Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

It is vitally important to make sure your vet knows which medications you pet is on when new medications are prescribed. Sometimes the notes are not clear or you may be visiting a new veterinarian. Sometimes you have old meds lying around which you have starting dosing to your pet without the vet’s knowledge. It is dangerous to use medications together when all their interactions may be unknown.

All medications have side effects. If you look on the information insert you will see that they are divided into severity and frequency and most of the more severe ones are uncommon. Even the most routine drugs, such as penicillin antibiotic, can have catastrophic side effects in some individuals. Once medications are combined, their positive effects can become exacerbated or blunted and their side effects may become more prevalent.

The health of the kidneys and liver are also important as these are the organs most involved in breaking down and excreting medications from the body. Delayed breakdown and excretion may result in accumulation in the blood stream and dangerously high doses.

Some medications stimulate liver enzyme function, thus increasing the metabolism of other drugs using the same mechanisms for excretion and decreasing effective blood levels. Other medications decrease the enzyme activation, causing increased and sometimes toxic doses of medication in the blood stream. If the kidneys are not 100% functional, drugs may also accumulate in the system. Liver and renal function tests are sometimes required to make dose adjustments to certain medications.

Additionally, certain medications can cause further renal damage if administered in a patient with decreased renal capacity. Certain drugs can sensitize the kidneys to damage from other drugs. So, when these medications are combined, extra caution needs to be taken. Medication label warnings must be adhered to. Medication should be immediately stopped and your vet contacted if you have concerns. Rather too early than too late.

As an example, certain drugs have risk to the kidneys and when combined, their action is compounded – these include heart medications such as diuretics and ACE inhibitors, which may decrease renal blood flow.

Non-steroidal anti-inflammatory medications have an inherent risk of causing kidney injury and gastric ulcers in predisposed patients; usually those who are dehydrated or septic. As soon as a patient on anti-inflammatory drugs doesn’t eat a meal or shows gastro signs, stop the medication and check at the next meal or take to the vet if concerned.

This is a problematic combination of interactions, as often older dogs have degenerative disease conditions of the kidneys as well as the heart and the joints. Often choices have to be made as to which condition will be predominantly managed with medications and which with diet and nutritional supplements.

Certain medications will bind and make any drugs given at the same time unavailable for absorption. Antacid medications will bind other meds, so they need to be separated by about two hours. Other medications, such as proton pump inhibitors, need to be administered at least 30 minutes prior to feeding, as food decreases absorption.

It is vitally important to take note of the exact dosing instructions of dispensed medications and to make sure that your vet is aware of all the medications your pet is on.