Contraindications are adverse effects of a medication when taken with something else. These can be as minor as a small rash for a day or two, or extremely severe and life-threatening
“Something else” can be a pre-existing condition, another medication, supplement, or food; any reason a medication or treatment should not be administered
Contraindications are not isolated side effects of any one medication, though having an allergy (pre-existing condition) to a medication can be
Why is it Important
As a pharmacy technician, it is your responsibility to understand general contraindications, allergic reactions, and side effects to best serve the patient in a hospital pharmacy or customer in a community pharmacy
You will see more examples of each in retail than in a hospital setting. In retail, the customer controls their diet, supplementation, and medication times whereas a hospital controls most (if not all) of these things
In retail, the technician often sees the prescription (RX) before the pharmacist so they input the RX before the pharmacist reviews and approves it. Catching mistakes on an RX before they reach the pharmacist makes for a proactive and successful technician.
Be mindful of the differences between an allergic reaction, side effect, and contraindication
An allergic reaction will occur when the immune system overreacts to a substance—in minor cases, sneezing during the high pollen volume during springtime. In severe cases, anaphylaxis causes respiratory collapse and potentially death.
A side effect is an effect of a medication that goes beyond the desired bodily response. It can be minor such as a small rash or severe with permanent internal damage
The Exam
40% of the PTCB exam covers medications, and 2 of the 10 topics in this category are side effects, reactions, and contraindications.
The exam will most likely ask at least 2 questions about these topics, though a thorough understanding of each will translate into a better understanding as a technician helping patients
Contraindications
There are thousands of potential contraindications, most of which you probably will not see on your exam. Listed below are the questions most likely to be asked about on your exam…
Drug-Alcohol Interactions
As a general rule of thumb, you shouldn’t drink any alcohol while taking any medications
Drug-Nutrient Interactions
Grapefruit and Statins
Statin refers to cholesterol medications like Atorvastatin (Lipitor) or Simvastatin (Zocor)
The juice in grapefruit decreases the enzymes needed to metabolize statins, resulting in potential muscle pains and aches
Dairy Products
Dairy products contain several multivalent ions (Al3+, Ca2+, Mg2+, Zn2+) which bind to or interfere with the drug. The drug is not fully absorbed due to it’s ionic interactions
Levothyroxine, tetracyclines, antibiotics, bisphosphonates, and fluoroquinolones should not be taken with dairy
Greens and Warfarin
Warfarin has a narrow therapeutic window, meaning dosing needs to be near-perfect to have the right effect. It is used to prevent blood clots in at-risk patients
Green, leafy vegetables (ex: kale) are high in vitamin K. Vitamin K aids clotting, contradicting the function of Warfarin.
Tyramine and MAO Inhibitors
Tyramine is found in fermented foods, cheeses, soy sauce, alcohol (beer), and cured meats.
MAO inhibitors increase neurotransmitters like dopamine, serotonin, and norepinephrine in the brain. Mixing with tyramine risks a hypertensive crisis (critically high blood pressure)
Drug-Drug Interactions
Potentiation (synergy) refers to when 2 drugs with similar effects are taken together resulting in a more powerful result than when taken alone
Antagonism refers to drugs that negate or reduce the effect of another drug when taken together
Antiplatelets, Anticoagulants, and NSAIDS
Antiplatelets (Aspirin, Clopidogrel), anticoagulants (Warfarin, Heparin), and NSAIDs (Ibuprofen, Meloxicam) all increase the risk of bleeding in patients
By taking any combination of these medications clotting and bleeding issues may arise
Aminoglycosides and Loop Diuretics
Aminoglycosides (Gentamycin, Tobramycin) increase permeability in the cell membrane of the inner ear causing ototoxicity (inner ear damage)
Kidney damage is also a side effect of aminoglycosides which is increased when taken with loop diuretics
ACE Inhibitors and Potassium-Increasers
ACE inhibitors (Ramipril, Lisinopril) lower blood pressure but tend to increase potassium (K) levels
Pairing this with a potassium-increasing medication (supplements, Trimethoprim) can cause hyperkalemia in patients
Beta-blockers and Calcium Channel Blockers
Beta-blockers (Carvedilol, Metoprolol) slow heart rate by blocking adrenaline and norepinephrine
Calcium Channel Blockers (Amlodipine, Verapamil) block calcium from entering the heart, relaxing blood vessels and lowering blood pressure
Taking both slows heart rate significantly risking bradycardia and heart failure
Nitrates and PDE5 Inhibitors
PDE5 inhibitors include Sildenafil and Tadalafil, which have hypotensive effects
Nitrates such as Nitroglycerin or Isosorbide Mononitrate also cause hypotension
Taking both medications at the same time could result in dangerously low blood pressure for the patient (bradycardia)
Warfarin and Broad Spectrum Antibiotics
Broad-spectrum antibiotics (cephalosporins, penicillin) can increase the risk of bleeding by decreasing vitamin K production
Warfarin, which prevents clotting, paired with these antibiotics puts the patient at risk of fatal bleeding
Antihistamines and Benzodiazapines, SSRI, and Antipsychotics
Antihistamines (Benadryl, Zyrtec) have a sedative effect
Benzodiazepines, SSRIs, and Antipsychotics can escalate this effect
Clopidogrel and Omeprazole
Proton pump inhibitors (Omeprazole) combined with antiplatelet medications (clopidogrel) contradict the anti-clotting effects
Macrolides and Statins
Macrolides are antibiotics (clarithromycin) that inhibit Cytochrome P450 (CYP) enzymes
CYP enzymes break down statin medications, and taking the two together increases the risk of side effects
Corticosteroids and NSAIDs
NSAIDs increase the risk of bleeding as well as ulcers and gastrointestinal bleeding
When taken with corticosteroids, these risks are elevated
Phyentoin and Estrogen, Warfarin, Progestogens
Phyentoin treats seizures, initiates CYP enzyme function, and metabolizes toxins.
This enzyme also reduces the concentration of other medications (Estrogen, Warfarin, and Progestogens) in plasma which decreases their effect
Sulfonylurea, Metformin, and Thiazolidinediones
All three medications are used to lower blood sugar and may cause hypoglycemia
When taken together, blood sugar levels can get dangerously low without proper supervision
Ritonavir and Protease Inhibitors
Ritonavir blocks CYP enzymes which break down medications like Protease Inhibitors
This means there is more medication in the body, available for use. Dosing Protease Inhibitors is lower when the patient is also on Ritonavir
Drug-Supplement Interactions
St. John’s Wort and… Everything
St. John’s Wort has historically been used as a natural solution to ailments including depression, insomnia, and wound healing.
However, it has contraindications with almost all medications to some degree.
Other Contraindications to Know
Drug-Laboratory
Certain medications can distort otherwise baseline lab tests in patients
Some can spike blood pressure or blood glucose, which can skew the diagnosis following the lab tests
Drug-Disease
Some medications have more profound effects on those with pre-existing conditions
For instance, a prediabetic patient should avoid taking a medication that may spike their blood sugar
Terms and Definitions
- Bradycardia: Heart rate is slower than normal (below 60 to 100 beats per minute). While this is normal in some healthy athletes, it can cause dizziness, fainting, and chest pain among other unwanted symptoms.
- Hyperkalemia: Potassium (K+), essential for nerve and muscle function, that is too high in the blood. Severe cases result in weakness and cardiac arrhythmias
- Hypertension: High blood pressure; higher than 140/90 mmHg
- Hypotension: Low blood pressure; lower than 90/60 mmHg
- Loop Diuretics: Medications to treat fluid overload conditions
- Tachycardia: Heart rate is higher than normal (above 60 to 100 beats per minute)
Sources
Antibiotic and Anticoagulation: Watching Warfarin Levels – Contemporary Clinic
Side effects of aminoglycosides on the kidney, ear, and balance in cystic fibrosis – Thorax
Top 20 PTCB Drug Interactions to Know – PTCB Test Prep