Health Tips

With the rising incidence of non-communicable diseases, it’s not uncommon for individuals to be diagnosed with multiple diseases and are required to take different medications.

💡 Non-communicable diseases refer to diseases which are not transmitted directly from one person to another. Some of these diseases can include hypertension, diabetes and cardiovascular disease.

However, just like what you’re taught during your high-school chemistry lesson: you shouldn’t mix certain substances together.

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The same analogy applies to the medications you’re taking, and this is known as drug-drug interactions. 

Drug-drug interactions (DDI) can be classified into two types: pharmacodynamic DDI and pharmacokinetic DDI.

Pharmacodynamic DDI

Pharmacodynamic DDI refers to the interactions in which drugs influence each other’s effects directly. 

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If both drugs are mutually potentiating in the same direction. This leads to what we known as the synergistic effects. For instance, if you mix the medication commonly used for anxiety, e.g. alprazolam (Xanax®) and drinking alcohol subsequently (yes, alcohol is considered as a drug), the sedating effects may be stronger. As a result, you may experience extreme lethargy, reduced in physical responses, reduction in cognitive abilities, or even fatal ramifications.

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However, some synergistic effects are actually desirable. As an example, in acute pain management, it is not uncommon for doctors to give patients more than one types of painkillers, i.e. NSAIDs/paracetamol with opioids. 

⛔Combining different painkillers must be done under the supervision of a healthcare professional. You shouldn’t take different painkillers without consulting a doctor!

Pharmacodynamic DDI can also include antagonistic interaction, i.e. they cancel each other effects out. For instance, taking ibuprofen and aspirin together can negate the effect of aspirin, thus increasing cardiovascular risk. This is because both ibuprofen and aspirin bind to the same receptor called COX-1 protein. The reversible binding of ibuprofen to the COX-1 protein prevents ASA from doing its job onto the receptor, thus failing to exert its effects. 

Image credit: Pharmacovigilance

Pharmacokinetic DDI

On the other hand, pharmacokinetic DDI refers to the interactions in which drugs influence each other’s absorption, distribution, metabolism and excretion. 

Pharmacokinetic DDI is a huge topic in itself and we don’t want to bore you down with the nitty-gritty in this article. Here are some of the common pharmacokinetic DDIs:

1. Taking simvastatin together with clarithromycin

Simvastatin is a common medication used to treat high blood cholesterol, while clarithromycin is an antibiotic. Clarithromycin can inhibit an enzyme called CYP3A4 in the body, which happens to be the metabolising enzyme for simvastatin. If such inhibition takes place, the metabolism of simvastatin is reduced, which leads to a higher level of simvastatin in the body. In such a case, you may experience simvastatin toxicity, which can be manifested as muscle pain or kidney failure.

Common brand names: simvastatin - Zocor®, clarithromycin - Klacid®

Image credit: Abbott

2. Taking itraconazole together with rifampicin

Itraconazole is a medication used for fungal infection, whereas rifampicin is an antibiotic commonly used for treating tuberculosis (TB). Rifampicin is a strong inducer for the CYP3A4 enzyme, which is the metabolising enzyme for itraconazole. As opposed to scenario 1, the metabolism of itraconazole may be increased, and in some cases lead to a 90% reduction of itraconazole level in the body. Instead of toxicity, the patient may experience a diminished response to itraconazole, thus leading to treatment failure.

Image credit: National Jewish Health. Image shows tuberculosis.

3. Taking probenecid together with penicillin 

This is an interesting one: probenecid inhibits a receptor in the kidney called OAT1/3 transporter, which is the ‘exit door’ for penicillin to be excreted out from the body. This inhibition leads to a longer retention of penicillin in the body, thus prolonging its effect. In some cases, doctors may deliberately co-administer both in patients to improve clinical outcomes. So far no major toxicity cases have been reported in such usages, however, more data is needed in the future. 

Probenecid is a medication used for gout, whereas penicillin is antibiotic. 

Key takeaways

So, it is sufficed to say that although not all drug-drug interactions are bad, the majority of them can bring upon harmful effects to various extents, hence it should be managed by a professional medical team.

If you have concerns about drug-drug interactions, talk to our online pharmacist or doctor on Doc2Us app or any healthcare providers you know.

Happy taking medicine!

References:

1. UpToDate

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3444856/#R8

3. Cover image credit: HealthXChange

Written by

Ms Joyce Toh