Adverse effects of drugs

Any undesirable or unintended consequence of drug administration may be trivial, serious or fatal can be seen, these are known adverse effect of drugs. All drugs are capable of producing side effects.

Not uncommon seen in 10 –25% of the cases. Still drugs are used considering the benefit vs risk.

Side effects of drugs can be classified in two types- Predictable (type I) based on the pharmacological properties of the drug. Eg.- Side effects, toxic effects and drug withdrawal symptoms and Unpredictable (type II) based on peculiarities of the patient and not on known drug effect.

Severity of drug adverse effect

1. Minor – no therapy needed
2. Moderate – may need change in drug / or its dosage or prolong hospital stay
3. Severe – potentially life threatening, causes permanent change or requires intensive medical treatment
4. Lethal – contributes to the death

Steps for prevention of adverse effects of drugs

1. Avoid inappropriate uses
2. Use correct dose and route of the drug
3. Consider previous history of reactions, if any
4. Find out if any other allergic disease existed, and take caution
5. Rule out harmful interactions among drugs prescribed
6. Adopt correct drug administration technique
7. Carry out correct lab. procedures to rule out reactions

Types of adverse effects

1. Side effect – expected effect and unavoidable – eg.. dryness of mouth in atropine treatment
2. Secondary effect – indirect consequences of a primary effect. examples are weakening of host immunity by corticosteroids flare up of TB.
3. Toxic effect – due to over dosage. examples are Paracetamol induced liver damage, coma by barbiturates, auditory disturbance in streptomycin.
4. Intolerance – appearance of toxic effects at therapeutic doses in some individuals.. eg..only few doses of carbamazepine ataxia in some patients
5. Idiosyncrasy– genetically determined abnormal reactivity to a chemical and also some uncharacteristic reactions to drugs egg. Barbiturate induced excitement and confusion in some patients.
6. Drug allergy– immunologically mediated reaction – not related to the action of the drug ( hypersensitivity but not super-sensitivity) – needs a priming dose and the second dose produces violent reactions. drug acts as antigen (hapten) and capable of stimulating the body to produce Antibodies against it.
7. Type I– anaphylactic (Immediate hypersensitivity) – itching , urticaria, asthma etc..
8. Type II – cytolytic – causes decrease of blood cells and organ damage
9. Type III – Arthus reaction – on vascular endothelium – serum sickness, fever, arthralgia etc..
10. Type IV – (delayed hypersensitivity) – takes more than 12 h to develop. examples are contact dermatitis, rashes, fever etc.
11. Treatment – stopping the offending drug, administration of antihistamines, glucocorticoids,  adrenaline etc.
12. Examples of drugs causing hypersensitivity: Penicillin, sulfonamide, tetracycline, salicylates, quinolones, Anti TB drugs, etc.
13. Photosensitivity – cutaneous reaction due to drug induced sensitization of the skin to UV light or radiation. Eg.. phenothiazine ( phototoxic), sulfonamide, griseofulvin ( photoallergic)
14. Dependence – psychological – patient feels that he will be alright only if he takes the drug
15. Withdrawal reactions – for non addictive drugs.. eg.. seizures on withdrawal of an antiepileptic drug.
16. Teratogenicity – ability to cause fetal abnormalities eg.. thalidomide, anticancer drugs, tetracyclines.
17. Mutagenicity and carcinogenicity– examples are anticancer drugs, estrogen, radioactivity, tobacco etc.
18. Drug induced diseases – (iatrogenic – physician induced)—examples are ulcer by NSAIDs.