question: Why do different injections go in different parts of the body?
comment: Different routes absorb at different rates is the primary reason. Where you want the medication to go is another. You can push a smaller amount of a medication through a vein and have it take affect quickly or you can push a large dose into a muscle and have it start working over time. Also, you might be injecting a medication like lidocaine to numb a specific location; lidocaine in the veins is done to treat certain heart conditions and could be fatal otherwise.
passages: The placement of the bolus dose depends on the systemic levels of the contents desired throughout the body. An intramuscular injection of vaccines allows for a slow release of the antigen to stimulate the body's immune system and to allow time for developing antibodies. Subcutaneous injections are used by heroin addicts (called 'skin popping', referring to the bump formed by the bolus of heroin), to sustain a slow release that staves off withdrawal symptoms without producing euphoria.
   Common sites of intradermal injections are the forearm and lower back.
  
  Section::::Depot injection.
   In an Intradermal Injection, medication is delivered directly into the dermis, the layer just below the epidermis of the skin. The injection is often given at a 5 to 15 degree angle with the needle placed almost flat against the patient's skin. Absorption takes the longest from this route compared to intravenous, intramuscular, and subcutaneous injections. Because of this, intradermal injection are often used for sensitivity tests, like tuberculin and allergy tests, and local anesthesia tests. The reactions caused by these tests are easily seen due to the location of the injections on the skin.
   BULLET::::- The front of the thigh, midway to the outer side, 4 inches below the top of the thigh to 4 inches above the knee. This has a slower rate of absorption than the upper arm.
  
  BULLET::::- The upper back.
  
  BULLET::::- The upper area of the buttock, just behind the hip bone. This has the slowest rate of absorption among the sites.
  
  Section::::Equipment.
   In a subcutaneous injection, the medication is delivered to the tissues between the skin and the muscle. Absorption of the medicine is slower than that of intramuscular injection. Since the needle does not need to reach the muscles, often a bigger gauge and shorter needle is used. Usual site of administration is fat tissues behind the arm. Certain intramuscular injection medicine such as EpiPen® can also be used subcutaneously. Insulin injection is a common type of subcutaneous injection medicine. Certain vaccines including MMR (Measles, Mumps, Rubella), Varicella (Chickenpox), Zoster (Shingles) are given subcutaneously.
  
  Section::::Intradermal injection.
   Damage to the valves and endocardium can be caused by:
  
  BULLET::::- Altered, turbulent blood flow. The areas that fibrose, clot, or roughen as a result of this altered flow are known as jet lesions. Altered blood flow is more likely in high pressure areas, so ventricular septal defects or patent ductus arteriosus can create more susceptibility than atrial septal defects.
  
  BULLET::::- Catheters, electrodes, and other intracardiac prosthetic devices.
  
  BULLET::::- Solid particles from repeated intravenous injections.
  
  BULLET::::- Chronic inflammation. Examples include auto-immune mechanisms and degenerative valvular lesions.
   Section::::Injection sites.:Vastus lateralis muscle.
  
  The vastus lateralis site is the recommended site for infants less than 7 months old and those unable to walk, with loss of muscular tone. To locate the site, divide the front thigh into thirds vertically and horizontally to make nine squares and inject in the outer middle square. 
  
  It is also recommended for epinephrine autoinjectors, in such cases in the middle of the outer side of the thigh, corresponding to the location of the vastus lateralis muscle.
  
  Section::::Injection sites.:Dorsogluteal site.
   Subcutaneous tissue has few blood vessels and so drugs injected here are for slow, sustained rates of absorption. It is slower than intramuscular injections but still faster than intradermal injections.
  
  Section::::Injection sites.
  
  Sites include,
  
  BULLET::::- The outer area of the upper arm.
  
  BULLET::::- The abdomen, from the rib margin to the iliac crest and avoiding a 2-inch circle around the navel. This has the fastest rate of absorption among the sites.
   Intramuscular injections (IM injections) deliver a substance deep into a muscle, where they are quickly absorbed by blood vessels. Common injections sites include the deltoid, vastus lateralis, and ventrogluteal muscles. Most inactivated vaccines, like influenza, are given by IM injection. Some medications are formulated for IM injection, like Epinephrine autoinjectors. Medical professionals are trained to give IM injections, but patients can also be trained to self-administer medications like epinephrine.
  
  Section::::Subcutaneous injection.
   BULLET::::- --- infusions, intravenous
  
  Section::::--- investigative techniques.:--- drug administration routes.:--- injections.
  
  BULLET::::- --- injections, intra-arterial
  
  BULLET::::- --- injections, intra-articular
  
  BULLET::::- --- injections, intralesional
  
  BULLET::::- --- injections, intralymphatic
  
  BULLET::::- --- injections, intramuscular
  
  BULLET::::- --- injections, intraperitoneal
  
  BULLET::::- --- injections, intravenous
  
  BULLET::::- --- injections, intraventricular
  
  BULLET::::- --- injections, spinal
  
  BULLET::::- --- injections, epidural
  
  BULLET::::- --- blood patch, epidural
  
  BULLET::::- --- injections, subcutaneous
  
  BULLET::::- --- injections, intradermal
  
  BULLET::::- --- injections, jet
  
  BULLET::::- --- biolistics
  
  BULLET::::- --- microinjections
  
  Section::::--- investigative techniques.:--- epidemiologic methods.
  
  Section::::--- investigative techniques.:--- epidemiologic methods.:--- data collection.
  
  BULLET::::- --- geriatric assessment
  
  BULLET::::- --- health surveys
   BULLET::::- Less injection pain (as polished and coated needles are not dulled by insertion into a vial of insulin before a second insertion into the skin)
  
  It is important that proper injection sites on the body be used. A healthcare provider helps determine the best injection site for a patient. In general, recommended injection sites include the abdomen, parts of the buttocks, parts of the upper arms and thigh areas.
  
  Section::::Disadvantages.
   Injection is generally administered as a bolus, but can possibly be used for continuous drug administration as well. Even when administered as a bolus, the medication may be long-acting, and can then be called depot injection. Administration by an indwelling catheter is generally preferred instead of injection in case of more long-term or recurrent drug administration.
   A 25 to 31 gauge thick, 3/8" to 1" long needle can be used. The size is determined by the amount of subcutaneous tissue present, which is based on patient build. The 3/8" and 5/8" needles are most commonly used. Usually, no more than 1 mL of solution is given, compared to intradermal injections, where no more than 0.5 mL is usually given.
  
  Section::::Procedure.
   Section::::Injection sites.
  
  Common injection sites include the inner surface of the forearm and the upper back, under the shoulder blade..
  
  Section::::Equipment.
  
  Equipment include syringes calibrated in tenths and hundredths of a milliliter. The dosage given is usually less than 0.5 mL, less than given subcutaneously or intramuscularly. A 1/4" to 1/2" long and 26 or 27 gauge thick needle is used.
  
  Section::::Mantoux Procedure.
   Intravenous injections involve needle insertion directly into the vein and the substance is directly delivered into the bloodstream. In medicine and drug use, this route of administration is the fastest way to get the desired effects since the medication moves immediately into blood circulation and to the rest of the body. This type of injection is the most common and often associated with drug use.
  
  Section::::Intramuscular injection.
   Section::::In nature.
  
  Many species of animals, and some stinging plants, have developed poison-injecting devices for self-defence or catching prey, for example:
  
  BULLET::::- Venomous snakes
  
  BULLET::::- Stinging insects
  
  BULLET::::- Weevers (a fish)
  
  BULLET::::- Sting rays
  
  BULLET::::- Bloodsucking insects: some of them first inject an anticoagulant to make feeding easier
  
  BULLET::::- Cnidocyte cells in the animals called cnidaria
  
  BULLET::::- Stinging nettles
  
  Section::::See also.
  
  BULLET::::- Dart injection
  
  BULLET::::- Jet injector
  
  BULLET::::- Injection port
  
  BULLET::::- Lethal injection
  
  BULLET::::- Needlestick injury
  
  BULLET::::- Needle remover
  
  BULLET::::- Safety syringe
  
  Section::::External links.
  
  BULLET::::- Information about injections from the "Merck Manual"
  
  BULLET::::- Information about intradermal injections
   A wide variety of drugs are injected. Among the most popular in many countries are morphine, heroin, cocaine, amphetamine, and methamphetamine. Prescription drugs—including tablets, capsules, and even liquids and suppositories—are also occasionally injected. This applies particularly to prescription opioids, since some opioid addicts already inject heroin. Injecting preparations which were not intended for this purpose is particularly dangerous because of the presence of excipients (fillers), which can cause blood clots. Injecting codeine into the bloodstream directly is dangerous because it causes a rapid histamine release, which can lead to potentially fatal anaphylaxis and pulmonary edema. Dihydrocodeine, hydrocodone, nicocodeine, and other codeine-based products carry similar risks. Codeine may instead be injected by the intramuscular or subcutaneous route. The effect will not be instant, but the dangerous and unpleasant massive histamine release from the intravenous injection of codeine is avoided. To minimize the amount of undissolved material in fluids prepared for injection, a filter of cotton or synthetic fiber is typically used, such as a cotton-swab tip or a small piece of cigarette filter.
   Ports are usually worn on the abdomen, but can also be worn on other areas such as the buttocks, thigh or arm. Typical injection ports are worn for 3 days and then replaced with another port.
  
  Insulin is injected via a syringe into the injection port. Medication immediately flows through the device's cannula into the subcutaneous tissue layer. No medication is stored in the device (other than the small amount of dead-space in the medication channel within the device).
  
  Section::::Advantages.
  
  BULLET::::- Reduces skin punctures
  
  BULLET::::- Reduces fear and anxiety associated with multiple daily injections
  
  BULLET::::- Reduces bruising around injection site
   BULLET::::- Site of desired action: the action may be localised and approachable or generalised and not approachable.
  
  BULLET::::- Rate of extent of absorption of the drug from different routes.
  
  BULLET::::- Effect of digestive juices and the first pass metabolism of drugs.
  
  BULLET::::- Condition of the patient.
  
  In acute situations, in emergency medicine and intensive care medicine, drugs are most often given intravenously. This is the most reliable route, as in acutely ill patients the absorption of substances from the tissues and from the digestive tract can often be unpredictable due to altered blood flow or bowel motility.
  
  Section::::Choice of routes.:Convenience.
   The deltoid muscle site (upper arm) is recommended for use with injections of small volume, usually equal or less than 2 ml, including vaccinations. This site is not recommended for repeated injections, due to its small area, it is difficult to rotate the injection site. To locate the site, palpate the lower edge of the acromion process. Inject in the upside down triangle that forms with its base at the acromion process and its midpoint in line with the axilla.
  
  Section::::Injection sites.:Ventrogluteal site.
   BULLET::::- Concentration differential between tissues.
  
  BULLET::::- Exchange surface.
  
  BULLET::::- Presence of natural barriers. These are obstacles to a drug's diffusion similar to those encountered during its absorption. The most interesting are:
  
  BULLET::::- Capillary bed permeability, which varies between tissues.
  
  BULLET::::- Blood-brain barrier: this is located between the blood plasma in the cerebral blood vessels and the brain's extracellular space. The presence of this barrier makes it hard for a drug to reach the brain.
  
  BULLET::::- Placental barrier: this prevents high concentrations of a potentially toxic drug from reaching the foetus.
  
  Section::::Factors that affect distribution.:Plasma protein binding.
   BULLET::::- low dead space to reduce complications caused by improper drawing order of different insulin strengths.
  
  Section::::Medical syringes.:Multishot needle syringes.
  
  There are needle syringes designed to reload from a built-in tank (container) after each injection, so they can make several or many injections on a filling. These are not used much in human medicine because of the risk of cross-infection via the needle. An exception is the personal insulin autoinjector used by diabetic patients.
  
  Section::::Medical syringes.:Venom extraction syringes.
   The V of a drug represents the degree to which a drug is distributed in body tissue rather than the plasma. V is directly correlated with the amount of drug distributed into tissue; a higher V indicates a greater amount of tissue distribution. A V greater than the total volume of body water (approximately 42 liters in humans) is possible, and would indicate that the drug is highly distributed into tissue.
   BULLET::::- Intramuscular injection: the needle is inserted perpendicular to the skin into the muscle, beneath the skin and (subcutaneous) tissues that rest on top.
  
  BULLET::::- Subcutaneous injection: the needle is inserted at a 45 degree angle into the (subcutaneous) tissue between the outer layer of the skin and the muscle.
  
  BULLET::::- Nasal: the vaccine is sprayed into the nose and absorbed through the nasal passage.
  
  BULLET::::- Oral: the vaccine is swallowed and ingested.
  
  Section::::Nutrition.
   Once a drug enters into systemic circulation by absorption or direct administration, it must be distributed into interstitial and intracellular fluids. Each organ or tissue can receive different doses of the drug and the drug can remain in the different organs or tissues for a varying amount of time. The distribution of a drug between tissues is dependent on vascular permeability, regional blood flow, cardiac output and perfusion rate of the tissue and the ability of the drug to bind tissue and plasma proteins and its lipid solubility. pH partition plays a major role as well. The drug is easily distributed in highly perfused organs such as the liver, heart and kidney. It is distributed in small quantities through less perfused tissues like muscle, fat and peripheral organs. The drug can be moved from the plasma to the tissue until the equilibrium is established (for unbound drug present in plasma).
  