1⃣Type A reactions: Predictable effect.In this case the reason is known and the conditions can be reversed by reducing the dose or switching over to another medicine.
2⃣Type B reactions: Non – predictable effect:is mainly due to genetic differences in the metabolism of the drug, immunoligically mediated effects and the main reason is that the outcome can be fatal since the mechanism for the adverse reaction is not known. Common adverse effects of drugs:
Respiratory depression: is a pattern of regular respirations with a rate of less than 12 breaths a minute. The respiratory centers regulate the breathing in coordination with the medulla and pons. When there is a reduced cerebral perfusion to activate the neurons of the respiratory center or when there is a change in the levels of arterial carbon dioxide and they trigger the chemoreceptors, or when there is a reduced effectiveness in changing the levels of carbon dioxide by the respiratory neurone there can be respiratory depression. Mainly caused by CNS depressants.
Anaphylactic Shock:is an acute dramatic reaction characterized by respiratory depression, angio – oedema, cardiovascular collapse, vomiting and urticaria. Mainly when there is an allergic reaction to the drug for e.g. penicillin.
Dizziness: is a sensation of imbalance, associated with weakness, confusion , blurred or double vision. These episodes are usually short . it is mainly due to irregular blood flow to the brain and spinal cord. Cause: CNS depressants, narcotics etc
Constipation: Involves infrequent and difficult bowel movements. It is the ANS which is responsible for controlling the bowel movements. It may lead to lack of appetite and abdominal discomfort. Cause: Narcotics, analgesics, antacids, too much laxative.
Hypertension: Blood pressure relates to the force exerted on the blood vessels and is affected by the cardiac output, peripheral vascular resistance and blood volume. Raised bp is referred to as hypertension and in this case the arterial walls thicken , become less elastic and resistant to blood flow. Cause: sympathomimetics, corticosteroids, oral contraceptives, MAOI, CNS stimulants
Hypotension: is decreased Bp to oxygenate the body tissues. Can occur due to vasodilation, dehydration and severe bleeding. Cause: calcium channel blockers, diuretics, antihypertensives, general anesthesia.
Oral Candidiasis: it is a mild superficial fungal infection caused by the candida species in the mouth. These bacteria are found in the normal flora of the mouth and when the drug alters the balance of this flora it leads to infection and can result in blue – white patches on the tongue, mouth and pharynx. Cause : antibiotics
Rash:Type of skin eruption. Cause: antibiotics
Dry Mouth: decreased salivation, involves the decreased production of saliva resulting from mouth breathing. Cause: antimuscarinics, narcotics and excessive irradiation of the mouth or face.
Nausea: involves profound aversion of food or an impeding desire to vomit. The medication tends to produce this by stimulating the vomiting centers in the medulla oblongata or by irritating the GI tract. Cause: narcotics, analgesics
Drowsiness and sedation: decreased level of consciousness follows after the use of medication that depresses the CNS.
Fever: or pyrexia: arise from any medical condition that can affect the body system. Cause: hypersensitive reactions, chemotherapy, drugs that impair sweating.
Photophobia: is an abnormal sensitivity to light results from ocular dilation and reduction in aqueous humour drainage. Cause: mydriatics, ophthalmic viral drugs
Stomatitis: characterized by recurrent, painful ulceration of the oral mucosa. Can be a cause of an allergic reaction. Cause: Cytotoxic drugs, radiation therapy.
Diarrhoea: is an increase in the frequency and fluidity of the bowel movement. Cause: antibiotics, antacids, laxative abuse.
Angogenital candidiasis; mild fungal infection caused by the candida species in the vaginal, anal or penile areas. Cause: Oral contraceptives, other oestrogen containing preparations.
Vomiting:is the expulsion of the gastric contents by the mouth as a result of coordinated contraction of abdominal muscles and reverse oesophagal peristalsis.
Blistering: is a small thin walled raised vesicle containing clear, serous, purulent or bloody fluid. Can result due to allergy reaction. Antibiotics, cytotoxic drugs.
Photosensitivity: is an increased reactivity to sunlight: anticancer drugs, phenothiazine
Postural hypertension: is an abnormally low bp that occurs when an individual takes a standing position. It is often associated with medication that block the alpha – adenoreceptors. Cause: sympatholytics, phenothiazines antihypertensives
