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

“No good deed goes unpunished’ is a nice cynical saying, but unfortunately often too true. I am thinking of this more in relation to the use of medications and the side effects they cause.

We pop pills every day. How often do we actually read what the package insert says about contra-indications and side effects.

I was looking through the insert of one of my medications the other day and there were some really serious side effects mentioned. Rare, but possible, and if you are the unlucky one – life-threatening.
So, what happens if you are the 0.1% of people who get hit with this drug reaction? The same applies in our veterinary patients.

Some side effects are mild and well known. The routine antibiotics, such as penicillin and cephalosporin, can cause gastrointestinal upset. Some, such as metronidazole, are extremely bitter and will cause severe salivation, especially in cats.

Then we have medications which cause side-effects, such as increased appetite and weight gain, medications such as glucocorticoids (prednisolone). This medication is extremely effective in controlling itching, and some of our dog breeds are highly allergic. While the medication allows for some relief, the side effects of long-term use can be severe weight gain and a decrease in the function of the immune system.

So, in this case we generally try to limit the use as much as possible and weigh up the comfort of the patient against the side effects. Alternative medications have also been developed in the field of anti-allergic medications, not always because they are better, but also because they don’t have the side effects of the prednisolone.

Then we get medications which may have one or several known serious side effects, but the disease requiring the treatment is serious and there is no other drug which can be used.

In these cases the pros and cons are definitely weighed up with the owner and the risks made clear.

Early warning signs are explained and the patient is carefully observed for any symptoms. Dosages are carefully calculated and may be combined with other medications designed to limit the possibility of side effects.

Conditions where this applies include cancers and chemotherapy. For example, endoxan: chemotherapy is excreted unchanged in the urine and chemically burns the lining of the bladder if it sits in the bladder too long.

Methods to limit the risk include simple measures, such as always administering the drug in the mornings and giving the dog free access to the outside to urinate. Some also administer it with a small dose of a water pill (diuretic) to cause increased urination for 24 hours.

Then we get what we call idiosyncratic drug reactions. In these cases in some animals and people the drug just causes strange side effects. Good old anti-inflammatories can cause bone-marrow damage in very rare cases. Some people and animals will get allergic reactions to a medication.

This can often be dependent on the specific mixture of the drug used, as it is often other carrier molecules in the solution, and not the active ingredient, which cause the reaction. We used to have a very effective anaesthetic agent which caused allergic reactions in dogs; puffy eyes, feet and sometimes quite a severe allergic reaction. The drug has now been reformulated so that it can be used as easily in dogs as in cats and other species.

I have noticed that I seldom get my medications from the pharmacy in the box with the package insert. The same occurs at your vet. We warn people of side effects where they fall into the more serious “watch out for this” category, but each medication we hand out has the potential to cause side effects.