📏 Measurement Systems & Conversions

• Metric system – gram (g), liter (L), meter (m) → most accurate.
• English system – less accurate, used for liquids/powders.
• 1 tsp = 5 mL
• 3 tsp = 1 Tbsp = 15 mL
• 2 Tbsp = 1 oz = 30 mL
• Other systems – “units” (e.g., insulin, heparin).

🏷️ Drug Labels

• Contain: trade name, generic name, amount, lot #, expiration, storage info, controlled substance marking.
• Precautions:
• Watch for look-alike/sound-alike names.
• Always check label 3 times with MAR.
• Some meds require reconstitution (with sterile water, saline, or special diluent).

🧮 Drug Calculation Methods

👉 Always use one method consistently.

1. Basic Formula (BF):

D÷H×V=AmountD ÷ H × V = AmountD÷H×V=Amount

Example: Order 0.5 g (500 mg), Available 250 mg/tab → 2 tabs.

2. Ratio & Proportion (RP):

H:V::D:xH:V :: D:xH:V::D:x

Example: 250 mg:1 tab :: 500 mg:x → x=2 tabs.

3. Fractional Equation (FE):

H/V=D/xH/V = D/xH/V=D/x → cross multiply.

4. Dimensional Analysis (DA):

Converts across units with label factors.

5. Body Weight (mg/kg):

Convert lb → kg (2.2 lb = 1 kg).

Example: 88 lb = 40 kg. Order 20 mg/kg/day → 800 mg/day → 400 mg per dose.

6. Body Surface Area (BSA):
• West Nomogram (height + weight).
• Square root formula → Drug dose × BSA (m²).

Example: Order 100 mg/m², BSA = 1.8 → 180 mg/day.

🔄 Rounding Rules

• Round tablets/caplets to nearest ½ if scored.
• Round to ¼ if tablet is scored that way.

🥤 Enteral Administration

• Forms: tablets, capsules, powders, liquids.
• Do NOT crush sustained-release or enteric-coated.
• NG/G-tube:
• Don’t mix with feeding.
• Dilute with 15–30 mL water.
• Flush with 15–30 mL water after giving.

💉 Parenteral Administration

• Consider dose, syringe, vial/ampule, technique.
• IV routes: IV push (IVP), IV piggyback (IVPB), continuous infusion.
• Always check rate of administration and dilution to prevent vein irritation.
• Use infusion pumps, secondary sets, safety devices.
• Extra caution with heparin & critical care drugs.

💧 IV Flow Rate Calculations

1. mL per hour (pump)

Volume (mL)÷Hours=mL/h\text{Volume (mL)} ÷ \text{Hours} = \text{mL/h}

Volume (mL)÷Hours=mL/h

2. Drops per minute (gravity drip)

mL/h×gtt/mL60=gtt/min\text{mL/h} × \frac{gtt/mL}{60} = gtt/min

mL/h×60gtt/mL=gtt/min

Example:

• 1000 mL in 8 hr with 10 gtt/mL set:

1000 ÷ 8 = 125 mL/h.

125 × 10 ÷ 60 ≈ 21 gtt/min.

Example 2:

• 75 mL over 40 min with 60 gtt/mL set:

(75 × 60) ÷ 40 = 113 gtt/min.

🚑 Critical Care Drugs

• Usually titrated to patient’s response.
• Must monitor patient continuously (e.g., cardiac drips, pressors).

✅ In short:

• Use metric system (most accurate).
• Know 3 calculation methods (basic formula, ratio/proportion, dimensional analysis).
• Adjust doses by weight or BSA for pediatrics/oncology.
• Apply correct IV flow rate formulas.
• Always double-check high-risk drugs, look-alike/sound-alike names, and rounding rules.