10 Drug Contraindications to Know for the PTCB Exam.

What are Contraindications?

Contraindications refer to situations in clinical practice where a drug or treatment should not be used because it is harmful to the patient.

There are two main types:

• Absolute contraindications – situations in which a drug must never be used (for example, in case it causes a severe allergic reaction).
• Relative contraindications – where the drug may be used if the benefits outweigh the risks.

For the PTCB exam, pharmacy technicians are not required to learn all contraindications. Instead, only the most important and common examples need to be learned.

Throughout today’s guide, we will learn about 10 key drug contraindications to know for the PTCB exam – the type of interactions that almost always appear on the exam.

Aspirin and Young Children.

Aspirin is contraindicated in patients under the age of 16 who have recently experienced a viral infection (such as chickenpox or influenza).

This is due to the risk of Reye syndrome, a potentially fatal condition characterized by liver dysfunction and encephalopathy (brain dysfunction). Symptoms usually begin with severe vomiting and progress to confusion, seizures, and coma. The average fatality rate of Reye syndrome is approximately 20 percent.

Safer alternatives to aspirin in pediatric populations include:

• Ibuprofen
• Acetaminophen

Beta-Blockers and Asthma.

Beta-blockers are contraindicated is patients with asthma because they can cause bronchospasm (tightening of the airways, making it even more difficult to breathe).

Not all beta-blockers carry the same risk. There are two main types of beta receptor:

• Beta-1 receptors – located in the heart
• Beta-2 receptors – located in the lung

As a memory tool, consider “1 Heart, 2 Lungs”!

Some beta-blockers are cardioselective, meaning they almost only act on the heart. These drugs therefore have a lower risk of causing bronchospasm. At high doses though, even these drugs may lose selectivity and cause bronchospasm. Non-selective beta-blockers target both receptor types – and it is these beta-blockers that carry the highest risk of causing bronchospasm.

Non-selective drugs include:

• Propranolol
• Nadolol
• Timolol

This bronchoconstrictive effect can be life-threatening in patients with asthma, particularly those with poorly controlled disease.

Tetracyclines and Pregnancy.

Tetracyclines are contraindicated in pregnancy because they bind to teeth and bones during fetal development. They are also contraindicated in children under the age of 12 and in patients who are breastfeeding for the same reason.

Tetracyclines bind to calcium ions, leading to permanent discoloration of teeth (typically yellow-brown staining). They also cause enamel hypoplasia in children, where enamel on teeth doesn’t form properly. In fetuses and infants, tetracyclines can cross the placenta and are excreted in breast milk, interfering with bone growth and skeletal development. Their deposition in calcifying tissues results in long-term cosmetic and structural damage. This is among the top drug contraindications to know for the PTCB exam.

Nitrates and PDE5 Inhibitors.

Nitrates are drugs used in the treatment of acute angina (for example, isosorbide mononitrate and glyceryl trinitrate). PDE5 inhibitors are drugs used in the treatment of erectile dysfunction – examples including sildenafil, tadalafil, and vardenafil.

Both drug classes produce significant hypotension. Taking both drugs together is contraindicated because it can produce severe, life-threatening hypotension (low blood pressure).

For the same reason, nitrates are used with caution in patients taking antihypertensive drugs.

NSAIDs and Peptic Ulcer Disease.

NSAIDs are contraindicated in patients with peptic ulcer disease because they are well-established causes of gastrointestinal toxicity.

NSAIDs inhibit an enzyme called COX-1.

Ordinarily, COX-1 has gastroprotective effects, shielding the gastric mucosa from harm. But by blocking this enzyme, NSAIDs remove this gastroprotective effect, increasing the risk of peptic ulcer formation and GI bleeding. In severe cases, this interaction can lead to gastric perforation, where a hole forms in the stomach wall that can leak stomach contents into the abdominal cavity.

The risk is particularly high in elderly patients, those with a prior history of ulcers, and patients using corticosteroids or anticoagulants. Proton pump inhibitors may be co-prescribed to lessen this risk.

Live Vaccines and Immunocompromised Patients.

Live vaccines are contraindicated in patients with weakened immune systems due to the risk of uncontrolled replication of the live organism.

These live vaccines include:

• measles-mumps-rubella (MMR)
• varicella
• yellow fever
• intranasal influenza vaccine

Patients may have weakened immune systems due to disease, such as advanced HIV, or because of medicines – notably corticosteroids.

In immunocompromised patients, inactivated vaccines are preferred.

ACE Inhibitors and Pregnancy.

ACE inhibitors are drugs used in the treatment of conditions such as hypertension and chronic heart failure. Examples include ramipril, lisinopril, and perindopril.

ACE inhibitors are contraindicated during pregnancy, particularly in the second and third trimesters, due to their association with serious fetal toxicity. Exposure to ACE inhibitors during pregnancy can lead to fetal complications including impaired fetal kidney function, pulmonary hypoplasia, cranial malformations, and even fetal death. Neonates exposed in utero may present with hypotension and renal failure.

Safer alternatives, such as labetalol or methyldopa for hypertension, should be used in pregnant women requiring antihypertensive therapy.

MAO Inhibitors and SSRIs.

MAO inhibitors (monoamine oxidase inhibitors) and SSRIs (selective serotonin reuptake inhibitors) are contraindicated to be co-administered due to the risk of serotonin syndrome, a potentially life-threatening condition caused by heightened serotonin levels in the body.

Both drug classes increase serotonin levels in the brain, but through different mechanisms.

MAO inhibitors prevent the breakdown of serotonin, while SSRIs block its reuptake into neurons. When combined, serotonin accumulates excessively, leading to symptoms such as agitation, confusion, hyperthermia, muscle rigidity, and tremor.

Metformin and Severe Kidney Damage.

Metformin is contraindicated in patients with severe renal impairment due to the increased risk of lactic acidosis, a rare but serious complication.

The kidneys are responsible for eliminating metformin, and when renal function is reduced, the drug can accumulate to dangerous levels. Lactic acidosis, characterized by an accumulation of lactate in the bloodstream, can lead to symptoms such as rapid breathing, muscle pain, abdominal discomfort, and confusion.

To reduce this risk, metformin should not be used in patients with severe renal impairment. In cases of moderate renal impairment, close supervision is warranted.

Lithium and Dehydration.

Lithium is contraindicated in patients with dehydration due to its narrow therapeutic index and the risk of toxicity.

Dehydration can reduce the elimination of lithium, leading to elevated blood levels and an increased risk of lithium toxicity. Symptoms of lithium toxicity include tremors, confusion, ataxia, vomiting, and even seizures or coma in severe cases. Dehydration can occur due to various causes, including illness, excessive sweating, or diarrhea.

Therefore, patients on lithium should be monitored closely for signs of dehydration, and hydration status should be maintained to prevent complications related to lithium toxicity.

PTCB Cheat Sheet on Contraindications.

Below, we put together a neat summary of all contraindications covered in the course of today’s review.

If you’d like to test your knowledge of this topic, take our PTCB Contraindications Quiz.

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