Want slower absorption go with sub-Q if you want faster do IM...simple. I prefer for every day. no high no low. Everyone is different.
From a medical text:
Why reinvent the wheel? I’ve been lazy here and have attached this information as written for my textbook. It is probably more detailed than you require but I am sure it will give you all the answers you need.
Subcutaneous injections
The blood supply to the subcutaneous tissue is poor, so
absorption of an injected drug will be relatively slow.This
is often an advantage with drugs that cannot be given by
mouth.An example is the protein insulin, which would be
digested if given orally; when injected intravenously, the
resultant fast action is not always desirable.
Absorption rate of drugs given by subcutaneous injection
can be slowed down further by incorporating
adrenaline in the injection. Adrenaline promotes vasoconstriction,
which decreases the distribution of the
injected material. This vasoconstriction will also decrease
bleeding when adrenaline is injected with a local anaes-thetic for minor surgical procedures. Conversely, if the
enzyme hyaluronidase is added to a subcutaneous injection,
the tissue cement hyaluronic acid (which helps cells
to adhere to each other) is destroyed, enabling the other
drug to diffuse into the tissues. Sustained effects can be
achieved, using subcutaneous injections, by dissolving the
drug in a slowly dispersible oil or by implanting a pellet
containing the drug in the tissues. Steroid hormones used
for contraception or for treating menopausal symptoms are
sometimes given this way. Subcutaneous injections are
useful when other routes may be hazardous, as is the case
with heparin.When injected into a muscle, heparin, being
an anticoagulant, could lead to intramuscular haemorrhage
producing a painful haematoma.
Tablets, especially some of the sex hormones, can be
implanted into subcutaneous tissues for prolonged action.
Table 7.14 contains information about the administration of
medications by the subcutaneous route.
Intramuscular injections
Skeletal muscle is highly vascular, and its capillaries contain
small pores that enable substances of small molecular
weight to pass through into the bloodstream. Lipid-soluble
drugs are taken up rapidly by direct diffusion through the
capillary walls. Substances of high molecular size, which
are lipophobic, can be slowly absorbed into the lymphatic
system. Several muscles of the body have considerable mass
and are able to be injected with quantities of up to several
millilitres of fluid, generally without undue discomfort to
the patient.The gluteus medius of the buttocks is the best
muscle to use in this respect. The deltoid muscle of the
upper arm has a richer blood supply than the gluteus
muscle so is good for rapid absorption of many drugs, but
its size limits the injectable amount to about 1 mL.
Intramuscular injections are not always given for quick
action; if the drug is mixed with an oil such as peanut oil,
the oil is not absorbed rapidly from the injection site.The
drug thus diffuses slowly from the oily solution into the
muscle’s capillaries. This can take a few weeks to occur.
This type of injection is known as a depot injection.
Exercise, which causes an increase in skeletal muscle
blood flow, improves absorption of a drug after intramuscular
injection.This was demonstrated by a footballer who
was given a phenothiazine, an antipsychotic agent (see
chapter 33), as a depot injection and who subsequently
suffered from a fairly serious adverse reaction, due to rapid
absorption of the drug, brought about by increased muscularThe main danger from intramuscular injection is
damage to nerves, especially in the case of gluteal injections,
as the large sciatic nerve passes through this region.
Knowledge of anatomical positions of major nerves and
blood vessels is necessary in order to avoid irreparable
damage or injection into these structures. Apart from pain
and irritation to tissues, sterile abscesses can occur with
intramuscular injections.
Not all intramuscular injections act faster than using
enteral routes; for example, diazepam (see chapter 34) is
faster-acting when given rectally or orally.Table 7.15 contains
information about the administration of medications
by the intramuscular route.
Regards
Dr Alan Galbraith