CST Surgical Pharmacology Review: Maximum Doses, Concentration Math and Malignant Hyperthermia

Six scored questions is the smallest share on the CST, tied with Microbiology, yet pharmacology is where a single conversion slip costs a point that knowing the drug should have earned. NBSTSA's outline is unusually specific here, naming the drugs whose maximum doses you should know. This review sticks to what the FDA-approved labels say, with the arithmetic labeled as Passy's.

What the CST surgical pharmacology lines ask

NBSTSA's content outline has two task lines for Surgical Pharmacology:

1. Apply principles of surgical pharmacology to operative practice: anesthesia-related agents and complications from drug interactions, with malignant hyperthermia as the example; methods of anesthesia (general, local, block, MAC); types, uses, actions and interactions of drugs and solutions such as hemostatic agents, antibiotics and IV solutions; and weights, measures and conversions.
2. Maintain awareness of maximum dosage, with Xylocaine (lidocaine), Marcaine (bupivacaine), heparin and epinephrine as the examples.

NBSTSA's 2023 job analysis report records the committee's view that 77% of Basic Science items are recall. Expect most of these six to ask for a fact or a calculation rather than a judgment call. Labeling medications on the field is an Intraoperative task, covered in the CST Intraoperative Procedures review.

Percent and ratio strengths: the conversions behind CST dose questions

Two ways of writing strength come up again and again: percent (grams per 100 mL) and ratio (1 gram in a stated number of milliliters). The arithmetic is Passy's; the label column shows where an FDA label states the same value.

Two shortcuts follow. For percent, multiply by 10 to get mg per mL. For ratio, 1:1,000 is 1 mg per mL, and each extra zero divides by ten. Keep the metric steps straight too: 1 g is 1,000 mg and 1 mg is 1,000 mcg, and for weight-based doses, 1 kg is about 2.2 lb.

Maximum doses for lidocaine and bupivacaine, from the FDA labels

The two local anesthetics the outline names have their limits in their labels:

Neither label treats these as targets. The Xylocaine label says to use the lowest dosage that gives effective anesthesia and that children's maximums depend on age and weight, and the Marcaine label says the maximum must be individualized to the patient's size and physical status. The current Marcaine label (October 2026) presents 175 and 225 mg as the infiltration amounts in its dosage table, with a 400 mg ceiling in 24 hours. If a textbook gives a different figure, note its edition and the label date: the FDA label is the primary source for a drug's limits, and NBSTSA says its committee uses the most current edition of each reference.

Worked examples (Passy arithmetic):

• 80-kg adult, 1% lidocaine without epinephrine. 4.5 × 80 = 360 mg, above the 300 mg ceiling, so the limit is 300 mg: 30 mL of a 10 mg/mL solution.
• 50-kg adult, 2% lidocaine without epinephrine. 4.5 × 50 = 225 mg, under 300 mg, so the limit is 225 mg: 225 ÷ 20 = 11.25 mL.
• 80-kg adult, 1% lidocaine with epinephrine. 7 × 80 = 560 mg, above the 500 mg ceiling, so the limit is 500 mg: 50 mL.

The habit to build: compute the weight-based figure, compare it with the total cap, take the lower, then convert milligrams to milliliters. On the field, the related tasks are monitoring how much medication has been used and reporting the amount at the end of the case. For quick recall of the limits themselves, maximum doses are among the topics the planned CST flashcards cover.

Epinephrine and heparin: strength traps on the CST

Epinephrine appears in two very different forms. In local anesthetics it's dilute: the Xylocaine label lists lidocaine with epinephrine 1:100,000 and 1:200,000, and Marcaine with epinephrine is 1:200,000. A vial of Adrenalin is 1 mg/mL. Some Passy arithmetic: 1 mg/mL is 200 times as concentrated as the 5 mcg/mL in a 1:200,000 solution, which is why the ratio on the label is worth reading aloud when it's verified.

Heparin is the outline's other named drug. The heparin label carries a warning about fatal medication errors:

• Heparin comes in several strengths, including a highly concentrated 10,000 units in 1 mL.
• Pediatric patients have died after 1 mL heparin vials were confused with 1 mL catheter lock flush vials, and the label says to confirm the correct strength before administration.
• Its reversal agent is protamine sulfate: the label says each milligram neutralizes about 100 USP units of heparin, given by slow infusion, no more than 50 mg in any 10 minutes.

Malignant hyperthermia: triggers, signs and dantrolene

The outline names malignant hyperthermia (MH) as its example of an anesthesia complication. MedlinePlus Genetics, from the National Library of Medicine, describes it as a severe reaction to certain anesthetic gases, given alone or with a muscle relaxant. The Ryanodex label names the triggering agents as volatile anesthetic gases and succinylcholine.

• Signs (MedlinePlus): a rapid rise in heart rate and body temperature, abnormally fast breathing, muscle rigidity, breakdown of muscle fibers (rhabdomyolysis) and acidosis. Without prompt treatment it can lead to cardiac arrest, kidney failure and a clotting disorder.
• Not every exposure. MedlinePlus says MH may not occur every time anesthesia is used; many people who react had earlier exposures without one. It occurs in 1 in 5,000 to 50,000 instances in which people receive anesthetic gases.
• First steps (Dantrium Intravenous label). As soon as MH is recognized, stop all anesthetic agents and give 100% oxygen. Give dantrolene by continuous rapid IV push, starting at a minimum of 1 mg/kg and continuing until symptoms subside or a maximum cumulative dose of 10 mg/kg is reached. Supportive care includes managing metabolic acidosis and cooling when needed.

The preparation details are classic test material:

Sources: the Dantrium Intravenous label and the Ryanodex label. Some Passy arithmetic shows how much preparation the first dose involves: for an 80-kg patient, 1 mg/kg is 80 mg, which is four 20-mg vials of Dantrium Intravenous and 240 mL of sterile water to reconstitute them. Questions like this sit in the same subject area as anatomy and microbiology: Basic Science practice is planned with 195 CST questions.

The other CST pharmacology lines

The outline also lists methods of anesthesia (general, local, block and monitored anesthesia care) and drugs and solutions such as hemostatic agents, antibiotics and IV solutions. These are broad, and NBSTSA's reference list names a dedicated text, Pharmacology for the Surgical Technologist (6th edition, 2023), for them. Study them from that text or your program's equivalent, and use the outline's examples as your checklist: for each agent, know what it's for, how it's supplied, and what has to be verified before it goes on the field.

Two original CST-style questions on surgical pharmacology

Written by Passy for this guide. They are not NBSTSA items and don't come from any exam or practice test.

Question 1: a bupivacaine volume

Local infiltration with 0.25% bupivacaine with epinephrine 1:200,000 is planned for a healthy adult. Using Table 3 of the Marcaine label, what is the most that may be given as one dose?

• A. 30 mL (75 mg)
• B. 70 mL (175 mg)
• C. 90 mL (225 mg)
• D. 160 mL (400 mg)

Keyed answer: C. The label's table allows up to 90 mL, 225 mg, of 0.25% with epinephrine for local infiltration. B is the amount without epinephrine, D is the 24-hour ceiling, not a single dose, and A is a common vial size, not the label's limit.

Question 2: dantrolene preparation

During a malignant hyperthermia crisis, the CST helps prepare Dantrium Intravenous. What does the label say to reconstitute each vial with?

• A. 60 mL of 0.9% sodium chloride injection
• B. 60 mL of 5% dextrose injection
• C. 60 mL of sterile water for injection
• D. 60 mL of bacteriostatic water for injection

Keyed answer: C. The Dantrium Intravenous label specifies 60 mL of sterile water for injection without a bacteriostatic agent and says 5% dextrose, 0.9% sodium chloride and other acidic solutions are not compatible. D adds the bacteriostatic agent the label excludes.

Your next step for CST surgical pharmacology

Make a one-page sheet with the conversion table, the five label limits and the dantrolene table, and work one new dose problem a day until the steps are automatic: weight-based figure, cap, lower of the two, milliliters. Then try the lidocaine item in the CST practice test guide. If a limit keeps slipping, ask the planned AI Rescue for a memory trick when a dose limit won't stick.