Five types of drugs that should not be used together
If you are taking medication for an illness, the doctor will definitely not prescribe just one type of drug; it could be a combination of multiple drugs. This situation is very common in clinical practice. Rational combination therapy can improve efficacy and reduce adverse reactions. However, irrational combination therapy can lead to decreased efficacy or increased toxicity. Due to the wide variety of drugs used in clinical practice, irrational combination therapy often occurs. The following are some situations of combination therapy that are easily overlooked or incompatible, and patients should take note.
Five types of drugs that should not be used together
Medications with different names but the same chemical composition should not be used together
Currently, drug names include generic names, brand names, and aliases. It is very common for drugs to have multiple names. For example, acetaminophen (an antipyretic and analgesic drug) is commonly known as Paracetamol, Tylenol, Panadol, and Tempra. Similarly, metformin (an antidiabetic drug) is known as Glucophage, Diabex, Metforbell, and Glycomet. When we are unfamiliar with the names of drugs, there is a possibility of repeated use of drugs in combination therapy. For example, many people take both Paracetamol tablets and Tempra suspension when they have a fever, or they take both metformin tablets and Glucophage tablets for diabetes, which is considered as repeated use of drugs.
Repeated use of drugs with the same ingredient is equivalent to doubling the dosage, which can lead to increased toxicity. When acetaminophen is used in high doses, it can cause damage to the hematopoietic system as well as the liver and kidneys. Therefore, when using combination therapy, it is important to first determine the names of the drugs and their corresponding ingredients to avoid repeated use of drugs with the same ingredient. This is especially important when purchasing and taking medication on your own.
Drugs of the same class should not be used together
Usually, drugs of the same class (classified by pharmacological action) have similar chemical structures and physical properties, and their pharmacological actions are basically the same. For example, azithromycin and clarithromycin are both macrolide antibiotics that primarily act on the 50S subunit of bacterial ribosomes, inhibiting bacterial protein synthesis and exerting antibacterial effects.
When drugs of the same class are used together, their similar mechanisms of action can result in pharmacological antagonism, leading to decreased efficacy. For example, when azithromycin tablets and clarithromycin tablets are used together to treat respiratory tract infections, the competition for binding sites on the bacterial ribosomes can result in pharmacological antagonism and decrease the antibacterial efficacy. Furthermore, the use of drugs from the same class can also lead to increased toxicity. For example, long-term use of amlodipine tablets and nifedipine sustained-release tablets to treat hypertension can exacerbate adverse reactions such as lower limb edema, palpitations, and headaches. Therefore, drugs of the same class should not be used together to avoid decreased efficacy and increased toxicity.
Drugs of different classes but with the same mechanism of action should not be used together
Two drugs belong to different classes (classified by pharmacological action), but their mechanisms of action are the same. When used in combination, they can result in pharmacological antagonism and decrease efficacy. For example, glipizide is a sulfonylurea antidiabetic drug, while repaglinide is a non-sulfonylurea antidiabetic drug. Both drugs can promote insulin secretion by pancreatic beta cells and lower blood glucose levels. Since they have the same target site, their combination can lead to competitive antagonism, resulting in decreased hypoglycemic efficacy.
Drugs with the same ingredients should not be used together
In commonly used medications, some different drugs (especially compound preparations) contain the same ingredients. For example, calcitriol capsules contain activated vitamin D3, and Caltrate-D3 tablets (a compound preparation) also contain vitamin D3. Another example is that both theophylline sustained-release tablets and compound methoxamine capsules (Asmei) contain theophylline. When these drugs are used together, it actually results in repeated use of a certain ingredient, which can easily cause adverse reactions. If calcitriol capsules and Caltrate-D3 tablets are taken together for the treatment of osteoporosis, the repeated use of vitamin D3 can lead to accumulation and even cause chronic poisoning. Early symptoms include loss of appetite, nausea, vomiting, constipation, and diarrhea. In severe cases, it can cause hypercalcemia, leading to kidney damage and soft tissue calcification. Similarly, long-term use of theophylline sustained-release tablets and compound methoxamine capsules for respiratory diseases can result in increased blood levels of theophylline due to the combined dosage, which can cause adverse reactions such as nausea, vomiting, excitement, insomnia, tachycardia, and arrhythmias.
Therefore, when choosing combination therapy, it is important to first determine the ingredients of the drugs (especially compound preparations) to avoid adverse reactions caused by the combination use of drugs with the same ingredients.
Drugs with the same toxic side effects should not be used together
Certain drugs of different classes can have the same toxic side effects. When used in combination, the toxic side effects can be additive, leading to increased toxicity. For example, cephradine (a first-generation cephalosporin) has certain ototoxicity, while furosemide (a potent diuretic) can induce tinnitus and hearing impairment. When these two drugs are used together, the ototoxicity can be increased, leading to hearing impairment. Therefore, drugs with the same toxic side effects should not be used together to avoid increased toxic side effects.
Doctor's reminder
Repeated use of drugs with the same ingredient is equivalent to doubling the dosage, which can increase the drug's toxic side effects.
