Routes of Administration

The oral route is preferred in most circumstances. Other routes are also used.
Switching the route of administration may require dose adjustment.

Medicines can be administered:

• via the gut (enteral): e.g. oral, sublingual, buccal, nasogastric/PEG/PEJ tube, or rectal.
• parenterally: e.g. intravenous, subcutaneous, intramuscular.
  • depots are a special case.
• topically: e.g. transdermal, ocular, inhalation, intranasal.
• via other routes: e.g. intrathecal, intraperitoneal.

For advice about converting medicine doses (e.g. morphine) when switching route of administration, see the Pharmacokinetic Table. When switching from oral to a parenteral route for medicines with low bioavailability, dose reduction will be needed. When switching from parenteral to oral for medicines with low bioavailability, dose increase will be needed. For specific medicines, discuss with the Ward Pharmacists or contact Medicines Information ( 80900).

Oral (PO)

• Most frequently used, convenient, well tolerated, and usually lowest cost. There are numerous dose forms (e.g. tablets, capsule, and oral liquids).
• Different formulations of the same active ingredient are usually not bioequivalent.
• Be aware of the impact of changing dose form on efficacy and adverse effects. Make a plan to monitor for these.
• For switching specific medicines, discuss with the Ward Pharmacists or contact Medicines Information (80900).
• Issues to consider:
  • Not suitable in some patients (e.g. unable to swallow, vomiting).
  • Not suitable for some medicines (e.g. insulins).
  • Interactions with food.
  • Local GI adverse effects such as drug-induced oesophagitis (e.g. alendronic acid).

Sublingual/Buccal

• Results in rapid delivery of the medicine into the systemic circulation allowing a quick onset of action.
• Not affected by gut transit or vomiting.
• Issue to consider:
  • Appropriate for only a few medicines (e.g. glyceryl trinitrate spray, prochlorperazine buccal tablet).

Nasogastric Tube (NG) and Percutaneous Endoscopic Gastrostomy (PEG)

• An alternative enteral route to oral (PO). Primarily for nutrition, but sometimes also for medicines when swallowing is affected (e.g. post‑stroke).
• Immediate release tablets (not enteric coated or modified release preparations) can sometimes be crushed and mixed with water for administration via this route, or formulated into a suspension. Check with the Ward Pharmacist for suitability and compatibility.
• Issues to consider:
  • Cytotoxic medicines must never be broken or crushed and are usually not suitable for nasogastric and percutaneous endoscopic gastrostomy due to occupational risk. Check with a pharmacist for guidance around alternatives for safe administration.
  • Some medicines are not suitable for administration via fine-bore enteral tubes and may result in blockage. Flushing reduces this risk.
  • Painful insertion of nasogastric tubes.
  • Aspiration risk.
  • Incompatibilities between medicines and nasogastric tubing material (e.g. ciclosporin liquid) or feeds (e.g. phenytoin).

Rectal (PR)

• Useful for medicines with a local effect (e.g. glycerol suppositories or corticosteroid enemas) or for systemic effect (e.g. diclofenac suppositories). Useful if oral route is compromised. However, rectal administration of oral dose forms is not usually licensed (e.g. metoprolol tartrate). Check with the Ward Pharmacist.
• Issues to consider:
  • Acceptability to patient
  • Local irritation
  • Variable absorption
  • Limited availability of drugs in rectal formulations such as suppositories or enemas

Intravenous (IV)

• Where multiple medicines are being administered via a single lumen line simultaneously, check Note on Injectable Drugs (NoIDs). If further advice is required, discuss medicine compatibility with the Ward Pharmacist.
• With multiple lumen lines (e.g. PICC) it may be possible to deliver several medicines simultaneously via different lumens. Check with the Ward Pharmacist for medicine compatibility.
• Issues to consider include:
  • Lack of suitable access
  • Extravasation (See Management Flowchart and Tool for classification of injury)
  • Accidental removal
  • Infection risk
  • Incomplete delivery if the infusion set is not flushed (e.g. approximately 20% dose loss with gentamicin)
  • Rapid distribution of medicine may result in adverse effects not commonly experienced when medicines are slowly absorbed following oral administration (e.g. CNS effects of opiates).

Subcutaneous (SUBCUT)

• Useful when the oral or intravenous route is unavailable or inappropriate (e.g. in elderly, agitated patients, palliative care).
• Usually administered into the abdomen (thigh and upper arm are alternatives where abdomen not appropriate)
• Can be used to administer fluids to a maximum of two litres/day in patients with difficult or no intravenous access.
• Improved compliance with some medicines (e.g. testosterone or contraceptive implants).
• Issues to consider:
  • Pain or necrosis at site of administration, particularly with irritant medicines (e.g. undiluted potassium and glucose. See Management Flowchart and Tool for classification of injury.)
  • Difficulty removing drug implants or depot injections.
  • If adverse reactions occur, the long duration of action may be problematic. Using short-acting dose forms initially to establish efficacy and tolerability reduces this issue.

Intramuscular (IM)

• Quick and easy access and depot injections allow for good compliance (e.g. antipsychotics and contraceptives).
• Usually administered into the gluteus (upper outer quadrant), or as an alternative, into the thigh.
• Different formulations and/or salts of the same active ingredient are usually not bioequivalent. Be aware of short-acting and depot formulations. Switching between formulations may impact efficacy and adverse effects. Seek medicine advice and make a plan to monitor efficacy and adverse effects.
• Issues to consider:
  • Small volume only (further decreased in very thin patients).
  • Painful.
  • Relies on good tissue perfusion.
  • Risk of bleeding (high risk in some settings e.g. thrombocytopenia).
  • Deep-seated infection.

Transdermal

• Usually in the form of a patch which delivers a medicine continuously through the skin (e.g. fentanyl, estrogens, and nicotine patches).
• Useful non-invasive route for those unable to swallow, medicines with short half-lives, medicines with low fractional oral bioavailability (e.g. glyceryl trinitrate).
• Different patches have different durations of application (e.g. fentanyl is three days, clonidine is seven days).
• Issues to consider:
  • Variable delivery rates which can be affected by environmental factors (e.g. heat increases absorption of fentanyl from patches).
  • Continued medicine delivery after the patch is removed (drug depot remains under skin).
  • Erratic absorption of medicine when patch is damaged; or skin is damaged, wet, hairy, or other barrier present (e.g. dirt or sunscreen).
  • Patches should be checked before MRI (see Transdermal patches: MRI safety concerns).
  • Patches containing metal should be considered for removal when planning for an elective cardioversion.

Topic Code: 191688

must be prescribed or recommended by a consultant.