Bioavailability, release profile and licensed uses are some of the considerations needed when changing between solid dose and liquid formulations.

Reasons for switching

Tablets and capsules (solid dose formulations) are the most commonly prescribed medication formulation. However, there are some scenarios in which solid dose formulations may not be appropriate. These include:

  • swallowing difficulties (dysphagia)
  • dry mouth (xerostomia)
  • psychological aversion to swallowing solid dose formulations

Considerations when switching

Consider the following factors before changing the formulation of a patient’s medication.

Administration differences

Administration instructions may differ between formulations, for example, with respect to taking it with or without food.

Licensed uses

Licensed indications or contraindications may vary between different formulations of the same medicine. Ensure that the required formulation is licensed for the indication being treated. If a decision is made to prescribe a medicine outside the product licence, follow the MHRA guidance on prescribers’ responsibilities.

Unlicensed formulations

Take care when transferring between licensed and unlicensed formulations, as bioequivalence and bioavailability data for unlicensed formulations may be lacking.

Using unlicensed medicines contains further information to help inform decisions made to prescribe an unlicensed medicine.

Brand vs. generic medicines

Some medicines require prescribing by brand as there may be:

  • bioavailability differences
  • release profile variations
  • licence variations
  • multi-ingredient formulations

Exercise caution and ensure monitoring is in place when changing the formulation of medicines prescribed by brand, both when changing formulation within a brand or between brands.

Prescribing by generic or brand name in primary care provides further information.

Bioavailability differences

There are differences in equivalent doses of oral formulations of the same medicine for a small number of medicines. Dose adjustments and/or additional monitoring may be required when switching a patient from one oral formulation to another.

Narrow therapeutic index

Be vigilant for a fall in efficacy or increase in adverse effects when changing formulations, unless two formulations have been proven to be bioequivalent. This particularly applies to any medicine for which therapeutic levels are monitored.

Site of action

Some formulations are designed to deliver the medicine to a particular location in the gut. Changing the formulation may change the site to which the medicine is delivered, and subsequently the therapeutic effect. This has particular significance for certain groups of patients, such as those fed via an enteral feeding tube or treated for bowel disorders.

Release profile variations

The frequency of dosing may be different for liquids, plain tablets or plain capsules than for the modified-release formulation, even if the total daily dose remains the same.

Excipient differences

Switching formulations may expose a patient to different excipients. This may be problematic in patients with allergies, intolerances, dietary or religious beliefs. Examples of excipients that may cause problems for certain groups of patients include (list is not exhaustive):

  • arachis (peanut) oil
  • sesame oil
  • sugars and artificial sweeteners (including aspartame or sorbitol)
  • ethanol (alcohol)
  • propylene glycol
  • gluten
  • lactose

Handling questions about excipients provides further information.

Health and safety

Medicines which are cytotoxic, carcinogenic, genotoxic or teratogenic may have different handling requirements for different formulations. Ensure personal protective equipment (PPE) is used when preparing doses for administration to other people.

Advice for specific medicines

Specific medicine switches for solid dose and liquid formulations

Certain medicines require additional monitoring and dose adjustments when switching between solid dose and liquid formulations.

Update history

  1. Link removed to peanut allergy article (now archived).
  1. Published

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