There are multiple problems with trying to dose a medication all at once that is intended to be taken multiple times daily. These problems include:
- Potential overdose adverse effects
- Under dosing for the majority of the day
Drugs that need to be dosed multiple times a day for therapeutic effects are prescribed to be taken that way for a reason and is discussed below.
One of the main issues with taking your dose all at once is that side effects are often dose related, meaning higher doses tend to cause more side effects.
In your case, you are suggesting to take 3 times the dose of spironolactone than your doctor intended. This can greatly increase your risk of side effects occurring. This can be especially dangerous when using medication with a narrow therapeutic index. Narrow therapeutic index drugs are those in which the therapeutic concentrations and toxic concentrations of the drug are very close to one other. It is unsafe to overdose with narrow therapeutic index drugs.
To use an example of a commonly used over the counter medication, take ibuprofen. The maximum daily dose of ibuprofen is 2,400 mg to 3,200 mg depending on the situation. However, taking over 800 mg per dose greatly increases the risk of adverse effects such as nausea, cramping and GI distress.
The vast majority of drugs aren't metabolized and eliminated at a consistent rate. Instead, most are metabolized in the body under what is known as "first-order kinetics". The concept of pharmacokinetics can be complicated. Simply put, for drugs that follow first order kinetics, the rate of elimination is proportional to the drug concentration. In other words, the higher the concentration of the drug, the faster it is metabolized.
Below is a graph that illustrates first order kinetics:
Taking all your doses at once as opposed to multiple times daily will not only result in a possible overdose, it will most likely lead to an overall under dose throughout the day. The high concentrations of the drug will be metabolized quickly and will result in lower than usual blood levels of the drug compared to dosing three times daily.
Dosing three times daily will allow drug concentrations to reach therapeutic levels throughout the day.
Taking a medication that is intended to be dosed multiple times daily all at once, can increase side effects and will generally cause you to have sub-therapeutic levels of the drug for most the day.