Bioavailability

Bioavailability is the proportion of an administered drug that reaches the systemic circulation and is therefore available for distribution to the intended site of action.

Drugs that are given by direct injection are said to have 100% bioavailability. Some drugs that are particularly well absorbed by the gastrointestinal mucosa may have bioavailability comparable to that of an dose – for example the antibiotic ciprofloxacin. Most drugs do not have this availability by the oral route so the dose given orally is usually higher than that given parenterally. For example, the beta-blocker propranolol when given orally is administered in doses of 40mg and above. The equivalent dose is 1mg.The route of administration and its formulation (tablet, capsule, liquid) can clearly influence the bioavailability of a drug.

The main and side effects of the medicines are distinguish.

The main action of medicines, when it acts according to the purpose of prescribing, and side effects, when preparation negatively influences on the organism and appear as:

a) intolerance of medicines (so-called idiosyncrasy) with allergic reactions, apeaaring of some pathology (for example, candidosis at the using of antibiotics);

b) tolerance (habituation of medicines that are taken for a long time, for example, after prolonged treating with nitroglycerine its efficiency considerably falls and the grater dose of this medicine is needed to attain medical effect. It concernes also purgative and soporific.

The therapeutic action of any medicinal matter appears only at introduction of its certain amount. Taking into account there are such doses:

Ÿ Therapeutic dose: (average therapeutic) is the ordinary dose of medicinal preparation, that vary upon the age, sex of patient, physiology state of organism, presence of other diseases. Thus single and daily doses are distinguished. the usual dose or average dose it is the amount needed to produce the desired therapeutic effect

Ÿ Dosage range: A term that applies to the range between the minimum amount of drug and the maximum amount of drug required to produce the desired effect.

Ÿ Minimum dose: The least amount of drug required to produce a therapeutic effect.

Ÿ Maximum dose: The largest amount of drug that can be given without reaching the toxic effect.

Ÿ Toxic dose:The least amount of drug that will produce symptoms of poisoning.causes poisoning of organism;

Ÿ Minimum lethal dose: The least amount of drug that can produce death.

Ÿ mortal dose causes death of patient.

In case of prescribing of few medicines the potentiation (strengthening of action) of medicinal preparations can appear; incompatibility of medicinal preparations: chemical (simultaneous setting of preparations that have acid and alkaline reactions), pharmacological (opposite influence on the same organ or their functions have been taken at ones).

Date: 2014-12-29; view: 885