Therapeutic
Incompatibility is that form of disagreement whereby ingredients
of antagonistic medicinal activity are prescribed together. It
includes other changes which take place after a drug is administered,
like for example the destructive effect of the digestive juices on
pancreatin, insulin, hormones, etc.
This type of incompatibility
occurs so rarely that it is hardly deserving of mention. In majority
of cases it may be assumed that it happens in a moment of
forgetfulness on the part of the physicians, so that his attention
must be called. The pharmacist, however, must use proper judgment as
to the existence of an actual intended combination, as well as to the
possible harm to be expected from its use, before assuming the role
of adviser to the physician. Furthermore it must be remembered that
certain agents of at least partially antagonistic qualities are
sometimes prescribe together for a certain purpose. Sometimes if
drugs have both desirable and undesirable effects, it may be
prescribed with drugs which oppose the unwanted action. E.g. when
morphine is prescribed as an analgesic the physician may use atropine
to prevent the excessive depressant action of morphine in the
respiratory center. Another instance is the use of opium to
counteract the laxative effect of calomel when latter is given in the
treatment of syphilis.
The following
combinations are liable to produce therapeutic incompatibilities when
administered at the same time:
- Sedatives and stimulants
- Demulcents and irritants
- Laxatives and astringents
- Atropine and morphine
- Caffeine and chloral hydrate
- Strychnine and barbital derivatives
- Tannin and aloin
In some cases, however, one
drug may increase the toxicity of the other as in the case of emetine
and antimony compounds or epinephrine and cocaine, these, therefore,
should not be administered together. Castor oil and other fixed oils
should not be given with santonin or aspidium oleoresin as the oil
increases the solubility of the active principle and thus increase
their toxicity.
It is generally held,
however, that therapeutic incompatibilities are the responsibility of
the physician rather than the pharmacist. For the pharmacists the
really important consideration in the this class are dangerous doses.
The pharmacist must detect such errors and see that they are
corrected not by himself but by the prescriber. The pharmacist can be
held legally responsible for dispensing a prescription which, because
of an overdose or a reaction may cause the death of the patient,
although filled according to the physicians order. It is, therefore,
absolutely essential that the pharmacist be constantly on the look
out for dangerous doses in prescription. The doses of all the potent
drugs and preparation must be well learned. In case of doubt the dose
should be verified, he should not rely entirely upon his memory.
Examples of prescriptions
illustrating therapeutic incompatibilities:
Rx
Hydrarg. Chlorid. Corros
......................xii gr
Sacchari
…............................................ss oz
M. ft. chart. # vi
Sig. One at night.
There is an overdose of
corrosive sublimate. Probably the intention of the physician is not
corrosive sublimate but calomel the average dose of calomel is
approximately 2 grains.
Rx
Sodii salicylatis
............................ii oz
Hydrarg. Chlorid. Mitis
…............xii gr
M. ft. pulv. #xii
Sig. One every 3 hours.
The sodium salicylate
increases the salivating power of calomel, and the dose of the
latter, considering the frequency of administration, is questionable
though not necessarily dangerous.
Rx.
Acidi Acetylsalicyli /
aa ..................2
g
Quinine sulphatis /
M. ft. chart. no. x
Sig. 1 pow. Every 3 hours.
This is alleged to produce
poisonous quintoxin (quinocine). But this was proven false so this
may be dispensed.
Rx
Morphine sulphat
….......................i oz
Quinine sulphat
…..........................i gr
M. ft. pil. Xii
The quantities should be
transposed or an overdose of morphine will be given.
Rx
Acid Acetylsalicyl
................................xxx gr
Codeinae
...............................................vi gr
Amodopyrinae
......................................xxx gr
M. ft. chart. No. vi
Acetylsalicylic acid
intensifies the narcotic action of codeine. This combination is
questionable.
Rx
Hydrargyri chloridi mitis /
Potassii Bromidi
/ …...................aa xx gr
Sacchari Lactis
/
M. Ft. chart. no. x
Sig. 1 t.i.d.
This is a case which may be
considered as both chemical and therapeutic incompatibility. A
reaction takes place between the mercurous chloride and the potassium
bromide in which the mercurous chloride is decomposed with the
formation of mercuric bromide and the liberation of metallic mercury,
as may be seen in the following reaction:
2 HgCl + 2 Kbr
→ Hg + HgBr2 + 2 Kcl
Toxic substances are formed
in the above reaction.
Important! The use of any
mercury and its derivatives are prohibited due to toxic activity that
it can cause to the humans. The following examples are for
illustration and educational purposes only. Do not dispense or
prescribe.
