspension in sodium bicarbonate, baclofen oral suspension).

2. Water-Containing Topical, Dermal, and Mucosal Liquids and Semisolids:

   • Maximum BUD: 30 days
   • Storage Requirement: Controlled room temperature ($20^\circ\text{C}$ to $25^\circ\text{C}$)
   • Rationale: Topical applications carry lower risks of systemic microbial infection compared to ingested liquids, but microbial bioburden and phase separation remain significant risks over time.
   • Examples: Compounded hydrophilic creams, lotions, topical gels, and mucosal ointments.

3. Non-Aqueous Formulations:

   • Maximum BUD: 6 months (180 days) or the earliest expiration date of any raw active pharmaceutical ingredient (API), whichever is shorter.
   • Storage Requirement: Controlled room temperature ($20^\circ\text{C}$ to $25^\circ\text{C}$)
   • Rationale: In the absence of water (water activity $a_w < 0.60$), microbial growth is inhibited, and hydrolytic degradation cannot occur. Chemical oxidation and physical stability dictate longevity.
   • Examples: Anhydrous ointments (white petrolatum base), polyethylene glycol (PEG) troches, gelatin capsules containing dry powder mixtures, and oleaginous suppositories (cocoa butter).

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Master Formulation Records vs. Compounding Records

NAPRA standards mandate two distinct, auditable documentation systems to guarantee consistency, traceability, and quality assurance in compounding operations:

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Equipment Calibration, Maintenance & Volumetric Accuracy

Compounding precision depends directly on the proper maintenance, calibration, and operational boundaries of pharmacy equipment:

1. Prescription Balances and the Minimum Weighable Quantity (MWQ)

Electronic prescription balances must be verified daily using National Institute of Standards and Technology (NIST) Class 1 or Class 2 standard weights. To prevent unacceptably high percentage errors when weighing small quantities, compounders apply the Minimum Weighable Quantity (MWQ) formula:

$\text{MWQ} = \frac{\text{Sensitivity Requirement (SR)}}{\text{Maximum Acceptable Error Percentage (0.05)}} = \text{SR} \times 20$

For a traditional Class A torsion balance or electronic balance with a sensitivity requirement of $6\text{ mg}$ and an acceptable error of $5\%$ ($0.05$):

$\text{MWQ} = \frac{6\text{ mg}}{0.05} = 120\text{ mg}$

If a prescription requires less than $120\text{ mg}$ of active drug powder on such a balance, the compounder cannot weigh it directly; an aliquot dilution (solid-in-solid or solid-in-liquid) must be performed using an inert diluent (e.g., lactose) to ensure the weighed mass meets or exceeds the MWQ.

2. Volumetric Glassware and the 20% Capacity Rule

Volumetric measurements must be conducted using certified pharmaceutical glassware:

• Cylindrical Graduates: Possess uniform internal diameter and provide high volumetric accuracy throughout the column. Always preferred over conical graduates for precise measurements.
• Conical Graduates: Have flared sides; measurement accuracy decreases rapidly as volume increases. Used primarily for facilitating mixing or dissolution, not precision measurement.
• The 20% Volumetric Rule: A liquid volume must never be measured in a graduate cylinder if the volume is less than 20% of the cylinder's rated capacity (e.g., do not measure less than $20\text{ mL}$ in a $100\text{ mL}$ cylinder, or less than $10\text{ mL}$ in a $50\text{ mL}$ cylinder). Measuring below 20% introduces unacceptable meniscus parallax and surface tension errors.
• Small Volumes (< 5 mL): Must be measured using calibrated oral syringes, analytical pipettes, or micropipettes rather than graduated cylinders.

Meniscus Reading: Read at the EXACT BOTTOM of the concave liquid curve at eye level.
Rule of Thumb: Select the smallest graduate cylinder that will hold the desired volume (> 20% capacity).

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Pharmaceutical Excipients: Roles and Physical Pharmacy

Excipients are inactive substances intentionally added to active drug substances to facilitate manufacturing, enhance physical stability, prevent microbial proliferation, improve palatability, or optimize bioavailability:

1. Suspending Agents and Stokes' Law

In pharmaceutical suspensions (coarse dispersions of insoluble solid particles in liquid media), particles tend to settle over time. Sedimentation rate is governed by Stokes' Law:

$v = \frac{2 r^2 (\rho_p - \rho_f) g}{9 \eta}$

Where $v$ is sedimentation velocity, $r$ is particle radius, $\rho_p$ is particle density, $\rho_f$ is fluid density, $g$ is gravitational acceleration, and $\eta$ is dynamic viscosity of the medium.

• Mechanism: Suspending agents (e.g., methylcellulose, carboxymethylcellulose sodium, xanthan gum, acacia, carbomers, commercial vehicles like Ora-Plus) are hydrophilic polymers that increase vehicle viscosity ($\eta$). By increasing $\eta$ and reducing particle size ($r$) via trituration, sedimentation velocity ($v$) is minimized, preventing rapid caking and ensuring uniform dosing upon shaking.

2. Wetting and Levigating Agents

Hydrophobic drug powders (e.g., sulfur, hydrocortisone) trap air pockets on their surfaces, causing them to float on liquid vehicles rather than dispersing. Wetting agents lower the interfacial tension and contact angle between the solid particles and liquid vehicle, displacing entrapped air.

• Levigation: The process of reducing particle size and dispersing powders into a smooth paste using a small amount of liquid (levigating agent) in which the solid is insoluble.
• Polarity Matching Rule:
  • For water-soluble / water-washable bases (e.g., vanishing cream, hydrophilic petrolatum, polyethylene glycol): use glycerin, propylene glycol, or purified water.
  • For oleaginous / greasy bases (e.g., white petrolatum, mineral oil bases): use mineral oil.

3. Antimicrobial Preservatives

Preservatives prevent microbial growth in multi-dose water-containing preparations. Common agents include sodium benzoate, benzoic acid, potassium sorbate, methylparaben, propylparaben, and benzyl alcohol.

4. Antioxidants

Antioxidants inhibit oxidative chemical degradation by terminating free-radical chain reactions or acting as sacrificial reducing agents:

• Aqueous Systems: Ascorbic acid (Vitamin C), sodium bisulfite, sodium metabisulfite.
• Oil Systems: Alpha-tocopherol (Vitamin E), butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA).

5. Emulsifiers and the Hydrophile-Lipophile Balance (HLB) System

Emulsifiers stabilize immiscible oil-and-water blends by forming interfacial films around dispersed droplets. The HLB scale ranges from 1 to 20:

• Low HLB (3 to 6): Lipophilic agents that stabilize water-in-oil (w/o) emulsions (e.g., sorbitan monooleate [Span 80]).
• High HLB (8 to 16): Hydrophilic agents that stabilize oil-in-water (o/w) emulsions (e.g., polysorbate 80 [Tween 80]).

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Clinical & Dispensing Case Scenario: Compounding an Oral Suspension

A community pharmacy receives a prescription for pediatric spironolactone 5 mg/mL oral suspension, 100 mL, for a 6-month-old infant with congestive heart failure. Commercial liquid spironolactone is not marketed in Canada.

Step-by-Step Procedure:

1. Level of Compounding: Spironolactone appears on the NIOSH 2016 hazardous drug list as a Group 2 non-antineoplastic drug. Because manipulating commercial tablets into powder creates hazardous dust, the risk assessment places this occasional preparation at Level B: a dedicated room and a ventilated containment device (CVE). It would move to Level C if the pharmacy compounded large quantities routinely.
2. Master Formulation Verification: Retrieve the validated MFR. Spironolactone 5 mg/mL compounded from commercial 25 mg tablets in a 1:1 mixture of Ora-Plus and Ora-Sweet is supported by published stability data (Allen & Erickson, Am J Health-Syst Pharm).
3. Trituration & Levigation: Count 20 spironolactone 25 mg tablets ($500\text{ mg}$ total). Pulverize to a fine, uniform powder in a glass mortar. Add a few drops of glycerin (wetting agent) to form a smooth, uniform paste.
4. Vehicle Incorporation: Geometrically incorporate 50 mL of Ora-Plus (suspending vehicle) into the paste. Transfer quantitatively to a calibrated cylindrical graduate, rinsing the mortar with portions of Ora-Sweet. Bring to a final volume of 100 mL with Ora-Sweet.
5. Quality Control & Packaging: Measure pH (target $4.0 - 5.0$), inspect color and uniformity, package in an amber, child-resistant oral bottle with an oral syringe adapter. Affix auxiliary labels: "Shake Well Before Use" and "Hazardous Drug - Handle with Care".
6. BUD Assignment: Supported by peer-reviewed published stability data, assign a BUD of 60 days stored at controlled room temperature (or 14 days refrigerated if relying on default USP/NAPRA guidelines without stability citations).