Mercaptamine eye drops for ocular symptoms of cystinosis

This leaflet is for parents and carers about how to use this medicine in children. Our information may differ from that provided by the manufacturers, because their information usually relates to adults. Read this leaflet carefully. Keep it somewhere safe so that you can read it again.

Name of medicine

Mercaptamine eye drops (cysteamine)

This leaflet is about the use of mercaptamine eye drops for ocular (eye) symptoms of cystinosis. 

Why is it important for my child to take mercaptamine?

In cystinosis there is an increase in the amount of an amino acid called cystine in the eyes and other organs of the body. The cystine can build up and form crystals in the eyes, which could lead to blindness. Mercaptamine eye drops will reduce the build up of cystine in your child’s eyes.

What is mercaptamine available as?

Eye drops:  0.11% (10 mL) and 0.55% (50 mL) available from a special-order manufacturer or specialist importing companies

When should I give mercaptamine

Mercaptamine eye drops are usually given four to six times a day. Ideally, these times are at least 2–4 hours apart.

Give the drops at about the same time(s) each day so that this becomes part of your child’s daily routine, which will help you to remember.

How much should I give?

Your doctor will work out the amount of mercaptamine (the dose) that is right for your child. The dose will be shown on the medicine label.

It is important that you follow your doctor’s instructions about how much to give.

How should I give mercaptamine?

Eye drops

You may need help from another adult to help give eye drops, especially in small children and babies. One of you can hold the child still and one can give the drops. You may find it helpful to wrap a small child or baby in a blanket to help keep them still.

  • Use the eye drops in both eyes, unless your doctor has told you otherwise.
  • Wash your hands thoroughly with soap and hot water before and after giving the drops.
  • The eye drops are easiest to give when your child is lying down.
  • For older children, gently pull the lower lid out and squeeze the bottle gently so that one drop goes into the pocket that is formed.
  • In small children and babies, place the drop into the inner corner of the eye (preferably with the eye open, but the liquid will still drain on to the eye even with a closed eye if you can hold your child’s head still for a few seconds).
  • After giving eye drops, your child should keep the eye closed for as long as they can (5 seconds if possible) so that the eye drop doesn’t spill out.
  • If you think the drop didn’t go into the eye, you can repeat the process but do not try more than twice.
  • Try to avoid the tip of the bottle/dropper touching any part of your child’s eye if possible.
  • Wash your hands again with soap and water.

When should the medicine start working?

The mercaptamine eye drops should start working in a few days and your child’s vision should start to improve.

What if my child is sick (vomits)?

You do not need to worry if your child is sick, as the medicine will still work.

What if I forget to give it?

If you miss a dose, wait until the next normal dose. Do not give the missed dose.

What if I give too much?

You are unlikely to do harm if you give an extra dose of mercaptamine eye drops.

If your child accidentally swallows mercaptamine, it is unlikely to do harm. However, if you notice any unusual effects or are worried, contact your doctor or NHS Direct (111 in England and Scotland; 111 or 0845 4647 in parts of Wales). Have the medicine or packaging with you if you telephone for advice.

Are there any possible side effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side-effects). Your child is unlikely to get side-effects with mercaptamine eye drops. Any side-effects that do occur are usually mild and will wear off after a few days.

Other side-effects you need to know about

  • The mercaptamine eye drops may cause your child to have an unpleasant smell on their breath. This can be masked using breath fresheners.

Can other medicines be given at the same time as mercaptamine?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal and complementary medicines.

Is there anything else I need to know about this medicine?

Mercaptamine eye drops are manufactured by special-order manufacturers and therefore it may take longer than normal for your local pharmacist to get hold of them. Make sure that you go to your GP for a new prescription at least 3 weeks before you are going to run out.

A separate leaflet about mercaptamine for nephropathic cystinosis is available on the Medicines for Children website, 

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember.
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses, as you may do harm.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm.
  • Make sure that you always have enough medicine. Order a new prescription at least 3 weeks before you will run out.
  • Make sure that the medicines you have at home have not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.
  • If you think someone else may have taken the medicine by accident, or swallowed some eye drops, contact your doctor.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight.
  • It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information?

Your child’s doctor, pharmacist or nurse will be able to give you more information about mercaptamine eye drops and about other medicines used to treat ocular symptoms of cystinosis.

England: NHS 111

Tel 111

Scotland: NHS 24

Northern Ireland: NI Direct

Wales: NHS Direct

Tel 111 (free) or 0845 46 47 (2p per minute)

Cystinosis Foundation UK

Copyright disclaimer

Version [1]. © NPPG, RCPCH and WellChild, all rights reserved. Review by March 2016.

The primary source for the information in this leaflet is the British National Formulary for Children. For details on any other sources used for this leaflet, please contact us through our website,

We take great care to make sure that the information in this leaflet is correct and up-to-date. However, medicines can be used in different ways for different patients. It is important that you ask the advice of your doctor or pharmacist if you are not sure about something. This leaflet is about the use of these medicines in the UK, and may not apply to other countries. The Royal College of Paediatrics and Child Health (RCPCH), the Neonatal and Paediatric Pharmacists Group (NPPG), WellChild and the contributors and editors cannot be held responsible for the accuracy of information, omissions of information, or any actions that may be taken as a consequence of reading this leaflet.