The mode of action of drugs on cells / by A.J. Clark.

  • Clark, A. J. (Alfred Joseph), 1885-1941
Date:
1933
Catalogue details

Licence: In copyright

Credit: The mode of action of drugs on cells / by A.J. Clark. Source: Wellcome Collection.

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    to oxidize the alcohol is directly proportional to the dosage. Moreover, since there is a linear relation between the concentra- tion of and the action produced by alcohol, therefore the total amount of any effect produced by this drug will also be directly proportional to the dosage. The simplicity of these relations is very exceptional, and we may next consider the relations likely to occur in ordinary cases. In the first place the relation between dosage and intensity of action usually either follows a hyperbola or else is logarithmic. Secondly, it is very rare for an excess of drug to be retained in the body. In the case of all hormones except thyroxin the body either excretes or also breaks down rapidly any excess of hormone. The Duration of Action of Drugs The duration of the action produced by any dose of drug depends, in the first place, on the length of time for which an efficient concentration of drug is maintained in the circulation, and this depends on the rate at which the drug is eliminated from the blood. Most hormones are removed rapidly ; for example, acetyl choline and adrenaline are broken down by ferments, whilst other hormones such as oestrin are excreted rapidly. The only outstanding exception to this rule is thyroxin, which is removed from the body very slowly. As regards other drugs there are a few, such as digitalis and the heavy metals, which are removed slowly from the body and hence tend to produce cumulative poisoning, but the majority of drugs are excreted rapidly, and as a general rule the process of excretion follows a die-away curve and there is an approximately linear relation between the logarithm of the amount of drug remaining in the body and the time. The relation between the dosage of atropine and the duration of the action produced is shown in Fig. 48, and it will be seen that there is a linear relation between the logarithm of the dose and the duration of action. This relation implies that a very large dose is required to maintain an action for a long period. Fig. 48 shows that a dose of 0-ly produced an action for 10 hours and that 1 y produced an action for 50 hours, and extrapolation indicates that a dose of lOy would be needed to produce an action for 100 hours. Burn (1931) measured the relation between the dose of M.A.D. P